I've said for a while that it's only a matter of time before life is found on Mars. I know most of you aren't space geeks like me, so I want to issue the disclaimer that I am not talking about animals or plants here, just bacteria. The evidence is always present in minute amounts that, when taken together, add up to more than coincidence.
First there is the fabled Martian meteorite ALH84001 that made headlines in 1996. This meteorite was found to have carbonate globules consistent with biological activity, organic molecules associated with the globules that are also consistent with biological activity, and controversial structures that resemble fossilized nanobacteria similar to bacteria recently discovered on Earth. None of these can't be explained by geological processes, but the odds of all three occurring at identical locations in a specific piece of rock are slim.
NASA's Mars Exploration Rovers have confirmed the past flow of water on the surface of Mars, giving life opportunity to arise in the first place. Then there was the discovery of higher concentrations of methane in the Martian atmosphere than predicted by ESA's Mars Express orbiter. Methane can be produced by geological processes, but can also be the product of methanogenic bacteria. Most interestingly, when mapped, the atmospheric regions with the highest concentration of methane also have the highest concentration of water vapor, and are over ground that is believed to have subsurface ice and possibly liquid water. Water is neccessary for life. Again, we have a remarkable congruence of evidence that is unlikely to be purely coincidental.
Now NASA scientists have discovered a new form of underground microbial ecosystem on Earth in an area that closlely matches Martian conditions in the regions that exhibit the signature of methane. Among the similarities is the presence of the sulfate jarosite, known to exist on Mars in comparatively wet regions. On Earth, this sulfate is associated with underground ecosystems in acidic bodies of water. Once more, the evidence supports the existence of life.
It will probably be decades before the question of life on Mars is definitively answered. Even the most capable robotic mission projected would be unable to explore the sheer diversity of possible niches to rule out life, and for that matter, human missions may be limited by time constraints. But eventually we will know.
My money is on yes.
Update, February 20: Turns out Space.com fabricated the above story. The people involved are real, they've really discovered some cool stuff, but they didn't discover any hard evidence nor are they publishing a paper in Nature about it. None of that changes my belief -- and I could always be wrong -- about bacterial life being present due to the other evidence. But it is just another example of people doing stupid things.
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