Mars methane from biology or geology?
By Tariq Malik
SPACE.com
(SPACE.com) -- A trio of research teams independently probing the martian atmosphere for signs of methane have confirmed the presence of the gas and raised a host of explanations for how it got there.
Among the most tantalizing, if unlikely, scenario is the possibility that the Mars methane could be the byproduct of some form of microbial life, said scientists. But a safer bet, they say, is that geological activity on Mars, including anything from volcanic activity to long-ago impacts of methane-carrying comets, may have released methane into the atmosphere.
"It's of course very exciting and quite a surprise," said Augustin Chicarro, project scientist for the European Mars Express mission, which detected methane while orbiting the planet. "Mars seems to be a planet that is always surprising us, one week it's an ocean...now this."
The methane discovery comes just weeks after NASA's Mars Exploration Rovers Spirit and Opportunity found conclusive evidence that water once flowed on the surface of the red planet, providing firm evidence that Mars could have been more hospitable to life.
While not a rover itself, the Mars Express orbiter pieced together its methane picture after successive turns around the planet, detecting a small amount of the gas in the atmosphere. Two other projects, one led by NASA scientist Michael Mumma of Goddard Space Flight Center and the other by Vladimir Krasnopolosky, a researcher with the Catholic University of America in Washington, D.C., used ground-based telescopes to detect Mars methane as well.
"I would say that they confirm our results," Krasnopolosky said, adding that his study predicted almost the exact concentration of methane, about 10.5 parts per billion, seen by Mars Express.
Since methane has a relatively short lifetime on Mars for atmospheric gases, about 300 years or so, scientists believe there must be some process at work to keep replenishing its concentration in the atmosphere.
On Earth, methane is belched into the air during volcanic eruptions. It seeps out from fissures in the crust. It is also expelled by methanogenic bacteria as a waste product. While the idea of subterranean microbes living just under the martian surface is attractive, Mars researchers are hesitant to put their full weight behind it.
"I think the first possibility, volcanism, is probably best," Chicarro said. "Volcanism has not been ruled out as a modern phenomena on Mars."
Nothing so explosive as an eruption is needed to expel the gas. It could seep out through gentle, consistent hydrothermal activity, Chicarro said.
Krasnopolosky, on the other hand, said while he believes that martian microbes are the most likely methane culprits, he cannot definitely rule out other factors. It is just as possible, he said, that methane formed in martian volcanoes and outgassed through primordial surface vents, or even arrived on the planet during comet and meteorite impacts.
Locating the source of Mars methane could pare down at least some of those scenarios if researchers are able to determine local concentrations. Both Mars Express and Krasnopolosky's study measured Mars methane on a global scale. However, it may be possible for Mars Express researchers to use their spacecraft's mineralogical mapping instrument to scan the surface for signs of volcanic activity, then compare the results with methane observations.
In the meantime, researchers plan to continue their Mars studies.
"It seems like with every set of missions to Mars, instead of a gradual increase in our understanding we have a quantum leap," Chicarro said. "It's really a complicated place."
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