They seem to have discovered methane on Mars.

I find this much more exciting than water for two reasons. First, while there are abiological means of methane production (e.g., vulcanism), if there’s been any recent (i.e., in the past few hundred years) such activity, this would be the first and only evidence of it, so some form of life is definitely a strong possibility. Water means that life might have once been there. Methane means much more strongly that it might be there now, since it doesn’t persist that long.

It’s also potentially a source of fuel, though it may be too trace to easily collect.

[Hat tip to “cspackler” at Free Republic, from an amusing thread on this topic.]

[Update a couple minutes later]

The best place to go for in-depth and smart blogging on subjects Martian is probably Oliver Morton’s Mainly Martian site. He’s all over this one, and has taken the effort to come up with flatulent cow equivalents. He thinks it’s just a couple thousand for the whole planet.