The Geography of Mars

Lecture Notes for the Final

Second order of relief: gigantic features and the dominant processes shaping the martian surface
- Mars' surface physiography shows conspicuous evidence of several geomorphic processes: impacts and cratering, volcanism, rifting, glaciation, hydraulics, and æolian processes.
  - These processes have created enormous landscape features, some visible with telescopes from Earth, which constitute the second order of martian relief.
  - These features are between 1,000 km to 8,000 km in diameter or length: four enormous impact basins, the other great volcanic rise, the Valles Marineris rift system, the possible mega-slide of Thaumasia, the polar ice caps, the Chryse Trough drainage system, and the Syrtis Major wind-cleared basalt region.
  - Together with the first order great crustal dichotomy, these second order features provide a framework on which to hang an increasingly detailed mental map of Mars.
- The great impact basins
  - Much of Mars is cratered, but there are four impact craters that stand out by their tremendous size, ranging from 1,500 km to 3,300 km in diameter. They also feature positive gravitational anomalies (mass concentrations, or mascons, coïnciding with topographic lows), which seem counterintuitive, given the tremendous excavation of mass from them.
  - Hellas Planitia
    - This crater spans about 50° of longitude and 30° of latitude, centered about -42° at 70° E.
    - It is some 2,300 km across and 8 km deep relative to the surrounding countryside (about 4 km below the geoid)
    - Striking thought: If all the material excavated by the impactor that created Hellas were sifted evenly all across the contiguous continental United States and slowly built up, it would cover us up to a depth of 3.5 km or so
    - Indeed, the material blasted out of Hellas accounts for a large share of the higher elevation of the Southern Highlands over the Northern Lowlands, according to Arden Albee (2000, Annual Reviews of Earth and Planetary Science). It amounts to several hundred kilometers in width by some 2 km in depth.
    - This argument is what got me to thinking that, if Hellas could disgorge this much ejecta, wouldn't the Northern Lowlands impactor have deposited vastly more ejecta, perhaps accounting for a very significant share of the raised elevation of the Southern Highlands?
    - The Hellas event is believed to date from the end of the Noachian era (which ran from the beginning of the planet's coalescence to maybe 3.8 billion BP).
      - When an impactor of this size hits, it vaporizes and melts solid rock.
      - Magma containing iron minerals (which the basalts of Mars' Southern Highlands have a lot of) aligns with the then prevailing magnetic field
      - Hellas shows no such remanent magnetization, so it formed after the collapse of the Martian magnetic field
    - The crust is very thin here, < 10 km thick, perhaps as little as 7 km, related both to the explosive excavation and to the rebounding of the mantle afterwards.
    - Hellas went through extensive reworking after its excavation:
      - It may have contained a great inland sea, with a volume about two thirds that of the proposed Northern Lowlands ocean.
      - The floor deposits are largely Hesperian in age (younger than the Noachian times of its formation, but younger than the Amazonian age of the Northern Lowlands surface)
    - Hellas shows all sorts of interesting erosional and depositional landforms expressing this complex geological history:
      - Depositional:
        
        Volcanic wrinkle ridges and pyroclastic flows
        Mass wasting/landsliding
        Fluvial alluvial fans
        Lacustrine/marine layered deposits
        Æolian dunes
        Ground ice or glaciers
      - Erosional:
        
        Fluvial outflow channels
        Lacustrine/marine shorelines
        Æolian yardangs
  - Argyre Planitia
    - Another girnormous crater centered around -49° lat. and 318° E. lon.
    - It's not as large as Hellas, with a diameter about 1,800 km and a depth of 5 km
    - It is visually distinctive due to the rugged mountain massifs that form ring and radial fretting patterns around the floor of the crater.
    - The radial pattern is enhanced by five major channels flowing into and out of the basin: four entering from the south and one flowing out of the north rim.
    - Muddying my tidy nested regionalization scheme, apparently, Argyre, a second order feature, is involved in another second order feature I'll discuss later, a tremendous seemingly fluvial system draining from beneath the south polar cap through a chain of crater lakes and river channels leading to Ares Vallis and Chryse Planitia.
    - Many of the same erosional and depositional features seen in Hellas Planitia can be found in Argyre Planitia
    - Of the four great impact basins, the floor of Argyre is the oldest, judging from the superposed crater density, probably late Noachian in age.
  - Isidis Planitia
    - Isidis is the third of the great impact basins found in the Southern Highlands, but, unlike the previous two, it is found right on the first order crustal dichotomy border, again kind of messing up my tidy "orders of relief" scheme.
    - It's centered roughly at 15° at 90° E.
    - Very distinctively, Isidis has almost no remnant of its northern and northeastern rim structure: The crater opens out onto the Northern Lowlands over a gradual rise of only about 500-600 m from the lowest point of the crater flow.
    - It also has the thinnest crust of the four great craters, ~6 km.
    - It also features a higher level of post-impact fill, nearly 3 km deep, giving it the flattest floor of the three, with a slope about 0.015°, tilting down toward the southwest and then reversing to form a smooth but steeper slope rising to the southwest into Syrtis Major.
    - There has been energetic debate about what the nature of that flat fill is.
      - One group argues that this is a basalt flow from the Nili and Meroë Patera volcanoes in the Syrtis Major region to the west the likeliest sources
      - Others point out that most of the basin tilts downward toward the southwest, so that would be weird if this were lava from those volcanoes.
      - Another argument against the Nili and Meroë Patera volcanoes is that their lavas have much greater surface roughness than the Isidis fill.
      - There's been speculation that the fill might be catastrophic debris flows triggered by Syrtis Major volcanic dikes interacting with ice-rich soils, particularly ices rich in carbon dioxide. That interaction would trigger an explosive outflow, perhaps destroying the crater's northeastern rim.
      - Going against that idea, though, is the lack of chaos terrain and channeled outflows of the sort we see farther west in the borderlands of Tharsis.
      - Still others think that, however that northeast rim was broken, its failure allowed a marine intrusion from the posited Northern Lowlands ocean, kind of a big lagoon, complete with smooth marine deposits.
      - The various positions on this debate are summarized in Hiesinger and Head, 2004, Lunar and Planetary Science Conference.
    - Like the previously discussed craters, Isidis has a very complex geological history: volcanic, marine, permafrost, mass wasting, and æolian features
    - Among these are a lot of dunes forming fields with ripple structures
    - It has a high density of smaller craters. It is probably younger than Hellas, though, basically puncturing its annular ring.
      - However, many of these craters are eroded mounds with pits at the top
      - Their appearance suggests that there was once some kind of sediment or other filling in Isidis even higher than it is now, which was then smacked by craters, which consolidated the areas around the impacts under the ejecta blankets.
      - Later, erosion (wind?) removed whatever these beds were, leaving the consolidated crater rims to stick out more and more prominently above the lowering floor: rampart craters.
    - This intriguing crater is where Beagle 2 was to land on 25 December 2003
  - Utopia Planitia
    - A lava plain in the northern lowlands, located roughly at the antipode from Argyre, about 46° lat. and 119° E lon.
    - This is where Viking 2 landed in 1976.
    - This is where Viking 2 recorded the formation of thin frost layers on rock and soil, which may form when CO₂ in the atmosphere freezes out, attaches to dust particles (themselves the condensation nuclei for water), and then settle down like a kind of fog frost
    - The consensus now is that Utopia Planitia is a humongous crater buried in whatever it is that resurfaced the Northern Lowlands. This was first proposed in 1989, when G.E. McGill published an article in JGR arguing from geomorphic evidence that there was some kind of circular structure buried in the Northern Lowlands. His argument has basically received increasing support with every new data source collected on it, though there are still some holdouts saying that not all alternative explanations have been systematically ruled out.
    - There are odd circular grabens on that Northern Lowlands surface material.
      - These look almost like the draping and sagging and fracturing of some layered material over buried crater structures
      - Mars Express has ferreted out buried craters on Chryse Planitia
      - This would be consistent with ocean sediments in an argument by Debra Buczkowski and George McGill in 2002
      - Might that consistency not preclude low viscosity lavas?
    - If this is, indeed, a crater, it is the largest of the four discussed here as second order features at 3,300 km across (conservative estimate) to 4,700 km across (more inclusive definition).
    - It is, moreover, covered by the buried "quasi circular depressions" that MOLA and Mars Express have found all over the Northern Lowlands, revealing an ancient surface under that smooth resurfacing. Since, the resurfacing is newer, Amazonian material and the QCD are necessarily much older (probably Noachian like much of the Southern Highlands), then something buried under them is older still.
    - Utopia is far from the equator and gives a lot of evidence of ice-related features and processes:
      - Viking 2 documented the first evidence for the frequent formation and sublimation of frost and ice fogs.
      - There's patterned ground, the polygons often seen on Earth over permafrost.
      - There's evidence of sublimation of subsurface ice in the form of scalloped pits and thermokarst.
      - There are lobate debris aprons of the sort you see in solifluction affected Arctic terrain.
      - Pedestal craters are found here and in other high latitude locations: An impact crater sits at the top of a mesa several times wider than it is, surrounded by a steep scarp that perches the whole landform dozens of meters above the surrounding plains. These have been interpreted as impact-hardened ground and ejecta blankets set in a soil substrate susceptible to æolian erosion.
- The other great volcanic rise: Elysium Rise
  - Another huge rise, dwarfed only by the sheer scale of Tharsis
  - "Only" 2,000 km
  - "Only" 6 km thick
  - Also houses multiple volcanoes:
    - Elysium Mons on the west central side of the rise (12.5 km high)
    - Albor Tholus to the southeast (4.5 km high, with a 3 km deep caldera!)
    - Hecates Tholus to the northeast
  - Hecates may have been active at least as recently as 350 million BP and this looks like an explosive event creating a flank caldera on the northwest side of the volcano
    - An article by a team led by Ernst Hauber, based on Mars Express HRSC data, discusses an elongated depression running NE to SW at the bottom of the northwest slop of the volcano (~45 km by 20 km)
    - It contains some 50 m wide ridges that look like terminal moraines on Earth
    - Another, shorter depression is completely full of striated materials running downslope and have some cracks perpendicular to them that look like stuff that would be deposited in crevasses and then exposed as the glacier melted or sublimed back
    - There are steep sided valleys pouring out onto the top of the bigger depression: Could these be hanging valleys carrying materials onto the top of the "valley glacier"?
    - These features have few craters on them, implying an age of something like 100-ish million BP
    - Similar features have been reported on the northwest flanks of Olympus, Arsia, Pavonis, and Ascraeus, too
    - Ice age?
  - Elysium may have erupted 20 million BP, meaning it could well be an active volcano (error bars X 4 - 80 million BP to 5 million BP)
  - The "recent" vulcanism has put dust in the eye of the traditional theory that Mars, being a dead planet with a cooled core, stopped being volcanically active two billion years ago!
  - As with Hecates, Elysium may have been glaciated, but 5-24 million BP, judging from glacial deposit features and crater counting on the Hecates flank caldera and nearby depressions:
    - There is (and cannot be) stable ice at these low latitudes now.
    - Such glaciation suggests climate change on Mars and the timing coïncides with a time of increased obliquity and seasonal extremes on Mars.
    - Again, tantalizing suggestions of an ice age on Mars
- The great canyons: Valles Marineris
  - Overview:
    - Extensional rifting, related to the extensional stresses on the Tharsis Rise
    - Pitting, which is another indicator of extensional strain -- thought to reflect dilational faulting, which creates voids below, into which unconsolidated surface regolith collapses
    - Water or water mixtures in subsoil or, in Hoffman's argument, carbon dioxide ices or mixtures
    - Landslides
    - Massive outflows, like jökulhaups on Earth when vulcanism-related warming hits a glacier or ground ice or when an ice dam or moraine dam liberates a huge lake
    - Not quite a canyon in the Earth sense, since the eastern end is higher than the center
  - Subsidiary chasmata
    - Ius Chasma in the west on the south side (note the alcove-headed short tributaries, so like groundwater-fed networks in arid regions in the American Southwest)
    - Melas Chasma in the middle on the south side, some 9 km below the edge of the surrounding plains, shows some sulfates on its floor and sides, which could indicate the presence of a lake here.
    - Coprates Chasma to the east on the south side, the location of the subsidence pits I showed you in discussing extensional stresses.
    - Eos Chasma, the southern fork on the east side, shows patches of chaos terrain toward the west and the kinds of braiding patterns and flow structures that add to the impression that Valles Marineris once carried water, yet it also contains a layer of exposed olivine toward the bottom, which weathers rapidly in the presence of water. Perhaps Mars dried up quickly after the olivine layer was exposed?
    - Capri Chasma, the northern fork on the east side, has hæmatite "blueberries" like those in Meridiani that Opportunity imaged. Hæmatite is an iron (III) oxide ((Fe₂O₃) that can be formed from prolonged exposure of iron to water.
    - Tithonium Chasma in the west to the north of Ius shows deep layered deposits of sulfates and iron oxides, suggestive of water alteration: The layering basically goes all the way down the sides of the canyon for kilometers. Could these indicate miles of sedimentary deposition?
    - Candor Chasma in the center north of Melas and south of Ophir. It is itself split into two sections, East Candor and West Candor. Calcium sulfate and kieserite (hydrated magnesium sulfate, or MgSO₄-H₂O) have been identified by the OMEGA spectrometer on Mars Express, and these are commonly products of water alteration.
    - Ophir Chasma is on the north end of the main Valles Marineris sequence of chasmata. It features landslides on a stupendous scale.
    - Ganges Chasma to the east north of Coprates/Eos/Capri, that "Rat Fink hotrod" shaped canyon, where Lab 1 was situated. This canyon also shows olivine, a mineral that alters very rapidly in the presence of water, so its presence here goes against the impression of water alteration minerals in other canyons (unless the climate drastically dried immediately after the olivine layer was exposed).
    - Juventae Chasma off to the northeast is an almost totally boxed in canyon, with an exit to the north, at the head of Maja Valles, a major outflow channel forming the boundary between Xanthe Terra and Lunæ Tera. It contains a mountain about 2.5 km high, which is made of sulfate deposits. The canyon shows a number of water-altered minerals.
    - Hebes Chasma off to the northwest shows exposures of gypsum (a very soft sulfate mineral, CaSO₄-2H₂O. It is an evaporite, suggesting a wet phase in Mars' history.
    - Echus Chasma to the immediate west of Hebes, forms the head of the enormous Kasei Valles. It also shows a sickle-shaped dike. The vast outpouring down Kasei Valles may have been triggered by dike formation, which would catastrophically have liberated huge amounts of frozen groundwater.
- Chryse Trough
  - A large arc of locally depressed topography loosely rings the Tharsis Rise, most likely the result of the loading of lava on the lithosphere below the Tharsis volcanoes.
  - Timothy Parker in 1985 suggested that this depression east of Tharsis, dubbed the Chryse Trough, might have housed an actual channel for catastrophic flooding, comprising several tributary channels flowing from near the South Polar Ice Cap into Argyre.
  - From a presumed lake in Argyre, the flow would move through Uzboi Vallis into a chain of smaller craters linked by channels that flowed into Margaritifer Terra east of Valles Marineris. From there, drainage would move into Chryse Planitia and the proposed northern lowlands ocean.
  - The topographic resolution of even the best imagery was too coarse and the elevational uncertainty too great for testing of the direction of flows in the proposed system until MOLA data arrived (1997-2006).
  - The resulting high resolution topographical information seems to confirm the existence of an 8,000 km drainage system
    - Two valley networks originate in Dorsa Argentea around 320°. near the South Polar Cap and, along with a third network, lead to Argyre Planitia.
    - An outflow channel with steep walls and great depth, Uzboi Vallis, runs out of Argyre to the northeast, cutting into the rim of Holden Crater, where signs of a delta or alluvial fan are found.
    - The northeast rim of Holden Crater is blunted and forms a ramp leading down to Ladon Basin where the channel structure disappears into what may have been a lake.
    - The channel morphology re-appears leading out of Ladon Basin to the northeast into large outflow channels in Margaritifer Terra.
    - These channels, Margaritifer Valles, then debouch into Chryse Planitia, forming a possible delta structure at the higher of Parker's two proposed shorelines, the Arabia shoreline.
  - If, in fact, this system did move water or other fluids from the area around the South Polar Cap to Chryse Planitia, even as a sporadic and perhaps not always continuously connected drainage, at some 8,000 km in length, the Chryse Trough would constitute the longest fluvial network in the solar system.
- Massive outflow: Kasei Valles
  - Kasei Valles is the enormous channel that seems to erupt out of Echus Chasma to the north of Valles Marineris, flow due north, and then make a nearly right angle turn to divide into two main branches that debouch into Chryse Planitia to the northeast.
  - Its northern channels are fringed with chaos terrain, too, such as Sacra Fossae.
  - The channel could carry a staggering amount of fluid, dwarfing the outflow channel in Ares Valles, not to mention the most gigantic jökulhlaup floods on Earth (e.g., the Missoula and the Bonneville floods).
  - Kasei Valles cuts across the Hesperian lavas of eastern Tharsis and of Lunæ Planum (forming the western boundary of Lunæ Planum).
  - There is evidence of subsequent lava or pyroclastic flows into Kasei Valles on its western edge, creating a marked softening of the edge there. This flow may have come from Tharsis Tholus, the easternmost volcano of Tharsis Rise.
- Thaumasia Block: Plate or Megalandslide?
  - A distinctive wedge- or lozenge-shaped plateau region on the southeasternmost part of the Tharsis Rise
    - To its north is Valles Marineris (it is sometimes bounded by Valles Marineris, though some consider it to extend just beyond Vallis Marineris)
    - To its south lie the Thaumasia Highlands, the only folded/faulted mountain ranges on Mars that resemble the most common types of mountains on Earth.
    - These continue east as Coprates Rise.
    - Claritas Fossæ lie to the west between Tharsis Montes/Dædalia Planum and the Thaumasia feature. Claritas Fossæ run about 1,800 km and the terrain is fractures by a series of north-south striking normal faults and grabens, some of them offset, reflecting tensional and some shear stress associated with the uplift of Tharsis.
    - North of Claritas Fossæ and west of Valles Marineris is the distinctive Noctis Labyrinthus chaotic terrain.
  - Internally, Thaumasia is divided into:
    - Syria Planum, the highest elevation portion at the northwest corner of Thaumasia, enclosed within the arch of Noctis Labyrinthus and north of the beginnings of Claritas Fossæ
    - Sinai Planum lies to the east of Syria PLanum, south of the junction of Noctis Labythinthus and Valles Marineris
    - Solis Planum is a large, flat expanse dominating the center of Thaumasia, characterized by northeast-southwest trending wrinkle ridges, indicative of compressional stress crumpling the thin lava beds of Solis, stresses from the uplift of the Syria Planum area to the northwest
    - Thaumasia Planum or Thaumasia Minor, is a circular planum south of Coprates Chasma in Valles Marineris and west of the Coprates Rise. There's some evidence that it contains a large buried crater: http://plate- tectonic.narod.ru/watters_2006-02-01123a_figure4_l.jpg.
  - Analogies with Earth plate tectonic features early suggested incipient plate tectonics, with Valles Marineris the rift zone and possible divergent boundary and Thaumasia Highlands and Coprates Rise the subduction zone features.
    - Plate tectonics even of the most incipient variety, is not the consensus view today, and most workers consider Mars to be a one-plate planet with tectonic uplift concentrated almost exclusively in a single mantle plume rising up under Tharsis.
    - Plate tectonics is not completely out of the picture, however. Recent work by An Yin (2012) argues that the rounded southeastern boundary of Melas Chasma is, in fact, a large crater. The crater is missing its northern rim. Yin points to a rounded structure in northwestern Melas Chasma that may be its displaced northern rim. If so, there has been about 150 km of left-lateral movement along what he argues is a shear fault boundary, like our own San Andreas Fault. Could, then, Valles Marineris divide adjacent plates, the way the San Andreas divides the Pacific and North American plates?
  - A recent argument by Montgomery et al. in 2009 proposed that Thaumasia constitutes a "mega-slide" resulting from "thin-skinned" deformation of multiple shallow layers of lava on top of deeply impact shattered regolith. This regolith contains mixtures, not only of basaltic impact gardening debris, but of ices and evaporite beds as well.
    - A lot of the subsurface is Noachian, meaning it could well have had streams and ponds with evaporite beds forming in any local depressions.
    - Evaporites often concentrate salts, and salts form materials that are much less resistant to shear stresses than regular crustal rocks are and capable of viscous flow in response to stresses (especially if water or brine gets in there).
    - Magma intrusion under subterranean ices, especially in Syria Planum closest to Tharsis Montes, could create highly confined supercritical aquifers (water unable to boil because of the confinement of subterranean water under high pressure). A bomb waiting to go off.
    - Shear-induced detachments could allow movement of these thin layers, while the size of Thaumasia (and the low gravity of Mars and the low angle of Thaumasia) implies this process of detachment must go down quite far, to enable deep detachments to let the whole Thaumasia complex begin to move.
    - Meanwhile, Tharsis, the source of subterranean heat, would continue its upward movement, creating tremendous tensional stress around Thaumasia's highest point, Syria Planum. That would account for the normal faulting seen around Noctis Labyrinthus and the original rifting of Valles Marineris, as well as the grabens of Claritas Fossæ and their slight right lateral motion (as Thaumasia began to detach and slide southward).
    - The creation of some of these rifts could explosively liberate the trapped supercritical fluids in the subsurface, possibly accounting for the megaoutflows associated with Valles Marineris and the chaos terrain of the undermined Noctis Labyrinthus.
    - As the megaslide moved along its various detachments, crumpling would occur in the thin lava layers as they experienced compressional stress between the moving slide and the stationary terrains of Aonia Terra and Noachis Terra to the south and east, respectively. This compressional stress is visible in the many wrinkle ridges in the middle and lower reaches of the proposed megaslide, running in quasi-parallel "waves" from east-northeast to west-southwest. You can easily see them in Google Mars, through much of Solis Planum and Thaumasia Planum to the immediate east of Solis Planum.
    - The toe of the proposed megaslide would be the folded and thrust-faulted mountain ranges of the Thaumasia Highlands and Coprates Rise.
  - So, the large Thaumasia "lozenge" that is so conspicuous in MOLA maps might be a second order expression of yet another mega geological process: landsliding on an epic scale.
- END 03/18/15
- Syrtis Major "Blue Scorpion" and æolian processes
  - This feature was the first martian landform recorded in a sketch map drawn by Christiaan Huygens in 1659 (and, debatably, as early as 1636 by Francisco Fontana)
  - It is that large, triangular low albedo object that dominates the area west of Isidis Planitia and north of Hellas Planitia, connected loosely to a band of low albedo surfaces in the Southern Highlands.
  - The feature is persistent though the edges shift around through time.
  - Its dark color and stability invited early speculations about an ocean or vegetation-dominated area, seeming greenish or blueish from Earth in contrast to the bright orange/ocher light albedo areas surrounding it.
  - Orbiter imagery has revealed it as a volcanic province (lavas from Nili Patera and Meroë Patera in Syrtis Major Planum, which has been swept clean of dust by a prevailing northeast wind (winds are named for the direction from which they blow).
  - One of the striking demonstrations of this prevailing wind pattern is imagery of craters on the lava, which feature bright tails of dust deposited in the lee of the crater rims: Winds deflecting around an obstacle rejoin leeward of it, creating cross-interference, which reduces the resultant velocity of the wind, and this reduces its carrying capacity for supporting dust, which then deposits in the low-energy zone leeward of the obstacle.
  - This persistent prevailing wind seems related to the global circulation of Mars as distorted by topographic effects (deflection of the global circulation's wind systems by the Tharsis Rise).
- Polar ice caps
  - North Polar Ice cap:
    - The ice cap itsel is about 1,000 km in diameter.
    - The North Polar Cap and the Planum Boreum plateau structure underlying it cover approximately 800,000 km² and, with thickness ranging to nearly 3 km in places, the ice cap volume amounts to somewhere between 1.2 and 1.7 million cubic kilometers.
    - Its extent varies seasonally and also over centuries with climate change.
    - During the northern hemisphere fall and winter, the North Polar Cap is obscured by hazes and clouds and even sometimes hurricane-like storm systems that develop north of 50°, a cloud cover referred to as the polar hood.
    - Through precipitation or through frost sublimation, carbon dioxide ice on the ground expands to roughly 60° of latitude
    - This ice cap is mainly composed of water ice, which dominates the residual ice that persists through all seasons.
      - The water does sublime, whenever summer temperatures get above 205 K (-68° C or -91° F), which it sometimes does on the south-facing walls of the ice cap, which exaggerates the steepness of the south-facing slopes.
      - In the Northern Hemisphere winter, water freezes out of vapor, first at the pole and then farther and farther out, to build the seasonal water ice cover. Some of this is contributed by polar cyclones, first spotted by Viking, which can produce snow.
    - Carbon dioxide sublimes around 150 K (-123° C or -190° F), so it freezes out as frost as winter approaches, developing a seasonal carbon dioxide veneer. This seasonal carbon dioxide ice extends out quite far from the polar ice cap.
    - During summer, first the carbon dioxide frost sublimates away entirely and then some of the water ice does, too, noticeably shrinking the ice cap during the Northern Hemisphere summer.
    - This adds a significant pulse of carbon dioxide to the atmosphere in the Northern Hemisphere winter, the partial pressure of which raises martian air pressures quite significantly: There's nothing like this pressure pulse on Earth.
    - The Northern Hemisphere summer is noticeably longer than the winter, so there's that much longer for air temperatures to exceed 150 K and even 205 K, so it's not surprising that the carbon dioxide veneer disappears and even some of the water ice sublimates.
    - One of the weirdest features of the Northern ice cap, which has no parallel on Earth, is the existence of deep chasmata in the ice.
      - These are very deep and curve outward in a counterclockise spiraling pattern.
      - The largest is Chasma Boreale, which opens out from the ice cap about 300-320o E, where it is about 350 km wide and cuts back some 600 km ... and spirals at an angle different from most of the others.
      - These features are etched as much as a kilometer into the cap and often their depth takes them below the elevation of the surrounding countryside.
      - Their floors have lower albedo than the surrounding polar layered deposits, suggesting that they may be traps for dust blown into them.
      - Very oddly, though, they trend counterclockwise outward, while katabatic winds generated by the polar high tend to spiral clockwise off the northern cap. One of those martian "yes, but ..." moments.
      - There is all kinds of speculation about what causes these weird features: Wind erosion? Jökulhlaup erosion?
    - Internal stratigraphy was revealed by the Shallow Radar (SHARAD) sensor on board the Mars Reconnaissance Orbiter (MRO):
      - Four laterally continuous concentrations of fine layers of dust
      - Three homogeneous zones of nearly pure water ice
      - A basal unit of æolian origin, comprised of dark sand-sized grains. It is believed to be of Amazonian age, meaning the ice cap is no older than the Early Amazonian.
      - This layering of pure water ice and dusty ice is a record of Amazonian climate change and coring it would be of intense interest to future human expeditions to Mars.
  - South Polar Ice Cap
    - This cap is quite different from the northern cap.
      - Much smaller, about 350 km in diameter, but it is somewhat thicker, getting over 3 km thick in places.
      - Like the North POlar Ice Cap, the South Polar Ice Cap features deep chasmata cutting down into the ice. These seem to spiral clockwise off the cap. That would be weird, if these are carved by katabatic winds, since those would spiral counterclockise out of the Southern Hemisphere polar regions. In this, the southern cap is just as baffling as the northern, with their counterintuitive chasmata.
      - The seasonal carbon dioxide frost extends farther out than seen in the Northern Polar Cap, though: It gets down to about -45°
      - Located on the Southern Highlands, it is about 6 km higher up than the North Polar Cap, which means that it gets colder (think of lapse rates up a mountain on Earth).
      - The Southern Hemisphere winter is noticeably longer than the summer because of the planet's great orbital eccentricity, which means Mars is moving relatively slowly at aphelion, protracting winter.
      - Aphelion is 121% as far from the Sun as perihelion, which itself means a drastically colder winter than experienced in the Northern Hemisphere.
      - Also, the Southern Hemisphere summer features more dust devils and dust storms than the Northern Hemiosphere summer, meaning the Southern Hemisphere summer is dustier and the surface is slightly shadier, also meaning the summer is cooler.
      - This means that, even in the relatively short Southern Hemisphere summer, temperatures are not going to get above 150 K for long enough to sublimate away all of the carbon dioxide ice. The permanent carbon dioxide ice remains about 8 m thick through the summer.
    - Suspicions that there was water ice below the residual carbon dioxide ice cap were affirmed by ESA's Mars Express Minerological Mapping Spectrometer or OMEGA and NASA's Mars Odyssey Thermal Emission Imaging System or THEMIS).
      - Sublimation pits have long been observed on the South Polar Cap, where carbon dioxide sublimates explosively in geysers, sometimes pulling dust up with it.
      - These steep-sided pits consistently show flat floors about 8 m below the surface ice.
      - Spectra from these floors evidence water ice.
      - So, the South Polar Cap has a residual carbon dioxide cover about 8 m thick on top of a permanent water ice core.
      - This water ice core probably saw some basal melting in the past, as seen in imagery of stream channels emerging from below the ice.
      - This creates at least some plausibility for the Argyre to Ares fluvial system, or Chryse Trough system proposed by Timothy Parker.
      - The South Polar Cap dominates the large air pressure swings in the atmosphere.
        
