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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

Lecture Notes for the Midterm

  • History of Mars exploration
    • History of Mars observation from Earth
    • Telescope-aided observation
      • See Viewgraphs: "Later Earth-based explorations by telescope"
      • In 1609, the same year Kepler published his Laws of Motion, Galileo built and operated the first astronomical telescope (other telescopes for viewing things on Earth up close had dé:buted a year earlier in a patent filed by Hans Lippershey). He trained it on Mars and began recording his observations. He was looking for evidence of Mars showing phases like the Moon, which Copernicus and Kepler reasoned the planets would show. His telescope was too primitive and Galileo honestly reported that he couldn't see the changing phases but he did say Mars did not look perfectly round to him. For his defense of Copernicus' heliocentric theory against specific orders of the Church, Galileo got into trouble with the Inquisition and was ordered into prison, a sentence later commuted to lifelong house arrest.
      • In 1636, another Italian astronomer, Francisco Fontana, used a telescope to observe Mars and made the first drawing of the planet. His drawing showed Mars in gibbous phase, showing that the planet shows lunar-like phases, as Copernicus and Kepler expected. He also said its surface wasn't of an even shade. His drawings show a dark spot in the middle, now thought to be a defect in his telescope (he found a similar "pill" on Venus).
      • In 1659, Dutch astronomer Christiaan Huygens was able to get such a good bead on Mars that he could establish that Mars rotates around a north- south axis and its daylength is slightly longer than Earth's. He drew sketch maps of what he was seeing and recorded a dark triangular patch near Mars' equator, which we now call Syrtis Major.
      • In the 1660s, Jean Dominique Cassini observed the polar caps of Mars as bright spots. He also refined Huygens' estimate of Mars' day length to about 24 hours and 40 minutes. In 1672, he figured out the distance between Mars and the earth by coördinating with a friend in French Guiana in South America to take measurements at the same time. He could use this parallax to figure out how far Mars was. From Kepler's Third Law, Cassini knew that Mars' orbital period was roughly 1.5 times that of Earth, so, if he could figure out how far apart Earth and Mars were at opposition, he knew that the Earth-Sun distance would be approximately twice the Earth-Mars distance. Using this, Cassini figured the Astronomical Unit (or Earth-Sun distance) at 140 million km is awfully close to the actual distance known today of roughly 150 million km.
      • In 1719, Cassini's nephew, Giacomo Maraldi, noticed that his uncle's white spots grew and shrank, and that the dark areas on Mars changed in shape. From this, he figured Mars had seasons.
      • In 1786, William Herschel also observed these changes. He was able to surmise the angular tilt of Mars' axis ofrotation as roughly 25°, which, again, confirmed that Mars had to have seasons. He thought the dark areas might be seas and some of the light areas that moved around might be clouds and vapors. He also figured that the bright polar spots were thin sheets of snow and ice. He noticed that faint stars that passed near Mars were not dimmed, and he inferred from these occultations that Mars had a very thin atmosphere.
      • In 1809, Honoré Flaugergues spots variations he calls "yellow clouds" on the surface of Mars. These were probably dust storms.
    • The Geographic Period: Telescopy plus mapping
      • As telescopes improved, sketches of Mars did, too. In 1800, Johann Hieronymus Schroeter makes detailed drawings of Mars.
      • People really began to look forward to martian oppositions (when Mars is on the opposite side of Earth from the Sun, thus lined up at their closest). Some oppositions are closer than others, depending on where in the two planets' orbits the opposition occurs. The 1830 one was a good one, and folks were out there with their telescopes.
      • William Beer and Johann H. von Mädler assembled the first real map of Mars in 1840. They came up with the latitude and longitude grid used pretty much today. They also refined Cassini's refinement of Huygens' estimate of the martian day or sol: 24 hours 37 minutes 22.6 seconds.
      • William Whewell started speculating about life on Mars in 1854, saying that the dark areas might be greenish seas contrasting with red land.
      • Jesuit monk Angelo Secchi draws a map in 1863 and refers to "canali" or channels for the dark areas. He also calls the dark triangle of Syrtis Major the "Atlantic Canal."
      • In 1860, the dark areas are suggested to be vegetation, changing with the seasons, by Emmanuel Liais.
      • In 1867, Richard Anthony Proctor creates a map of Mars and his pinpointing of the prime meridian is the one used today.
      • Pierre Jules Janssen and Sir William Huggins pioneer the application of spectroscopy to Mars in 1867. They try to detect oxygen and water vapor. They are not successful.
