Methane on Mars

You probably already saw the news–there has been independent confirmation of the current existence of methane gas in the thin Martian atmosphere.
Is it a lot? No. The pdf abstract on the paper, available through the BBC site here. mentions that it is a pretty thin component (which is why no one has spotted this before in spectral analysis).
The thing is, though, methane is unstable, especially in an environment without an ozone layer. In a few hundred years, any reservoir of methane not replenished would all be lost.
As scientists see it, there are two known possibilities, both exciting.
1. Vulcanism. Despite no evidence of same, rather than being a completely dead world, Mars must still have some active vulcanism. Mars would no longer be a dead world, geologically.
2. Methanogens. There are bacteria on earth which produce methane gas. What’s more, they are anaerobic, they die in oxygenated environments. Not very advanced, considerably primitive…but if they are there on Mars, even in isolated oases, it would be life. Life on another world…
Of course, there could be another, unknown possibility, something unknown and unforseen. And that, too, would be just as exciting.
See why we need to visit Mars? We can only do so much with just robots…