        At the Viking 1 landing site in Chryse Planitia, air pressure varied annually over a range from 6.9 to 9 hectopascals or millibars, something like a 30% increase.
        Air pressure would go up like crazy in the Viking 1 fall and winter, back down somewhat in spring, go up in late spring/early summer, and drop like a rock in late summer.
        This coïncides with the cycle of sublimation of a lot of carbon dioxide off the South Pole Cap in its spring and summer and the migration of that CO₂ to the North Polar Cap. The same thing would happen in the North Polar Cap's spring and summer, but the effect was smaller.
        So, the southern cap has a stronger effect on the semi-annual march of air pressures on Mars, because the CO₂ ice is more extensive than on the northern cap, and the winter there is longer and colder than the northern cap due to the exaggerated ellipticity of the planet's orbit interacting with the marked tilt in the axis.
    - Another weird feature of the South Polar Ice Cap is that it isn't, exactly, "polar."
      - The winter cap and seasonal hood is pretty symmetrical, extending up to ~ -45°, as noted above.
      - The residual ice cap, however, is markedly askew, developing on the western end of the actual pole and missing from the eastern end.
      - Marco Giuranna and his team in Rome used the Mars Express Planetary Fourier Spectrometer in 2008 to measure temperatures through vertical profiles above the polar region and found that there are two temperature régimes there, which they relate to the general air circulation of Mars.
      - Like Earth, Mars has a prevailing westerly air flow in the southern mid-latitudes. This is strongly affected by topographic contrasts, such that a lot of this air flow falls into Hellas Planitia (around 60° - 90° E) and then flies up the other side, creating a massive undulation, or Rossby wave, in the westerlies circulation. This airflow is deflected poleward as it first undulates up into the upper troposphere and then comes down around the eastern side of the South Pole.
      - This descending airflow, as on Earth, would be dry, which would preclude carbon dioxide or water snows (though it would not prevent surface frost developing in the extreme cold). So, the east side of the South Pole, while frost covered in winter, does not receive snow to support ice buildup.
      - Meanwhile, the air rises on the west side of the pole, creating lower pressure there and supporting, in addition to frost, a bit of snow, which can sustain glacier development on that side of the pole.
- So concludes our tour of the "second order" features of Mars. These are large and conspicuous features that do not nest tidily within the first order features (the crustal dichotomy and the Tharsis rise) but in some ways are nearly as conspicuous, particularly on the MOLA maps. They sometimes transcend the first order, with, for example, Valles Marineris reaching beyond Tharsis to drain into the Northern Lowlands. The system of great craters, too, is found on both sides (and on top) of the crustal dichotomy. Together with the first order features, they create an easily memorized structure of reference points, lines, and polygons, with which we can fill out the details of our mental map of Mars. We can refer to a feature, for example, as "comprising a large region between Hellas Planitia and Argyre Planitia" (Noachis Terra) or "a subregion of Noachis Terra found west of the Chryse Trough and east of the Thaumasia Block" (Bosporos Planum). Interestingly, each of these features seems to be a huge example of a given geological or geomorphic process, such as cratering (the four big bruisers), rifting (Valles Marineris), jökulhlaup-type massive outflows (Kasei Valles), huge volcanic province (Elysium Rise), glaciation (polar ice caps), wind erosion ("Blue Scorpion" of Syrtis Major, hydrological drainage (Chryse Trough), and megalandslide (Thaumasia Block).
Third order of relief: Variations in crater density
- The third order of relief includes regions smaller in extent than most of the second order features, though some are very large, as large or larger than many second order features already described.
- As mentioned earlier, they do not "nest" within second order features (though they do within the first order), as I reserved the second order as the level of really conspicuous large features of the planet.
  - Third order features are broad regions, but they are not visually conspicuous in the way of, say, Syrtis Major or the seasonal polar ice caps.
  - They typically range in diameter from ~1,000 km (e.g., Meridiani Planum) to 5,500 km (e.g., Noachis Terra).
  - They are all named as:
    - Terra ("extensive land mass")
    - Planum ("a plateau or high plain")
    - Planitia ("a lowland or low-lying plain")
- It is at this order that we can clearly see the variations in crater density, size, and condition, which are used to establish relative dating on the martian surface. In discussing the third order of relief, then, I'll first cover the crater-counting system of relative aging and then the epochs of martian geology. Each epoch will be used to frame the third order landscape features.
- Crater-counting
  - The idea here is that the longer a planetary surface has been around, the more "opportunity" it has to be the target of solar system debris.
  - This debris consists of the small dust grains to planet-sized objects that have accreted, largely through gravitational attraction, out of the planetary gas and dust nebula and disk that surrounds the proto-sun and sun.
  - There is a magnitude-frequency relationship here, similar to what we see with many other hazards: The smaller impact events are vastly more common than the larger ones.
  - The ideal size-frequency distribution follows a power law pattern, that is something along the lines of Y = aX^-b, or, alternatively, log Y = log a - b(log X), where Y = the number of craters in a given size range or larger; X = crater diameters; a = the Y intercept (a calculated constant); and b = the slope of the curve (the other calculated constant).
  - Doing this as a log-log chart, the association, ideally, forms a straight line, with slope b.
  - The older the surface is, the higher a will be. The curve for an older surface will have the same slope but its height on the chart will be greater.
  - Past a certain point, though, you reach saturation, a level of bombardment so severe, a landscape so old, that there is literally no more room for a new crater: Each new crater necessarily obliterates traces of older craters.
  - Once saturation is reached, it is no longer possible to say that one saturated landscape is older or younger than another saturated landscape. Once saturation is reached, all you can say is that surface is crazy-old, on Mars, over 4 billion years old.
  - To do a crater count study, you need to calculate the area of your study area and normalize it (so that counts can be scaled to a common areal base): A common system (Hartmann and Neukum 2004) uses a square kilometer.
  - Then, you identify every crater on your image, recording its diameter in meters or kilometers.
  - Then, you establish size bins: The common standard is an X axis with each bin's upper boundary equal to the lower boundary times the square root of 2. So, starting at 1 km, the next bin boundary would be 1 * √2, or 1.414. The next one would be 1.414 * √2, or 2. The next one would be 2 * √2, or 2.828, followed by 2.828 * √2, or 4, and so on.
  - After you have your size bins, you compare each of your crater diameter measurements to your bins and count up the craters that fall within each of the bins and then convert the counts so that they are proportional to 1 km², instead of the original size of your actual study area. So, if your study area were 100 km², you'd divide your counts by 100 (and, yes, it seems weird to count the number of 5 km wide craters in a 1 km² standardized area).
  - That done, you plot the adjusted number of craters in each bin on the Hartmann-Neukum "isochron" graph, available at http://www.psi.edu/research/mgs/template2008.JPG.
  - You'll find that the pattern of dots you plot at the intersection of the middle of the bins and the number of craters per square kilometer will align roughly with one of the dotted or solid lines on the isochron plot. This can be very roughly: Typically, the rightmost dots, especially, are more widely divergent from the isochrons. The counts in the larger bins are smaller and smaller, so you get statistical small-sample effects that allow the dots to range pretty far afield.
    - The dotted lines are labelled with years ago (y = years; My = millions of years; Gy = gigayears or billions of years).
    - The long, straight solid line is saturation somewhere past 4 Gy. The longer of the two short solid lines represents the boundary between the Noachian Epoch and the Hesperian and the shorter, lower of the two short lines represents the boundary between the Hesperian and the Amazonian (about which, later).
    - By looking at the height of the line your craters align with, you can estimate the relative age of your study area (Noachian, Hesperian, or Amazonian) and put some constraints on the absolute age of that surface, based on an elaborate adjustment of lunar cratering rates with corrections for Mars location in the solar system, its greater gravity, and its atmosphere.
  - There are a few "plot complications" with the use of the crater magnitude and frequency distribution for the estimation of absolute ages on Mars.
    - If you look very closely at the dotted isochrons, you will see that they do not form completely straight lines: They turn down somewhere around 64 km. This reflects the drop in the supply of humongous potential impactors after about 3.7 billion years ago, at the end of the Late Heavy Bombardment. The LHB is a point of some controversy:
      - Did it simply mark the end of the era of accretion and the removal of available big impactors by their making themselves unavailable by, well, impacting into something in the solar system?
      - Was there a tumultuous and dramatic increase in the number of big items stirred up in the solar system about 4.1 to 3.7 billion years ago (perhaps by the movement outward of the outer two giant gas planets at that time)?
    - The exact meaning of the LHB is controversial but its existence is not: Things really quieted down in the inner solar system after about 3.8 or 3.7 billion years ago.
    - If you look at the other end of the X axis, you'll see a much steeper turn upward at roughly (and variably) 1 km in crater diamter. This has really been controversial.
      - Some argue that there really is a break in the size of potential impactors, because there really is a qualitative break in the numbers of smaller objects.
      - Others suspect that the upward break in the curves reflects secondary impacts: Ejecta that lands at various distances from the primary crater, creating craters of their own.
      - There's a whole cottage industry in trying to figure out ways of differentiating secondary craters from primary ones just to get a handle on how many of them there are and how their presence may distort estimated ages of a surface.
        
        They may have different shapes or different depth to diameter relations than primaries because they would be coming in at less than supersonic speeds (but that is true mainly for the secondaries that fall close in; those that get tossed out a far way may well attain very high velocities coming back to ground).
        They seem to have a propensity for falling in distinct lines or rays. Fresh craters generate rays of finer ejected materials interspersed with bigger objects. The rays may erode away on Mars but the alignments of the secondary craters may preserve that rayed appearance (this is the subject of my own research on Mars, using statistical techniques to pick out potential alignments of craters that might identify secondaries).
    - If you look still farther to the left of the X axis, you'll notice yet another inflection point in the isochrons around 10-12 m, where the lines curve back down a bit. This probably reflects one or more of the following:
      - the differential susceptibility of smaller craters to obscuring by erosional and depositional processes
      - the greater susceptibility of smaller objects to ablation and shattering en route through the martian atmosphere
      - resolution issues -- some craters are so small that they may not be discernible, even on a high resolution image.
    - So, power law mathematics are a great starting point, but Mars doesn't completely coöperate with the simplicity of mathematics. The power law seems to work with a slope of -1.8 or 2.0 for most martian surfaces for craters with diameters in the ~1 km to ~64 km size range. Outside that range, b would be larger and of different magnitudes at either end of the X scale (about -3.82 for craters < ~1 km; about -2.2 for those larger than ~64 km).
    - Neukum tried to get around this by using higher order polynomial modelling, but he and Hartmann reconciled their different approaches to develop that isochron chart linked above. So, there's now a more or less standardized approach to calculating relative ages and constraining absolute ages, but there remain all kinds of controversies over secondary cratering.
  - So, variations in crater density and size distributions is converted into a periodization scheme for Mars. Unfortunately, the scheme most commonly used maddeningly departs from the system developed for geological time on Earth. Here's a quick overview of geological time and rock units on Earth.
    - A distinction is made between geological time and geological rock units: Geochronology and chronostratigraphy.
    - At the coarsest level is the eon time unit, which is associated with eonothem rock units. On Earth, there are four of these: Hadean (planet formation to ~4 Ga), Archean (~4 Ga to 2.5 Ga), Proterozoic (2.5 Ga to ~542 Ma), and Phanerozoic (~542 Ma to present).
    - These eons/eonothems are broken down into eras and corresponding eonothems, such as the Palæozoic, Mesozoic, and Cenozoic within the Phanerozoic eon/eonothem.
    - Eons/eonothems are broken down into periods and the corresponding systems, and some of these are differentiated into subperiods and subsystems. So, for example, we have the Tertiary and the Quaternary periods/systems within the Cenozoic era/erathem. The Tertiary is divided into the Palæogene and the Neogene subperiods/subsystems.
    - Periods/systems and, where they exist, subperiods/subsystems, are further subdivided into epochs or the corresponding rock series (such as our own Holocene Epoch [from ~11,500 BP] and the Pleistocene Epoch from 1.8 Ma to ~11,500 BP), which fit within the Quaternary Period/System (which doesn't have subperiods/subsystems).
    - Some periods are subdivided even further into ages or the corresponding rock stages (e.g., the Calabrian or late Pleistocene and the Gelasian or early Pleistocene).
    - There are some inconsistencies and arguments, but the general pattern of eons, eras, periods, epochs, and ages is widely recognized. Here is a link to a USGS geological time scale: http://pubs.usgs.gov/fs/2007/3015/.
    On Mars, given that we don't really have much detail yet, we have three main subdivisions, each of which may be subdivided to one more level. The basic levels you'll see referred to as periods, epochs, or eras, and I'll probably use all three in what follows. Usage is converging on using "period" for these, even though it's pretty inconsistent with Earth geological time scale customs. These divisions are based on relative crater densities and superposition relationships. From oldest to youngest, these are the:
    - Noachian (formation of the planet to the end of the Late Heavy Bombardment, featuring the formation and collapse of the planetary magnetic field and the initiation of intense volcanism in several locations and gradual concentration largely in the Tharsis complex)
    - Hesperian (progressive desiccation, sulfuric acid buildup in the atmosphere and hydrosphere due to volcanism, great outwash events, and loss of most of the atmosphere, starting about 3.7 or 3.8 Ga to, debatably, ~3.5 or 3.0 or 1.8 Ga)
    - Amazonian (desiccation and oxidation, from the Hesperian to the present)
  - Geochemical periodization. A new system has been proposed by Jean-Pierre Bibring and a large team of colleagues in a Science journal article in April 2006 (312, 5772: 400-404). It divided Mars' history, not in terms of the traditional crater-counting derived Noachian, Hesperian, and Amazonian periods but in terms of dominant geochemical processes. The result was the following periodization (which they do call eras, which is more consistent with Earth geological time at least!):
    - Phyllocian Era: dominated by neutral or alkaline aqueous chemistry, resulting in the deposition of phyllosilicate clays. This would be the geochemical régime most friendly to "life as we know it, Jim." Early to middle Noachian time-frame.
    - Theiikian Era: dominated by acidic water chemistry, as a result of the massive volcanism of the later Noachian and early to middle Hesperian. Volcanic activity ejected massive amounts of sulfur dioxide into Mars' atmosphere, which would interact with water to produce sulfuric acid, drastically acidifying surface and subsurface waters.
    - Siderikian Era: dominated by æolian processes and oxidative geochemistry, resulting in the production of anhydrous iron oxides. This was a time of progressive loss of surface waters and most of the atmosphere after the collapse of the planetary magnetic field. Water photodissociated in the atmosphere, freeing its hydrogen to scoot off into space in the exosphere and drawing the heavier oxygen to bind with iron-bearing minerals ("rust") in dry conditions. This would coïncide with the late Hesperian and the entire Amazonian periods. In what follows, we'll use the traditional crater-counting periodization but with attention paid to the geochemical issues at the heart of the Bibring et al. system.
- Noachian surfaces: The oldest
  - From the earliest formation of the planet through the gravitational accretion, collision, and consolidation of planetesimals, asteroids, comets, meteoroids, and dust.
    - Some people are dividing the traditionally understood Noachian into the "pre-Noachian" and the Noachian proper, with the pre-Noachian reserved for the time of planetary accretion, differentiation, and development of the planetary magnetic field. These folks would end the pre-Noachian at the point where crater saturation doesn't allow you to discern really old surfaces, a time by which the dynamo had clearly shut down (the time of the Hellas and other huge impacts).
    - Traditionally, though, the whole period from the time of the planet's origins to the end of the Late Heavy Bombardment is referred to as the Noachian. So, the Noachian includes:
      - The kinetic, compressional, and radioactive heating of the accreted materials
      - Differentiation begins with melting of these materials and the "iron event," when iron, melting first, began to drift in blobs toward the center of the planet, pulling some siderophiles with it (particularly nickel).
      - Formation of the mantle magma ocean.
      - Formation of a crust on top of the magma ocean, in Mars' case, apparently quite a thick one, for reasons unknown.
      - Mantle overturn because of the gravitational instability created when magnesium-rich olivine cumulates that crystallized out first at the hottest temperatures were overlain by denser iron-rich olivine cumulates that crystallized out later at a somewhat cooler temperature.
      - Initiation of the planetary magnetic field through motion in the outer, liquid iron-dominated core.
      - The sustained bombardment of the differentiated planets as the solar sys tem was cleaned up of most of the stray smaller objects by the gravitational fields of the early planets.
      - Some differentiated bodies were themselves smashed into asteroids and � meteoroids, giving rise to the many different types of meteorites: chondrites � and carbonaceous chondrites from primordial material and achondrites, irons, � and stony irons from previously differentiated bodies.
      - This hellacious era went on until about 3.9 to 3.7 billion years ago in most accounts and as "recently" as 3.5 billion BP in others: There are still a lot of controversies about when, exactly, the Noachian drew to a close. The most commonly cited time in recent writings is 3.8 or 3.7 Ga.
  - The Noachian roughly corresponds with the Hadean time on Earth (4.5 � to 3.8 GYr), but, unlike on Mars, we have no rocks on Earth that date from this time because of the intense geological activity here.
    - Well, let me qualify that: There are a few grains of zircons that old on � Earth, small crystals that were once part of igneous and metamorphic rocks.
    - Zircon contains some uranium, thorium, and lead, the ratios among which has allowed them to be radiometrically dated to as old as 4.4 billion years on Earth, in the case of the Jack Hills zircons from Australia!).
    - There's been a controversy more recently about the age of actual mafic rocks in Canada that might be as old as these zircons: the Nuvvuagittuq greenstone belt just east of Hudson Bay in northern Province Québec. These have been dated to 4.4 Gya but the results are contested with claims that they're no older than a "mere" 3.8 billion years old.
    - So, where on Earth Hadean eon materials consist of a very few zircon grains and a controversial claim for Canadian greenstones, on Mars, roughly 40% of the planetary surface dates back to the comparable Noachian (Barlow 2010). If you're on campus or logged into the library from home, you can view Barlow's map of martian age distibutions here: http://bulletin.geoscienceworld.org.mcc1.library.csulb.edu/content/122/5-6/644/F8.large.jpg.
  - So, while Mars is geologically active, it's nowhere near the level of activity seen on Earth with its plate tectonism, and that has allowed the preservation of ancient surfaces on Mars and their obliteration on Earth (except for those zircons and maybe the Canadian greenstones)
  - The constraint on the Noanchian timeframe is based on analysis and dating of Moon rocks from similarly cratered surfaces brought back to Earth by Apollo.
    - This is a fairly elaborate reasoning process. Rocks were taken back to Earth from the Moon by the Apollo astronauts from regions that had been previously relative-dated by crater-counting techniques. The returned rocks, then, allowed for an absolute date to be assigned to surfaces of previously described as of particular relative dates.
    - Then, the size-frequency curve for the Moon had to be calibrated for use on martian surfaces, factoring in Mars' atmosphere (which would both destroy more of the smaller objects and slightly reduce their incoming velocity), Mars' location closer to the putative source of orbiting debris in the solar system (closer to the asteroid belt and to Jupiter, the gravity of which dislodges objects and puts them on new orbits, including orbits that intersect the inner solar system bodies).
    - You can get an overview of the Moon to Mars isochron correction system (optional link for the curious: http://www.psi.edu/research/mgs/isochron.html).
  - Characteristics of Noachian surfaces
    - Noachian surfaces on Mars are intensely cratered: craters on top of craters to the point that it becomes challenging to pick out which ones are superposed on which others
    - Noachian surfaces also show a great diversity of crater sizes, with some big craters mixed in with medium and small ones
    - Noachian craters, too, show a lot of geomorphic reworking:
      - Very distinctive softening of the rims, as though they'd sagged and spread out.
      - Hardened ejecta blankets with that "wet splat" look, sometimes with two or more layers of flowing ejecta, sometimes with the kinds of striations produced by very rapid and fluidized movement, often ending in a rampart edge.
      - Some of these craters were clearly buried by wind or water deposits, and then subsequently re-exposed by erosion as pedestal craters perched like crater-dented mesas high above the remaining landscape level.
      - floors flattened by the deposition of alluvial, lacustrine, marine, or æolian materials in them: You do not see that on the Moon, which lacks such familiar geological activities as wind and water erosion, transport, and deposition.
    - There was quite a bit of this geological work back in Noachian times:
      - Valley networks are found almost exclusively on Noachian surfaces, showing fluvial action by what is more and more accepted as water, even precipitation-fed channelization.
      - There was some early and distinctive vulcanism in the highlands, featuring plains formed from very low viscosity lavas (flood basalts, possibly emanating from long rupes or fossæ), small cones, and very shallow-sided vent-volcano edifices (pateræ).
      - Later in the Noachian, volcanic activity became increasingly concentrated in the two great volcanic rises, Tharsis and Elysium, which built up at this time. The viscosity of lavas associated with the later volcanism allowed the construction of very tall shield edifices and, in some cases, ashy eruptions were part of the mix, which allowed the construction of steep sided tholi.
      - The Late Noachian saw such extensive and massive volcanism that global geochemistry was drastically changed.
        
        Early Noachian geochemistry was dominated by phyllosilicate chemistry (alteration of basalts in water to liberate silicas, including the kind of one silicon/four oxygen tetrahedrons that produce micas, talcs, and clays).
        Late Noachian and Early Hesperian geochemistry shows a strong sulfate signal, as volcanoes spewed out massive amounts of sulfuric acid, carbon dioxide, and water and created a strongly acidic aqueous chemistry.
        This would explain the near lack of calcium carbonate on Mars: The presence of sulfate (SO^2-₄) and sulfur dioxide (SO₂) prevents the formation of calcium carbonate and favors the formation of hydrated calcium sulfite (CaSO₃ - H₂O) instead, which can oxidize to create sulfates, iron oxides, and more acidity.
        Most of the arguments about possible oceans on Mars place it in the Noachian time frame, and, given the previous argument about sulfate chemistry, if those oceans were strongly acidified, the lack of calcium carbonate on the putative ocean floors becomes more comprehensible.
  - Tour of Noachian regions
    - I'll use a "walkabout" style of presentation, starting with the type province (Noachis Terra) just west of Hellas Planitia and then go generally west through Aonia Terra, Terra Sirenum, Terra Cimmeria, to Promethei Terra, which takes us back to Hellas Planitia. From there, we'll swing up north to Terra Tyrrhena and then go west and northwest into Terra Sabæa, Arabia Terra, Margaritifer Terra, Xanthe Terra, and then Tempe Terra, leaving us northwest of Alba Patera.
    - Noachis Terra, the prototype, is a large region to the west of Hellas and east and north of Argyre.
      - This is a contender for the greatest crater density on Mars prize.
      - Mariner 4 got images of Noachis Terra during its flyby, which created the (then rather shocking) image of Mars as a dead, dry planet much like the Moon.
      - Subsequent closer looks showed it to be a lot more interesting:
        
        The craters themselves turned out to be pretty strange
        They often have softened rims and flattened floors, including some "ghost craters" that are so softened and infilled that they have practically vanished.
        Softened craters turned out not to be the result of standard-issue erosion and deposition mechanisms: It's as though entire landscapes of old craters sagged, spread out, and flattened, but new craters haven't.
        This suggests that there was a lot of soil moisture and ice back then, which could flow, deform, and relax, softening the look of the ancient craters.
        Pedestal and rampart craters were found here, too.
        
        These look like impacts into surfaces loaded with ice, which vaporized and liquefied on impact, creating that "wet splat" look.
        The ejecta blankets appear to have solidified as a particularly resistant material, which functioned kind of like a cap rock of resistant material.
        Erosive agents attacked the surrounding landscape, but the area under the ejecta blankets was protected from whatever the regionally dominant erosive agent was, leaving the crater and its ramparts of ejecta perched high above the worn-down landscape, kind of like mesas with holes punched in the top.
      - Drainage networks that looked like fluvial systems on Earth showed that water or some other similar fluid ran over martian landscapes and eroded them.
        
        Long networks featuring several tributaries, most of them fairly short with few of their own tributaries, such as Nirgal Vallis
        Several smaller drainage basins with relatively long tributaries and drainage densities larger than the Nirgal Vallis system's but smaller than typical for Earth catchments and with nowhere near the degree of interfluve dissection common on Earth
        The origins of such valley networks have long been contentious.
        
        Some authors argue for a precipitation-fed runoff history and the evidence their existence gives to arguments that Noachian Mars had higher atmospheric density and warmer temperatures, allowing at least for snow to fall and liquid water to exist long enough to flow overland into drainage channels (e.g., Gulick and Baker 1990; Ansan and Mangold 2006). This would pertain to the dendritic drainages.
        Others have pointed out that most such networks have fewer, shorter tributaries than most Earth valley networks and that many of the short tributaries originate in alcoves or theater-shaped headwalls most akin to the slope morphologies of groundwater sapping-fed networks in arid Earth environments (e.g., Laity and Malin 1985; Malin and Edgett 2000)
        Such morphologies can also be produced by meltwater from under snow or ice cover even in very cold, arid conditions, as seen at a small scale in and around Haughton Crater on Devon Island in northern Canada (Lee et al. 1999).
    - Aonia Terra southwest of Noachis Terra and Argyre Planitia
      - Its central areas are classic Noachian landscapes, highland cratered units with many small dendritic valley networks.
      - There is much evidence of contemporary æolian processes, including large dune deposits at the base of some crater rims, with some evidence of dunes overtaking older dunes trapped against a topographic barrier.
      - Much of the Aonian cratered landscape shows signs of being subdued in contrasts, very akin to the crater softening and flattening seen in the discussion of Noachis Terra.
      - There is a heavy profusion of larger craters in Aonia Terra, many showing the pedestal structure seen in Noachis Terra. The pedestals preserve craters on a surface once higher than today's, about 500 m higher (Head et al. 2003), which was eroded away around the craters and their resistant ejecta blankets by, presumably, meltwater from once larger polar ice deposits.
      - Aonia Terra has extensive development of Hesperian aged flat and rather featureless plains, particularly in the northern part of the region just south of the Tharsis mountains. These have been interpreted as being comprised of thick beds of alternating lava flows and æolian deposits that have buried underlying terrain (Scott and Tanaka 1986).
    - Terra Sirenum west of Aonia and south of Tharsis
      - Terra Sirenum is a profusely cratered basaltic terrain of the Southern Highlands, located to the southwest of the Tharsis rise.
      - It shows a diversity of surface ages, though the preponderant surface exposure is Noachian
      - There are several large craters with diameters exceeding 100 km and some exceeding 300 km.
      - Again, we have the valley networks of apparent fluvial origin
      - A particularly striking feature of Terra Sirenum and its neighbor, Terra Cimmeria, was revealed by the Mars Global Surveyor magnetometer: marked linear bands of alternating remanent magnetization, trending east-west across these two adjacent regions.
        
        Linear magnetic bands like Earth's spreading zones that record polarity changes in our planetary magnetic field?
        Accretion of terranes through plate tectonics, each with a different magnetic signal from the long-vanished martian magnetic field?
        Intrusion of magnetite/ilmenite dikes associated either with rift zone spreading or some other magmatic source?
    - Terra Cimmeria northwest of Sirenum
      - In many ways, Terra Cimmeria is essentially the westward extension of Terra Sirenum into the eastern hemisphere, out to ~ 120° E: It shares the same common range of elevations, the same general distribution by size class of ancient craters, and, with Terra Sirenum, houses the same east-west bands of remanent magnetization, and it is rarely discussed without its neighbor.
      - It retains a separate name as its inheritance from the names given to albedo features seen from Earth in the nineteenth century.
      - It made news in its own right when an aurora was recorded by ESA's Mars Express SPICAM instrument (Bertaux et al. 2005) at 177deg; E at -52°.
      - It also was the destination of Mars Exploration Rover, Spirit, which landed in Gusev Crater at the end of Ma'adim Vallis in the northeastmost corner of Terra Cimmeria.
        
