firm detection of methane in Mars' atmosphere announced in 2009 (confirming earlier, more ambiguous results) it's been tough waiting for the next steps, impatience abounds. Methane is one of those compounds that has a predominantly biological origin on the Earth. Both here and on Mars, simple models of atmospheric chemistry suggest that methane molecules shouldn't last for very long - so if you see them then something is actively putting them into the air. Originally the models indicated that on Mars methane might last for as much as a couple hundred Earth years. The big shocker was that it was getting wiped out in less than one Earth year - showing large seasonal dependency.
We still don't understand either this result, or what's producing the methane (future measurements of isotopic compositions - heavy vs. light carbon and hydrogen - may indicate if biology is involved, since life usually prefers light nuclei). Some beautiful new results by Fonti & Marzo, using Mars Global Surveyor data, add much needed detail, but also add further layers to the mystery.
Their extraordinary map (click on the image) shows the atmospheric distribution of methane during the Martian fall, three Martian (6 Earth) years ago. Where does the methane hover over? It lurks around both regions sculpted by past volcanism (Tharsis and Elysium) and - rather provocatively - around a region where we know there are large amounts of subsurface water ice (Arabia). This is wonderful news - there's definitely a connection with the most recently active geophysical sites, the same sort of places that could produce the kind of warm, chemically rich, subsurface environments loved by the types of microbial life we are familiar with. Whether the methane itself is geophysically produced, or comes from extinct or extant life, we now know that there are places on Mars where conditions have been pretty juicy.
The hitch is that by the end of Martian winter most of this methane vanishes. Something is very efficiently scrubbing the atmosphere on Mars. Prime candidates are wind driven particulates and tough oxidizers like perchlorates (which are good for making fireworks, no, honestly) that may sweep through the skies. But come the relative warmth of spring and summer, the methane reappears, either released from frozen deposits or, just possibly, maybe, tantalizingly, the result of ongoing biological activity - the blooms of Mars. Are we witnessing the first signs of a very alien ecological system? If biology is responsible then what does this cleaning system imply for the lifestyle of organisms? In effect the methane excreta is tidied up before it can pollute, like some efficient recycling program. Is there anything equivalent here on Earth?