Life on Mars

A few weeks ago active releases of methane gas have been discovered on Mars. This has led some scientists to say that this is strong evidence for microbial life. Yet there is more than one way that methane can be produced on the surface of a planet.

Methane is commonly released through geologic activity. Yet geologic activity is accompanied by sulfur dioxide, which has not been detected. Not to mention that we have never observed active volcanoes or recorded seismic activity. This doesn't mean it isn't there, just that it is less probable.

Methane could also have been seeded by a comet impact. But there is no evidence of a recent comet impact on the surface. Due to the fact that methane dissipates at a significant rate, a comet would have had to impact within the last few hundred years.

For now we have narrowed, but not definitively limited, the source of methane to microscopic life. But these are still conjectures. We won't know anything more until we send the Mars Science Laboratory in 2011.