        Ma'adim Vallis is, like Nirgal Vallis discussed under Noachis Terra, a long channel with several short tributaries suggesting some sort of sapping process more than the dissection of a fluvial network fed by precipitation and spring flow.
        It may have had at least one jökulhlaup massive outflow episode.
        Its morphology and the presence of delta-like deposits in southern Gusev Crater led to the selection of Gusev Crater as the landing site for the Mars Exploration Rover Spirit in the hope of finding sedimentary deposits.
        Spirit landed, instead, on a basaltic lava flow, probably from Apollinaris Patera to the north, which was emplaced after the Ma'adim Vallis flows
        Water-altered strata were not found for 159 sols until Spirit reached an outcrop of groundwater-altered volcanic ash exposed in the Columbia Hills.
        This was quite a "Mars, the yes, but ..." planet scenario.
    - Promethei Terra just east of Hellas Planitia
      - West and southwest of Terra Cimmeria, Promethei Terra lies adjacent to the eastern margins of Hellas Planitia.
      - Like all the Noachian regions, it is generously covered with craters in a profusion of size ranges
      - The landscape features ancient rugged highland terrain interspersed with lower elevation basins filled with sediments eroded and transported from the highland massifs.
      - In southernmost Promethei Terra is a roughly half-circular ridge, Promethei Rupes, which is evidently the remnant of a very large impact basin now mostly covered by Planum Australe.
      - Evidence of valley networks is apparent, as well, and northernmost Promethei Terra is the source region for one of the great outflow channels debouching in eastern Hellas: Harmakhis Vallis, its tributary Reull Vallis, and the tributary of the latter, Teviot Vallis.
      - The region is quite dusty, and dust piles up in great beds dozens of meters thick in many a crater.
      - Lighter coverings of dust often show networks of ornate dark streaks and curlicues, which were shown to be dust devil tracks disturbing the dust and exposing the basalt below, a phenomenon first clearly documented in the process of formation in Promethei Terra and since found all over Mars.
      - Many of Promethei Terra's craters are dramatically softened, with eroded or sagging rims and floors flat with infill. This has long been posited as the result of a large amount of interstitial soil ice and permafrost close to the surface that has undergone viscous relaxation over time, the surface layers flowing and deforming in lineated and lobate structures, sagging and creeping into arcuate ridges in valleys and crater bottoms.
      - Interestingly enough, these thaw/melt/flow features were pole-facing at latitudes less than 45° and equator-facing at latitudes greater than 45°, reflecting a dependence on total solar radiation rather than intensity of solar radiation.
      - Total solar radiation is affected, not only by slope aspect with respect to sun angle as it varies over the course of the day and the seasons, but with changes in orbital eccentricity and obliquity.
      - Evidence of glaciation during Mars' last high obliquity phase about 5.5 Ma are abundant in Promethei Terra, including a particularly striking hourglass-shaped pair of craters with a fill showing flow lines leading from the higher to the lower, which turned up in HRSC imagery.
    - Terra Tyrrhena north of Hellas Planitia and south of Isidis Planitia
      - Like most Noachian surfaces, Terra Tyrrhena's is a crater-littered landscape, its central plateau dating back to the Late Noachian and Early Hesperian and its surrounding lower elevation plains made up of younger Hesperian materials, largely volcanic.
      - Many of the craters show substantial filling and flattening of the floors and erosion of the rims.
      - The region shows signs of fluvial dissection in the zones between the older highlands and the younger lower elevation surfaces, with well-developed and often well-integrated valley networks, with tributary systems attaining up to the fourth order in the Strahler system of stream ordering.
      - Unaltered olivine of the original Noachian surface rock is shown in CRISM spectroscopy, sometimes covered with somewhat altered lavas but then excavated by impacts. Olivines are very rapidly altered in the presence of water into such minerals as serpentine, goethite, iddingsite, or hæmatite.
      - The team operating the OMEGA spectrometer on the European Space Agency's Mars Express found the first clear evidence of phyllosilicates exposed in crater walls and in eroded ejecta blankets around craters in Terra Tyrrhena, notable for the dependence of phyllosilicate formation on the interaction of rock with abundant neutral to high pH water. Phyllosilicate clays are alteration products of fairly neutral water acting on basalts.
      - Subsequent work has shown that the phyllosilicates are widely distributed on Mars, but only on Noachian terrain, such as Terra Tyrrhena, and of a diverse range of specific minerals (Marble et al. 2008).
      - The presence of phyllosilicates and the neutral or somewhat alkaline aqueous chemistry they indicate goes against the impression created by all the unaltered olivine and basalt. That "yes, but ..." quality again.
    - Terra Sabæa northwest of Hellas Planitia
      - Terra Sabæa is a heavily battered low albedo landscape located northwest of the Hellas Planitia rim and wrapping around Syrtis Major to its east.
      - It shows a wide range of crater sizes, again in nearly saturated profusion, as well as a number of Late Noachian fluvial valley networks.
      - Terra Sabæa, of all the Noachian regions, seems underrepresented as a setting for particular investigations, as I found out when I did my secondary crater prospecting study there.
    - Arabia Terra northwest of Hellas Planitia, north of Noachis Terra, and east of Chryse Planitia
      - Crater density is so great here, vying with Noachis Terra for the greatest densities on the planet, that superposition breaks down as a method of picking out the oldest craters.
      - The region is bounded to the north by the transition scarp down to the Northern Lowlands but, here, it is far less distinct and more fretted and intricately graded than it is in other parts of Mars.
      - The crust is considerably thinner under Arabia than under other parts of the Southern Highlands, too, more akin to the crust under the Northern Lowlands.
      - The northern and western portions of Arabia Terra are distinctive for areas of older cratered terrain, "inliers," standing isolated as buttes and mensæ towering over the far lower terrain comprising the bulk of the landscape there.
        
        These inlier features often expose marked layering, as, for example, in Cydonia in northwestern Arabia and its infamous "Face on Mars" mensa.
        The layering suggests burial of a Noachian surface and then its exhumation from under younger materials.
      - Construction of a 1 m resolution digital terrain model from the Mars Reconnaissance Orbiter's HiRISE instrument's stereo images permitted Lewis et al. (2008) to construct detailed topographic profiles of bedding outcrops in four Arabia Terra craters and measure layer widths.
      - Beds show rhythmic variations in width, which authors attribute to extraplanetary climate drivers, such as changes in orbital eccentricity, precession, and obliquity.
      - Arabia Terra's rhythmic sedimentary layers, then, join the polar deposits as potential archives of martian climate change and calibration of the crater counting based geological record.
    - Margaritifer Terra east of Valles Marineris, west of Arabia Terra, north of Noachis Terra, and south of Chryse Planitia
      - About 60% of its area is comprised of surviving heavily cratered surfaces of Noachian age.
      - It is quite distinctive, however, for the concentration of outflow channels and chaos terrain.
      - Most of these show the reduced cratering of Hesperian age surfaces.
      - Margaritifer Terra collected outflows from the following sources:
        
        the eastern end of Valles Marineris (Hesperian outflows)
        the Chryse Trough drainages (probably Noachian fluvial systems of varying connectivity and continuity)
        sources internal to the region, in the form of the many chaos terrains that themselves would have created massive jökulhlaup-like outflows during the Hesperian:
        
        Auroræ
        Pyrrhæ
        Asrinoses
        Aureum
        Margaritifer
        Iani
        Hydraotes
        Hydaspis
        Aram chaoses
      - The outflow channels cutting through Margaritifer Terra do not show the dendritic structure of precipitation-derived surface and groundwater-fed fluvial networks, such as the many small valley networks seen on Noachian surfaces and such channels as Ma'adim Vallis and Nirgal Vallis, respectively.
        
        That is, they do not originate in a series of low-order streams fusing their flows into progressively higher-order, larger discharge branches and trunks per Strahler.
        Rather, they originate in chaos terrain and emerge at full width below it, which they generally substantially preserve throughout their lengths, dwindling only far downstream.
        They show close to U-shaped or even box-shaped cross-sections, which suggests massive, sudden, and probably short-lived flooding of the jökulhlaup character, perhaps triggered by warming of subsurface ices by magmatic intrusion, perhaps in a system of dikes.
        Indeed, the outflow channels of Margaritifer Terra, Xanthe Terra, and Lunæ Terra have been characterized as, by far, "by orders of magnitude the most voluminous known fluid-eroded channels in the Solar System (Rodriguez et al. 2007).
        The chaos features at the heads of these channels and the hummocky, lineated, terraced lower reaches have been characterized as thermokarstic on the basis of Earth analogues in Siberia.
      - One of the "yes, but ..." qualities of these massive outflow channels, here in Margaritifer Terra and in the other borderlands of Chryse Planitia is the question about how much atmospheric density Mars would have had to have to sustain that much liquid for the duration of the jökulhlaup-type event and for what looks like ponding or pooling of this water in the Northern Lowlands. When would Mars have been above the triple point of water? Noachian times, but the crater density pattern in the Margaritifer Terra outflow channels is much lighter and not as diverse in size as we see on Noachian surfaces: They are more in line with Hesperian times.
      - This discrepancy has fed skepticism that the fluid involved was, in fact, actual water.
        
        Probably the most commonly proposed fluid is brine. The brine would be comprised of the chlorine and sodium in magma, which can combine to form salt or sodium chloride. Under impact gardening conditions, this salt would be joined by calcium and magnesium and other elements in subsurface water to form a very complex brine, and such brines have very low freezing points, in some cases as low as 225 K or -48° C.
        
        Concentrated brines might thus account for the ability of subsurface fluids to sustain the kinds of flows in the outflow channels of Margaritifer Terra, as well as the small seeps and gullying witnessed even today on martian crater walls (Knauth et al. 2001; Knauth and Burt 2002).
        The brines would be activated by subsurface warming, perhaps due to magma intrusion regionally or in the form of dikes ascending into frozen soil brine.
        
        Another scenario proposed by Nick Hoffman is that the fluid involved is actually carbon dioxide: Carbon dioxide sublimes extremely violently upon depressurization and the kinds of flows seen in Margaritifer Terra and Valles Marineris could have been gas-supported flows more like pyroclastic flows in their behavior. Talk about popping the soda bottle after too long a trip in a car with bad shocks!
        Still another proposal is that lava deposition during the formation of Tharsis could have heated thick underlying deposits of hydrous sulfate evaporites, as may be exposed, for example, in the walls of Valles Marineris. If so, the heat could have caused dehydration of the evaporites and segregation of the water, which would have increased their volume and thereby pressured the segregated water into explosive release (Montgomery and Gillespie 2005).
    - Xanthe Terra west of Margaritier Terra and northeast of Valles Marineris
      - Like any Noachian landscape, Xanthe Terra is badly battered with a wide range in sizes of craters, including many with diameters in excess of 10 km.
      - Like Margaritifer Terra next door, Xanthe Terra also has a number of outwash channels crossing it but in a more organized north/northeast direction:
        
        Shalbatana Vallis
        Nanedi Vallis
        Maja Vallis, which comprises Xanthe Terra's western boundary (with Lunæ Terra)
        There is some discrepancy in regional usage in the literature: Some authors refer to Tiu Vallis, Simud Vallis, and Ares Vallis as part of Xanthe Terra, using Ares Vallis as the eastern boundary, but the USGS, NASA, and IAU, in the planetary gazetteer prefer to confine Xanthe Terra to the area directly north of eastern Valles Marineris. I'm only mentioning it here, because you may encounter discrepant usage in older writings.
      - While many Noachian regions show modification of the basic crater-pocked surface by wind, ground ice, groundwater, or surface water, Xanthe Terra, however delimited, shows an unusual concentration of different types of modification:
        
        groundwater sapping
        weak fluvial network development
        the massive outflows (jökulhlhaup) mentioned earlier
        permafrost
        chaos terrain formation (subsurface fluid withdrawal and surface collapse)
        volcanism
        landslides
        æolian processes
        diagenetic processes (alteration in situ) generating layering that resemble the stratigraphy of sediments or volcanic flows
    - Tempe Terra far northwest of Xanthe Terra and northeast of Tharsis.
      - Lying well to the northwest of Terra Xanthe and off the northeastern edge of the Tharsis Rise, Tempe Terra is the northernmost reach of the cratered Southern Highlands and a kind of isolated outlier of Noachian territory.
      - It is the lowest lying of the "highlands," as well, with perhaps half of the region lying below the geoid, though Tempe Terra surfaces may stand as high as 3-4 km above nearby Northern Lowlands elevations.
      - The transition scarp is quite steep in northern Tempe Terra.
      - As in Arabia Terra, much of the transition from the cratered highlands to the lowlands is marked by taller mensæ and knobs separated by swaths of lower and smoother terrain that descend to the lowlands in a series of steps.
      - Though much of the region lies below the geoid, the southwestern and central portions are mostly above, and there are areas in the center and scattered along the west and south that reach above 1,000 m.
      - Making Tempe Terra quite distinctive among the Noachian regions is the presence of long and sometimes sinuous fossæ, as well as catenæ (linear arrangements of subsidence pits often set off by extensional stresses), which fan out from a common center on the northern portion of the Tharsis rise, e.g.,
        
        Mareotis Fossæ
        Tempe Fossæ
        Labeatis Fossæ
        the largest catena is Baphynis Catena
      - This is the region of Mars showing the greatest seismic strain, according to a team headed by Matthew Golombek, who measured fault throw and distortions in the shape of craters to estimate the degree of extensional stress in Tempe Terra.
    - So, that concludes our tour of Noachian Mars, which comprises most of the planet. Each of these terræ, plana, and planitiæ share dense cratering approaching saturation levels, with a "striking" mix of different crater diameter sizes. It is in Noachian Mars we see valley networks, some of them quite dendritic and approaching fourth level stream order. There are also quite a few long trunk/short tributary systems with theatre-headed alcoves in their upper reaches, possibly groundwater-seepage systems akin to those in the American Southwest. Noachian Mars also shows a range of volcanic types, from the common flood basalts and ridged plains to shield volcanoes and some steep-sided volcanic edifices, with evidence that concentration of magma sources had taken place over the Noachian, culminating in its concentration in the two great volcanic rises, Tharsis and Elysium. Many of the ancient Noachian surfaces have been reworked, sometimes dramatically, by various geomorphic agents, such as wind, fluvial processes, glaciation, volcanism, and permafrost in more recent Hesperian and Amazonian times.
END 03/25/15
Hesperian surfaces: Intermediate
- The Hesperian is the shortest of the three conventional divisions of martian geological time.
- Persistent uncertainties in absolute surface dating (the transformation of lunar age-crater relationships into martian ones and the question of secondary cratering) are especially evident in this time period.
  - So, it's said to begin at the end of the Noachian, somewhere between 3.9 and 3.5 billion years ago. That transition is less contentious, and the most commonly cited date is converging on 3.7 or 3.8 Ga.
  - The transition from the Hesperian to the Amazonian, however, is more divergent in the community, ranging from as early as 3.55 billion years ago to 1.8 Ga. The most commonly cited boundary is 2.9-3.0 Ga.
  - The Hesperian was an era of fundamental change in the way the martian system operated:
    - The impact flux dropped off and the truly large impactors came no more as the solar system was cleared of the larger objects.
    - The Hesperian was also a time of widespread volcanism, following on the increase in volcanic activity in the Late Noachian, when volcanic flows began to build up Tharsis, with shield vulcanism beginning to create edifices there, probably starting with Alba Mons.
    - One consequence of all this was a dramatic increase in the sulfur dioxide (SiO₂) content of the dwindling atmosphere and the sulfuric acid (H₂SO₄) content of the dwindling water. So, all that volcanic activity in the transition from the Noachian to the Hesperian would have resulted in much more acidic water in oceans, in groundwater, and in any precipitation. Here are some (TMI?) details:
      - Sulfur dioxide oxidizes into sulfur trioxide (SO₃, which can combine with water (H₂O) to form sulfuric acid, making water acidic.
      - Sulfuric acid itself can dissociate readily in water to create hydrogen sulfate ions (HSO₄^- and, very importantly, hydronium ions or H₃O⁺. Concentrations of hydronium ions are the essence of the pH scale of acidity/alkalinity: pH is the negative logarithm of the hydronium ion concentration. As hydronium ions increase, pH drops, that is, becomes more acidic.
      - Hydrogen sulfate ions in water can also dissociate into more hydronium ions and sulfate ions (SO₄^2-). On Earth, there are certain bacteria and archæa that can reduce sulfate ions (park electrons/energy onto them, taken from hydrogen and hydrogen ions) turning the sulfate into water and hydrogen sulfide or H₂S (in order to oxidize organic compounds or hydrogen for anærobic respiration). Chemosynthetic "critters" tend to be extremophiles on Earth and may have been among the very earliest life-forms on Earth. So, if life got going on Mars as chemosynthetic microörganisms, they might have been able to survive in certain situations in the sulfur-enhanced world of the Early Hesperian. Life on Earth may have arisen during the Eoarchæan, which roughly parallels the Early Hesperian on Mars, and it probably began as chemosynthetic microörganisms.
    - Planetary geochemistry really changes in response to this acidification, favoring the production and deposition of sulfates and evaporites within and on top of rocks, such as those in the Columbia Hills of Gusev Crater that some of you may have "met" in GEOG 400/500. This is a marked change from the phyllosilicate clay formation and deposition seen in the early Noachian. Water alteration of volcanic rock leads to different minerals, now, such as jarosite, goethite, gypsum, and hæmatite. The change is so drastic that it led the Bibring team to propose a resequencing of geological time on Mars based on geochemistry (the Phyllocian and the Theiikian -- drastically different chemistries).
      - Jarosite is a hydrous sulfate of potassium: KFe³⁺(OH)₆(SO₄)₂ associated with very low pH water (pH of 1-3) and low water to rock ratios: It tends to dissolve and allow formation of goethite and gypsum in less acidic water
      - Goethite is a hydrous iron oxide, FeO(OH).H₂ (it often forms from jarosite as a water body begins to evaporate or as pH becomes less acidic)
      - Gypsum is a hydrous calcium sulfate (CaSO₄) (it tends to dissolve in very acidic water, making the formation of jarosite likely). It was found by the Opportunity rover in veins in bedrock where water had deposited gypsum in cracks in the rock.
      - Hæmatite is anhydrous ferric oxide or anhydrous iron (III) oxide or Fe₂O₃. It was found by the Opportunity rover as spherules formed within sedimentary bedrocks rich in sulfates, such as jarosite, probably as iron-rich groundwater concentrated ferric oxide in concretions within the evaporite beds.
    - Volcanism continues its shift in eruption style from low viscosity flood eruptions (effusive eruptions) into vented shield volcanoes and a more viscous or sticky/gassy style of eruption (often explosive).
    - Too, there's a spatial concentration in volcanic activity from more diffuse fissure-and-intercrater plains flows to distinct vent focussed eruptions and the construction of large edifices around large calderas and increasing spatial confinement to the Tharsis and Elysium bulges.
    - Wrinkle ridges are common on Hesperian plains, especially those ringing Tharsis to the east, which indicates compressional stress and strain outward from the Tharsis pile.
    - Faulting and the formation of linear grabens (fossæ) in areas of evident extensional tension (parts of Tharsis, for example)
    - The Hesperian is when the majority of the gigantic outwash floods flowed, a fluvial behavior drastically different from the smaller groundwater and possibly precipitation fed valley networks of Noachian areas.
      - The connection between these outflows and chaos terrain and the association of chaos terrain with explosive subtraction of subterranean fluid and subsidence are often linked with volcanism.
      - Magma may have intruded into or near subsurface or surface ice, often in the form of dike swarms, which heated the undersides of ice-rich beds and/or the ice-plugged slope walls of craters and grabens, creating confined aquifers.
      - These liquids would pour through broken megaregolith or any break in the cryospheric layers capping or plugging them and into channels, sometimes quietly at a small scale and sometimes explosively and massively.
    - Another fundamental change in the martian system during the Hesperian was the loss of most of the atmosphere and the drop in air pressure below the triple-point of water at martian temperatures. Here is a phase diagram for water showing the triple point. Mars now averages about 6 mb or hPa, and its temperatures rarely get above 0° C or 273K, very close to the triple point. At that pressure, water goes from ice to vapor with a warming of temperature, though there may be very low elevation places that transiently experience higher pressures and, thus, potentially brief episodes of liquid water.
      - Along with the bulk of the other gasses in the atmosphere, Mars lost as much as 95% of its water, as water vapor in the atmosphere dissociated under the barrage of the solar wind and its more extreme pulses, and the very light H+ ions easily escaped (and still escape) into space. The remaining water on Mars sank underground into permafrost and, perhaps, liquid water under that.
      - As a consequence, rates of erosion declined dramatically on Mars, other than those spectacular, if sporadic, outwash floods that peaked during the Hesperian.
      - The Hesperian was the time, then, during which martian climate began to dry out and become really dusty and water began to concentrate in permafrost, soil ice, the polar ice caps, and very tenuous cloud activity.
      - Hesperian surfaces cover about 34% of Mars (Barlow 2010). If you're on campus or logged into the library from home, you can view Barlow's map of martian age distibutions here: http://bulletin.geoscienceworld.org.mcc1.library.csulb.edu/content/122/5-6/644/F8.large.jpg.
- Tour of Hesperian regions:
  - The Hesperian landscapes cover a smaller area than the Noachian regions, and most of the regions are, on average, considerably smaller than the Noachian units.
  - The itinerary of discussion below starts with the type region, Hesperia Planum, to the northeast of Hellas Planitia, and then moves to the southwest through Hellas Planitia's surface deposits to Malea Planum. From there, it moves southwest into the circum-polar regions around the South Pole to review Sisyphi Planum and then, farther west, Argentea Planum. Then, we continue north for a look at Argyre Planitia floor desposits. After that we head northwest up onto the Thaumasia block. There, we'll look at four plana that form subregions within Thaumasia and the sequence of volcanic flow ages. In eastern Tharsis north of Thaumasia and across Valles Marineris, we'll move over to Lunæ Planum and then down the dichotomy boundary into Chryse Planitia. From there, we'll examine Vasitas Borealis, returning to the edge of the Southern Highlands through the Isidis Planitia floor deposits and the surface of Syrtis Major Planum to the northwest of Hesperia Planum.
  - Hesperia Planum to the northeast of Hellas and southeast of Isidis Planitia.
    - Hesperia Planum is the type region for the Hesperian Period.
    - What distinguishes Hesperia Planum visually is the fairly sharp drop-off in cratering, both in size and in density, when compared with the adjacent Noachian regions of Terra Tyrrhena to the west, Terra Cimmeria to the east, and Promethei Terra to the south.
    - Closer examination brings out a large, low angle volcano in the west central part of the region, Tyrrhena Patera. Possible point of confusion: Tyrrhena Patera (or Tyrrhenus Mons) is not in Tyrrhena Terra but is the volcano associated with the younger lavas of Hesperia Planum.
    - This volcano is typical of the highland pateræ, with slope angles so low that they were named for saucers rather than shields.
    - Tyrrhena Patera may be the earliest central vent volcano on Mars and, thus, a marker from the extremely low viscosity flood basalt/fissure eruptions of the Noachian toward the slightly higher viscosity, vented shield style common in the Hesperian, including the vast shields along the spine of Tharsis and those of Elysium.
    - Highland pateræ all over Mars seem to date from the middle of the Hesperian, in this case on top of earlier Hesperian flood basalts that had been worked over by impact gardening into badly brecciated megaregolith.
    - This megaregolith would have permitted the accumulation of subsurface water or brines and ices, which would be available to interact with rising magma and produce phreatic eruptions and pyroclastic flows, scoring channels into the sides of such pateræ, as seen on Tyrrhena Patera. The style of eruption is, thus, characterized as consistent with hydrovolcanism (Greeley and Crown 1990).
    - The construction of Tyrrhena Patera then seems to have generated the kinds of loading stresses needed to produce the network of wrinkle ridges found in Hesperia Planum, the Hr or Hesperian ridged terrain
    - Here's something kind of weird: though the planetary magnetic field is believed to have shut down by 3.9 or 4.0 Ga, and the highland pateræ date from after that time, ~ 3.85-3.65 Ga, they yet show strong remanent magnetization, kind of like those strange bands in Terra Sirenum and Terra Cimmeria. These highland pateræ include Tyrrhena Patera. Lillis et al. (2005) argue that the anomaly suggests that the planetary dynamo might have gotten a second wind before shutting down permanently and leaving no magnetic trace in the later Tharsis and Elysium volcanoes.
  - Hellas Planitia floor deposits
    - Hellas contains the lowest point on the planet at -8,200 m!
    - As such, it is the ultimate base elevation for a large watershed, which would have included much of the Southern Highlands.
    - There are two possible strandlines ringing the basin, one at -5,800 m and the other at -3,100 m and the lower one can be traced most of the way around Hellas, except where some younger volcanics buried it to the south. They are well developed, suggesting the lakes/seas they bounded lasted for a long time.
    - Dao Vallis and Harmakhis Vallis end at the elevation of the lower strandline, and Niger Vallis seems to debouch at the upper one, above Dao.
    - There are no outlets from Hellas, so how would these two sea levels equilibrate like that for so long?
    - So, the floor of Hellas Planitia contains layered deposits consistent with deposition of sediments in quiet waters.
    - It is possible that Hellas was filled with a variety of materials to quite a depth, including Noachian lacustrine deposits, Hesperian lava and ash deposits from Tyrrhena Patera and the nearby Hadriaca Patera in southern Tyrrena Terra or from vents in Malea Planum to the southwest, and wind deposits in Hesperian times.
    - Then, these Noachian and largely Hesperian materials were etched out by wind erosion during Amazonian times, creating a peculiarly complex terrain.
    - There may have been glaciation, too, and permafrost, as well as collapse of ice-filled soils due to the subtraction of subterranean support, as with thermokarst:
      - Signs of these include chaos terrain: Hellas Chaos
      - Hummocky, blocky terrain in Alpheus Colles
  - Malea Planum south and southwest of Hellas Planitia
    - Malea Planum lies to the south of Hellas Planitia, along the south and southwestern rim of the crater where it shows a smooth and gradual slope of younger mantling materials.
    - The region contains four volcanoes believed to be of the patera variety: Amphitrites Patera (~61° E at ~ -59°), Peneus Patera (~53° E at ~ -58°), Malea Patera (~52° E at ~ -63°), and Pityusa Patera (~37° E at ~ -68°), all believed to date to ~3.8 Ga, except for Amphitrites Patera at ~3.6 Ga (Williams et al. 2009b), in other words, all after the Hellas impact around 4.0 Ga.
    - In 1978, it was suggested that these then odd volcanoes were sited on ring fractures caused by the Hellas impact, which provided surface access for magma intrusion Peterson 1978b; Wichman and Schultz 1988).
    - These four pateræ, together with the Tyrrhena and Hadriaca pateræ northeast of Hellas Planitia, have been described as the product of the earliest edifice-building volcanism on Mars, the first non-rift flows, with magma extrusion for the first time confined to particular vents. As such, these pateræ mark the earliest departure from the extremely low viscosity flood basalts, akin to lunar maria, that characterized the earliest volcanic activity on Mars (and Earth, for that matter).
    - The overall regional surface is predominantly flat and made of volcanic materials, and it is the flow of lavas and ash that poured into southern Hellas Planitia from Malea Planum.
    - These are often deformed with ridges. These may mark compressional stresses, like the wrinkle ridges around Tyrrhena Patera or the Tharsis complex, perhaps similarly associated with volcano build up.
    - Alternatively, some of these ridges could be exposed remnants of dikes that could have been responsible for ancient fissure eruptions of flood basalts.
    - With the basalts, there are also ash flows, which would result from pyroclastic activity set off by the phreatomagmatic style of eruption produced when magma interacts with volatile-rich materials, a wet mantle or ice-rich surface materials.
  - Sisyphi Planum
    - Sisyphi Planum is located about midway between Argyre Planitia and Hellas Planitia, roughly halfway between them and the South Polar Ice Cap. It is centered roughly 5° E and -70°
    - This is countryside strongly marked by its high latitude loccation, with abundant evidence of permafrost, seasonal ground ice, as well as the frost and snow cover of the South Polar Ice Cap's seasonal hood.
    - Western Sisyphi Planum contains an odd area called Sisyphi Cavi. This is a terrain pockmarked by irregular pits. All sorts of explanations have been put forward for these.
      - Perhaps æolian deflation, as when wind blows out a depression in the landscape?
      - Perhaps the area had once been covered by the glaciers of the South Polar Ice Cap and then something caused basal melting, which created these pits, and then these were exposed as the glacier receded?
      - Perhaps there had been an ice sheet here and the basal melting mechanism was magma and lava from subglacial volcanoes? Subglacial eruptions would have resulted in explosive cratering of the ice and terrain under the ice, and this may have been preserved as the glaciers finally receded.
      - In some ways, these things resemble those explosive sublimation pits on the polar ice cap produced by the summer warming of the upper ice, causing the carbon dioxide veneer to explode, carrying dust to the surface as it explodes.
    - Other interesting details in Sisyphi Planum include the familiar polygon patterning of the ground produced by the freeze-thaw cycles of polar regions (on Earth as well as on Mars).
    - Another surface feature of interest here is the presence of the mantling unit. This is a deep layer of deposited dust, like lœss on Earth. In periglacial environments, this l*oelig;ss-like material can accumulate quite a bit of ice in the interstices between soil particles. Over long cycles of cold climates, this can gradually build up to the near saturation of the soil. At greater depths, this stuff becomes permafrost.
      - Closer to the surface, however, the soil ice can sublimate within the soil spaces when climate warms (perhaps with increasing obliquity) and make its way to the atmosphere.
      - The dust covering then becomes more and more "spongy" as the ice evaporates out of all those tiny soil spaces. It starts to look pretty pitted at the surface and, in fact, may sag and settle down. This is the mantling unit, and it creates a distinctive softening of the surface, a masking of sharp-edged features, kind of like a soft blanket draped over the underlying landscape. It is common in high latitudes that have thick accumulations of dust.
      - The images shown in the viewgraphs for this lecture show striking examples of the mantling unit, in this area draped over what looks like patterned ground below, softening the patterns. So, we see a landscape here that is clearly ice-rich, in the form of permafrost evidenced by the polygonal patterns and the mantling unit, which represents æolian deposition and then frost and ice filling of the interstitial spaces between the dust grains. That subsurface frost and ice then sublimates, leaving behind a visually distinctive covering.
    - Another interesting sort of feature in these images of Sisyphi Planum is the abundant evidence of small-scale gullying. These are common on steeper slopes (such as crater rims) in mid-latitudes on Mars between about 30 and 60°, especially in the Southern Hemisphere. Those in Sisyphi Planum are a litle unusual, being found well poleward of the main distribution of gullies.
      - Like many other gullies, they are more common on poleward-facing slopes.
      - This may reflect the ubac effect, the coldness of shadier poleward-facing slopes preserving frost, snow, and soil ice longer into warm seasons as a source of flows.
      - These also tend to be at lower elevations, and Sisyphi Planum is relatively low in the Southern Highlands. This may produce higher air pressure, allowing some liquid water or brine to form and persist for a while after summer and daytime warmth causes the frost or soil ice to change state, thus enabling gullying.
      - The equatorward-facing slopes may warm too intensely and too fast, causing faster direct sublimation of ice into vapor.
      - You can see that adret/ubac dynamic in the viewgraphs for Sisyphi Planum, showing a crater rim with the sunward slope dark and the poleward slope still covered with frost and ice.
      - There's also been some consideration of the way that long-term climate change induced by changes in Mars' axis obliquity might affect the orientation and distribution of gullying. At high obliquity, the poles would get much more sunlight, causing loss of the polar ice caps and an increase in air pressure as all that carbon dioxide and water joined the atmosphere. Liquid water or, especially, brines would form and persist longer under those conditions, and then the poleward-facing slopes would be warmer and you'd see gullying on the sunny slopes, too.
  - Argentea Planum
    - This is a similar terrain to the neighboring Sisyphi Planum, but further west. It lies south and southwest of Argyre Planitia.
    - It, too, is widely covered by the mantling unit.
    - Gullying is not common here, however.
    - It is notable for the numbers of sinuous ridges running across it and the dendritic pattern many of these form. These ridges have been interpreted as eskers (e.g., Fastook et al. 2012; Kress and Head 2015), or the beds of streams that form under glaciers from basal meltwater. The beds fill with debris, the way normal, subæreal stream beds do, and may be partly cemented by compounds in the water. When the glaciers recede, these are left perched above the exposed landscape. This implies that the South Polar Ice Cap once extended much farther from the pole than now seen.
  - Argyre Planitia floor deposits
    - The floor of Argyre Planitia is complex, much as Hellas' floor deposits are. A variety of explanations have been put out there to account for one or another geological unit there:
      - Parker has argued that a Noachian polar ice cap and a large watershed contributed enough water to fill Argyre as an ancient ocean/sea. The sea overtopped the northern rim and formed Uzboi Valles and the upper Chryse Trough hydrological drainage. Others (e.g., Hiesinger and Head 2001) have looked for evidence of sea still-stands/shorelines and found that any such features are too low to have topped the northern rim. Hiesinger and Head (2001) report calculating the amount of water that could be released by the much larger Southern Polar Ice Cap of Noachian and Hesperian times and didn't think there was enough to fill the crater to the brim. So, the crater may well have had ponding of water from the valles pouring into it over its southern rim, but that water probably did not head the Chryse Trough drainage system.
      - There are Hesperian ridged units in Argyre or at least units that look like the Hesperian volcanic wrinkle ridged surfaces, so, if that's what they are, that would be a resemblance to the Hellas floor. It's unclear where the lava would have come from, though, and fine-scale analysis of the ridges don't show the same asymmetries (the stair step leading down analogy), the sharp ridges usually seen at the crest of wrinkle ridges, and the height of other wrinkle ridges. They also seem to form sinuous, braided, and somewhat dendritic patterns, which is reminiscent of eskers, akin to the eskers discussed under Argentea Planum. So, the waters that poured into Argyre may have formed an icy sea in Noachian times, rather like our own Arctic Ocean, and then froze all the way down, creating a glacier by Hesperian times. Glaciers may have flowed into Argyre, too, from the south. Basal melting could have created eskers, which were then exposed when the ice finally sublimed away or the waters sank into the regolith.
      - Frost still forms here each winter, the crater typically covered by the seasonal hood of the South Polar Ice cap.
      - On top of the potential volcanic layers, lacustrine/marine sediments, and glacial/periglacial features, the increasing dustiness of Mars during the later Hesperian and Amazonian deposited dust and sand on the floor, which produces dunes here and there.
  - Thaumasia block plana
    - This complex, originally discussed in the second order of relief, comprises several subregions:
      - Syria Planum to the west and northwest, encircled by Noctis Labyrinthus and the northern reaches of Claritas Fossæ
      - Sinai Planum to the north, bordering the western part of Valles Marineris proper.
      - Claritas Fossæ to the west, a horst-like block of Noachian materials, fractured by a series of north-south striking normal faults and grabens, some of them offset laterally
      - Thaumasia Highlands to the south, a concentration of folded and faulted mountains, the only major collection of folded/faulted mountains on Mars.
      - Solis Planum, the large flat surface, somewhat concave, in the middle of the block, characterized by northeast-southwest trending wrinkle ridges.
      - Thaumasia Planum aka Thaumasia Minor, south of eastern Valles Marineris, a circular planum partly surrounded by folded/faulted hills to the east, called Nectaris Fossæ or the Coprates Rise. It has been suggested that this circular feature might be a large crater buried by Tharsis lava flows, such as those wrinkle ridge plains covering Solis Planum. Thaumasia Planum, too, is covered with wrinkle ridges.
    - The entire Thaumasia block seems to be tilted as a unit from the high point of Syria Planum, around 8 km above the geoid, to the folded and thrust-faulted perimeter highlands, themselves buckled up to 4 - 6 km high, with the plateau lands between descending to 2.5 to 3 km behind the highlands.
    - There's an age progression across the block: Wrinkle-ridge plains material in Thaumasia Planum (Late Noachian) is older than those of Solis Planum (Early Hesperian), which is older than the Late Hesperian material to the west in Sinai and Syria Planum. To the west of Noctis Labyrinthus lie Amazonian aged volcanic materials.
    - The wrinkle-ridge features imply radial compression and contraction on the circumference of the Tharsis complex, probably of superposed shallow strata of basalt, crater ejecta related breccias (megaregolith), Hesperian lavas and ash flows (Mueller and Golombek 2004).
      - They have been argued to be the result of deep rooted thrust faults, and this is supported by analysis of MOLA topographic data, which shows they form a downward-stepping stair with offsets of the plains on either side of them in the 50-180 m range (Golombek et al. 2001).
      - The layers crumpled into wrinkle ridges may represent the kind of surface originally deformed by the uplift of Tharsis, which were then covered by lava and pyroclastic flows from the Tharsis Montes.
    - The whole rather tidy progression of ages across Thaumasia suggests the history of Tharsis:
      - Late Noachian commencement of Tharsis volcanism, perhaps as flood basalts pouring layer upon layer of lava over a very extensive area, the weight of which began to distort the crust of the planet.
      - By Early Hesperian times, some of this was organized into edifice-constructing volcanic vents, creating the patera and tholus types of volcanoes, perhaps first at the Uranius group in northern Tharsis Rise (Uranius Mons, Uranius Tholus, and Ceraunius Tholus), Tharsis Tholus, and/or those west of Tharsis Montes (Jovis Tholus, Biblis Tholus, Ulysses Tholus). Early Hesperian lavas covered a lot of terrain, but didn't get as far as Thaumasia Planum.
      - By Late Hesperian times, shield volcanism establishes itself on Tharsis, eventually creating several very tall mountains. Alba Mons and then Tharsis Montes had begun to build up. Lavas from Tharsis Montes only reached to Solis, Sinai, and Syria plana.
      - By Amazonian times, these and Olympus Mons spewed lava between and among themselves west of Thaumasia.
      - So, the whole series of Thaumasia plana exposes the history of lava flows from Tharsis and the spatial confinement of Tharsis lavas even as Tharsis Montes and Olympus Mons began to grow vertically to their current unimaginable heights.
  - Lunæ Planum
    - Lunæ Planum is located between the central portions of the Valles Marineris complex and the lowlands of Chryse Planitia. It lies west of the Maja Vallis outflow channel and east of the massive Kasei Vallis channel.
    - In many ways, it seems to be a continuation of the wrinkle-ridged plains of Solis Planum in Thaumasia to the north of Valles Marineris.
    - The wrinkle-ridge features imply radial compression and contraction on the circumference of the Tharsis complex.
    - Lunæ Planum may be a surviving exposure of the Early Hesperian countryside affected by Tharsis' buildup and flood vulcanism.
    - As seen in the discussion of the Syria-Thaumasia block, there is a sequence of progressively younger surfaces from east to west, running from the Noachian surfaces of Xanthe Terra through the Hesperian surfaces of Lunæ Planum, to the Amazonian surfaces west of Kasei Vallis running up the Tharsis Rise to the northern Tharsis Montes and the Uranius group of volcanoes.
    - Unlike Solis Planum and the rest of Thaumasia, however, Lunæ Planum is one of the surfaces cut by the great jökulhlaup outflows, being bounded by Kasei Vallis on one border and Maja Vallis on the opposite border.
  - Chryse Planitia
    - Chryse Planitia is the semicircular embayment of the Northern Lowlands that received the flows of the major outflow channels from Kasei Valles on the northwest to Ares Valles on the east.
    - Given its semicircular boundary with Xanthe Terra, Lunæ Terra, and Tempe Terra, it was long suspected that Chryse Planitia may be another gigantic impact basin (Frey 2008), an impression supported by analysis of MOLA topographic data, which has revealed quasi-circular depressions that may be buried craters (Frey et al. 2002; Carr and Head 2010) and backed up by Mars Express MARSIS data (Watters 2007). If so, this one is over 1,500 km across!
    - The surface of Chryse Planitia is overwhelmingly comprised of Hesperian aged surface materials.
      - These include Early Hesperian ridged plains (Hr1) with relatively unaltered impact craters and sharp wrinkle ridges.
      - Somewhat newer are similar plains materials (Hr2), but showing modification of craters and wrinkle ridges, many of which are eroded or partly buried, possibly by fluvial sedimentation in standing water bodies during the major channel outwash flood events -- or by pyroclastic or volcanic flows.
      - There are also drifts (large dune-line deposits), which are often oriented northwest to southeast, though prevailing winds today are biased northeast to southwest. These "shifts in the drifts" suggest a change in the æolian régime from deposition to erosion, as many of the dune- like features are scoured.
      - Many other æolian features were revealed by Viking 1, including deflation hollows, tails of wind deposits in the lee of rocks and scours along the base of rocks, leading to an appreciation of the power of æolian processes on Mars, even though the atmosphere is less than 1% as dense as our own.
      - Further complicating the picture, close examination of drifts seen in the Viking 1 panchromatic images and their reprocessing to enable stereoscopic analysis revealed coarse granular material embedded within the drift deposits, which are too large to be moved by the wind and, so, probably were emplaced by water in the drifts after their formation.
      - The ambiguities about the nature of the ridged plains, whether they are of volcanic or fluvial origin, were not settled by analysis of the results of the Viking 1 lander or of the Pathfinder lander and its Sojourner rover.
        
