Methane in Mars' atmosphere lasts less than a year meaning something -- either geologic or biological -- keeps belching it out.
The first planet-wide studies of methane on Mars shows gas concentrations peak in autumn and plummet in winter.
The methane could be produced by geologic or biological activity.
The rapid removal of the chemical from the atmosphere is as much a mystery as what's producing it.
A six-year study of methane in Mars' atmosphere shows the planet is far from dead, though whether it is merely geologically active or host to microbial life is unknown.
An Italy-based team of researchers combed through billions of measurements taken by NASA's Mars Global Surveyor to compile seasonal maps of the gas, a simple chemical compound that appears in minute quantities in Mars' carbon dioxide-rich atmosphere.
Methane breaks down in ultraviolet light from the sun, so scientists know it is being replenished in some way from the planet itself. The speed at which the methane is being depleted -- less than a year -- is as great a mystery as what's causing it.
"We're trying to simulate what kind of mechanisms are possible and are active on Mars in order to see this behavior," Guiseppe Marzo, a researcher with ENEA, the Italian National Agency for New Technologies, Energy and Sustainable Economic Development, told Discovery News.
Marzo and colleagues found three regions in the planet's northern hemisphere with consistently higher concentrations of methane -- Tharsis, Elysium and Arabia Terrae. Tharsis and Elysium are home to Mars' most massive volcanoes and Arabia Terrae has large quantities of subterranean frozen water.
Methane concentrations are highest in autumn and tail off dramatically in winter. Levels build up again in spring and climb rapidly during summer, causing the gas to spread across the planet, the researchers found.
Lead researcher Sergio Fonti, with Italy's Universita del Salento, says the seasonal pattern rules out the possibility that the methane is due to cosmic ray bombardment or meteorite impacts.
"It could be geology or biology, but it is not coming from another source. There is a seasonal pattern, so it could only be a local origin," Fonti told Discovery News.
NASA and Europe are planning a joint mission in 2016 to make more detailed maps of Mars' methane. NASA's Mars Science Laboratory, scheduled for launch next year, also has an instrument that can detect atmospheric methane.
"The release appears to be episodic, so we need much more compete coverage of methane than what we can achieve on the ground," said NASA space scientist Michael Mumma, who last year published highly cited research on Mars' methane made from ground-based observatories.
On Earth, colonies of bacteria that consume methane have been found living right along species that produce it.
"We could easily have a similar situation on Mars," Mumma said.
Fonti and Marzo's research was presented this week at the European Planetary Science Congress in Rome. It will be published in an upcoming issue of Astronomy & Astrophysics.