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Mystery deepens as Martian methane eludes Curiosity

The Mars rover Curiosity has taken a good, long whiff, and finds no hint of methane in the planet's atmosphere. The result means previously detected methane plumes, seen by some as a sign of active life on the Red Planet, remain a mystery. However, it doesn't rule out the possibility that Mars has a cache of the gas stored underground.

Around 90 per cent of the methane in Earth's atmosphere comes from living things or the remnants of past life. Finding methane on Mars isn't a sure sign of life there, as the gas might also come from geological processes or might be deposited by asteroids or comets. But it would be a glimmer of some kind of activity on modern Mars.

"When people think about Mars, they think it's a dead planet with nothing going on," says Geronimo Villanueva of NASA's Goddard Space Flight Center in Greenbelt, Maryland. "Most of the focus has been on the past of Mars. But if you see things in the atmosphere that are dynamic, you are seeing things going on right now."

That's why excitement swelled in 2004, when three independent teams using telescopes on the ground and orbiters around Mars reported large amounts of methane in the planet's atmosphere. A later analysis of 2003 data from telescopes in Hawaii revealed distinct plumes of methane coming from three regions on Mars, including one plume reported to contain roughly 19,000 tonnes of the gas.


That should not be possible: sunlight exposure and other chemical effects can break down the molecule, but only over hundreds of years. "Methane is very stable. It's almost boring in that sense," says Chris Webster, a member of the Curiosity team at NASA's Jet Propulsion Laboratory in Pasadena, California. So where did it all go? Or was it ever truly there?

Powerful loss



"If all the other observations are true, the only way to reconcile the measurements is to make the already powerful loss mechanism even stronger," says Webster. "You would need to decimate that methane at least 100 times faster than known chemistry."


"They have a set of measurements for a particular season in Gale Crater," says Villanueva, who was on the team that reported the 2003 methane plumes and has done subsequent searches using ground-based telescopes. "I think this is only the first results of the rover, and I would like to see more conclusive measurements in future."

Locked in the ice


There could still be methane lurking somewhere on Mars, Webster adds. It could be locked up in cage-like ices called clathrates, which exist in Earth's Arctic regions and are highly likely to have formed on Mars, perhaps in an icy subsurface layer. What's more, methane isn't the only gas that would hint at life.

"Seeing low methane abundance now tells us that methane-making microbial activity is very limited, but it doesn't weigh in on the possibility that there are other microbes that don't produce methane still in existence in the subsurface," says Webster.

Journal reference: Science, DOI: 10.1126/science.1242902


Curiosity tries to sniff out the missing methane<i>(Image: NASA/JPL-Caltech/Malin Space Science Systems)</i>

Curiosity tries to sniff out the missing methane(Image: NASA/JPL-Caltech/Malin Space Science Systems)


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