        Soil analysis showed elements seen with alteration of basaltic materials: iron-rich phyllosilicates, some magnesian sulfates, and small amounts of carbonates and iron oxides.
        This is consistent with several explanations: water alteration, global homogenizing of a basaltic source rock turned into the ubiquitous dust, Theiikian style sulfate-aqueous alteration. So, big help.
      - The surfaces at both Viking (western Chryse) and Pathfinder/Sojourner (eastern Chryse) were scattered with angular, often pitted rocks, mostly andesitic and drastically different in chemical composition from the soils nearby that the soils could not have been derived from these rocks. So, they must have been brought to Chryse from elsewhere, perhaps in outflows.
  - Vastitas Borealis
    - Vastitas Borealis is a part of the Northern Lowlands, a depression surrounding the North Polar Deposits, mostly below -4,500 m.
    - Judging from MOLA profiles, this is the apparent ultimate destination for the fluids and deposits of the circum-Chryse outflow channel floods, which may have periodically created or recreated the ocean in the Northern Lowlands.
    - Vastitas Borealis is largely covered with Late Hesperian deposits.
      - These feature a set of low linear ridges running roughly parallel with one another in a north-northwest to south-southeast direction, which Head et al. (2002) interpret as wrinkle ridges continuing from Chryse Planitia and, indeed, from Lunæ Planum, Solis Planum, and Syria Planum.
      - So, they seem to reflect the contractional stresses in the areas around the periphery and circumferential to the Tharsis Rise.
      - They are generally less distinct than these highland versions, softened or partially buried. But by what? Hesperian lavas and ash flows? or Oceanus Vastitas marine deposits?
    - The Hesperian ridged plains are in places covered by younger Hesperian channel deposits of some variety, no doubt emanating from the outflow channels of the circum-Chryse Planitia regions of Lunæ Planum, Xanthe Terra, and Arabia Terra.
    - Under the ridged plains material is evidence of a profusion of buried craters, some so indistinct in the MOLA data as to be termed "stealth craters" (Head et al. 2002).
      - The number and size distribution of these hidden craters imply a truly antique surface is buried under the far younger surface materials of the Northern Lowlands, making them at least as old as the battered Southern Highlands surfaces.
      - This realization has further undermined plate tectonic interpretations of the great crustal dichotomy.
    - To summarize this as an historical narrative, Vastitas Borealis seems to had had a primordial basaltic basement of some sort after whatever process operated to create the crustal dichotomy. This was crater-battered, and the hidden craters suggest it may be as old as the earliest Noachian. As volcanism ramped up in the Late Noachian to Early Hesperian, volcanic materials (ash and lava) were deposited in the North Polar Basin, covering the earlier surface and its cratering. This material was subjected to the circum-Tharsis compressional stress field as the great volcanic complex began to build up, creating wrinkle ridges in the basin. These were then subjected to sedimentation, possibly at times under oceanic conditions, by the stupendous outwash floods from the circum-Chryse outwash channels. These seemingly marine deposits eroded and partly buried the wrinkle ridge surface and the ancient craters.
  - Isidis Planitia floor deposits
    - I discussed the origins of the Isidis impact feature under the second order of relief. Here, I want to focus on the Hesperian aged surfaces that cover most of the Isidis Planitia floor.
    - This forms a generally smooth surface interrupted by ridges of wrinkle-ridge appearance and a scattering of mounds in the 500 m diameter range.
    - This surface has been interpreted as Late Hesperian lava flows emanating from Syrtis Major to the west, possibly covered with sedimentary deposits and perhaps some periglacial ice features.
    - A very peculiar feature of this complex in western Isidis is "thumbprint" terrain, which consists of strings of low, often fused, conic structures that have circular depressions at their apices.
      - The individual cones are generally about 400 or 500 m in diameter at their bases and typically range from 10 - 50 m in height, averaging under 35 m and rarely attaining 70 m in height.
      - These strings, some of them several kilometers long, form subparallel curves reminiscent of fingerprints, leading to the name for this kind of landscape.
      - Thumbprint terrain has been the subject of far-ranging hypotheses:
        
        volcanic features ("rootless cones" or phreatomagmatic cones from the interaction of magma intrusions with soil ice and water) and lava flow patterns
        ice-related structures, e.g., moraines (unsorted debris dumped by a glacier), eskers (subglacier streams from basal melting), pingoes (earth-covered ice lenses forming mounds, sometimes topped by crater-like breaks at the top), or boundaries between ice floes.
        shorelines and sediments deposited in a body of standing water
  - Syrtis Major Planum surface
    - We already talked about Syrtis Major in the second order of relief, with reference to the persistent low albedo feature that dominates it, the so-called "Blue Scorpion" or the "Hourglass Sea."
    - This turned out to be an area where the Mars global circulation features prevailing winds that keep the surface clean of the otherwise pretty ubiquitous bright dust, revealing a basaltic surface. This was produced by the two calderas on the planum, Meroë Patera (the older, smaller, more mafic of the two) and Nili Patera (larger, younger, less mafic). Both may be vents for a single volcano or magma chamber.
    - That surface includes:
      - Basaltic lava flows that form a very slightly sloped surface, the kind of very low viscosity flow seen in flood basalts and in the very early vented edifices of Mars.
      - Very interestingly, there is also some dacite on the floor of the Nili Patera caldera, Nili Patera being the younger of the two volcanoes on Syrtis. Dacite is an igneous rock that is somewhere between andesite and rhyolite or granite in composition, that is, some of the most felsic and silicic rock found on Mars, the product of advanced differentiation at the top of a magma body. Mars' igneous rocks, as we've seen before, are predominantly basaltic, ranging up to basaltic-andesite or andesite. So, this is quite a find. Dacitic magmas, too, tend to be quite viscous or sticky, loaded with gasses, which makes its eruption an explosive event.
      - Very, very interestingly, there are all kinds of signs of water-altered minerals, including phyllosilicate clays (neutral water) and carbonates, the long-presumed but rarely seen mineral that one would expect to form in any water interacting with a carbon dioxide atmosphere. The next major rover, Mars2020, may be sent here to explore these minerals.
      - Given the abundant evidence of water, it's odd that olivine has also been found there, especially in Nili Fossæ (the concentric grabens on Syrtis Major that center on Isidis Planitia). Olivine, being one of the first minerals to crystallize at the highest temperature in a magma body, is also one of the most susceptible to water alteration, changing to iddingsite, serpentine, and magnesite. So, finding it here unaltered is intriguing.
      - Extremely interestingly, Nili Fossæ is believed to be the major source of the great methane plumes that have been sporadically detected on Mars! Methane can have biotic origins. So, this area has become a top priority for the next rover!
END 04/08/15
Amazonian surfaces: Youngest
- The Amazonian began with the (contested) date of the ending of the Hesperian era, and it continues until the present day
  - The Hesperian-Amazonian transition is far less distinct and much more transitional than the more dramatic Noachian-Hesperian transition, with its defining fall-off in the arrival of large impactors, the end of the Late Heavy Bombardment.
  - The transition between the Hesperian and the Amazonian is marked by inherently less sharply bounded changes in dominant processes, so that uncertainty leads to some pretty divergent estimates of the transition.
  - These range from as early as 3.5 Ga ago to as late as 1.8 Ga ago
  - The most commonly cited date for this gradual transition is around 2.9 to 3.0 Ga
- Things are much more peaceful in the Amazonian, as compared with the bombardment and flood volcanism that characterized the Noachian and the edifice and shield volcanism and massive outflow flooding seen throughout the Hesperian.
  - Volcanic eruptions were still pretty intense at the beginning of the Amazonian, as volcanic activity increasingly concentrated on Tharsis and Elysium and the construction of the great montes.
  - It probably still goes on (there is evidence of eruption activity within the last 2 million years, based on crater-counting) but not at the clip of Late Noachian, Hesperian, and Early Amazonian times
  - Water or brine continues to be released from the subsurface somehow, creating those fresh looking gullies we've seen in MOC, HRSC, and HiRISE imagery on the sides of craters and the animation of damp or wet flows I showed you a while ago.
  - Massive outflows may occasionally still occur, judging from crater counting studies in channels leading into Amazonis Planitia, which show outflows as recently as 10-100 million years ago, though this is not universally accepted (lava often flows down pre-existing outflow channels and the crater counts record the ages of the recent lavas more than the underlying channels they exploit).
  - Meteorites still smack down from time to time, even being spotted by repeated imagery of the same sites.
  - There may even be ice ages in the Amazonian, which coïncide with periods of exaggerated obliquity in the martian axis of rotation.
  - Dust devils and dust storms kick up, mixing dust from all over Mars into wind deposits of globally homogenized composition.
  - Martian geochemistry during the Amazonian is dominated by oxidation of iron into anhydrous iron oxides (including hæmatite or rust, magnetite, maghemite, and ilmenite), giving the ubiquitous planetary dust that light reddish tint. This anhydrous oxide chemistry is the basis for the Bibring et al. team's proposal of the Siderikian (iron-loving) as their third era in Mars geochemistry, which includes all of the Amazonian and parts of the later Hesperian.
- Tour of Amazonian regions:
  - Despite being by far the longest time division on Mars, Amazonian-dominated surfaces cover the least surface on Mars, approximately 26% of it (Barlow 2010). If you're on campus or logged into the library from home, you can view Barlow's map of martian age distibutions here: http://bulletin.geoscienceworld.org.mcc1.library.csulb.edu/content/122/5-6/644/F8.large.jpg.
  - Our travel itinerary for Amazonian Mars starts with the type region, Amazonis Planitia, west of Olympus Mons. From there, we'll move west into Elysium Planitia, up onto the lavas of Elysium Rise, and then down onto the surface of Utopia Planitia. We'll pause in Acidalia Planitia and the North Polar Deposits, then visit Arcadia Planitia and return near our starting point among the lava flows mantling Tharsis Rise.
  - Much of our discussion will focus on the interactions among lava, outflow debris, and periglacial phenomena.
  - Amazonis Planitia to the west of Tharsis and east of Elysium
    - This is the type region for the Amazonian time division, the youngest of the three.
    - It has one of the most spectacularly smooth surfaces on Mars, which you could see for yourself doing a few transects across it in Gridview. Many of you found yourselves frustrated in the crater-counting lab, because this was a natural spot to try to count craters in a very young area, except the Robbins database is confined to craters at least 1 km in diameter, and those are very scarce in Amazonis Planitia!
    - The surface is covered with evidence of many, often very recent effusive basaltic lava flows, the kinds of low viscosity lavas that can flow great distances in sheets and maintain an extremely flat or low slope surface.
    - Now, Amazonis Planitia was used as the type region for all the younger plains of the Northern Lowlands, but it turns out that Amazonis Planitia may be a rather eccentric representative of Amazonian times, being kind of a dammed in basin allowing all kinds of flows to pond:
      - There's apparently a huge Noachian era crater basin buried under it toward the northwest, and that badly degraded rim has acted as a partial dam.
      - There's a large Late Hesperian era lava flow that's been traced to Olympus Mons from before the time it developed that weird aureole feature. It's about 100 m thick and also acted like a barrier to flow movement northward out of the Amazonis basin. It's a classic Hesperian ridged plain, like the ones we've seen in such places as Lunæ Planum and Solis Planum, but the ridges are considerably lower than the 100-150 m height seen in those other regions. It's as though something has partially buried the ridges.
      - Then, the Olympus aureole formed, perhaps from a megaslide, and that acted as yet another dam toward the eastern side of Amazonis.
    - So, there are these three damming features to the northwest, north, and east, which caused lava flows and water or water/brine outflows and even some marine incursions to back up and pond in Amazonis Planitia, producing very smooth surfaces.
    - Recent lava flows from Tharsis Montes and from Elysium Montes have gotten into Amazonis Planitia. Some of these may have been less than 10 million yeas ago (Fuller and Head 2002).
    - There have also been extensive sedimentary deposits from massive outflows, which emanated from the Mangala Vallis region to the south and, via Marte Vallis to the southwest, from the Elysium Planitia region.
    - Subsequent lava flows have exploited the channels created by these outflow events, so you sometimes see lava flowing almost like water down one of these pre-existing outflow channels.
    - The Parker et al. ocean Contact 2 (-3,760 m) covered Amazonis Planitia, too, so the region could have been under water back in Noachian times, also helping smooth the surface over which the later lava and outflow deposits would be laid.
    - So, we have a landscape that, because of the ponding created by the Noachian crater rim, the probable Noachian ocean, the Late Hesperian Olympus Mons flow, and the later Olympus Mons aureole collapse event, contains an extremely smooth but very complex mix of lavas and outflow deposits.
  - Elysium Planitia
    - Elysium Planitia is a broad wedge-shaped region, about 3,000 km from west to east and 1,000 km from north to south. It is directly south and to the southeast of Elysium Rise and to the southwest of Amazonis Planitia. It abuts the crustal dichotomy border.
    - Nomenclature is a little inconsistent: Sometimes the Elysium Rise is called Elysium Planitia, while more contemporary usage confines the term to that flat area south of the Rise.
    - It is not as smooth in texture as Amazonis, nor is it as low in elevation.
    - Like Amazonis Planitia, however, it represents a similar mix of volcanic flows and fluvial deposits, with a similar pattern of lava and dikes interacting with volatiles in the regolith to create outflows and using channels earlier carved by fluvial processes.
    - At roughly -3,000 m, it lies above the Parker et al. Deuteronilus (lower, -3,760 m) contact but below the Arabia (higher, -2,000 m) contact, so it may have been covered by a frozen ocean in Noachian times.
    - There are weird surfaces in Elysium Planitia, which consist of large, dark plates, with light-colored material in between. In some places, it's possible to re-arrange them in such a way that they fit together pretty well. They have been the subject of competing hypotheses:
      - Might these be lava plates? Some flood basalts on Earth show patterns like that, perhaps from crusts forming on the flow, fracturing, rotating in the flow, crashing into one another, creating smaller slabs, or pushing up ridges between one another.
      - Another Earth process that can create this kind of slabbing, rotation, pulling apart, and pushing up is ice, like the pack ice that forms around the Arctic Ocean or in lakes and rivers when surface ice starts to break up in spring. Maybe this stuff is pack ice or pack ice covered with the ubiquitous martian dust.
    - Crater counts indicate that the surfaces of Elysium Planitia are in the tens to hundreds of millions of years old, on the younger end of the Amazonian time frame. The pack ice/lava raft stuff is more like a few million years old, really young stuff.
    - Elysium Planitia, like Amazonis Planitia "next door," shows signs of ponding against low hills to the northeast, which look like outcrops of older materials, possibly Noachian in age, complete with valley networks, such as Rahway Vallis. A large channel, Marte Vallis, cuts through these and connects Elysium Planitia with Amazonis Planitia.
      - The whole thing looks as though Elysium Planitia and Amazonis Planitia were sitting there, minding their own business, each with permafrost saturating their regoliths, maybe even with liquid water under that cryosphere material.
      - The Elysium volcanic system, or Apollinaris Patera just south of Elysium Planitia, would have built up magma chambers and these may have been fringed with dike swarms.
      - The dikes, on contacting the ice, water, or other volatiles in the regolith, would trigger massive flooding, which may have poured out of Elysium Planitia through Marte Vallis down into Amazonis Planitia.
      - The waters or brines would eventually sublime or work their way back into the regolith and freeze.
      - Then, if any of the dikes actually made it to the surface, perhaps through such fissures as the Cerberus Fossæ toward the north, you would have lava floods and flows, many of which would seek out the pre-existing fluvial channels and, where these generated enough heat penetrating downward to the permafrost, you might get the production of rootless cones through such phreatomagmatic interactions. There are quite a few of these.
    - Speaking of Cerberus Fossæ, these are extraordinarily long and narrow trenches in the surface, which run from Elysium Rise southeastward toward the middle of the Tharsis Rise.
      - There has been speculation that these might be an incipent rift, like a Valles Marineris system in the making, a great system of cracks due to an underlying extensional stress field, perhaps associated with the Elysium Rise.
      - They are pretty new in the sense that they crack through the relatively new lava flows of Elysium Planitia (rather than having these newer lavas flooding over their sides).
      - In some places, they seem to be the source of lavas flooding out over the surrounding countryside. In other places, they seem to be the source of great water flows. Again, we see that intimate interaction between lava and fluvial processes. Maybe this is because of magma diking creating the extensional stresses/faulting, the catastrophic release of subterranean water, and the occasional flood basalt lava flow.
      - In one case, a Cerberus Fossa is crossed at an angle by Athabasca Vallis, which is a channel for massive outflows, which is linear like a fossa because it runs along a wrinkle ridge from an older surface, which supported it.
  - Utopia Planitia to the northwest of the Elysium rise
    - We already discussed the huge impact crater that formed this basin in the second order of relief: Here the focus is on the mantling deposits.
    - The Noachian impact basin was covered by subsequent materials back in the Noachian, which continued to receive impacts: There are many craters buried in Utopia, which have been revealed by Mars Global Surveyor's MOLA, the SHARAD radar sounder on the Mars Reconnaissance Orbiter, and the MARSIS radar instrument on Mars Express.
    - These ancient surfaces, however, are covered by materials from the Hesperian and, mostly, the Amazonian:
      - the Late Hesperian Vastitas Borealis Formation lavas, which, when exposed here, has a knobby and polygonally cracked appearance
      - smooth lobate flow terrain, interpreted as a more recent lava flow, early Amazonian, probably of the pahoehoe type
      - rough lobate flow terrain, interpreted as lahars triggered by the interaction of lavas with groundwater or ice, generally on top of the smooth lava flows
    - There is also etched terrain, or landscape features showing the effects of wind erosion during the long, dry, windy Amazonian time.
    - In fact, related to this, the Viking 2 lander showed a lot of perched rocks, that is, rocks that seemed to have had a lot of the soil support around them blown away
    - There are also extensive fluvial deposits and the kinds of shattered and pulverized debris from magma and volatile interactions (dikes moving through ground ice, lava flowing over surfaces with a lot of water, brine, or ice in them).
    - These are associated with great outflows, rather than valley networks, which seem to come out of a series of outflow channels and grabens on the western side of the Elysium Rise.
      - Granicus Vallis
      - Tinjar Vallis
      - Hrad Vallis
  - Acidalia Planitia to the north/northwest of Arabia Terra and north of Chrys Planitia
    - It is a large region, mostly very flat and smooth, and it has a low albedo, giving it a rather dark color and making it visible from Earth back in the 19th century.
    - The few craters that are found here have that "wet splat" look to them, an indicator of subsurface volatiles and ground ice.
    - Further indicating the presence of subterranean ice is the large polygonal structure on much of the surface.
      - These are large polygons, perhaps 5 or 10 km wide, which is large enough and far enough out of the norm for polygon-patterned ground on Earth to cause some skepticism about the permafrost analogy.
      - Surrounding the polygons are sometimes sharp canyons.
      - The polygons increase in height toward the Arabia Terra borderland, shading into that mensæ territory, where the Face on Mars is found.
    - On top of the polygon surfaces can often be found the pimply signal of those odd little depression-tipped cones we've seen in other places, which may be phreatomagmatic rootless cones or, in a newer interpretation, possibly mud volcanoes.
      - Mud volcanoes are found on Earth in situations where hot water infiltrates fine soil materials and, if the water is under pressure, the water, now dirty with mud, burps up onto the surface, forming a small cone, complete with a vent on top.
      - Mud volcanoes are connected with actual volcanism in the sense that magma intrusions are what heats subterranean water or ice and the movement of magma, as well as the thermal expansion of the water, creates the pressure that leads to mud eruptions.
      - So, you tend to find them in subduction zones on Earth, places you would also find true igneous volcanism.
    - One of the wilder ideas about Acidalia Planitia is that it may have once contained a natural fission reactor! This was presented at the 2011 refereed Lunar and Planetary Science Conference by J.E. Brandenberg.
      - The basis of his argument is analogy with an actual natural fission reactor that developed in the Oklo region of Gabon, Africa, about 1.7 billion years ago (Cowan 1976, Scientific American)
        
