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from the surface of Mars. The big unanswered question is, What belched? Subsurface Martian cows are highly unlikely. But scientists are seriously considering the possibility of bacteria. " As The Independent picks up the story: " One possibility is that the methane is produced by Martian microbes living deep enough for underground water to be in liquid form. At this depth they could be living off hydrogen formed when water molecules split apart, along with carbon dioxide which could act as a source of carbon, producing methane as a waste product. " The alternatives to bean-eating Martians are about as exciting as finding hydroxyl radicals in interstellar space. That would include volcanic activity (unlikely, given the lack of other telltale gases); a methane-toting comet (but we should see a big impact crater); Martian fossil fuel (OK, that would be fairly cool); or geochemical reactions well known on earth that also produce methane. The Boston Globe poured cold water on the story, using logic — darn them — to deflate the claim. " Scientists agreed that the origins of the gas were more likely to be geological, some citing Occam's Razor, the principle that the simplest explanation is usually best. " Those more prosaic possibilities seem like something we would have read about in Scientific American. Oh — wait. We did. In an issue from spring of 2007. That's right. The subject of methane on Mars is actually not exactly a revelation. " Mars, it seems, occasionally burps sizable volumes of methane gas, " Sky & Telescope noted on its website. " This, in itself, isn't exactly fresh news. Both ground-based telescopes and Europe's Mars Express orbiter detected whiffs of Martian methane several years ago. " The twist here is that the gas is not emitted constantly. This latest batch seems to have been belched during the Martian summer of 2003. In fact, almost as interesting as where the methane originated is what happened to it. The Washington Post garbled that mystery with this attempt at analysis: " The methane does not last long in the Martian atmosphere, which is made up largely of carbon dioxide that breaks down the gas much more quickly than on Earth. " Actually, methane is slowly degraded by sunlight, not CO 2 , and should persist for hundreds of years. Instead, there is apparently an oxidant on Mars that is removing the methane rapidly from …