Is there life on Mars?

Mars, the Red Planet, has inspired endless fascination and over forty exploratory missions (even if most have failed to reach their destination).  From Giovanni Schiaparelli's early maps of Martian canali -- interpreted by Percival Lowell as a global network of channels built by extraterrestrials -- to H.G. Wells' War of the Worlds, in which the denizens of a dying Mars invade Earth, mankind has imagined life on one of our closest celestial neighbors.


The Viking missions in the mid-1970s carried four life detection experiments to Mars, to look for signs of bacteria in Martian soil.  One of the tests reported evidence of metabolic activity, but none of the other tests could confirm; most discouraging, a GC-MS analysis found no evidence of organic compounds.  Scientific consensus deemed the seeming metabolic activity a false positive, a result of highly reactive chemicals in the soil, and Mars a lifeless planet.

Or is it?

Interest in the possibility of extraterrestrial life on Mars has been growing, especially since the unambiguous detection of water -- potentially in large amounts -- existing just beneath the surface.  Water is required for all life on Earth, and one primary strategy in the search for extraterrestrial life is 'Follow the Water.'

Satellite images revealed what appear to be water carved gullies, but debate circled around the age of these features.  Four billion years ago, Mars was wet, covered with oceans.  At roughly half the size of Earth, Mars cooled much more quickly and was not able to sustain a thick atmosphere.  The atmosphere of Mars today is too thin for liquid water to persist, any water would sublimate directly from a solid to a gas and likely escape into space.

In 2008, a robotic arm on the Phoenix lander scraped away a small area of soil and found ice.  There could well be oceans of permafrost hiding beneath a dusty red veneer, and deep subsurface aquifers with liquid water heated by geothermal processes, that occasionally bubble to the surface as geysers.  The question now is not whether water exists on Mars, but how much?

Some scientists speculate there is greater biomass existing within the Earth than on its surface.  Even in mine shafts carved a mile deep, there is life.  Bacteria buried in the rock, living in slow motion, with high heat and punishing pressures, extracting energy from chemicals normally considered poisonous.

Given what we know, it seems reasonable to suspect that if life ever managed to become established on Mars, it probably still exists there.  Conditions on Mars are not so different from what certain extremophiles here on Earth tolerate.  I imagine the first mission to drill into the surface will find a thriving Martian community of microorganisms, protected from the harsh UV conditions by a meter or two of rock.  Perhaps not the aliens promised by science fiction, but still infinitely fascinating.

The Phoenix lander also detected a high concentration of perchlorates in the Martian soil.  Recent studies with Earth soil suggest the levels of perchlorate present in Martian soil would break down any organic material under the conditions of the GC-MS experiment performed by the Viking lander.  Maybe... we did detect actually life back in the 70's, and just didn't recognize it.