        About 2.3 billion years ago, oxygen concentrations on Earth had gotten just high enough to allow uranium in rocks to dissolve in water when cyanobacteria's photosynthetic production of oxygen outstripped the ability of iron-rich rocks to oxidize. Uranium needed to be dissolved from rocks and then moved by groundwater into places it could accumulate.
        In Oklo, uranium concentrations in an aquifer were bracketed by sandstones below and above and a granite mass further down.
        Groundwater moving through the aquifer could get into the uranium ore, where it turns "fast neutrons" into "thermal neutrons" moving slowly enough that they can enter the uranium nucleus and trigger a fission reaction, releasing huge amounts of energy by so doing. Thus, criticality was reached in the ore, which was contained by the sandstone and granite above and below..
        There would be runaway nuclear heat production and explosive ejection of water. This would dehydrate the aquifer, which would cool, relieving the pressure, stopping the runaway chain reaction, and dropping the uranium down over a couple of hours below criticality.
        Water would then be able to re-enter the now cool and dry aquifer, triggering the chain reactions once again.
        This would cycle back and forth between criticality and release in a 3 hour cycle for several million years, producing natural plutonium.
        Oklo is the only place on Earth where this process has been documented, because of the unique combination of oxygen buildup, groundwater leaching and concentration of ²³⁵U, and ore buildup in a contained aquifer with a lot of water.
        It shut down eventually and it can't re-appear there or anywhere else because, in the intervening 2 Ga, the supply of ²³⁵U has declined due to radioactive decay (half-life = 0.7 Ga). This kind of reaction needs ²³⁵U to be enriched to at least 3% of the fuel; radioactive decay has knocked that percentage well below this criticality requirement.
      - Brandenberg argues that the same conditions are found in northern Acidalia, especially in Acidalia Colles, except the reaction was bigger and led to a huge explosion that created concentrations of radioactive potassium and thorium there.
      - The process happened once on Earth, so it's not entirely impossible that it would happen on Mars.
      - If this intrigues you, here is the paper: http://www.lpi.usra.edu/meetings/lpsc2011/pdf/1097.pdf.
      - The proposed mechanism was received with the usual mix of neutral curiosity, positive interest, and skepticism that is normal in the scientific community.
      - But then Brandenburg has since gone way past the slack initially cut him: He's now going on about a nuclear war on Mars and some interstellar species wiping out martian civilization (the Face) and we should worry about them coming back around and nuking us on Earth. This Lowell-like trajectory is succinctly described on the Pharyngula science blog at http://scienceblogs.com/pharyngula/2014/11/22/the-two-faces-of-je-brandenburg, including commentary by Brandenburg.
  - Planum Boreum around and under the North Polar Ice Cap
    - This is the material underlying and supporting the North Polar Ice Cap.
    - It also extends out past the ice cap, being exposed in Olympia Planum and also inside Chasma Boreale.
    - It is a thick bed of material rising up above the North Polar Lowlands as much as 3 km.
    - It shows complex layering in the SHARAD radar sounder on the Mars Reconnaissance Orbiter and MARSIS sounder on Mars Express.
    - At a coarse level, there are two main divisions of these layers under the ice:
      - Polar Layered Deposits (PLD), subdivided into:
        
        Upper Layered Sequences (ULS)
        Lower Layered Sequences (LLS)
      - Basal Unit (BU)
    - The Polar Layered Deposits show alteration between water ice and dust layers.
      - That kind of layering suggests that the polar region is responding to climate changes, probably over the last 10-100 million years, judging from crater counts, which alternate between two phases:
        
        Accelerated deposition of frost or snow in the polar regions
        Decline in precipitation/sublimation and increase in dryer conditions that favor the liberation and depositon of dust.
      - These alternating phases may be connected with changes in the planet's obliquity, and Mars undergoes more extreme oscillations in obliquity than does Earth:
        
        As the axial tilt declines, the polar regions become more persistently cold, persistently at very low sun angles, which would promote frost deposition or even precipitation there.
        As the axial tilt becomes more extreme, the polar regions would experience higher sun angles in the summers and much longer day lengths, which would cause accelerated sublimation of the ice, more dustiness, and an increase in the dust to ice deposition ratio.
    - Below the PLD is the Basal Unit, which is an even more complexly layered and deformed unit.
      - It is easily made out from the PLD by a major unconformity in the SHARAD profiles and is a darker color.
      - The layering seems to be cross-bedding of sandy layers.
      - There's a lot of speculation about what the source of the BU is:
        
        Perhaps the classic channel outflow deposits carrying material there all the way from Chryse Planitia? (but why built up here?)
        Perhaps a marine depositional system? (again, why built up only here?)
        Maybe an older polar depositional system now decayed and eroded? (glaciation episodes much older than the ice caps we see now, with perhaps intervening times with little to no ice?)
        Maybe the ubiquitous martian dust so common through the Amazonian back before any martian glacial ages began? These could have been deposited and eroded in complex patterns, perhaps drenched from time to time and frozen, hardening them into layers.
      - Wherever the BU comes from, it seems to be the source of huge dune fields that immediately surround the North Polar Ice Cap in Olympia Undæ, ergs of sand like in certain Earth deserts.
    - Whenever climate conditions favor ice deposition, the North Polar Ice Cap begins to cover these outcrops; whenever conditions favor ice ablation, the PLD is exposed.
    - These deposits, then, are going to be a virtual goldmine of climate change data over the Late Amazonian for some future geoscientists!
  - Planum Australe lies around and under the South Polar Ice Cap
    - This is a thick stack of layered materials comparable to those in Planum Boreale, the South Polar Layered Deposits.
    - Again, we see a pattern of alternation between ice layers and layers containing dust, again in a rhythmic pattern suggesting climate change due to changes in Mars' orbital parameters, especially obliquity.
    - As we discussed earlier, the residual South Polar Ice Cap has turned out to be nearly all water ice, with a few meters of carbon dioxide ice on top (which expands like crazy in the winter to form the seasonal ice cap).
    - One difference is that, for some reason, the layers in the SPLD form a kind of staircase topography, like we see in, say, the Grand Canyon, where layers differ in terms of strength and angle of cliffs that can be sustained. The NPLD are clearly layered but there's greater uniformity in slope angle from one layer to the next.
    - Something interesting has turned up: There are pockets of carbon dioxide ice here and there among the ice layers and the SPD in places where parts of the layering has collapsed due to explosive sublimation. Apparently, carbon dioxide builds up in these holes and freezes, and there's enough of it in there that, if it were all released, it would double Mars' atmospheric density!
    - Faulting is found on the SPLD, too.
  - Arcadia Planitia to the northwest of Tharsis
    - Arcadia Planitia is another smooth Amazonian surface, just to the north of the type region, Amazonis Planitia.
    - It lies generally between 1 and 3 km below the geoid.
    - The surface seems to be dominated by younger lava flows.
    - Again, we see a pattern of interaction between subsurface volatiles and lavas, which produces strings of small cinder cones, probably of the phreatomagmatic rootless cone variety.
    - Some of the lower elevation areas show a pattern of furrowed ground with almost, vaguely parallel ridges. This looks a bit like solifluction in Earth's Arctic periglacial areas, those weird slumps produced by occasional thawings.
    - Cratering is sparse, as with all Amazonian regions, but the walls of these relatively few craters show gullying, as do the slip faces of now inactive, indurated sand dunes in Arcadia.
    - Many craters show signs of expansion and terracing, suggesting thermokarstic processes going on in deep layers of ice-rich soil, kind of like the scalloping seen in polygonal terrain in Utopia Planitia but distorting the shape of craters here.
  - Lavas of Tharsis Rise and Dædalia Planum
    - Again, Tharsis Rise was discussed under the second order of relief. Here the focus is the Amazonian lava covering much of the rise.
    - Volcanism probably began in the Late Noachian, probably as flood basalt eruptions: low viscosity flows from fissures over very extensive areas without much edifice-building around vents.
    - Much of these lavas have been buried by subsequent events, exposed here and there on the periphery of modern Tharsis, as on Thaumasia Minor Planum on the eastern end of the Thaumasia block.
    - The bulk of the Tharsis Rise built up in Hesperian times, but even the Hesperian eruptions have generally been covered up by subsequent Amazonian flows. We see the Early Hesperian flows exposed in Solis Planum and the Late Hesperian flows in Sinai and Syria plana.
    - Alba Mons, with its odd patera-like shape and the intense fracturing of its surface, seems to be the focus of the first shield-building volcanism in the Hesperian to Amazonian transition, while the Tharsis Montes and Olympus Mons show newer episodes, building extremely tall mountains. Olympus Mons is surrounded by Late Amazonian volcanic materials, and there aprons of Late Amazonian materials on the western slopes of the Tharsis Montes.
    - Crater counts indicate that there have been eruptions in this complex within the last 100 million years, and some are even younger than that: Olympus Mons shows areas as young as 2 million years at its western scarp!
    - The lava lump has bent the lithosphere, creating the Chryse Trough and other relatively low elevation areas ringing it, while the magma upward movement has created extension stresses on and radial to the uppermost surface of the Rise, creating fossæ
    - Dædalia Planum is that smooth area on the southernmost part of Tharsis Rise, south of Arsia Mons.
    - It's intriguing, because there seems to be yet another monster crater buried under there, some 4,500 km across!!! That would dwarf Hellas Planitia! It's thought to be among the earliest big impactors, maybe Early Noachian in age, older than Hellas (Craddock 1990). Whatever its origins, it is now blanketed with lavas dating from the Hesperian-Amazonian transition.
    - Tharsis shows a pattern of old volcanic activity that was very low viscosity and spread out over huge areas, followed by later episodes of more viscous eruptions and flows that didn't sprawl out as far but, instead, built edifices on top of the older material, eventually culminating in the great Tharsis Montes and Olympus Mons perched on top of the lava pile. Kind of a switch from Los Angeles style land use (sprawling, horizontal) to New York style (spatially more confined but vertical)!
  - Elysium Rise
    - We covered Elysium Rise under the second order of relief as one of the large and visually conspicuous features of Mars, one produced by epic volcanism.
    - Here, I simply want to comment on the young surfaces of this feature.
    - These surfaces are quite recent, with very little cratering, many under 100 million years old.
    - Most of the surface is covered with lava, in some places with pyroclastic deposits (especially around Hecatoes Tholus, the northernmost of the three large volcanoes). There is an exposure of a Late Hesperian volcanic field southwest of Elysium Mons, but the majority of the Rise's surface is covered with Hesperian-Amazonian volcanics.
    - There is also evidence of lahars, especially on the western side of the Elysium Rise. These are volcanic mudflows produced when an eruption liquefies or sublimates glaciers or permafrost, which then saturates pyroclastic material on the sides of the volcano and it all starts flowing downslope.
    - Elysium Rise is also characterized by grabens, which often are the site of origination of great outflows, especially on the west side.
    - On the east side, there are these mostly straighter channels that are believed to be lava channels, similar to lunar rilles.

END 04/15/15

Fourth order of relief (optional, text in grey: S/15)

This refers to landscape-scale features smaller than and nested within third order terræ, plana, and planitiæ.
Up through the third order of relief, my intent was to go over every single major region of Mars, and I think we have.
At this point, as we move into the much smaller fourth order features, the number of landscapes that could be considered here goes up exponentially, so I no longer aspire to a complete travelogue: Instead, I'll pick landscapes to discuss that seem interesting in terms of the processes shaping them.
Discussion, then, will be process-led (kind of like the second order), each major process illustrated by a selection of landscapes.
Fluvial processes
- Noachian valley networks: Some valleys seem to show the kind of dendritic structure and fine dissection you'd expect from a precipitation-fed surface flow and channelization system on Earth:
  - Channels in Echus Chasma, south of Kasei Valles, originating to the northwest of Valles Marineris
    - Dendritic pattern collecting flow in progressively higher order channels
    - Eventually poured over a 4,000 m cliff
  - Channels in Terra Sirenum: Viking imagery
  - Channels around Warrego Vallis in Thaumasia
  - Nanedi Vallis in Xanthe Terra (Viking)
  - Deltas in such places as:
    - Melas Chasma
    - Eberswalde Crater near Holden Crater north of Argyre Planitia
    - Gusev Crater
    - Jezero Crater in Syrtis Major Planum
- Groundwater sapping-fed systems akin to stream systems in arid lands on Earth, most of the larger ones probably Noachian in age:
  - These feature long main trunks.
  - Relatively few, short tributaries
  - Tributaries originate in theatre-headed alcoves.
  - Examples:
    - Ma'adim Vallis in Terra Sirenum, debouching into Gusev Crater
    - Nanedi Vallis in Xanthe Terra has some of these, too
- Non-equilibrium systems: Some fluvial systems seem to carry the overflow of water into or out of a crater or system of craters and over a series of sharp transitions in the landscape, with little evidence of the smoothing and construction of a graded profile (hence "non-equilibrium").
  - Ma'adim Vallis flows into Gusev Crater, which is where Spirit landed
    - Ma'adim Vallis is southeast of the Elysium rise and southwest of Tharsis
    - Seems to collect fluids from a series of possible lakes to the south to empty north into Gusev, astride the crustal dichotomy.f
    - Lakes identified by R.P. Irwin III and G.A. Franz at the Smithsonian from what look like deltas and terraces all at the same elevation around a surface that does not show channelization itself, perhaps protected from fluvial erosion by the deposition activities of a lake bottom.
    - A channel descends from them, winding sinuously for some 900 km down into Gusev
    - Gusev Crater was chosen for Spirit's landing site partly because it looked so clear that Ma'adim Vallis was carrying water from a wide watershed into the crater.
    - The hope was the crater would yield water-altered minerals.
    - Spirit did not find water-altered minerals at first, the way Opportunity did in Meridiani, but, after a year and a half, bedrock was reached and it was dramatically altered (not coatings and veins of water-deposited minerals but pretty wholesale alteration).
    - It's bromine, sulfur and chlorine found inside the rock "Clovis."
  - Then there's that enormous chain of craters and valleys linking the melt from under the south polar cap through Argyre and Holden craters, around Aram Crater, and through Ares Vallis into Chryse Planitia, some 8,000 km long!
- Catastrophic, jökulhlaup-like outflows
  - Kasei Vallis and Ares Valles you met earlier in the semester and saw how much of a flow they could have carried in a single event or series of massive events
  - Ares Vallis might have its source in collapsed terrain, such as Aram Chaos, where water or other fluids are suddenly liberated by heat or mechanical failure breaking a dam of it, which undermines the still-frozen surface terrain, producing the chaos landform
  - Earlier I mentioned Dao Vallis, Niger Vallis, and Harmakhis Vallis in eastern Hellas Planitia, with their odd "upside down" structure with wide, alcoved head"waters" and narrow V-shaped channels farther down
  - A very interesting case is Chasma Borealis, which might be a volcano-glacio-fluvial source of immense water volumes and catastrophic flooding
    - Kathryn Fishbaugh and James Head, III, have created a topographic map and profiles and used them to estimate volume of a catastrophic melt (perhaps subsurface vulcanism): 26,000 km³!
    - Picked out deposits from such an event: could fill lowest portion of north polar basin to a few 10s of m!
Small sapping alcoves, channels, aprons
- These structures form on Earth in layered terrain with a more resistant caprock as groundwater sapping from a subsurface layer exposed in a scarp (fault? landslide?) erodes scarp face material and undermines the caprock, which then collapses down the scarp
- MGS' Mars Orbital Camera has recorded many smaller scale versions of this on the walls of craters and caught a few of them in the act of having recently flowed
- Especially parallel is the imagery from Houghton Crater on Devon Island, Canada, north of Baffin Island: The only Earth impact crater on a Mars-like polar desert landscape
- Especially interesting is the geography of such gullies: They are found on poleward-facing slopes, especially in the southern hemisphere, at latitudes with absolute values >30°
  - This is odd, given that poleward slopes are colder than equatorward slopes and Mars is such a cold place with such low atmospheric pressure!
  - Mars' air pressure is typically between 500 and 600 Pa (5-6 mb), where Earth's is about 101,320 Pa!
  - Water has a triple point pressure, or pressure at which solid, liquid, and gas phases co-exist, of 610 Pa or 6.1 mb, at 0.01° C. If you hold pressure constant, warming it turns it into a gas. If you held the temperature constant and upped the pressure, you could cause it to change to liquid. Below the triple point, increasing the pressure would only cause it to become solid ice.
  - Sooo, at this low pressure, warming ice in the soil will only make it sublimate directly into vapor. Most of the time, Mars' temperatures are below the triple point, so increasing pressure would, perversely, keep it solid!
  - And yet you see these gullies and they aren't antiques: Malin's team has found new ones popping up between MOC imaging passes!
  - Some possible explanations for this maddening martian phenomenon:
    - Maybe it isn't water: Brine or some other such non-pure water mix might work. If you add salt to water, you depress the triple point, which allows the liquid phase to exist at martian temperatures and surface pressures. Various salts have been detected on the martian surface, so there might be something to this approach. Salts can be picked up from volcanic fines in the atmosphere that would interact with water or from groundwater's interactions with various rocks.
    - Maybe it's a signature from an earlier era a few thousand years ago when Mars' axis had greater obliquity. Martian obliquity swings from ~15° from the vertical of the plane of ecliptic to ~35° over a cycle of approximately 124,000 years (Earth's varies by only about 4°, with its rotation and axis stabilized by the gravitational tug of the Moon).
      - At a time of greater obliquity, Mars' polar regions would receive the concentration of solar energy, not the equatorial regions, as today and as on Earth. So, it would make sense that water might liquify on the warmer slopes, which would, paradoxically, be the poleward-facing slopes, an effect more pronounced as you approached the equator.
      - A French team led by F. Costard published a geographical analysis of 213 gullies that the MGS MOC camera had found: Almost all gullies from -28° to -40° faced south toward the pole, with 4% facing east; from -40° to -60° 55% faced south, 33% faced east or west, and 11% faced north toward the equator; in polar regions, 58 still face south, but 35% face north. This is consistent with the production of average daily temperatures above 0°C during times of high obliquity.
        
        Adding more credibility to this approach, Mars at high obliquity happens to have higher atmospheric pressure as more water vapor enters the atmosphere, and the sun-facing hemisphere will have higher temperatures, a combination that allows more plain water to remain liquid on the surface.
        Detracting from this is the obvious freshness of so many of these gullies, many caught with new activity or newly created between passes of MGS and the MOC imager.
Linear fossæ and catenæ
- There are linear graben type structures in several regions of Mars:
  - Cerberus Fossæ running from the southern parts of the Elysium rise to the southern parts of the Tharsis rise
  - Claritas Fossæ, the rough terrain south of Noctis Labyrinthus, west of Solis Planum, southeast of Tharsis and clearly subject to tension from its development, and northwest of the Thaumasia mountains
  - Alba Fossæ, scoring the entire old volcano and continuing on south-southwest toward the center of Tharsis: It's as though Alba Mons came up first and then the continuing uplift of Tharsis exerted tension on it, too, cutting it with these grabens
- These often seem to track off radially from the center of Tharsis or, to a lesser extent, Elysium Planum
- They probably reflect the extensional stress of the material coming up from the hot spots under them, leading to rock failure and faulting, and down dropping of terrain between faults, much as we see in the Basin and Range Province of east central California and Nevada with the tension exerted by the insertion of the Farallon Plate under western North America. Death Valley and Panamint Valley come to mind.
- There are a number of oddly linear patterns of pits, too, called catenæ. The term, "catena," is neutral, without a cause implied.
  - So, they sometimes describe impact craters lined up in a row, which you sometimes see when there have been secondary impacts from materials ejected from the primary impact or when an impactor has already broken up before impact, creating a streak of smaller craters.
  - The term can also be applied to strings of pits that are clearly not impact craters, not having the tilted up rim structures: These are just sharp-bordered lines of circular depressions.
  - We talked about them earlier, in discussing features found in the Valles Marineris system of chasmata:
    - Pits in Tithonium Chasma
    - Coprates Catenæ
  - Catenæ may be areas related to faulting and graben construction or even the collapse of lava tubes, in which a surface crust is undermined by extensional stresses and perhaps the extraction of some subsurface fluid and subsidence, leading to cave ins and pitting.
Secondary cratering issue
- We've encountered this issue before while discussing crater-counting as a system to constrain relative and absolute surface ages.
- The basic idea of crater-counting is the power law relationship between crater size and frequency.
- We saw that this is by no means a perfect power law pattern.
- https://home.csulb.edu/~rodrigue/geog441541/isochrontemplate08.jpg
  - When you straighten the relationship out by logging both crater diameters and frequencies, you find the "straight" line turns down above about 64 km (probably a reflection of the end of the Late Heavy Bombardment of the solar system and the resulting reduction in the number of big bombs still out there).
  - The far left side, below about 32 m, faintly turns down, too, possibly because little craters are readily buried or eroded on a planet as geologically active as Mars.
  - The really problematic stretch of this "straight" line bends upward sharply below roughly 1 km in size and above the very tiniest craters.
  - We saw that this is the subject of all kinds of debates about there being, perhaps, an actual increase in the supply of smaller objects out there, maybe from collisions among them in outer space or?
  - Another possibility is secondary cratering.
- We don't know what percentage of craters in the 32 m to 1 km size range are secondaries, so there is a real premium on trying to find ways of detecting them and differentiating them from small primary impact craters.
- The issue is important, because it affects the ages we assign to landscapes, and that can affect processual analysis of those landscapes.
- Some of the attempts to detect secondaries:
  - Looking for odd-shaped craters, on the assumption that secondary impacts aren't at the hypersonic velocities of most primary impacts, so they don't detonate in a nearly perfect hemispheric transient crater.
    - Nearly all primary craters are formed by objects coming in so fast that, no matter which angle they hit, they tend to produce a hemispherical transient crater.
    - Now there's a plot complication: It turns out that some oblique primary impacts CAN produce irregular craters!
      - Some experiments were done by Gault and Wedekind back in 1978 involving shooting various targets with various bullets at various angles. Indeed, incohesive targets hit at anything higher than about 7° produced circular craters; more cohesive targets would produce circular craters above about 30°.
      - Irregular craters seem to open out in the direction of arrival of the impact.
      - That experimental possibility seems to be reflected by certain craters or crater-like basins, such as Orcus Patera that one of your lab projects examined, and a few other craters on Mars, Mercury, and the Moon.
      - So, we now have a possible explanations for such weird landscapes as Orcus Patera, but we have less help in figuring out which craters are primaries and which are secondaries, and that is an important question. Mars, the "yes, but ..." planet.
  - Looking for clusters of small craters, especially linearities
    - For reasons not fully understood, secondaries tend to be aligned in roughly linear patterns.
    - This may reflect dynamics within the ejecta curtain, as fragments from the impactor and the target, including a lot of dust, interfere with one another while in motion. Perhaps this interference results in sorting of the curtain into ejecta-rich regions and ejecta-poor regions, which creates a splat of materials arranged in rays.
    - On the Moon, the rays are often well-preserved, fines and all, punctuated by impact craters, some of which are oddly shaped. It is easy, then, to follow the rays back to the guilty primary crater.
    - Mars is so active geologically in comparison with the Moon, that the fines are removed by the wind, leaving just the craters and no ray structure to link them and point back towards the guilty primary crater.
    - Linking them, then, entails a lot of guesswork and individual inspection.
    - I came up with a system to detect lineations of craters as potential candidates for secondary chains.
      - This entailed selection of a badly battered landscape (I picked a MOC image in Terra Sabæa), manually recording their centers and diameters, entering them in OpenOffice Calc, measuring their distances from one another, calculating for each of them (n=149) its nearest neighbor and then its next-nearest neighbor up to the 6th order, and then calculating the azimuths from each crater to each of its six nearest neighbors. That done, I could compare the second nearest through sixth nearest neighbors' azimuths with the azimuth of the original crater and nearest neighbor pair.
      - I then looked for at least four neighboring craters per crater that were aligned closely.
      - Now, humans are pattern-spotting critters, so just random processes can create "alignments." So, I used a Chi-square goodness-of-fit test to compare my distribution of various groups of "aligned" craters with the binomial probability distribution. That told me that azimuths should be ≤ 15° to be considered a real, non-random alignment, so that's what I used.
      - I wound up with 32 chains of 4 or more craters, suggesting that as many as 71 of the original 149 craters were secondaries, which is about what others have found doing manual classification of craters elsewhere.
      - I then "mapped" them, which was rather funny, given that I am not a GIS person and am a local legend for crappy cartography! I used OpenOffice Calc's graphing function, putting the original image in as the chartwall and then doing a scatterplot of the X and Y coördinates.
      - Much to my surprise, I found patterns among these short alignments: The chains formed longer chains or, even more interestingly, several short chains converged on a common location just off image!
      - Map didn't come out too badly, much to the amusement of Drs. Wechsler, Dallman, Ban, and Tyner!
      - Here's a link to my LPSC paper: http://www.lpi.usra.edu/meetings/lpsc2011/pdf/1014.pdf
      Stuart Robbins and Bryan Hynek mapped tight clusters of craters all over Mars and then fitted them onto great circle routes. Many of the various great circles converged at one point: Lyot Crater in the Northern Lowlands just north of Arabia Terra/Deuteronilus Mensæ.
      - Some of these were more than 5,200 km away from Lyot!
      - And some of the craters in the clusters were fairly large, nearly a km across.
      - This upends the idea that secondaries are little bitty guys and that they fall within a few radii of the primary.
      - It also brings out that, while secondaries impact at lower velocities than primaries, the lower velocities are closest in to the crater, which is where you likelier find oddly shaped craters, and are greatest for those that fall farthest out (something lobbed very high up on a ballistic trajectory will pick up a lot of velocity coming back to the ground far away).
      - So, how many of the global population of craters are secondaries, given that secondaries can fall so far from their primary parent, some of them are pretty large, and the farther and faster secondaries may well produce circular craters? This is a threat to the ability to assign absolute age ranges to given terrains, if not a threat to relative aging.
      - Here's a link to their LPSC paper: http://www.lpi.usra.edu/meetings/lpsc2011/pdf/1330.pdf
Lava tubes
- These form, as on Earth, when lava flows rapidly along a surface, while the top of the flow is cooling and solidifying, forming a crust protecting the fast flow underneath. This eventually drains out, leaving a tunnel in the lava deposit, which may cave in subsequently, exposing the tube system.
- There are lava tubes all over northeasternmost California on the Modoc Plateau, where Kintpuash or "Captain Jack" held off the U.S. Army for a long campaign of guerrilla raids followed by disappearance into the lava tubes that the Modocs knew all about but the army didn't.
- An example on Mars is the ESA Mars Express image of such tubes on the side of Pavonis Mons.
Layered mesas or mensæ
- These are all over the transition zone between the highlands of Arabia Terra, Sabæa Terra, and Terra Cimmeria with the northern lowlands: Cydonia Mensæ, Deuteronilus Mensæ, Protonilus Mensæ north of Arabia Terra; Nilosyrtis Mensæ north of Terra Sabæa and northwest of Isidis Planitia; Nepenthes Mensæ north of Amenthes Planum and west of Elysium Planitia; Zephyria Mensæ north of Gusev Crater and south of Elysium Planitia;.
- They may represent mesas topped by more resistant layers that form a caprock protecting the stack of sediments or lava flows or consolidated wind deposits below.
- These are attacked by erosive agents, notably wind on Mars, and sculpted into striking etched patterns wherever certain layers are more resistant than others.
- We see these all over the American Southwest, such as in Monument Valley, Arizona.
- Mars' answer to such structures include the Cydonia Mensæ region and its infamous Face on Mars. This has become the canals craze of modern times. NASA Headquarters ordered the Mars Global Surveyor mission to drop what it was doing on Mars and reprogram it to get an image of the Face, which cost a lot of money and effort that would have otherwise gone to data processing and scientific analysis of priority targets. It was like finding a needle in a haystack using a microscope. Here is Malin Space Science Systems' discussion of the issue (the team running the Mars Observer Camera): http://www.msss.com/education/facepage/face_discussion.html.
- There's also now the Heart on Mars, a 255 m mesa found in the south polar region by Mars Global Surveyor.
- Anyone who's taken one of my stats classes has heard me rant about the human bias toward seeing pattern even in completely random phenomena (we are the descendants of ancestors who over-reacted to perceived and imagined predators and made asses of themselves but survived to procreate: the rational folks who dismissed a rustling in the shrubbery as random wind sometimes wound up dinner! So, we come by it honestly). We are especially hard-wired to see faces. This kind of pattern-seeing in images is called pareidolia or apophenia. Layered mensæ aren't the only contexts for pareidolia:
  - The Elephant on Mars in Elysium Planitia is currently making the rounds, but that is actually a superimposed lava flow structure rather than mensæ.
  - As long as we're on this tangent, there's a Happy Face on Mars, too, in Galle Crater in the eastern rim of Argyre Crater. There's another, smaller one in a 3 km wide crater in Nereidum Montes in the northern rim of Argyre Crater.
  - Libya Montes on the south rim of Isidis Planitia has a cool-looking face wearing a crown popping out of a degraded crater rim structure.
  - We even have these on Earth: Do a search on the Badlands Guardian in Alberta, Canada!
Yardangs
- Erosional features created by wind, just as on Earth
- Sandblasting of features, sometimes with intense sculpturing at base and often creating long, linear features where the wind blows in a consistent direction
- Given the predominance of æolian processes on Mars, these structures have many similarities with mensæ
- An example is seen in the HRSC (Mars Express) image of yardangs south of Olympus Mons at ~6° at ~220° with a comparison image in the military illustration of yardang terrain (sometimes called grooved terrain)
- Another example is seen in the viewgraphs showing a MOC image of Æolis Mensæ (which is just south of Elysium Planum on the margins of the southern hemisphere highlands, around +1° by ~145°), again contrasted with a mystery military image of Earth yardangs
Dune fields
- Depositional features created by wind, just as on Earth
- Olympia Undæ is covered by a great erg or sand sea.
- On Earth, dunes are ominated by silica sand
- On Mars, they're dominated by basalt-derived dust, so they are sometimes dark.
- Often found in craters or other depressions, where wind drops its load and from which it's nearly impossible for sand to escape.
- If the wind comes from a consistent direction and the sand supply is still relatively sparse, it will group the sand into classic barchans, or crescent-shaped dunes with the horns pointing downwind: The viewgraphs show Nili Patera (Syrtis Major just west of Isidis) with its classic dark barchans
- If the wind is consistent in direction and there's a large sand supply, barchans will merge into long ridges running at right angles to the prevailing wind direction, rather like an ocean's waves on a sand sea. These are transverse dunes.
- If the wind comes from a variety of directions, sometimes it will bunch the sand into star dunes, which may have three or sometimes four ridges going out radially from the summit, as we see in the viewgraphs contrasting Opportunity's view of a dune field in Endurance Crater with another military mystery yardang photo
Patterned ground
- Polygons are often seen on Earth in periglacial environments due to the mechanical stresses caused by:
  - Freeze-thaw expansion-contraction of water
  - Expansion-contraction of other materials due to temperature changes, which can be considerable in such environments
  - Water in the active layer above permafrost is drawn toward the frozen face of ice at the surface of the polygons, the ground surface, and the permafrost itself. This desiccates the soil into blocks, and this partly explains the chunky look of these patterned grounds. Meltwater gets under these blocks seasonally and refreezes, wedging the blocks upward with their expansion. Subsequent melting does not allow the block to settle back down because fines/mud are pulled in under the block and prevent that.
  - Finer and coarser materials respond differently to these stresses of ice wedging and frost heaving, leading to segregation by particle size, which creates the sorting you see around the edges of the polygons, with the largest clasts in the crevices between hummocks
- Such patterned ground is found on Mars more and more frequently at higher latitudes, which is what you would expect from a planet with little permafrost or deeply buried permafrost in the tropics, a lot of permafrost closer to the surface in the mid-latitudes, and sitting atop the surface at the ice caps themselves.
Eskers
- These are streams that form under glaciers due to basal melting.
- Like any streams, they engage in erosion, transport, and deposition of weathered material.
- Like any streams, a lot of this winds up as bed load on the floor of the channel.
- Upon ablation of the glacier, the beds of these streams are exposed along with the ground till under the glacier (boulder-studded clay), where they look like sinuous, gravelly ridges.
- Dorsa Argentea shows good examples of what are believed to be South Polar Ice Cap eskers.
Evidence of mass wasting: Landslides
- Common on crater gully walls at a small scale
- Very evident as a major mechanism expanding the chasmata of Valles Marineris
  - We've looked at Coprates Chasma
  - Ganges Chasma, which was the site of your earliest lab
  - Candor Chasma contains a truly spectacular example
  - Noctis Labyrinthus to the west of Valles Marineris, seemingly at an earlier stage of development and facing different stress fields
Chaos
- Collapsed, jumbled terrain
- May be source of massive, possibly explosive outflows
- Catastrophic melting of water or brine, possibly accelerated by carbon dioxide outgassing, totally undermining the floors of canyons and craters
- Aram Chaos blasting a channel into the side of Aram Crater to get to Ares Vallis looks prototypical, as does Iani Chaos on the other side of Ares Vallis and Aram's crater walls
Softened craters
- Very characteristic of Mars, unlike the Moon (and yet not so far gone as the craters, or astroblemes, of Earth).
- Crater walls eroded through fluvial and æolian processes and, possibly, marine or lacustrine processes (if the state of the buried craters in the northern lowlands is an indicator).
- Crater floors fill with æolian debris, which eventually flattens the floor.
- Some may have been filled, too, with lakes and their bed deposits or, as with the Moon, even lava deposits.
  - Often these deposits, given their varying nature and climate change on Mars, will vary in cohesion, density, and resistance to weathering and erosion.
  - Once filled, these flattened deposits can be eroded by wind
  - As Dr. Laity's experiments showed, targets of varying strength will be etched by wind and the sand it carries (where targets of uniform composition and strength will not).
  - So, a very distinctive landform is created by æolian processes acting on crater fill, often intensely etched.
- As we've also seen earlier, in discussion of Promethei Terra, crater appearances can be softened also by the visco-elastic relaxation of ground ice over entire regions.
- Further softening the look of many martian craters is that "wet splat" fluidized look of rampart and pedestal craters
- Mars ends up with a distinctive look to its craters, a look that is unmistakably martian: You will always be able to look at Mars imagery and instantly suspect it is, in fact, Mars.

