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.