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Signs of Life on Mars


 
written by Luciano Méndez on February 21, 2005 | contact me
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This graph shows that the atmospheric O2 level in Mars´ atmosphere is the closest to Earth’s when our planet only harboured microscopic life forms.  The planets that harbour no life have an oxygen level that is 30-thousand fold smaller.
This graph shows that the atmospheric O2 level in Mars´ atmosphere is the closest to Earth’s when our planet only harboured microscopic life forms. The planets that harbour no life have an oxygen level that is 30-thousand fold smaller.
Credit: Luciano Méndez
Mars atmosphere presents low percentages of gases like methane—discovered in March 2004—and O2, that on Earth are produced by the metabolism of living creatures. Although there are other processes that could also produce those gases, scientists consider the possibility that microorganisms on Mars could be responsible for it.

Some photographs published in 2004 show non-identified objects both in the sky (lights in motion) as on the surface of Mars ("rabbit–like" mobile object) that are popularly interpreted as signs of life. However, evidence of life on Mars will come from discoveries less extraordinary, but still breathtaking.

The possibility of life on Mars still can not be discarded, since there is indirect evidence of its existence, as the promising traces of free oxygen in the atmosphere of the red planet. Given that this element tends to rapidly recombine with other atmospheric elements, for a large quantity to exist there has to be some process constantly producing it. The metabolism of some living organisms, like plants, is nearly the only process capable of producing oxygen and methane in abundance. Earth’s atmosphere contains 21% of O2. Mars has between 0,13 and 0,25% and the atmosphere of Venus, Jupiter, and the rest of the outer planets have less than 0,0001%. The famous British scientific James Lovelock (author of “Gaia” theory, about the living and self-regulated Earth planet) estimated that shortly after life first arose on Earth, the atmospheric O2 level produced by those first microorganisms reached about 3%. Although the O2 contained in Mars seems to be insignificant, it is just 10 to 20 times smaller than the existent in the ancient Earth, while in the rest of the planets the atmospheric O2 level is thirty-thousand fold smaller. This is just a personal theory, but it is very curious that the most likely planet to harbour life have an atmospheric O2 level much more similar to the one of a living planet than to the one of the uninhabited planets. I think it is essential to determine whether the abiotic O2-producing-processes are responsible for the totality of free O2 in Mars’ atmosphere. To start outlining an answer we will have to wait until 2007, when Phoenix Lander’s instrument for analyzing gases (TEGA) arrives at Mars.

Model proposed by a NASA scientist showing how liquid water could exist on the surface of Mars.
Model proposed by a NASA scientist showing how liquid water could exist on the surface of Mars.
Credit: Luciano Méndez
The only experiments to search for life on Mars were carried out by the Viking 1 and 2 in 1976. Two of the three experiments on board each space probe, gave positive results, but the scientist said that it was due to the soil’s chemistry rather than to living organisms. They concluded that the results could not prove nor refute the presence of life on Mars. Besides, among other things, they considered that the absence of liquid water on the surface was a strong impediment for life to exist. But in 1998, the scientist that designed the experiments –Dr. Gilbert Levin– said he believed that the tests pointed to life on Mars and explained how microorganisms on Mars could satisfy their requirements of liquid water during the brief moments of the day in which small amounts of frozen water on the surface become liquid and wet the soil (see the figure).

This brings up the possibility that certain organisms adapted to extreme conditions thrives on Mars, like the cyanobacteria Chroococcidiopsis, a photosynthetic microbe that produces oxygen. It could live rather comfortably under the pebbles of the regolith, the layer of ground-up rock and fine dust that covers the surface. Another candidate even more suitable would be the Deinococcus radiodurans, capable of surviving in the extremely high radiation environment of Mars’ surface. “Deinococcus radiodurans beats most of the constraints for survival of life on Mars – radiation, cold, vaccum, dormancy, oxidative damage, and other factors,” said Dr. Robert Richmond, a research biologist at NASA’s Marshall Space Flight Center. But until some space probe equipped to detect life forms of this type, their existence on Mars still cannot be confirmed.

Despite this, another theory would indicate that it is almost certain that Mars has living organisms…coming from Earth. Yes, terrestrial micro-organisms can travel to our red neighbour trough a phenomenon called “panspermia” in which cells are carried to neighbouring planets on the debris ejected to space by major impacts on Earth, an event that happens once every 26 million years. Protected inside the debris, in dormancy, some microorganisms could reach to Mars and thrive in its environment, somehow similar to some cold regions on Earth. Deinococcus radiodurans could survive this odyssey and live comfortably on Mars. It seems like an unlikely hypothesis, but remember that that is the way in which rocks coming from Mars reached the Earth, like the meteorite ALH 84001, that seemed to contain fossil microbes. Although it can take thousands of years for rocks to travel from Earth to Mars, dust grains are big enough to harbour microbes and light enough to be pushed by sunlight pressure, reaching Mars in less than two months, to slowly descend in the atmosphere, thus avoiding incineration, and land gently on the surface. Thus, the red planet would have been injected periodically with terrestrial micro-organisms dragged by dust clouds ejected to space.

So, after all, maybe life that will eventually be discovered on Mars will be a colony of microscopic inhabitants of our own planet.

Works Cited:

1) Liquid water and life on Mars - Dr Gilbert Levin
2) The Greening of the Red Planet
3) New Scientist magazine, 11 Nov 2000
4) Super Survivor Deinococcus radiodurans
5) NASA – Humble microbe could become an accidental space tourist
6) Life in Antarctic may compare to Mars
7) Pansperm & life on Mars

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