Methane on Mars Means?

Maybe life, maybe not. [Link]

Plumes of methane gas detected over certain locations on Mars in 2003 could point to active geological processes on the red planet, or perhaps even to methane-burping microbes deep below the Martian surface, a new study reports.

There is no firm evidence for life on the red planet, however, despite news reports early today suggesting as much. Rather, scientists are puzzled by the new findings.

Methane, a small (but important) constituent of Earth's atmosphere, makes up an even smaller percentage of Mars' atmosphere (which is 95 percent carbon dioxide), so detecting it on the red planet is a rare event.

In fact, it wasn't detected at all before 2003, when the European Space Agency's Mars Express orbiter (which is still circling the planet) picked up a possible methane signature.

A search conducted with three ground-based telescopes that covered 90 percent of the Martian surface over three Mars years (7 Earth years) detected extended plumes of methane that varied with the seasons and seemed to emanate from specific locations. These include the Arabia Terra, Nili Fossae and Syrtis Major regions of Mars. The work was supported by NASA and the National Science Foundation.

In 2005, scientists also found signs of water ice beneath the surface near Mars' equator and, interestingly, near an area where methane has been detected.

The methane plumes started to show up in the northern hemisphere spring of Mars, gradually building up and peaking in late summer. At one point during the study, the primary plume contained about 19,000 metric tons (21,000 tons) of methane, comparable to the amount produced at the massive hydrocarbon seep at Coal Pit Point in Santa Barbara, Calif.

"It's a heck of a signpost," said study author Michael Mumma of NASA's Goddard Space Flight Center in Greenbelt, Md.

Where exactly the methane comes from is still unknown, though scientists have some ideas. Mumma and his team detailed these ideas and their findings in the Jan. 15 early online edition of the journal Science.