      • In 1873, Camille Flammarion agrees with Liais that there might be vegetation there and wonders if it's vegetation that creates the reddish color of Mars.
      • The 1877 opposition was a doozy, which coïncides with the advent of powerful telescopes.
        • Asaph Hall was out there looking for moons, figuring Earth has one, Jupiter has four, so Mars should have two. He was about to give up but his wife kept after him and on the 11th and 16th of August, he spotted first one and then the other: Phobos and Deimos.
        • Giovanni Schiaparelli, head of the Brera Observatory in Milan, mapped the dark and light features of Mars, some 65 of them, and gave them names, most of which we still use today. His map showed a bunch of intersecting lines, which he called "canali," just like Father Secchi did. Schiparelli's canali become a huge growth industry, the Face on Mars of his time, taking on a life of their own in others' hands.
      • William Pickering of Harvard was seeing these channels, too, but in 1892, he saw one running across "Mare Eruthraeum," a dark area that Schiaparelli thought might be an ocean. Realizing that a "canal" can't cut across an "ocean," he realized something was amiss and that the dark areas were probably not water bodies after all. Maybe vegetation he thought.
      • In 1892, Edward Emerson Barnard spotted craters on Mars. No-one else paid much attention, but it's an interesting early counterpoint to the canals craze. He also said he tried and tried to see all these canals and couldn't for the life of him.
      • In 1893, someone gives one Percival Lowell a book about Mars for Christmas (Camille Flammarion's la planèe Mars). It bowls him over and he begins to obsess on it. Most of us obsess on whatever craze gets our attention, but Percival Lowell was the son of a rich Boston family with enormous resources to throw at his interests. He decided to build an observatory in Arizona (to reduce atmospheric twinkling due to moisture). He became a professional astronomer and in 1902 is appointed to MIT as non-resident astronomer.
      • In 1895, 1906, and 1908, he published a series of books called Mars, Mars and Its Canals, and Mars, the Abode of Life, in which he laid out his elaborate theories built on wild extrapolation from the data. These linearities so many people were seeing on Mars were, in fact, canals. Such extensive canalization he saw as signs of intelligent life, life desperate to cope with a drying planet and engaging in planet-scale engineering to survive. The book became a best-seller and really began to affect Western culture.
      • Scientists, however, were, as usual, skeptical creatures, and a few began to question this canals business.
        • Alfred Russell Wallace, who came up with the theory of evolution a little later than Darwin but almost beat him to the punch in publishing it, went after Lowell. He wrote a book describing his own experiments in measuring the light spectra from Mars and concluded that the place was really, really cold, about -35° F, so Lowell's claim of water canals had to be "all wet." He figured that the polar ice caps had to be mostly frozen carbon dioxide, not water ice. He said, near as he could tell, Mars was completely hostile to life.
        • In 1912, Svante Arrhenius argued that Mars might be covered with salts. In winter, the water on Mars freezes and the salts take on a light, playa color. When the warmer temperatures of summer melt the polar caps in summer, the salts wet and darken. No life necessary.
        • Other scientists reported having trouble seeing canals, let alone anything more elaborate based on canals.
      • Lowell responded to scientific criticism by turning to the public for support, giving public lectures and writing articles for popular magazines. In other words, he began to shun the peer review process that is the foundation of science.
      • When he did this, many other scientists began to shy away from Mars, figuring it had become the bailiwick of crackpots.
      • A few, however, got caught up in it all.
        • Nikola Tesla, inventor of Alternating Current among other things, claimed to detect radio signals from Mars in 1899 and worked on a "Teslascope" to communicate with Mars
        • Guglielmo Marconi, of radio fame, also claimed to have heard from an alien radio transmitter a few years after Tesla's reports. Critics thought he was just picking up another radio station's interference.
      • By the time of Lowell's death, most astronomers thought that the planet was not only uninhabited by canal-building intelligent aliens but uninhabitable.
      • Really powerful telescopes began to be aimed at Mars in the early twentieth century: The Hale 60" telescope at Mt. Wilson in 1909 turned up nary a single narrow, straight canal or any other geometric pattern.
      • In 1913, astronomer Edward Maunder did a psychological experiment showing how the human eye tends to see patterns linking random lines and circles and the farther the observer was from the random pattern, the more likely they were to report linearities linking things in the pattern.
      • A few hardy souls held out for canals right up until the Mariner flybys put the matter solidly to rest. Interestingly, Earl C. Slipher's map of Mars (1962) was used for planning of the NASA Mariner flyby missions in the mid-1960s!
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First placed online: 01/15/07
Last updated: 02/02/16