I think we're getting close to something big, very big. The European Space Agency's Mars Express probe has confirmed earlier findings that the Martian atmosphere contains traces of methane. Apparently there are only two plausible sources of methane in a planet's atmosphere, volcanic activity and biological processes. What's more, as methane only persists in the atmosphere for a relatively short period, it must be being constantly replenished. As Mars seems to be devoid of any obvious volcanic activity, well, draw your own conclusions, at least until someone sends up another probe with a methane sniffer on board. Ironically, the doomed Beagle 2 probe had such an instrument on board. Perhaps the Martians knew we were getting too close.