Fifth order of relief

This describes very small features, ranging from sub-centimeter in size up to a few meters wide.
This would be the scale of things observed or observable from something like a lander or rover or a small section of a high resolution sensor, such as MRO's HiRISE or MGS's MOC.
Boulders and rocks
- The Viking, Pathfinder, and Phoenix landers, and the Sojourner, Spirit, Opportunity, and Curiosity rovers have imaged individual rocks, and the rovers have carried APXS spectrometers to help identify oxides, elements, and minerals and constrain the kinds of surface the rovers traversed. The last three have also carried Mössbauer spectrometers, which specifically target iron-bearing minerals.
- Sojourner:
  - identified basalt rocks with very little quartz (i.e., igneous rocks not much fractionated), e.g., Yogi rock.
  - also identified more andesitic rocks (i.e., igneous rocks that had experienced some fractionation, some separation out of olivine and calcium plagioclase in favor of minerals coming out of solution at cooler temperatures and after reactions with the first minerals to "freeze" out at the highest temperatures), e.g., Barnacle Bill.
  - æolian fluting, pitting, and faceting are clearly visible on rocks imaged by Sojourner (e.g., Moe)
  - evidence of rock smoothing and rounding is also seen, and these can be produced by fluvial transportation, wave action, and perhaps even glacial transport. There's even evidence of relithification of smoothed pebbles and cobbles into conglomerates, which very much implies marine or lacustrine environments (e.g., Shark)
- Viking landers:
  - caught wind erosion in flagrante delicto
  - some circular feature on a rock is exposed downwind of a rock named Whale Rock
  - rocks are uncovered by sand next to Big Joe
- the APXS spectrometers shoot a stream of alpha particles (basically, helium nuclei), which are a form of highly ionizing particle radiation.
  - These particles smack into substances in front of the APXS.
  - Some of these are reflected directly back into the spectrometer by the heavier atomic nuclei they hit. These are unaltered in wavelength or electron volts because they were not absorbed.
  - In other cases, the alpha particles knock electrons out of the inner electron shells of an atom, which then allows electrons from outer shells to pop down to fill the suddenly abandoned lower orbital places (highly "desirable" electron real-estate).
  - To drop inward, however, the electrons have to pay out some of the energy they needed to hang out at higher orbitals, which they do by releasing X-ray photons.
  - The APXS then registers the distribution of these X-ray photons, generating spectra (line graphs of energy levels measured in electron volts by intensity measured in counts per second of reflected alpha particles or X-ray photons).
  - These spectra have peaks and pits arranged in shapes typical of particular substances.
  - You can use reference spectral libraries to find characteristic peaks and absorption lines and general shapes to figure out which elements and oxides are in a given surface and then use that to constrain the range of minerals present, which can tell you the kind of rock the spectrum was taken from.
  - This can be assisted by such statistical techniques as principal components analysis.
Frost deposits
- Viking 2 caught images of frost forming on Utopia Planitia
- Phoenix was ultimately killed by the sheer amount of carbon dioxide ice (dry ice) forming on its solar panels, which were, apparently, crushed by its weight.
- Frost may have an interesting röle to play in explaining new martian gullies, too!
Polygon patterned ground
- Phoenix caught images of polygon patterned ground that were at the right scale for this permafrost-related ground reworking.
- Large polygons had been seen from orbiters but usually at such a large scale that there was debate about whether this could be the same process that produced the smaller patterning in Earth's permafrost and periglacial environments.
Dust devil activities and tracks
- The Phoenix lander had an instrument called Telltale, which allowed recording of the martian wind through observation of, basically, a weight on a string. It took thousands of shots of the telltale, which were put together into a movie. There was an interesting episode where it wasn't just the weight and string moving all over but the base of the instrument as well. This was a strong shaking, which is believed to have been a direct hit by a dust devil on Phoenix.
- The Spirit rover also got some great movies of a swarm of dust devils coursing across Gusev Crater.
- It's believed that dust devils extended the lives of Spirit and Opportunity by cleaning the solar panels that were getting coated with so much dust that they were losing the ability to recharge the rovers' batteries.
Sand and dust streaks
- Wind deposits sand into moving heaps: Seen up close with Viking and Pathfinder/Sojourner.
- Barchans are classic crescent-shaped dunes with a slip face on leeward side and horns pointing downwind.
- Transverse dunes are related to barchans but ridges are straigher.
- Wind carves out hollows in soil at base of rocks and creates streaks and wind tails downwind.
Gullies
- One of the surprises from high resolution orbital imagers that can revisit and re-image small features has been the appearance of fresh new gullies, complete with detachment alcoves, runout channels, and depositional aprons.
- Malin Space Science Systems, which operates the MOC imager, on reporting this finding back in 2000 or 2001, thought that this might be evidence that water can still flow on Mars: They resemble Earth gullies point for point.
- It didn't take too long for the Mars community to have a "yes, but ..." moment and start arguing for alternative interpretations.
- Dr. Laity's collaborator, Dr. Nathan Bridges and another collaborator, Dr. Claire Lackner, argued that water is involved, but it's not so straightforward as seepage of liquid water down a slope.
  - They point out that the geography of these features isn't consistent with a straightforward seepage of groundwater.
    - Gullies are found on steep slopes, most commonly crater rims and walls (though some have been found on dunes), often starting at the very top (where groundwater is apt to be scarcest, though it should be noted that, in a given collection of gullies, the heads will be at pretty much the same elevation, which would be consistent with an aquifer, so this is still a point of confusion).
    - These are most commonly found between + ~30° and ~65°.
  - Bridges and Lackner argue that the specific surfaces carved by these gullies and the obliquity cycle need to be worked in.
    - They note that gullies are often correlated with a kind of geological unit called a mantling unit.
    - This, they think, was the precipitation or condensation of water ice around the abundant dust nuclei of the martian atmosphere, leading to a kind of "dirty snow" or "filthy frost."
    - This would happen at mid-latitudes during high obliquity cycles, when the concentration of solar energy in polar latitudes (higher sun angle and longer day length) would cause the polar caps to sublimate and the water (and carbon dioxide) vapor could then freeze out or snow out in lower latitudes.
    - This would build up a soft deposit of dust and ice, which seems to mantle underlying terrain, kind of dulling its edges.
    - Then, when Mars' obliquity went into a low phase, the fine ice in these mantling deposits would sublimate out and desiccate them, and the water and carbon dioxide vapor would freeze or snow out on the polar caps again. The mantling deposits would sag and settle.
    - Part of this might have included temperatures warm enough to allow melting as well as sublimation, and the melt fluid would dribble out and create gullies.
    - As obliquity became lower and lower, more and more of the mantling deposits would erode this way and this erosion could get pretty thorough in the mid-latitudes and less so in the lagging higher latitudes.
  - A "plot complication" with both the Malin team's and the Bridges and Lackner interpretations, though, is that gullies are more common in the Southern Highlands than the Northern Lowlands, meaning at higher elevations.
    - Higher elevations means lower air pressure and less likelihood of water getting above its triple point.
    - Higher elevations also means colder elevations and even less likelihood of water being found in a liquid state.
  - Some people, such as Jon Pelletier (2008), have argued that, in fact, these features, or at least some of them, are small dry avalanches, essentially sand or gravel sloughing downslope.
  - Yolanda Cedillo-Flores and Héctor Durand-Manterola (2010) and Serina Diniega argue that the sublimation of carbon dioxide or water ice in such substrates as the mantling deposits or even sand undermines the support of individual sand grains.
    - These then fall or roll down, entraining others that are precariously supported.
    - In fact, these dust and sand materials may fluidize or flow as bone-dry grains supported on the sublimating gas, more of which would sublimate as a result of exposure by a flow once it gets going. The fluidization refers to how the gas keeps the grains in buoyant suspension, so that their edges can't lock and put an end to the movement through friction.
    - Sirena Diniega (2010) adds that carbon dioxide frost may itself get so thick in the winter that it might start rolling down a steep slope, an avalanche of dry ice grains, which then entrains other material in it.
    - Donald S. Musselwhite, Timothy D. Swindle and Jonathan I. Lunine went further in 2001, arguing that we're looking at carbon dioxide vaporizing and, the moment it escapes the soil, refreezing outside the soil as frost. The frost grains then continue rolling downslope, buoyed up by more of the vaporizing ice in a suspended flow, eroding soft soils as they go.
Blueberries
- Opportunity was sent to Meridiani Planum because of orbital spectral evidence of hæmatite, which is an alteration product of olivine in neutral water.
- Olivine is found in a range of types, dominated by iron or magnesium, which sets it on somewhat different alteration courses, depending on exposure to water and whether the water is neutral, acidic, or basic.
- It often goes through substitutions of elements to create iddingsite (weird material that often preserves the shape of the original olivine).
- Iddingsite can be further altered into serpentine or, in other cases, into gœthite.
- Gœthite can give way to hæmatite, which sometimes forms concretions within the goethite.
- That appears to be what happened in Meridiani Planum: Hæmatite was deposited by water within beds of gœthite.
- Further weathering weakened the sedimentary beds and the spherules popped out and accumulated on the ground in great numbers.
- These spherules are a very clear evidence that Mars had water, that that water had been neutral in pH at some Noachian times and places.
- This amplifies the impression that Noachian Mars may have had water on its surface and did have it in the form of groundwater, enough to alter olivine in a few places all the way to hæmatite.
And so concludes our discussion of the regions of Mars organized by scale. End of S/15 optional section.

The martian atmosphere and a climatic regionalization of Mars

The Martian atmosphere: composition, structure, and weather
- Chemical composition and dustiness
  - Mars' atmosphere differs sharply from Earth's in its gaseous composition.
  - The most common gas in the martian atmosphere is carbon dioxide.
    - On Mars, it makes up 95.32% of clean air by volume.
    - On Earth, CO₂ is only about 0.037%.
    - On Earth that small bit of gas, which is rising as a result of human activities, is implicated in global warming.
    - On Mars, even 95% of air being CO₂ isn't going to create runaway global warming because, remember, the atmosphere is so insubstantial and doesn't have that much heat density.
  - The second most common gas on Mars is our own most prevalent gas: nitrogen, as N₂, but it's only a piddling 2.7% of martian air, versus 78% on Earth.
  - The third most common gas is argon.
    - This is a gas, which rarely reacts with any other element (its outer electron shell is already saturated with electrons so it isn't cruising around looking to swipe electrons).
    - It makes up 1.6% of the martian atmosphere but even less on Earth: only 0.934%.
  - Trace gasses include:
    - Oxygen, the second most common gas on Earth, is only 0.13% of Mars' atmosphere.
      - Oxygen is a chalcogen (member of Group 16 in the periodic table). It is, thus, highly, crazy-reactive, being two electrons short of a full outer orbital and hungry to acquire/share them.
        
        Because of this "electronegativity," free oxygen tends to attach itself to various metals and other substances ("oxidation"), as do the other members of its group.
        It is, therefore, really difficult for oxygen to build up in an atmosphere.
        It does build up in Earth's atmosphere, because plant photosynthesis and microbial chemosynthesis generate such copious amounts of oxygen that it outstrips the ability of rock materials to oxidize it all, so it builds up in the atmosphere.
        If we ever spot another planet with a strong molecular oxygen (O₂ spectral signature, we will then be almost certain that we have found life there.
        Mars, then, does not show evidence of photosynthesis going on because of the paucity of oxygen.
      - Because there is so little free oxygen, there is virtually nil ozone.
        
        Ozone is produced by the photo-dissociation of oxygen in the presence of ultraviolet radiation and its reconfiguration into O₃.
        Because of the lack of ozone, there is no real stratosphere on Mars
        There is, therefore, no protection from an ozone layer for surface life forms: Mars has high ultraviolet radiation at its surface.
        UV shielding will be one of the major problems faced by astronauts sent to Mars: Settlements may well be underground for this reason.
      - Carbon monoxide comes in at 0.07%, which is a lot more than on Earth (~150 parts per billion, 1.5 x 10^-7), despite all the faulty combustion going on here.
      - Water vapor makes up only 0.03% of Mars' atmosphere; on Earth, it is a highly variable gas, making up as much as 4% in certain situations.
      - There are some other gasses present on Mars, but at incredibly dinky doses, 0.0015 (hydrogen's abundance) or less.
- Vertical pressure and density structure
  - Mars' average pressure at the elevation of the "areoid" is roughly 0.67% that of Earth at sea level, or 6.75 hPa versus 1,013 hPa for Earth
  - It varies far more than Earth's:
    - It ranges from ~6 to ~10 hPa
    - Extremes on Earth range from Typhoon Tip's 870 hPa back in 1979 to 1,084 hPa in Agata, Siberia, in 1968
    - So, Mars surface air pressure varies something like 60% of its mean pressure, versus 20% for Earth
  - As on Earth, there is an inverse association between pressure and altitude, an exponential falloff in barometric pressure with a gain in altitude. For the morbidly curious, that would be:
    - P = 0.699 * e^{-0.00009 * A}, where P = pressure and A = altitude in meters
    - This is an inverse exponential curve (Y = a e^{b X} )
    - Multiply Altitude by -0.00009, then raise e (2.71818) by that answer, and, lastly, multiply THAT answer by 0.699. That gets you the predicted air Pressure (in hPa) for that altitude.
  - Temperature, too, drops with altitude, but in a linear fashion:
    - This is a simple linear regression of the Y = a +bX form, except the curve is different below and above ~7,000 m
    - Below 7,000 m, it's T = -31 - 0.000998 * A
    - Above 7,000 m, it's T = -23.4 - 0.00222 * A
  - Not too surprisingly, the drop in pressure causes a drop in density with altitude, modified by temperature:
    - D = P / [0.1921 * (T + 273.1)]
    - Where D = density in kg/m³; P = pressure in kP (kilopascals, 1/100th or percentage of Earth sea level average barometric pressure); and T is temperature in ° C.
    - To convert density into hectopascals/millibars, multiply by 10
  - Vertical temperature structure
    - Like Earth, Mars' lower atmosphere usually displays an inverse relationship between altitude and temperature: Temperature cools as you rise.
      - Sometimes called the troposphere
      - This band goes up to about 45 km above the ground, where on Earth, it extends up to only about 20 km or so (variable in thickness).
      - The martian troposphere, like Earth's, is the zone of active radiative interaction between the surface of the planet, which absorbs solar radiation and then re-emits it at longer wavelengths as thermal radiation and the atmosphere.
        
        The lower atmosphere is warmed by this re-radiation and its effectiveness drops with the square of the distance to the ground.
        Dustiness in the lower atmosphere plays an intriguing rôle:
        
        It can absorb a lot of insolation and also outbound surface thermal emissions, and this leads to elevated temperatures above the surface whenever there's a lot of dust present there. Dust absorbs and re-radiates, both insolation and planetary thermal re-emissions.
        Dustiness, however, can also shade the surface, reducing the surface absorption/emission of solar radiation and the warming from below.
        So, the presence of dust can produce elevated temperatures higher in the troposphere and reduced temperatures at the surface, leading to stable air.
        
        As on Earth, there is also heat transfer through adiabatic processes, as air masses move up or down, especially when rising air forces the freezing of water vapor or carbon dioxide.
        
        As air masses move up, they expand in volume as they move into zones with less air pressure from above.
        This expansion dilutes the energy density of the air mass, thus cooling it.
        Depending on the amount of water vapor or carbon dioxide in the air, this adiabatic cooling may reduce the temperature below the saturation condensation level, which on Mars will be below the triple point of either gas. The result is freezing and possible precipitation as snow.
        If that happens, the adiabatic lapse rate reduces because the phase change from vapor to ice liberates some latent heat as thermal heat, partly offsetting the dry adiabatic process.
        Going in the opposite direction, sinking air compresses, thus concentrating its energy density, which warms it (and precludes condensation and precipitation).
        This adiabatic effect is above and beyond any heat transfer due to conduction or radiation.
        
        At night, convectional uplift of the air closest to the ground falters and then ceases or even reverses.
        
        Meanwhile, the rapid chilling of the ground begins to reverse the flux of heat, drawing it out of the atmosphere into the ground, creating a chilled layer close to the ground.
        Above it, the collapse of the daytime convection column causes adiabatic warming and the construction of a warm layer on top of the chilled surface layer.
        So, at nighttime, you get temperature inversions, much as we see here on Earth at night.
      - The martian troposphere, like Earth's, is the location of weather: convection cells, clouds, dust devils, wind and dust storms
    - Unlike Earth, there is no real stratosphere
      - There is no ozone level, because its source, oxygen, makes up so very little of the martian atmosphere. Therefore, there is no band in the middle atmosphere in which molecular oxygen is absorbing ultraviolet radation during photodissociation into atomic oxygen and recombination into O₃. In other words, there isn't a zone of a direct relationship between altitude and temperature comparable to Earth's stratosphere.
      - On Earth, the stratosphere, containing the ozone layer, extends from roughly 25 km up to about 50 km.
      - On Mars, the middle atmosphere is an isothermal belt above the troposphere, which extends from roughly 45 km up to about 110 km.
        
        This is sometimes called the martian mesosphere, though I've seen some authors even call it the "stratosphere."
        On Earth, the mesosphere is a zone, in which temperatures resume an inverse relationship with altitude (temperatures go down as you go up), and it extends from about 50ish km up to about 80 km.
        On Mars, temperatures remain essentially static for kilometers, neither warming nor cooling consistently with a gain in altitude: isothermic
        It is a sort of transition zone between the inverse temperature-altitude relationship of the lower atmosphere and the direct relationship seen in the thermosphere.
        It is actually probably best analogous to the tropopause, stratopause, and mesopause in Earth's atmosphere, these isothermic bands that separate the different trends in the altitude and temperature relationship.
    - Above the mesosphere, as on Earth, there is a wide band in which temperatures rise with altitude: The upper atmosphere, sometimes called the thermosphere, the same name used for the same phenomenon on Earth.
      - This band extends from roughly 110 km up to the top of the martian atmosphere about 200 km out.
      - On Earth, by comparison, the thermosphere extends from about 90 or so km up to where Earth's denser atmosphere gives way to interplanetary space around 10,000 km up.
      - Temperatures really get up there (on Earth, it can hit 1,225° C), but that degree of molecular motion isn't all that impressive, really, when you think how very few molecules there are going nuts up there.
      - The thermosphere on Mars, as on Earth, can be further subdivided on the basis of and gravitational effects on composition.
        
        The inner thermosphere contains the ionosphere.
        
        On Mars as on Earth, this is made up of ions, or atoms and molecules stripped of electrons by the intensity of ultraviolet (short-wave, high energy) light.
        The electrons, with their negative charge, and the remaining atoms/molecules and even isolated protons or alpha-particles (two protons and two neutrons, with no electrons), with their positive charge, thus, are segregated, and the resulting ionized gas affects radio wave propagation.
        The ionosphere also glows as UV light alters the energy state within an atom or molecule.
        
        Electrons are blasted out of lower orbital shells (a process similar to the X-ray electron stripping in the APXS spectrometer on the various rovers).
        This causes those in higher shells to move inward, closer to the positive charge in the nucleus.
        When electrons move to the "desirable" lower energy state, they emit a photon or light particle as they move, creating a glow.
        
        On Earth, the ionosphere is markedly shaped by our still-strong planetary magnetosphere.
        
        Ions align with the magnetic lines of force due to their electrical charge.
        Where the field lines are concentrated, as at the magnetic poles, the airglow of the ionized gas will be concentrated to the point of visibility: aurora displays.
        On Mars, there is no planetary magnetic field, but there are local magnetic fields, and these have produced little, local auroræ through their effects on the martian ionosphere.
        We talked about that in the third order of relief, in the discussion of Terra Sirenum and Terra Cimmeria.
        
        The lower thermosphere (~110 km to ~125 km) is an extension of the homosphere on Mars, as on Earth. The homosphere is that portion of a planet's atmosphere that is maintained in a relatively homogeneous blend of the various gasses due to mechanical and thermal mixing: winds, convection cells.
        Above ~125 km, the gasses in the atmosphere are pretty much beyond the reach of these mixing forces, so that allows gravitation to exert a density layering effect, kind of like letting a shaken oil and vinegar bottle settle down and form layers.
        
        The area subject to this kind of quiet layering is called the heterosphere on Earth.
        Heavier molecules, such as nitrogen, carbon dioxide, and oxygen, settle out first, lowest down, letting lighter gasses, such as hydrogen, be pushed out farthest.
        This effect is also seen with different isotopes of a given gas: For example, deuterium or "heavy" hydrogen (with one proton plus one neutron in its nucleus) will be lower than regular hydrogen (with only one proton serving as a nucleus).
        The heterosphere layer defined chemically and mechanically is roughly equivalent to the exosphere, which is defined by the motion of those few stray atoms and molecules out there.
        
        In most of the atmosphere, molecules and atoms are so tightly packed that any one of them ricocheting after a collision with another one isn't going to get too far before being blocked in its travels by yet another one.
        Out here in the exosphere, however, a quick moving molecule or atom may rarely bump into another, maybe going 10 km in a straight line before hitting something.
        Well, eventually, with few obstacles to tackle them, heated (and sped up) by the intense radiation out there, and less and less subject to the gravitation of the planet, they might bounce and just keep on going in a straight line right out into Space: The Final Frontier!
        Atmospheres tend to ablate in this way, losing disproportionately the lightest of all elements and isotopes: hydrogen more than deuterium, for example.
        Thus would have been lost much of any ocean on Mars once the atmosphere dropped in density back in the Noachian.
        
        Water ice, sublimated directly into vapor, then, is often photodissociated by solar radiation into hydrogen and oxygen.
        The oxygen, being a "promiscuous" chalcogen atom, will quickly recombine with something, perhaps an iron-bearing mineral on the surface.
        The hydrogen, meanwhile, may drift up into the exosphere, given its lightness, and be lost to Mars through random ricochets at the top of the exosphere.
- Horizontal (spatial) variations in pressure
  - As on Earth, there is relatively lower pressure in the equatorial regions and higher pressure over the polar caps.
    - This reflects the concentration of solar energy at the equator and convective uplift there, which lowers surface pressure.
    - The extreme cold at the poles creates subsiding air there, and this raises barometric pressure.
  - As on Earth, there is a Hadley circulation:
    - There are the familiar temperature and pressure variations just mentioned:
      - Air warms in the tropics and rises there, spreading poleward in the upper atmosphere.
      - Air chills in the polar regions, sinks, and spreads equatorward along the surface.
      - Since the planet is rotating, horizontal air flows are distorted by the Coriolis Effect.
        
        In the northern hemisphere, horizontal motion is deflected to the right with respect to the planet's surface.
        In the southern hemisphere, deflection is to the left.
        There is no Coriolis deflection along the equator, and the deflection becomes progressively stronger farther and farther from the equator.
    - These generate surface air flows:
      - Air rising in the equatorial regions pulls surface air into a westward moving (easterly) system of winds, rather like our easterly Trade Winds.
      - Air sinking over the polar caps is squeezed out in a clockwise surface circulation that corresponds to our Polar Easterlies.
    - As on Earth, Coriolis Effect distorts the circulation by breaking it into smaller eddies.
    - As on Earth, too, the Hadley circulation tends to move first north and then south with the seasons as the obliquity of Mars' axis points first the northern hemisphere and then the southern hemisphere toward the sun.
    - Unlike Earth, however, there is a marked difference in the strength of the Hadley circulation and the pattern of flow over the course of the year, due to the much greater eccentricity of the martian orbit compared with Earth's.
      - The Hadley cells develop best and in a most earthlike way during the martian spring and fall, when the sun's direct rays strike the equatorial regions. This is the familiar pair of Hadley cells we see on Earth.
      - During the summer and winter, however, when the greater axial tilt of Mars leads to a more pronounced shift of solar energy into or away from the polar regions, there tends to develop a single big Hadley engine in the warmer hemisphere, which extends into the other hemisphere.
        
        The companion cell in the cold hemisphere is lost in the strong vortex circulation that develops at the surface around the dark pole.
        This is due to the interaction between descending and adiabatically warming air over the pole and the really, really cold and denser winter air mass that develops in the darkened "Arctic" or "Antarctic" regions, which is enough to disrupt the Hadley cell in that hemisphere.
    - Due to the planet's high eccentricity, too, the Hadley circulation is best developed during northern winter/southern summer rather than during southern winter/northern summer: Remember, perihelion hits during southern summer on Mars as on Earth, but there really is a marked difference in energy receipt between perihelion and aphelion.
    - Interestingly, the Hadley cells are associated with aurora-like faint glows in the ultraviolet and the infrared.
      - As we saw in the discussion of the thermosphere, carbon dioxide and molecular nitrogen are photodissociated there to create atomic nitrogen and oxygen and carbon monoxide.
      - These get caught up in the descending branch of the Hadley circulation and sink there on the night and winter sides.
      - This brings them into greater density with the adiabatic concentration there, so a lot of these loose-cannon atoms recombine into molecular oxygen (accounting for the tiny trace amounts of oxygen in the martian atmosphere) and nitrogen and nitrous oxide.
        
