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| Mercury | Venus | Terra and Luna | Mars |
This is classic science fiction featuring the valiant Earthman, John Carter,
who rescues princesses, fights the monsters, and pacifies the
warring races of Barsoom.
Telescopic observations showed that Mars was a dynamic place.
Its white polar caps waxed and waned with the seasons. The reddish surface was
mottled with dark, apparently green (the color of vegetation), regions,
and their shapes too changed with time.
In 1877
Giovanni
Schiaparelli published drawings of Mars as seen through his
telescope. He identified canali, dark linear features on the surface.
The tern canali is Italian; it translates most directly as
channels.
Percival Lowell,
who was to found the
Lowell Observatory on
Mars Hill in Flagstaff, AZ, mistranslated this as canals.
Canals imply intelligent life, and deliberate construction. Lowell built
up a mythos of Mars as a dying planet, whose intelligent denizens built canals
to collect the melting polar ice, and to distribute the water among the oases
(dark regions at the intersections of the canali.
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| Chesley Bonestell Surface of Mars © Bonestell Space Art |
We now know that this mythos arose from two optical illusions. The first is that the brain, when confronted by a disordered pattern of dots, attempts to provide order. When these dots are blurred as seen through a telescope, the human brain tends to connect the dots, which results in apparent linear features. The second illusion is that dark grey, when viewed next to red, appears green. Mars is not a red planet with green vegetation outlining water canals, it is a red planet with dark grey regions. The brain is not an objective observer!
Mariner 4 flew b at a distance of 9800 km in 1967. The Mariner 6 and 7 spacecraft flew within 4000 km of Mars in 1969. In 1971, Mariner 9 went into orbit around Mars and returned thousands of images. Our view of Mars changed radically.
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| Craters seen by Mariner 4 (1965) |
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| Meridiani Sinus and Deucalionis Regio | Rilles in Mare Sirenum |
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| Phobos | Phobos from MGS | Diemos |
Important Results from the Mars Rovers
Radar mapping by the Mars Express shows H2O ice under the south polar cap of Mars. The amount of water would cover the planet to a depth of 11 meters. Press report (3/16/07)
Our brains are hard-wired to look for recognizable patterns. It would be surprising if we did not see them. Witness these:
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| Happy Face crater | The Heart of Mars |
A giant worm,
a glass tube, or
aeolian
(wind-blown) dunes?
There is no macroscopic life on Mars today.
Is there microscopic life on Mars? The Viking Landers undertook three biochemical tests, with inconclusive results - but any life is likely to be buried down where the subsurface water is.
Was there life on Mars?
In the Summer of 1996, David McKay and his co-workers made quite a splash when they announced that they may have found evidence of life in a Martian meteorite. ALH84001 is about 4.5 billion years old; about 3.6 billion years ago water (or some other liquid) flowed through the rock, depositing carbonate globules wherein was found the purported evidence for life. The meteorite was ejected from Mars during a meteorite impact about 16 million years ago. It orbited the Sun for 16 million years, and fell to Earth in Antarctica about 13,000 years ago. It was picked up by an expedition looking for Antarctic meteorites in 1984.
ALH84001 is of 30 known SNC meteorites. These are undoubtably of Martian origin, because their compositions and isotopic abundances match those of Mars (isotopic abundances are like fingerprints: each planet has a unique pattern).
The evidence consists of a number of separate items, none of which independently provides striong evidence, but which together look fairly strong. There is evidence for
The data are intriguing, but like most controversial issues in science, the data are inadequate to confirm the finding beyond any reasonable doubt. McKay and colleagues take the holistic approach: that the simplest explanation of all the data involves biologic origins, and hence life on Mars about 3.6 billion years ago. Critics often take the reductionist approach, showing that all of the evidence can be created by inorganic processes, though there is no single process that can create all the data.
Using the infrared spectrometer on the Mars Express orbiter, scientists have confirmed the presence of methane in the Martian atmosphere (press release), at a level of 10 parts in a billion. Methane is oxidized under the influence of solar UV radiation, and should disappear in a few hundred years.
The methane is concentrated along equator in regions where water vapor is also concentrated.
It has been suggested that perhaps life on Earth arose on Mars. After all, Mars was more hospitable to life early on, and it did have a significant atmosphere and running water. The Earth took longer to develop a solid surface (large planets retain heat longer).
Some consider it a problem that there is evidence of microbial life on Earth a mere 200 million years after the Earth's surface is thought to have solidified. They think it more likely that life evolved on Mars, and was carried to Earth in the same way the ALH84001 got here.