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
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
- In 1636, another Italian astronomer, Francisco Fontana, used a telescope
to observe Mars and made the first drawing of the planet. His drawing
Mars in gibbous phase, showing that the planet shows lunar-like phases,
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-
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
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
- 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
- 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
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
of Mars in 1840. They came up with the latitude and longitude grid
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
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
- The 1877 opposition was a doozy, which coïncides with the advent of
- 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
not water bodies after all. Maybe vegetation he thought.
- In 1892, Edward Emerson Barnard spotted craters on Mars. No-one
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.
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
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
- In 1912, Svante Arrhenius argued that Mars might be covered with
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
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
- 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
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