Could the presence of methane mean life on Mars? No one can say for now.
Scientists have discovered rich plumes of methane on Mars that not only disappear quickly, but are replenished by unknown sources that could be biological or geochemical in origin.
"Either way, it's very interesting," planetary scientist Michael Mumma, with NASA's Goddard Space Flight Center in Greenbelt, Md., told Discovery News. "Mars is not a dead planet."
Mumma and colleagues used infrared spectrometers on three ground-based telescopes to monitor concentrations of methane in Mars' atmosphere over time and made a rather startling discovery: Not only does the planet have methane-rich plumes over several discrete sites, it also has an as-yet undetermined method for replenishing the methane that puts Earthly processes to shame.
On Earth, most of the methane in the atmosphere comes from cows' digestive processes and bacteria in wetlands and landfills. It also is produced by geo-thermal processes, such as volcanic eruptions and decaying coal.
The gas is broken down over time by ultraviolet light from the sun.
On Mars, "it's clear that there is a mechanism at work that is more efficient than photochemistry -- on the order of 100 times more efficient," Mumma said.
Whatever the source, methane on Mars should stick around for about 300 years, all things being equal. Instead, Mumma and his team, who published their findings in this week's issue of Science, found that over parts of Mars the methane is disappearing in a span of time as short as one year.
"We really can't tell if it's biological or geochemical at this time," Mumma added. "On Earth, it can be produced by either mechanism."
The definitive way to determine the methane's origins is to analyze its isotopes. Methane produced from biological sources on Earth has distinctively different isotopic ratios than methane generated by geochemical processes.
"There's nothing in place on Mars today that can take a whack at this puzzle," said Cornell University's Steve Squyres, the lead scientist behind the Mars rover twins, Spirit and Opportunity, which have been scouring the planet for more than five years in search of evidence for past water.
Isotopic analysis would require landing a well-equipped robotic science laboratory in a methane-rich area for local analysis, or retrieving samples for return to Earth. While scientists have hopes both missions will fly, neither will happen in the immediate future.
NASA last month delayed this year's launch of the Mars Science Laboratory to 2011 due to technical issues. Managers also eliminated a leading potential landing site, the methane-rich Nili Fossae, from contention because of concerns the terrain would be too risky for landing.
But scientists don't plan to sit around and wait for new tools. A new effort is underway to search for other gases that, like methane, are tied to biological processes on Earth. Targeted compounds include ethane, propane and hydrocarbons. .
Another line of inquiry will be expanded to try and figure out the chemistry and physics behind the rapid breakdown of Mars' methane. Based on data from as far back as the 1970s-era Viking probes, scientists suspect Mars has strong oxidants, such as hydrogen peroxide, to do the job, but they haven't pieced together exactly how the process would work.
Mumma says the first order of business should be to thoroughly map Mars' methane to determine where it is being released and how that process changes over time.
The biggest plume of methane discovered during the three-year study released about a pound of methane per second, roughly the same rate as the Coal Oil Plant Natural Reserve near Santa Barbara, Calif.