Martian life appears less likely
If there's any life on Mars, it's not likely to exist on or just below the planet's surface, concludes a new study of Mars' mysterious methane.
The discovery of rich plumes of methane on Mars earlier this year fed theories that the planet could host underground colonies of micro-organisms.
But, rapid destruction of methane suggests that the planet's environment may be too hostile to support life.
Computer models show that if chemical reactions on the planet's surface are responsible for the rapidly declining levels of methane on Mars, it would leave "little hope that life as we know it can exist at present or that evidence of past life can be preserved in the shallow surface layer," says Franck Lefevre and Francois Forget of the Universitaire Pierre et Marie Curie in Paris.
On Earth, most of the methane in the atmosphere comes from cows' digestive processes and bacteria in wetlands and landfills. Methane is also produced by geothermal processes, such as volcanic eruptions and decaying coal.
Scientists are trying to understand not only what is releasing methane into the Martian atmosphere, but also what kills it off.
All things being equal, the gas should exist for centuries on Mars and be evenly spread throughout its atmosphere.
But Lefevre and Forget found that the methane disappears in less than 200 days.
"This implies an unidentified methane loss process that is 600 times faster than predicted," the authors write in a paper published in a recent edition of Nature.
Pinpointing the source
Dr Michael Mumma, a NASA scientist at the Goddard Space Flight Center, suggests that chemicals in the soil may be speeding the destruction of Mars' methane.
"We haven't tested that yet, so the plot thickens," says Mumma.
He also points out that subterranean microbial colonies could still be responsible for the gas, which might be released from cracks in cliff walls.
"It's an important paper," says Mumma. "It confirms plumes (of methane) can occur and that it requires a short lifetime."
Mumma and colleagues will attempt to pinpoint the source of Mars' methane and look for other gases tied to biological activity during a four-month observation campaign using Europe's Very Large Telescope (VLT) and the Keck telescope in Hawaii. Observations are scheduled to begin next week.
The team hopes that the VLT's new optics software will sharpen their view of Mars from a resolution of 400 to 500 kilometers to about 50 kilometres.