        The oxygen emits a concentration of near-infrared energy at 1.27 microns, which was picked up by the OMEGA spectrometer on Mars Express.
        The NO emits a similar spike in the ultraviolet, which was picked up by the SPICAM spectrometer on Mars Express.
        These constitute a faint nighttime emissions glow in the descending limb of the Hadley cells during winter. They would not be visible to us, though, because they peak well outside the 0.4-0.7 micron wavelengths of visible light.
- Temporal patterns in these spatial pressure variations
  - Strong temperature differences develop across the differing surfaces of Mars, especially in the mid-latitudes.
    - As on Earth, temperature differences create pressure differences, with warmer areas producing rising air and low pressure (cyclones) and vice-versa (anti-cyclones).
      - These cyclone/anti-cyclone patterns create wind flows between them.
      - These systems move eastbound around the planet, as on Earth.
      - Unlike on Earth, though, they tend to be more regular and predictable, with about a 3 or 4 day cycle.
    - They mix the atmosphere, moving surface and equatorial heat upward and toward the poles, a function that varies with the clarity of the atmosphere:
      - They are stronger during times when the atmosphere is clearer, perhaps because the clear sky allows more radiation to hit the surface, inducing those surfaces with a relatively low specific heat to heat up more rapidly and produce pressure variations.
      - They are weaker during dusty episodes, which might shade the surface and reduce the contrasts in surface temperatures.
  - There's an interesting diurnal thermal tide that develops between the day side of Mars and the drastically colder night side of the planet. The difference in temperatures can be as much as 50° C or 90° F, far worse than anything even a bone-dry desert on Earth experiences between night and day.
    - This sets up atmospheric tides of strong local winds that move around Mars with the sun.
    - They are much stronger when the air is clear and more subdued when the atmosphere is in one of its dustier "moods," shading surfaces in the daytime and keeping the atmosphere warmer in the nighttime.
  - At a smaller scale, the area around the northern ice cap gets some interesting weather in the northern hemisphere summer.
    - The ice cap shrinks due to heating and sublimation of carbon dioxide and water, which provides water vapor for clouds and storms.
    - You might remember those odd comma-like storms I showed you earlier in the semester, rather like the subpolar lows that get going on Earth
    - On Earth, this is more of a winter phenomenon, the source of the mid-latitude wave cyclones that give California its winter precipitation.
    - At the most local scale, there are small wind systems, kind of like the upslope-downslope breezes, land-and-sea breezes, and dust devils that develop in certain Earth locations.
      - On Mars, they are generated by localized, differential heating of air due to:
        
        Differences in surface albedo
        Differences in aspect: Adret (sun-facing) and ubac (shady) slopes
        Differences in soil thermal inertia and specific heat:
        
        Thermal inertia is a function of a substance's:
        
        heat capacity or specific heat (how quickly it changes in temperature in response to inputs of heat energy)
        density
        thermal conductivity (how quickly it transfers heat to something else or within itself)
        
        These are affected by state of matter (liquid vs. solid), grain size, interstitial spaces among grains.
        On Earth, water has high thermal inertia/high specific heat, and land has low thermal inertia/low specific heat, so land heats up and cools down quickly compared to nearby water, which then creates relative temperature differences, pressure differences, and compensating breezes.
        Mars doesn't have bodies of water, but the surfaces of Mars do vary in thermal inertia, specific heat, and albedo (solid lava flows, impact-gardened regolith, high albedo dust).
        
        Solid rocks, including the dark, low albedo basalts so common on Mars, have high thermal inertia as rock molecules and mineral grains readily conduct heat to their neighbors and away from the area receiving the energy: It takes more heat input to produce warming of their surfaces.
        Regolith and dust, with their abundant interstitial spaces between rock grains, transfer heat from one to the next only at the small points and edges where they touch one another. This is high thermal inertia. It takes relatively little energy input to produce warming of such a surface because the surface can't transfer the heat away as readily.
        
        These differences in thermal inertia and specific heat may be significant on Mars, creating analogues of diurnally reversing land-and-sea breezes there or even seasonally reversing monsoons, an effect significant enough to affect global circulation models of Mars' climate!
      - These local wind systems are strongest near perihelion, especially in areas with topographic extremes (e.g., Tharsis' gigantic volcanoes or the steep slopes leading down to Hellas Planitia). They are common around the "Blue Scorpion" of Syrtis Major, which plays a "sea" to the surrounding dusty areas as "continents." In a manner of speaking, the Syrtis Major "Blue Scorpion" is, indeed, the "Hourglass Sea" it was often called in early Mars telescopic observation, at least in terms of air flow!
- Martian weather
  - Seasonality
    - Seasons are more extreme on Mars, because the axial obliquity is more tilted than it is on Earth: ~25.19° versus ~23.4°
    - The greater orbital eccentricity of Mars significantly intensifies the solar radiation flux differences between the two hemispheres, where the difference is so minor it's trivial on Earth:
      - As noted earlier, the southern hemisphere's summer is warmer than the northern hemisphere's because it coïncide with perihelion.
      - The northern hemisphere's winters are colder, because aphelion coïncides with it.
    - The eccentricity also makes the seasons of different lengths on Mars, where they're nearly the same length on Earth:
      - The planet is moving faster at perihelion (Kepler's Second Law), so the southern hemisphere spring and summer are shorter, if more intense: 147 Earth days long and 158 Earth days long, respectively.
      - The planet is moving slower around aphelion, making the northern spring and summer longer (199 Earth days and 184 Earth days, respectively), if cooler.
  - Storminess is different in the two martian hemispheres:
    - There are more dust storms and dust devils in the southern hemisphere's spring, and some of these can spiral <sorry> out of control into regional or, sometimes, planet-covering dust storms.
    - Polar cyclones, complete with water-ice cloud bands circling counterclockwise about a central eye, reminiscent of a terrestrial hurricane, seem to be northern hemisphere phenomena, developing around the edges of the residual water ice-dominated northern polar cap in the northern summer.
      - They are not common, but they do tend to show this regularity in season and geography.
      - They might be closest in character to terrestrial polar "hurricanes," which are driven by strong contrasts between oceanic and air temperatures.
        
        What the analogous contrast on Mars might be is the difference between the air masses forming over the dark surfaces of Vastitas Borealis, which would heat up in summer what with the long days provided by the more extreme obliquity and the low elevation, and the extreme cold of the air above the residual ice cap reaching up to 3 km above the northern lowlands.
        It is possible that eddies might form in the interaction between the polar easterly air flow and winds blowing down Chasma Borealist, allowing a spiraling vortex of low pressure to form that reshapes air flow in the region into the familiar cyclonic pattern.
    - There are wind disturbances in the winter and spring of both hemispheres that seem to correspond to our own mid-latitude travelling wave cyclones, the kind of system that gives us our winter rain.
      - They propagate eastward, just like they do on Earth.
      - They seem to develop out of instabilities in the zonal temperatures, or variations in mean temperature along a parallel of latitude.
      - This creates zonal differences in barometric pressure: baroclinic instability.
      - This organizes waves in otherwise zonal air flow, giving them a meridional component (cross-parallel flow).
      - These march around the planet even more regularly than they do on Earth.
      - They rarely induce much cloudiness, however, unlike on Earth: You sometimes see some cirrus-type clouds.
    - The equatorial areas are dominated by the convergence of the Hadley cells around spring and fall equinoces:
      - Breezes and winds with a easterly bias, rather like our Trade Winds.
      - The uplift of air in this convergence zone results in more cloudiness in the equatorial area than anywhere else on Mars: There may be more water vapor in the air here because of the "warmer" temperatures, more water vapor available to freeze onto cloud nuclei when the air is lifted high enough.
- Martian geochemical cycles and weather
  - The hydrological cycle
    - This is very different from Earth.
    - There is very, very little water vapor in the martian atmosphere at any one time (0.03% on average, by volume)
    - This is in constant flux from one polar cap to the other, from the summertime pole as a source of vapor from sublimation to the wintertime pole as a place so cold that water vapor will freeze there.
    - As Mars Express has found in certain craters, water will apparently form glaciers in favorable locations away from the poles.
    - It also forms frosts, as the landers have documented in their locales and as Mars Express and MOC have documented on many crater rims.
    - Water vapor does freeze onto dust nuclei in the atmosphere to produce the many clouds and fogs that have been recorded on Mars.
    - There may be a lot of water ice also in the regolith (the impact-gardened debris that passes for soil on Mars) and rocks
      - Almost all of this will be permafrost
      - There may be small, transient active layers above or even below the permafrost, where water ice will change state into liquid, due to surface warming or geothermal activity. This may be what accounts for the fresh gullying documented by MOC. A geothermal disturbance might well account for the gigantic jökulhlaup-like outflow floods during catastrophic melting of permafrost.
      - At the present time, there may be almost no interaction between soil ice and the atmosphere, so the permafrost may not actively participate in the contemporary hydrological cycle on Mars.
  - The carbon cycle
    - Carbon has a very active cycle on Mars.
    - It moves from sublimation off the summertime polar cap to re-freezing on the wintertime polar cap, much as water does.
    - It, too, forms clouds and fogs upon freezing onto condensation nuclei provided by the abundant dust on Mars.
    - A very interesting aspect of the martian carbon dioxide cycle is the effect that its seasonal fluxes have on air pressures on Mars.
      - When the carbon dioxide ice on the poles sublimates (which can be rather a dramatic, geysering phenomenon sometimes), it pushes the martian air pressure up pretty drastically: remember that variation from about 6 hPa to 10 hPa, which is way more dramatic than we see on Earth.
      - The effect is especially noticeable when it's the south polar cap that sublimates during southern hemisphere summer: That cap is made up of far more carbon dioxide ice than the lower, warmer north pole, which is dominated by water ice.
  - The oxygen cycle
    - Not much there: ~0.13%.
    - What little oxygen there is seems derived from water and carbon dioxide in the planet's regolith.
    - This is based on the expectation that, in the exosphere, you would disproportionately lose the lighter isotopes of oxygen (¹⁶O and ¹⁷ O, versus ¹⁸O) over the billions of years of martian history.
    - On Mars, however, you find a more normal proportion of ¹⁸O, which means it must be getting replenished from somewhere: soil water, permafrost?
    - In fact, you could calculate how much water you'd expect was lost from Mars -- enough to create a global ocean on a smooth planet of something like 13 m in depth -- a lot of water.
    - Because there is a little oxygen and it's being replenished somehow, there is also a tiny bit of ozone, because of the intense UV exposure of the atmosphere: It breaks oxygen bonds and reforms them as ozone.
    - Ozone tends to be eroded quickly by exposure to hydrogen, so ozone tends to persist only in the very driest locations, as in the polar cap on the winter side of the planet.
  - The nitrogen cycle and implications for the past atmosphere
    - Also pretty puny on Mars: ~2.7%.
    - But it's overrepresented in the heavy isotopes of nitrogen (¹⁵N, instead of ¹⁴N), which means that much of the lighter nitrogen snuck off into space through the exosphere.
    - It's been estimated that fully 90% of Mars' primordial nitrogen escaped this way.
    - If that's the case, then that would mean the nitrogen content of the early martian atmosphere, besides having a lot of nitrogen, would contribute a lot to an increased atmospheric air pressure: maybe as high as 78 hPa
      - Remember the triple point of water?
      - Mars, with air pressure averaging around 6 or so hPa, typically sees water changing state directly from ice to vapor (sublimating) whenever temperatures rise above about 0° C or 273 K.
      - If the air pressure got as high as 78 hPa, water would go from ice to liquid at 0° C and then not evaporate until about 60 or 70° C!
    - That would mean that water might well have persisted as a liquid in pressures that high, explaining the fluvial features we see on Noachian landscapes.
Mars climates
- On Earth, the climate classification systems (e.g., Köppen and Thornthwaite) depend on measures of temperature, moisture/evaporation, precipitation, and may modify categories to incorporate vegetation (which, because of the rather sensitive environmental envelopes of many plant species, covary with environmental conditions, which can be read from vegetation in the absence of instrumental records).
- How can martian climates be classified? Basically, temperature, maybe dustiness, wind, water vapor content, maybe snow or frost. Henryk Hargitai has attempted a systematization of martian climates, inspired by Köppen's system but allowing seasonal migration of the underlying factors:
- At the coarsest level, we could differentiate:
  - North polar "frigid" climates north of the Arctic Circle at 64.9° N
  - Northern transitional "temperate" climates south of the Arctic Circle and the Tropic of Pisces (Mars' answer to our own Tropic of Cancer) at 25.1° N
  - Equatorial "tropical" climates between the Tropic of Pisces and the Tropic of Virgo (Mars' version of the Tropic of Capricorn) at 25.1° S
  - Southern transitional "temperate" climates from the Tropic of Virgo to the Antarctic Circle
  - South polar "frigid" climates south of the Antarctic Circle
- Just as on Earth, the whole system of climate factors would shift north and south with the shifting position of the thermal equator, or the location of the "noon-overhead sun" or direct, vertical ray of the sun, caused by the obliquity of the planet's rotational axis.
- On Mars, the northern and southern hemisphere versions of these climates would be much more different from one another than they would be on Earth, due to the plot complications of Mars orbital ellipticity and the elevation differences between the two hemispheres.
  - The southern hemisphere summers would be "hotter" than the northern hemisphere's summers because perihelion happens in the southern hemisphere summer, leading to more CO₂ sublimation off the South Polar Ice Cap and higher air pressures, more wind, more dust storms.
  - Southern hemisphere winters would be colder, too, because they coïncide with aphelion, leading to greater deposition of CO₂ ice in the seasonal cap, which extends further toward the equator than you see in the northern hemisphere. Enhancing the effect is the greater elevation of the Southern Highlands, leading to lower temperatures by normal and adiabatic lapse rates (drop in temperature with a gain in elevation, which is intensified if the air itself is moving vertically).
- Nested within the coarse bands, just as with the Köppen system, the basic climate classes can be modifed by terrain extremes and by persistent differences in albedo that create smaller regional climates. On Earth, for example, we have the H or Highland climates, and we can recognize that effect on Mars, too. We can see the need to modify our climate belts for areas of unusually low elevation/high pressure, too, and for areas of unusually low albedo, which affects air pressure and heat retention. So, here are the modifications to the main climate zones defined by Hargitai:
  - Equatorial zone highlands
    - Tharsis and Elysium
    - Extremely cold due to lapse of temperature with elevation
    - Air with tiny amounts of water vapor could rise and cool adiabatically enough on such tall slopes as to induce the formation of clouds, and these volcanoes often are topped with clouds.
  - Low albedo equatorial zones
    - Syrtis Major
    - This would be an area of high thermal inertia, meaning it would more slowly heat up and cool down than surrounding terrain.
    - This effect could produce "land and sea" breezes without an actual sea!
  - Low elevation equatorial zones
    - Valles Marineris
    - Extreme depth leads to increased air pressure.
    - This might push local barometric pressure above the triple point of water, enabling liquid water or brines to exist occasionally, depending on temperatures.
    - Temperatures would be relatively warm because of the equatorial location and could be warmer on the floor of the canyons because of the lapse of temperatures with elevation, making these transient excursions above the triple point a bit likelier.
    - The venturi effect of these aligned canyons, together with increased air pressure, could result in increased wind flow.
    - Greater warmth could also make for thermals coming up the canyon walls.
  - Low elevation transitional zones
    - Hellas and Argyre Planitia
    - Even though temperatures would be colder this far south of the equator, the floors of these two immense craters are so far below the areoid that they would be warmer than the surrounding terrain.
    - That and the increased air pressure could also lead to transient excursions above the triple point, resulting in increased gullying.
    - There could also be strong winds and updrafts, which, together with Coriolis Effect, can produce a lot of dust devils in spring and summer.
    - These two craters, particularly Hellas, do spawn a lot of dust devils, a few of which spiral up into planet-covering dust storms.
  - You can get to the Hargitai Mars climate page and a nice collection of temperature, dust, and pressure diagrams at http://planetologia.elte.hu/mcdd/index.phtml?cim=climatemaps.html
Relatively recent climate change on Mars
- Geography of gullying
  - We saw that the presence of gullying is concentrated on poleward-facing slopes in the lower and lower-middle latitudes, which makes sense if Mars had greater obliquity in its past.
    - Increased obliquity would position the sun during summer such that the poleward-facing slopes would essentially be the adret slopes and the sunnier slope would melt soil water, especially in the lower, warmer latitudes.
    - Mars' axis changes its tilt, much as Earth does, only over a more extreme range of values (~15° - ~45°) over about 124,000 Earth years, since it doesn't have our massive moon to stabilize it (Earth's obliquity ranges from ~22° to ~24.5° by comparison). There's some speculation that this could become as extreme as 0° to 60° over millions of years!
- Recent glaciation
  - We saw evidence of recent glaciation in the northern tropics near Elysium.
  - Like low and mid-latitude poleward-facing gullyng, mid-latitude glaciation could also be expected from more extreme obliquity, especially if aphelion coïncided with the northern hemisphere's winter.
- Recent accelerated polar cap sublimation
  - Interestingly, today, it seems that the martian polar caps are sublimating away measurably year to year.
  - Mars is apparently also experiencing global warming and shrinking polar caps!
  - Climate change deniers here on Earth are having a field day with this, claiming that global warming here couldn't possibly be coming from human actvities if it's also going on at Mars, that it's, therefore, merely the sun increasing in irradiance.
  - This is something of an "apples and oranges" non sequitur.
    - On Mars, increased polar cap sublimation seems connected with increased dustiness (Fenton et al. 2007, available at http://humbabe.arc.nasa.gov/~fenton/pdf/fenton/nature05718.pdf).
    - Dust in the middle and upper troposphere absorbs solar radiation and warms the atmosphere.
    - On Earth, you can evaluate the association among solar irradiance, volcanic sulfates, carbon dioxide, methane, nitrous oxide, and borehole temperature anomalies over the last four centuries by downloading this file, https://home.csulb.edu/~rodrigue/geog400/tracegas.ods.
    - You could try scatterplotting various drivers and borehole temperatures, doing correlations between them and borehole temperatures, or trying either multiple regression or principal component analysis modeling to see which drivers account for the borehole readings. If you have nothing to do.

END 04/29/15

Human-environment interaction: Mars of the imagination

Science fiction imagines Mars:
- Science fiction has rather a long history in literature:
  - Mary Shelley's Frankenstein: or, the Modern Prometheus of 1818, the first example of modern science fiction, which tells the story of a disastrous outcome of a scientific experiment.
  - Voltaire wrote a short story in 1752 called "Micromégas," which entailed the visit to Earth by two enormous aliens, one from Sirius and the other from Saturn, after deciding not to stop at Mars because it was too small for them, but the reference to Mars includes a comment that it had two small moons (which would not be discovered until 1877!). You can read it here, if you're curious about Voltaire's short foray into science fiction/fantasy: http://www.accuracyproject.org/t-Voltaire- Micromegas.html.
  - Some themes in science fiction, such as visits to alien planets, go back as far as the True History of Lucian of Samosata back in the 2nd century, though, as with Voltaire's "Micromégas," there's no attempt to incorporate a scientist or a scientific outlook. You can read that story online, too: http://www.lucianofsamosata.info/TheTrueHistory.html. You may enjoy his smart-aleck and rather modern sensibility!
  - Mars became a focus of Victorian science fiction:
    - The findings of the Geographic Era caught the imagination of the reading public.
    - The earliest novel set on Mars was Percy Greg's Across the Zodiac: The Story of a Wrecked Record (1880), which presented the first use of the word, "astronaut" (referring to the spaceship), the concept of anti-gravity propulsion ("apergy"), Mars confidently described with seas, clouds, thin but breathable air, and a martian society clearly drawn to rant about quirks of human society! You can read it here: http://www.fullbooks.com/Across-the-Zodiac.html (optional -- beach reading in the summer?).
    - Something that made Mars, specifically, of great interest among all the planets was Schiaparelli's canali and Lowell's promulgation of the canals craze, which led to the vision of Mars as a dying, drying planet, occupied by an intelligent species trying to prolong its existence by heroic hydraulic engineering.
    - The poignancy of this imaginative scenario flavors Earth-focussed theories about the beginnings of the Neolithic Revolution in a similar process of desiccation in the Middle East, leading to irrigation and domestication.
      - It seems the late nineteenth and early twentieth centuries were receptive to notions of the fall of civilizations, both on Earth and on Mars.
      - This might have had to do with the growing scientific realization that there had been drastic climate change on Earth, e.g.,
        
        Louis Agassiz's work on the Pleistocene ice ages starting in the 1840s
        Henri Schirmer's 1893 work suggesting the Sahara had progressively dried up
        Raphael Pumpelly's proposal in 1908 that domestication occurred when the Middle East dried up after the pluvials believed co-eval with the European glaciations and forced plants, animals, and people together on fewer and fewer oases.
    - It didn't take long for fiction authors to incorporate the theme of a desert Mars, a dying hydraulic civilization, and an excitingly exotic locale that had the thin veneer of scientific credibility, in the light of the scholarly discourses of the day.
- Themes pursued in martian science fiction and fantasy:
  - Space opera: adventures of a (nearly always male) hero, featuring almost cartoon-like evil characters, lots of fighting often against the kinds of odds that only a mythical hero could (im)possibly overcome (swords, guns, exotic weapons, such as stun guns, death rays, dematerializers), evocations of exotic society but without much attention to their sociology and psychology, descriptions of wondrous physical and cultural landscapes, and, sometimes, a damsel-in-distress love interest (very chaste and Puritan in the early decades of science fiction, sometimes more erotic in contemporary space opera). In some cases, space opera resembles classic Western movies but in a martian or outer space setting. Contemporary space opera is generally set in the space between the stars (e.g., Star Wars, Star Trek), while the earliest space opera often picked Mars as a destination far enough out and little enough known to be an almost plausible exotic setting.
    - Edgar Rice Burroughs' John Carter series (here's the trailer for the 2012 movie: http://www.imdb.com/video/imdb/vi2340397337
    - Garrett Putnam Serviss' Edison's Conquest of Mars
  - Xenophobia: the Martians are hostile to us and want to invade us and take over our beautiful planet. There are all sorts of explorations of this fearful Other in science fiction ("Independence Day"), including that dealing with Mars and Martians (right down to Marvin the Martian in the Bugs Bunny cartoons!). This strand in science fiction seems to draw on the psychological substratum powering recurrent anti-immigrant sentiment in the US and many other countries. It is sometimes coupled with a more beneficent representation about how confronting the truly Hostile Other brings squabbling humankind together, kind of the kumbaya counter-narrative (e.g., the movie, "Independence Day").
    - H.G. Wells' War of the Worlds (and the Orson Wells radio broadcast, the 1950s movie, and the Tom Cruise edition a few years back). Here's the trailer to the 1951 movie: http://www.imdb.com/title/tt0046534/
    - "Mars Attacks!"
    - "Cowboys and Aliens"
  - Hard science fiction: This is fiction set in the near future, focussing on extrapolations of technologies and scientific knowledge available at the time of writing. Characterization is usually more nuanced than in space opera, as is extrapolation of contemporary social structures and politics. Sometimes the author is a scientist moonlighting in the creative arts, so the science of the day shows that training and the aversion to bringing in supernatural fantasy elements may reflect a scientist's temperament. This genre evolves with the science of the author's day, so the hard science fiction of the 1950s may seem almost quaint or comical when judged by contemporary science, as, indeed, contemporary hard science fiction will quickly show its age. To enjoy the older variants, you need to make a double suspension of belief, not just the suspension any fiction requires but a second suspension of the inner critic of the science gotten so wrong. I think it is fair to judge it by how well it extrapolates from and is grounded in the science of the time it was written.
    - Robert Zubrin How to Live on Mars
    - Kim Stanley Robinson's trilogy: Red Mars, Green Mars, and Blue Mars
    - Gregory Benford The Martian Race
    - Arthur C. Clarke's The Sands of Mars
    - Andy Weir's The Martian: A Novel
  - Soft science fiction: This is fiction set in the near or distant future, generally with a grounding in contemporary science and technology extrapolated into the time of the story. The focus, however, is on anthropology, social structure, politics, and psychology, and characterization is often intricate and engaging. The intent is to sketch out alternative ways of organizing human society in the here and now and draw out their implications. Sometimes the tenor is utopian; other times dystopian. The social issue of interest to the author will vary drastically, depending on the author's agenda of exploration.
    - "Two Women of the West" Unveiling a Parallel (feminist science fiction from 1893, set on Mars). Available on Project Gutenberg: http://gutenberg.org/files/42816/42816-h/42816-h.html
    - Alexander Bogdanov Red Star (Soviet science fiction written before the success of the Russian Revolution)
    - Philip José Farmer's Jesus on Mars
    - Ray Bradbury's The Martian Chronicles
    - Maybe "Mars Needs Moms" fits in here, a rather underappreciated film! http://www.imdb.com/title/tt1305591/
  - Science fiction fantasy: May or may not build a world that is a credible extrapolation of the author's time. It incorporates elements that are metaphysical, occult, or supernatural and may really bend timelines, often playing with the themes of alternative timelines or time travel and its paradoxes.
    - The Doctor Who special "The Waters of Mars"
    - M.E. Brines The Queen's Martian Rifles
- Dead, dry Mars and its effect on science fiction
  - The Mariner 4, 6, and 7 flyby missions brought back imagery that showed a crater-battered ancient surface that looked, at first, much like the Moon: No canals, no flowing water, bone-dry, dead.
  - The Mariner 9 and Viking orbiters and landers confirmed the impression of a planet long since dead and now completely unsuitable for life but also possessed of spectacular landscapes on a scale unimagined on Earth:
    - Planet-covering dust storm on the arrival of Mariner 9
    - Olympus Mons and the other gigantic volcanoes of Mars emerging as the 1971 dust storm abated and the dust settled down.
    - Valles Marineris emerging from the dust as a gash utterly dwarfing the "Grand" Canyon.
    - Intriguing, if ancient, dendritic drainage networks
  - The Viking landers biological chemistry experiments did provoke reactions, but those reactions turned out to have possible abiotic explanations, which is far and away the consensus interpretation: Mars is singularly inhospitable to "life as we know it, Jim" -- indeed, a sterile dead world that may have had more water a long, long, long time ago, which it then lost.
  - The impact of these missions on the popular conception of Mars was tremendous. This was the sudden end to any lingering fantasy the public had about canals and romantically desiccating civilizations. The scientific community had known Mars had a thin atmosphere, comprised of gasses we can't breathe, no canals, no possible civilization for decades, since the advent of remote sensing and spectroscopy. Lowell and Tesla and others kept alive the hope that there was someone there, at least in the public's perceptions, and that public image is what informed decades of science fiction. The drying planet with its canal building civilization was a trope of science fiction well into the 1960s (e.g., the 1950s-era "War of the Worlds"draws on that in the opening sequence).
  - The new, dead, dry Mars then had to be worked into somewhat plausible science fiction, which was dutifully done. The New Mars is the setting for stories about colonizing Mars and maybe terraforming it, not about interacting with Martians.
  - Indeed, as Dr. Parker noted in his talk in the Spring 2012 Mars class, it's possible that the Viking lander experiments, which failed to find unequivocal evidence for even microbial life, may have set Mars missions back for decades. There was a hiatus in American missions to Mars from 1976 to 1992 (NASA Mars Observer, which failed) and then until the Mars Pathfinder/Sojourner lander/rover combination in 1997.
Popular crazes about Mars that spin off from scientific mistakes:
- Canals on Mars
  - As you remember from the midterm notes on the history of Mars exploration, light and dark variations had been repeatably observed on Mars as far back as 1659 (Huygens' drawing of Syrtis Major).
  - Jesuit monk Angelo Secchi drew a map of light and dark areas in 1863 and is believed to be the first person to use the Italian term, "canali," for the darker areas.
  - Giovanni Sciaparelli, a professional astronomer in Italy, used the excellent 1877 opposition to map light and dark patterns on Mars pretty systematically, giving a lot of them names we use even today. As you remember, he mapped lineations, which he also called "canali."
  - Translation is an inexact art, and his maps came into the English-speaking world showing "canals," rather than "channels."
  - Percival Lowell, himself a prominent amateur astronomer and rich patron of astronomy, took the canals far more literally than Sciaparelli could have imagined.
    - At the time of his first book in 1895, he was still within the bounds of speculation in the scientific community to raise the issue of canals.
    - While science is tolerant of new ideas, it expects them to be treated as hypotheses to be tested against data.
    - Powell erred in going way past the available data, becoming convinced of his interpolations, and parting company with science by not being willing to change his mind when observational data began to undermine his ideas: He would not and could not let go.
    - He marked his increasing alienation from science by turning to the public and shunning the peer-review process, essentially becoming a pseudoscientist.
    - The result of leaving peer-review behind and arousing public interest with his books and talks was an enduring popular craze, one that ignited decades of science fiction based on a drying, dying Mars, clear up to the Mariner era.
    - In other words, like Percival Lowell himself, the popular craze (and literary trend) was (were) unaffected by the improving telescopy, remote sensing, and spectroscopic evidence for an intensely cold Mars with a very tenuous atmosphere that could not support water in canals, civilized or otherwise.
    - The canals craze, then, had its origins in scientific speculation but then became completely unmoored from science.
- Radio communications from Mars
  - Nikola Tesla was the inventor of Alternating Current, various systems for wireless (radio) communication (possibly with higher claim to inventing radio than Marconi), X-ray generators, robotics and the electronic logic gate that underlies computing. He claimed that he had picked up unusual radio signals (clicks in groups of 1-4) that he thought had come from Mars or maybe Venus and might represent intelligent communication. You can read an article he wrote in 1091 about the episode for Collier's Weekly here: http://earlyradiohistory.us/1901talk.htm.
  - This is another idea that has fueled a minor craze (but nothing on the scale of the Lowell canals craze).
  - Tesla's great rival in the invention of the radio, Guglielmo Marconi, claimed that he received anomalous radio transmissions in 1921, but he didn't say anything about Mars specifically.
  - In 1924, David Todd at Amherst College, persuaded the US government to request all governments to shut off all radio broadcasts for 5 minutes each hour for 24 hours when Earth was nearest Mars: National Radio Silence Day. An elaborate system of radio imagers and film reels were set up to record every incoming radio signal. Sixteen reels had pulsed signals in clusters, separated by 30 second pauses. Like Tesla's signals, these might have been from the then unknown quasar phenomenon in the outer fringes of the detectable universe.
  - There are occasional blips of people claiming to be in radio communication with someone on Mars or deep space, most recently Gregory Hodowanec in the 1980s.
  - Radio communication with Mars (or elsewhere) is another of these persistent crazes that started from a scientific observation that takes on a popular life of its own.
- The latest craze: The Face on Mars
  - Like the others, this craze started out from a scientific observation.
    - The Viking 1 orbiter was being used to scout for a good potential landing spot for the Viking 2 lander (back then, location analysis was done nearly in real time!).
    - The "Face" popped up in imagery of Cydonia Mensæ, where northern Arabia Terra transitions into the Northern Lowlands in a series of mesas.
    - People at JPL passed the image around, commenting that it looked like a face.
    - Someone issued a press release, which you can see here: http://www.msss.com/education/facepage/pio.html, sharing the image with the public and commenting that it resembled a human head.
  - And we were off and running: A smart aleck comment on Lab, followed by a press release intended to engage the public ... did!
  - One of the people to run off with this is Richard Hoagland.
    - Early in his career, he had some ties to space science:
      - curating a space science program for a small science museum in western Massachusetts
      - serving as assistant director for another one in Connecticut
      - working as a consultant to CBS News during the Apollo Program
      - consulting for NASA Goddard Space Flight Center on public communications about an Earth science observation program
    - He grabbed onto the Face on Mars and wrote a book, Monuments of Mars: A City on the Edge of Forever, which argued that the mesa is, in fact, a human face and the mensæ nearby have various mathematical ratios in shapes and angles you get by connecting them with lines.
    - This was not well-received by NASA, and it has cost Mars Global Surveyor and the Mars Orbiter Camera teams a lot of time and money to get higher resolution images of the mensa to satisfy the public interest and silence the conspiracy theorists, instead of pursuing their science objectives.
    - Such chilly responses have annoyed Hoagland into claiming that NASA is part of conspiracies to hide and classify evidence of alien civilizations on Mars and elsewhere, that Phobos is artificial, and other conspiracies having to do with secret worship of Egyptian deities.
    - I can't do justice to it all. Grab some popcorn and visit his web site: http://www.enterprisemission.com/.
    - People who, like Hoagland, are really into this are unswayed by the more detailed imagery that the Malin Space Science Systems group half killed themselves to get ("of course, they altered the image to make it LOOK that way."), even when ESA's Mars Express later took equally devastating images of this feature.
    - Here's NASA's comments on the whole thing: http://science.nasa.gov/science-news/science-at- nasa/2001/ast24may_1/.
- Late breaking news: Nuclear war on Mars
  - The person who proposed that perhaps Mars had experienced a natural nuclear reactor similar to the one that developed on Earth about 2 Ga in the African state of Gabon, the Oklo natural reactor, John E. Brandenburg, has a long history of serious publication in peer-refereed journals about such topics as the carbonaceous chondrites and Mars (Geophysical Research Letters 1996)), the physics of plasmas (IEEE Transactions on Plasma Science 1998), cratering rates on Mars (Earth, Moon, and Planets 1995), and the possibility that Mars had had an ocean (Geophysical Research Letters 1986).
  - Since his natural reactor paper at LPSC in 2011, he's followed Lowell's transition away from refereed science into a variety of speculations about interstellar alien races wiping out Mars civilization with nuclear weapons, trying to prove that the Face on Mars is an alien artifact, that the aliens may come back and nuke us here on Earth, and completing Einstein's theory... He's appearing on Coast to Coast and biblical media and, essentially, trying to start a new craze. The way the usual suspects on the Internet are reacting, he may be succeeding at this.
  - I am quite baffled at what would make someone like this go right over the edge of the world late in his career.
Mars colonization
- As you've learned all semester, Mars is a really brutal environment, extremely hostile to human life and probably that of any multicellular Earth organism. Unicellular organisms from the Bacteria or Archæa domains of life might possibly be able to survive on Mars (extremophiles) and a key focus of Mars missions is to find martian bacteria or archæa or whatever the martian equivalents might be.
- Should Mars be the target of piloted missions and should humans establish a long-term presence on Mars, that is, settle colonies there?
- This is a complex question involving scientific, political-economic, and moral dimensions.
- Scientific rationale:
  - At the present and for the near-term future, the scientific "bang for the buck" ratio favors continued robotic missions.
    - The orbiters, landers, and rovers have proven extremely productive of scientific information, giving us an increasingly detailed image of Mars and enabling meaningful processual analyses, in some cases giving us more specific information than we even have for Earth (e.g., MOLA).
    - We can easily see the need for more robotic exploration (replacing lost capacity as missions degrade with age or die off) and new kinds of robotic missions:
      - A seismic network or geophysical lander to answer questions about seismic activity on Mars, the interior structure of the planet, and current rates of heat flow.
        
