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NASA Scientists Baffled --"On Mars Methane, a Sign of Life on Earth, Changes Inexplicably with the Seasons"

 
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One explanation "that no one talks about but is in the back of everyone's mind," is biological activity, says Mike Mumma, planetary scientist at Goddard Space Flight Center. "You'd expect life to be seasonal."

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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It is a variation on a very faint theme. Since landing in 2012, Curiosity has on 30 occasions opened a few valves to the martian night and taken a sniff of the thin, frigid air. In a small, mirrored chamber, it shines a laser through the air sample and measures the absorption at specific wavelengths that indicate methane. At the meeting, Webster reported vanishingly small background levels of the gas: 0.4 parts per billion (ppb), compared with Earth's 1800 ppb.

Where that whiff comes from is the heart of the mystery. Microbes (including those that live in the guts of cows and sheep) are responsible for most of Earth's methane, and Mars's could conceivably come from microbes as well—either contemporary microbes or ancient ones, if the methane they produced was trapped underground. But methane can also be made in ways that have nothing to do with biology. Hydrothermal reactions with olivine-rich rocks underground can generate it, as can reactions driven by ultraviolet (UV) light striking the carbon-containing meteoroids and dust that constantly rain down on the planet from space.

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