From the pasture to the swamp, methane emissions on Earth are the effluvia of life. So what are whiffs of the gas doing on barren Mars? Trace detections of the stuff, alongside glimpses of larger spikes, have fueled debates about biological and nonbiological sources of the gas. Last month, at a meeting of the American Geophysical Union (AGU) in New Orleans, Louisiana, NASA scientists announced a new twist in the tale: a seasonal cycle in the abundance of martian methane, which regularly rises to a peak in late northern summer.
"The thing that's so shocking here is this large variation," said Chris Webster, who leads the methane-sensing instrument on NASA's Curiosity rover. "We're left trying to imagine how we can create this seasonal variation," says Webster, who is at the Jet Propulsion Laboratory in Pasadena, California.
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