        This will be initiated by the new NASA InSight mission: Interior Exploration using Seismic Investigations, Geodesy, and Heat Transport.
        It is designed to measure heat flow from the interior of Mars, sink a seismic sensor, measure wobble in the planet's rotation to get at interior mass distribution, as well as instruments for monitoring weather and magnetic disturbances.
        InSight will launch in 2016 from California (not Canaveral), as early as March 4th, landing on September 28th in Elysium Planitia.
        The new mission's web site is http://insight.jpl.nasa.gov/.
      - A sample return lander:
        
        This would give us the ability to do direct radiometric aging of rock. samples
        Absolutely dated samples would finally allow us to constrain the absolute ages of the surfaces: We only have crater-counting to get at relative dates and, through a rather Rube Goldbergian set of transfer functions from lunar samples, a system of constraining absolute ages that is riddled with uncertainties and controversies.
        Martian samples of rock and soil could also give us information on martian life forms, if they exist or, as fossil traces, if they ever existed in the past.
        While an important next step, a sample return mission is not without controversy:
        
        Radioactivity issue: Such a mission will require radioisotope thermal generators, which will trigger concerns about radioactive releases here during launch or contaminating the martian environment (which does contain quite a bit of radioactive potassium, thorium, and uranium, so that might allay concern): This will re-trigger the movement that organized around stopping the Cassini-Huygens mission to Saturn (my article on that episode is here: https://home.csulb.edu/~rodrigue/risk01.html.
        The Andromeda Strain: There is a vanishingly small but non-zero probability that Mars has some form of microbial life, that life might survive the trip back to Earth, it could be released into Earth environments by a landing recovery or a laboratory accident, it might somehow develop the ability to infect the cells of humans or other Earth species, and it could then maybe trigger an epidemic or pandemic (and wipe out life on Earth?).
        Conflict within the scientific community: Bioscientists want to quarantine the samples and experiment on them for a long enough time to allow any surviving martian life to have a chance to express itself and for us to come up with ways to detect that expression; geoscientists want the samples to be sterilized as soon as possible, after a short delay to check for possible life, so they can start analyzing their element and mineral content and infer their histories.
      - A penetrator or drill rig mission to extract samples of water or other volatiles from the subsurface or even from below the permafrost and extract rock samples at depth for analysis in a robotic lab or perhaps eventual sample return as described above.
        
        Any surviving life forms will almost certainly be subsurface and probably in liquids below the permafrost, so this kind of mission would be critical to answering the life question.
        Such subsurface sampling could also help us understand what the exact nature of the volatiles on Mars is: water? brine? acid water? carbon dioxide?
        Deep sampling would also help us better understand weathering processes on Mars.
    - So, there is an awful lot of work for robotic missions into the foreseeable future.
    - Assuming human exploration of Mars becomes a reality, robotic missions remain critical to prepare for that eventuality, to reduce the considerable danger posed by the Red Planet: Remember that more than half of all Mars missions to date have failed, a rate intolerable if we're going to send people there!
  - At some point, however, it is clear that direct human involvement will be necessary, because the pace of robotic investigation is so slow:
    - Missions have to be planned over a very long timeframe, decades in some cases.
    - Scientific goals have to be formulated from a baseline of poor information, poor argumentation, or inadequate technology that may really age poorly during the process: Think of the reasoning behind the selection of Gusev Crater for the Spirit rover later revealed as faulty; the Pathfinder and Viking landers were confined to "safe" locations that were scientifically kind of bland; the laboratory experiments on the Viking landers proved not to be able to exclude critical alternative hypotheses to the "life" interpretation of the chemical reactions observed).
    - Even when successful, questions come up on the fly and have to be dealt with by an ensemble of investigators (some missions have quite a bit of internal politics) and then specific goals have to be conveyed to the orbiter, lander, or rover by software uploads.
      - The delay in communications between Earth and Mars can be as little as 3 minutes during opposition or as much as 21 minutes during conjunction (opposite sides of the sun) and, at conjunction, the sun is in the way generating thermal noise.
      - The orbiters are in direct line of sight only about 2/3 of a sol and, if an orbiter is being used as a relay station for communications with a lander or rover, the two can only communicate with one another for uploads and downloads for about 8 minutes per sol.
      - So, there is quite a lag effect.
    - At some point, this process will eventually become so cumbersome as issues and opportunities pop up rapidly that a scientist will be needed on the surface to handle these in real time, applying the field and laboratory skills of a geologist or geomorphologist, mineralogist, chemist, geophysicist, or biologist.
    - This will entail the deployment of a small team, including scientists with varying types of training, medical support staff who may themselves have biological field and lab skills, technical support staff to do requisite computer analyses (e.g., GIS, database management, communications), and habitat and infrastructure specialists. Such a team, with some redundancy of skill sets (e.g., someone with nursing skills who could cover for a doctor should s/he die or fall ill), would probably need to contain at least seven individuals.
    - For such a mission to be scientifically justifiable, it needs to be designed to last throughout much of a martian year (686.98 Earth days) and use the time between two launch windows: This entails a huge logistical challenge and a great deal of danger for the crew enroute between the two planets and while on Mars for such a protracted stay.
    - This is likely to be extremely expensive, dozens of billions of dollars, when you think of the launch mass entailed, the safety issues, the technological complexity, the duration. And that funding has to be secure for decades to develop the scientific goals, to design the mission, to get the components built and calibrated, and to supply the Mars team for that long.
    - This is not likely to be a high societal goal in the near future, especially in an era of political austerity campaigns and anti-scientific discourses. It is far beyond the resources of any private sector alternative, even if some kind of payoff could be imagined, and way past the next-quarter-statement mentality of corporations even if there were some imaginable payoff.
- Geopolitical and emotional rationales
  - Where scientific need may not move the public to support something as massive to fund as a human mission to Mars, there are some geopolitical and emotional factors that can and have supported mega-missions, such as Apollo. which cost $170 billion in 2005 dollars.
  - They are apparent in the language of President Kennedy in his "Man on the Moon" speech to Congres a month after the Soviets got Yuri Gagarin into orbit, which you can � watch at http://www.youtube.com/watch?v=TUXuV7XbZvU.
  - They also come across in a speech he gave at Rice University:
    But why, some say, the moon? Why choose this as our goal? And they may well � ask, why climb the highest mountain? Why, 35 years ago, fly the Atlantic? ...
    We choose to go to the Moon. We choose to go to the Moon in this decade and do � the other things, not because they are easy, but because they are hard; � because that goal will serve to organize and measure the best of our energies � and skills; because that challenge is one that we are willing to accept, one � we are unwilling to postpone, and one we intend to win
  - This plays to a number of emotional factors that strongly appealed and � may still appeal to Americans:
    - America's sense of omnipotence, of technological inventiveness, of � can-do of anything we set our will and imagination to do.
    - Tacit appeal to the Turner Hypothesis, an argument that America � was born as a frontier society and needs an expanding frontier to sustain some � fundamental part of its psyche and cultural identity (and the companion fear � that lack of a frontier somehow necessarily means American decline). A darker � variant is Manifest Destiny, the idea that America should expand its � frontiers, even if they are occupied by someone else (shades of � Lebensraum).
    - A broad-based human interest in what lies over the next hill, a love � of exploration for exploration's sake.
    - The vicarious thrill of imagining seeing an alien world through � the eyes of another person like yourself, who is idealized as a heroic figure.
    - The great geopolitical forces of the day, the Cold War rivalry � between the USA and the USSR, marshalled these tropes to support a huge � monument to the superiority of capitalism over communism and, presumably, of a � democratic government over the "dictatorship of the proletariat."
    - This kind of monumentalism had a wider audience than just the American people whose cultural values and emotions could be stirred into supporting it: The two superpowers were competing for bragging rights in front of the rest of the world, angling for influence over other countries.
    - The US had lost Round 1 and Round 2 of this particular contest, when the USSR launched Sputnik in 1957 and then put the first person in space, � Yuri Gagarin, in 1961 (shortly after the inauguration of JFK).
    - About a month after Gagarin's return from orbit, JFK made his famous "Man � on the Moon" speech to Congress. You can hear it here: http://www.youtube.com/watch?v=TUXuV7XbZvU&feature=related � and read the text here: http://homeofheroes.com/presidents/speeches/kennedy_space.html.
- If we decide to colonize Mars, what's the cheapest way to get there? Mars Direct
  - Robert Zubrin has been a strong advocate for a long-term human Mars � mission and colonization of Mars, in some of his writings appealing to a kind � of Turner hypothesis argument, with a twist. He feels that it is necessary � for a frontier in space to accommodate the kinds of creative � misfits who don't take well to life in a regimented society. America is, � in his view, becoming more ordered and its government more intrusive (and he � was writing before the response to 9/11) and stifling to creative people. He � envisions a kind of cowboy settlement of Mars on the cheap, developing a self-suffient economy based at least partly on the greater ease of exploiting � asteroids from Mars than from the more massive Earth, and eventually becoming � politically independent.
  - Zubrin's approach to sending people to Mars (and eventually settling � there permanently) has been called "Mars Direct."
  - Step 1: A single heavy-lift booster throws a 40 tonne robotic � spacecraft to Mars to deliver the Earth Return Vehicle, containing two � methane/oxygen rocket propulsion stages empty. It also contains 6 tonnes of � liquid hydrogen, a 100 kw nuclear reactor mounted on the back of a � methane/oxygen truck, some compressors, an automated chemical processing unit, � and a few small rovers.
  - Step 2: The truck is driven robotically a few hundred meters away � from the landing site, and the reactor is set to powering the compressors and � chemical processing unit. Over the next 10 months, it starts fueling � itself by combining the hydrogen from Earth with the carbon dioxide in � Mars' atmosphere, resulting in 108 tonnes of methane/oxygen rocket propellant: � 4H + CO₂ -> CH₄ + O₂. Most of this � will be used to propell the ERV back to Earth later, with some used to fuel � the rovers. Lots of oxygen can be produced for the crew's breathing and to � create water. This saves the mass needed to haul from Earth by making it on � Mars.
  - Step 3: Two more launches from Earth occur, one carrying a � habitation unit and a crew and three years of food and other � provisions to Mars, and the other a repeat of Step 1 (a second ERV) to � create a self-sustaining process. The crew lands where a fully fueled ERV � awaits them, together with fueled up rovers to allow scientific investigations � over perhaps thousands of kilometers in a stint about 1.5 Earth years long.
  - Step 4: The first team launches back to Earth, even as a � second crew lands at the second ERV site. They leave a usable habitat � for a later crew or even permanent settlers.
  - The upshot is going to Mars on a spacefaring technology little advanced � over lunar technology, using Mars' atmosphere for nineteenth century � chemical reactions that create rocket fuel, oxygen, and water. A great � deal of science could be done and possibly fairly cheaply, and the basis for � permanent settlement of Mars would be laid.
- Terraforming Mars
  - Proposals are occasionally floated about "terraforming" Mars, that is, doing planetary re-engineering to make it more comfortable for Earth organisms, especially us.
  - The idea variously entails one or more of the following:
    - Increasing the barometric pressure of the martian atmosphere to push it above the triple point of water, so that water can persist on the surface in liquid form.
      - There is also possibly a lot more CO₂ in the regolith that might be induced to outgas.
      - If CO₂ can be added to the atmosphere, a positive fe raised, perhaps up to 300-600 hP (instead of 6.75 hP, as now), wind might kick up even more, raising more dust, which can trap heat energy in the upper troposphere, though chilling the surface with microshading.
    - Changing the mix of gasses comprising the martian atmosphere to include more oxygen.
      - This might be done by introducing extremophile bacteria or archæa that might be capable of photosynthesis or chemosynthesis under martian conditions, releasing molecular oxygen and organic compounds. The organic compounds have to be buried (as in an ocean's pelagic sediments) to keep them from oxidizing again and allow oxygen to build up faster than oxidation can take it out.
      - Oxygen might also be liberated from its chemical bonds with metal oxides, perchlorates, or peroxides (all found on Mars) through a chemical oxygen generator, which ignites the oxygen compound with a mechanical strike, setting off an exothermic reaction that cuts molecular oxygen loose (this is the idea used in airline emergency oxygen supplies).
  - Terraforming is not expected to create an Earthlike planet, just one more useful for human occupation. Humans and other animals would still need to wear breathing masks, but there would be a significant reduction in ultraviolet radiation and cosmic ray exposure. These changes could make the surface of Mars capable of supporting plant life and agriculture and possibly standing or flowing water bodies.
  - Terraforming would take an extraordinarily long time to accomplish, easily thousands of years at current levels of technology and imaginable response rates from martian processes, the initial steps easily taking a couple of centuries. This is not a time scale at which humans excel in planning!
  - Basically, Mars would have to be settled as is, on its own terms, humans adapting to it more than reshaping it in their image. Mars is habitable under these conditions, if not happily, and such grim living conditions are best endured by those with the kind of obsessive personalities common among scientists doing research. It might be a bit much for people going there for romantic ideas about becoming extraterrestrials, trying to find economic opportunities, or getting away from big bad gummint.
  - Something that concerns me is going to all this terraforming effort and expense and gradually losing the precious atmosphere we build up to the same processes that robbed Mars of its primordial atmosphere 4 billion years ago: The lack of a planetary magnetic shield against the solar wind and exospheric loss of hydrogen and other light gasses.
    - There have been responses to this concern by people who think that the loss of the human-built atmosphere would take an extremely long time, far longer than our species is likely to be around (a sunny thought, that!).
    - There have been proposals that we try to find some way to reactivate the planetary magnetic field of Mars or create an artificial field, but I suspect that's way past our areoengineering pay grade!
  - Another issue is the ethics of terraforming: Should we do it, even if we can?
    - On the yes side, as the only sentient and technological species on Earth, we may have a moral obligation to ensure that the Earth life risk "portfolio" is diversified and spread around as many planets or even solar systems as we can reach to ensure that at least some small part of it would survive a great cataclysm (e.g., huge asteroid impact) or, longer term, survive the gradual increase in the sun's irradiance and its warming of Earth to the point of boiling off our oceans in ~1 billion years. Of course, planning out 1 billion years is a little extreme, given that multicellular life has only been around maybe 1 billion years!
    - On the no side:
      - What if there is life native to Mars, even if it's unicellular? Does it not have an intrinsic right to continue existing in the conditions to which is is adapted?
      - One consequence of our settling Mars, with or without terraforming, will be a load of pollution and environmental and æsthetic degradation.
      - By transplanting our fellow species to Mars, we are subjecting them to a brutal and probably short existence, which itself raises ethical issues. At least when we send teams of ourselves there, the discomfort, danger, loneliness, and pain of existence are a risk understood by the humans going there and they assume responsibility for their own misery there. Animals don't have that ability or choice.
        
        On the other hand, life generally ends brutally for most individuals of most wild species on Earth, so that might be a mitigating argument.
        Most people have no qualms about eating meat and overlook the often horrid conditions under which animals are raised and then brought to slaughter, so imposing further on animals for the sake of colonizing another planet is probably low on most folks'ethical concerns.
      - The colonialist/imperialist subtext of the Mars settlement and terraforming concepts needs to be noted, too, just a lot of rather jarring parallels with Manifest Destiny and even Lebensraum. Sort of humans as intentionally invasive species.
    - Discussions of the mechanics and desirability of terraforming can readily be found with online searches. A rather nice technical discussion is found at Terraforming Mars.

Presidents and the American space program

Dwight "Ike" Eisenhower (1953-1961):
- WWII general drafted by the GOP to be their presidential candidate in 1952 and 1956.
- Sputnik was launched by the USSR during his watch, and then two months later the NACA (National Advisory Committee for Aerospace) launch of Vanguard TV3 got approximately 4 feet off the launch pad and blew up, inducing the press to dub it Kaputnik.
- Eisenhower recognized the propaganda victory of the Soviets but didn't really think space was intrinsically all that important.
- He created NASA a year later as a new civilian agency because there was no way not to have a space program of some sort and it wasn't important enough to be a military agency.
John Kennedy - "JFK"/Lyndon Johnson - "LBJ" (1961-1963/1963-1969)
- JFK formulated a specific goal to get Americans on the moon within a decade, this within weeks of the USSR launching the first cosmonaut into orbit.
- Hugely expensive undertaking (~$170 billion in modern dollars) that he sounded almost apologetic to propose to Congress.
- His speech, however, underscored the Cold War symbolic importance of an American achievement decisively more ambitious than the Soviets were working on, referring to the audience of countries around the world trying to decide whether to follow capitalism or communism to build modern economies.
- Lyndon Johnson continued Apollo and planning for other missions (e.g., Mariner and Viking) upon the assassination of JFK.
- The dangers of the space program became obvious with the immolation deaths of three Apollo astronauts, Gus Grissom, Edward White, and Roger Chaffee, when the cabin of Apollo 1 exploded during a launch rehearsal.
Richard Nixon/Gerald Ford (1969-1974/1974-1977)
- Eisenhower's vice-president was actually the sitting president when Apollo 11 landed in the Sea of Tranquillity on 20 July 1969.
- As a Republican, however, he believed in reducing the röle of government and emphasizing the military and policing function of the reduced government.
- The space program was a propaganda coup, important in the military contest between the USA and the USSR, so he kept Apollo going through its lunar landing missions.
- But, that done, he felt it had outlived its usefulness: He wasn't all that interested in lunar or space science.
- He ordered a drastic cut in NASA, allowing Mariner and Viking to go forward but not any planning for an extension of Apollo-type missions geared toward human exploration of Mars. He did allow NASA to keep the Shuttle and that only because the shocked NASA promised that the Shuttle would become a profitable space-truck, hired to put commercial and military satellites in orbit and be a science platform in its own right without the space station it was in reality originally designed to supply.
- This episode and its consequences are discussed in a paper I gave at the Association of American Geographers in 2004: https://home.csulb.edu/~rodrigue/disbymgt/aagdisbymgt04.html.
Jimmy Carter (1977-1980)
- Triggered a series of studies to address the malaise and lack of real focus in the US space program in the 1970s.
- Presidential Directive 37 re-affirmed the principles behind the founding of NASA in 1958 and spelled out the first broad statements of objectives for the space program.
- Acknowledged the importance of space systems to national survival and military preparedness.
Ronald Reagan/George H.W. Bush - "Bush 41" (1981-1988, 1989-1992)
- Reagan was the sitting president when the Shuttle missions began to fly.
- He declared the Shuttle an "operational" vehicle after a few flights, but the Shuttles were experimental vehicles from then to the end of the program.
- He and Congress could not understand why the Shuttle was so expensive to operate and exerted extreme fiscal pressure on NASA over it.
- He conveyed some urgency to have Christa McCauliffe, the first "teacher in space," up there in time for his State of the Union address.
- The schedule and budget pressures on NASA culminated in the decision of Shuttle management to launch Challenger over the objections of engineers worried about ice compromising O-rings, and the Shuttle blew up in 1986,
- Reagan was quite interested in the military applications of space, most famously in the "Star Wars" initiative.
- He also encouraged the commercialization of space.
- A major Reagan initiative was the go-ahead to build the International Space Station.
- G.H.W. Bush essentially continued the Reagan space policy, being particularly interested in the International Space Station.
- He appointed Dan Goldin to head NASA, who implemented the "faster, cheaper, better" philosophy (which led to a few "faster, cheaper, ooops" incidents). He tried to abort the Cassini-Huygens mission, which was saved only when the European partner agencies indicated that, if the rug was pulled out from under them, that would be it for their participation in the ISS, which was important to G.H.W. Bush. He referred to it as "Battlestar Galactica," the opposite of "faster, cheaper, better."
- Mars Climate Observer failed in 1992.
Bill Clinton (1993-2001)
- Space seems not particularly salient in the Clinton administration.
- Construction of the ISS began in his administration.
- He kept on the managerialist Goldin.
- Mars Global Surveyor launched in 1996, arriving successfully at Mars in 1997.
- Pathfinder launched in 1996 and also arrived successfully in 1997, landing and deploying Sojourner.
G.W. Bush - "Dubya" - "Bush 43" (2001-2009)
- Mars Odyssey launched in 2001 and arrived successfully that year and remains in service.
- The Bush administration was dismayed at the increasing costs of the ISS and tried to rein them in by putting it adminstratively in with the Shuttle, stipulating that increases in cost for ISS would have to be covered by moving money from the "rest" of the "Human Flight Initiative" (that would be the Shuttle). He insisted on a completion date for the ISS, after which the US would cut back its commitments to it and let its international partners take most of it over.
- This led to an extremely tightly scheduled series of Shuttle launches to complete American commitments to the ISS in time. As with similar cost and schedule pressures in the 1980s, this led to the destruction of Columbia on one of these runs in 2003. For the details, see my article linked above.
- More happily, the Mars Exploration Rovers launched in 2003 and set down safely in 2004. Opportunity is still operational.
- Mars Reconnaissance Orbiter launched in 2005 and achieved orbit successfully in 2006 and remains operational.
- Bush decided to re-orient space policy in 2004 with his Vision for Space Exploration:
  - ISS should be finished by 2010 and all American involvement withdrawn by 2017.
  - The Shuttle should be retired in 2010.
  - A new Crew Exploration Vehicle (Orion) should be developed by 2008.
  - The CEV should conduct its first human spaceflight mission by 2014.
  - The US should explore the moon with robotic missions by 2008
  - The US should send humans to explore the moon by 2020.
  - Then, we should send people to Mars in an "Apollo II" mission.
  - A $16.2 billion budget was proposed and approved by Congress, but that did not cover the costs of the Vision as proposed, and NASA had to make up the gap by pulling money out of other missions: Earth Science, Mars Science, and Outer Solar System Science have all felt the suction.
Barack Obama (2009 - present)
- Ordered the Augustine Commission review of the Constellation program (CEV/Orion and associated launch development), which found that the return to the moon and human flights to Mars were out of NASA's current budget (an objection noted when the Bush Vision for Space Exploration was first announced).
- Space Policy announcement in 2010 calls for:
  - Continued the retirement of the Shuttle program.
  - Extending American involvement in the ISS five more years.
  - Supporting private companies undertaking launches to shuttle astronauts back and forth from/to the ISS, a major expansion of the private sector in the US space program.
  - Increased NASA budget by $6 billion over 5 years.
  - Completing the design of a new heavy-launch vehicle by 2015.
  - Focussing NASA on launch vehicles designed for missions out of low Earth orbit, apparently consigning routine low Earth orbit launches to the private sector (e.g., Sierra Nevada Corporation's Dreamchaser, SpaceX's Falcon 9),
  - US human exploration mission to Mars by the mid-2030s, which is essentially the Bush Apollo II approach -- one mission to "orbit" Mars, another to land on it (for how long?), not clearly thought through.
  - An asteroid mission by 2025.
  - Cancelled the Constellation system that was to replace the Shuttle (the CEV/Orion) because it was "over budget, behind schedule, and lacking in innovation" (it would have wound up costing $150 billion had it maintained the original schedule). Constellation was supposed to enact Bush's Vision of finishing the ISS and returning to the moon with a Crewed Exploration Vehicle (CEV, or Orion) that could carry seven.
  - Orion has been separated from the now defunct Constellation program as a smaller vehicle (carrying up to four) that can replace reliance on Soyuz and facilitate exploration beyond low Earth orbit. It is now called the Orion Multi-Purpose Crew Vehicle or MPCV. It has had its first successful uncrewed launch in December 2014 and will carry its first astronauts in 2021.

END 05/06/15

And that concludes our tour of Mars!

The Geography of Mars

Lecture Notes

Christine M. Rodrigue, Ph.D.

Department of Geography
California State University
Long Beach, CA 90840-1101
1 (562) 985-4895
rodrigue@csulb.edu
https://home.csulb.edu/~rodrigue/

Lecture Notes for the Final

Site maintained by Dr. Christine M. Rodrigue
© Christine M. Rodrigue, Ph.D.
First placed on the web: 02/24/02
Last revised: 05/06/15

The Geography of Mars

Lecture Notes

Christine M. Rodrigue, Ph.D.

Department of Geography California State University Long Beach, CA 90840-1101 1 (562) 985-4895 rodrigue@csulb.edu https://home.csulb.edu/~rodrigue/

Lecture Notes for the Final

Site maintained by Dr. Christine M. Rodrigue © Christine M. Rodrigue, Ph.D. First placed on the web: 02/24/02 Last revised: 05/06/15

Department of Geography
California State University
Long Beach, CA 90840-1101
1 (562) 985-4895
rodrigue@csulb.edu
https://home.csulb.edu/~rodrigue/

Site maintained by Dr. Christine M. Rodrigue
© Christine M. Rodrigue, Ph.D.
First placed on the web: 02/24/02
Last revised: 05/06/15