The Mars Science Laboratory rover may be retargeted to land near a methane vent on Mars to specifically seek direct evidence of current Martian life.

This new consideration of MSL landing sites comes in the wake of compelling new data that large pockets of methane found in the Martian atmosphere could have been exhaled or vented from abundant microorganisms living underground on Mars.

An artist's concept of the Mars Science Laboratory rover. Credit: NASA/JPL

The MSL rover's launch was recently delayed from 2009 to 2011 because of technical delays, but the slip could enable a new landing site selection related to the methane findings, says Michael Meyer, the lead Mars program scientist at NASA headquarters in Washington.

The car-sized rover will be launched from Cape Canaveral on a United Launch Alliance Atlas 5 booster.

The data that large localized pockets of seasonal methane are routine in the atmosphere of Mars is beginning to drive NASA's Mars exploration program toward a possible a shift in overall Mars exploration strategy.

The data are leading researchers to believe that NASA should be searching for Martian microbes that could be living there now, rather than focusing studies on ancient extinct life that lived billions of years ago when Mars had water flowing on its surface.

A NASA/University team found methane in the Martian atmosphere by carefully observing the planet for several Mars years with NASA's Infrared Telescope Facility and the W.M. Keck telescope, both at Mauna Kea, Hawaii, according to Michael Mumma, senior planetary scientist and director of the Goddard Center for Astrobiology. The team used spectrometers to detect three spectral absorption lines that together are a definitive signature of methane.

In the four Mars locations where the methane was found, it could have been produced at a rate of 1 pound per second, researchers say. There are no active volcanoes on Mars, which on Earth can also produce methane.

Although the methane is being observed regularly, most of the data subjected to intense study was obtained in 2003, before the European Space Agency's Mars Express orbiter also detected methane, which on Earth is given off by many living organisms.

The methane discovery indicates the planet is either biologically or geologically active presently. In addition to being formed in biological processes, methane can also be formed in rare rock and water interactions.

Other purely geological processes, like oxidation of iron, also release methane. "Right now, we don't have enough information to tell if biology or geology -- or both -- is producing the methane on Mars," said Mumma.

"But it does tell us that the planet is still alive, at least in a geologic sense. It's as if Mars is challenging us, saying, hey, find out what this means." Mumma is lead author of a paper on the methane research appearing next week in Science Express.

Although such rock and water interactions occurring deep underground are known to occur on Earth, they are rare, and likely even more rare on Mars, according to Lisa Pratt, professor of geological sciences at Indiana University, Bloomington.

"Given the lack of compelling evidence for deep active fracturing and faulting to keep water/rock reactions going on Mars, it is time and prudent that we begin to explore Mars looking for the possibility of a life form that is alive now and exhaling methane," Pratt says.

Even if the methane is not exhaled or vented as part of biological activity, the new findings are extremely significant because some organisms use methane as a food and energy source.

The Phoenix Mars lander discovered perchlorate salts which also can be used as a food and energy sources.

And the methane data also provides additional evidence for current liquid underground water on Mars.

MSL will be capable of detecting extremely small amounts of methane that could be coming from surface areas overlying areas of underground Martian life. But MSL would not be capable of directly sampling the kind of microbial life scientists believe could be causing the methane.

From what is known of Martian rock strata, the kind of rock, water and temperatures that could support life would be tens of feet or more underground.

This would require drilling equipment that could only be carried on much larger and more advanced landers than MSL.

"On Earth, microorganisms thrive 2 to 3 kilometers (about 1.2 to 1.9 miles) beneath the Witwatersrand basin of South Africa, where natural radioactivity splits water molecules into molecular hydrogen (H2) and oxygen.

"The organisms use the hydrogen for energy. It might be possible for similar organisms to survive for billions of years below the permafrost layer on Mars, where water is liquid, radiation supplies energy, and carbon dioxide provides carbon," said Mumma.

"Gases, like methane, accumulated in such underground zones might be released into the atmosphere if pores or fissures open during the warm seasons, connecting the deep zones to the atmosphere at crater walls or canyons," he says.

"Microbes that produced methane from hydrogen and carbon dioxide were one of the earliest forms of life on Earth," noted Dr. Carl Pilcher, Director of the NASA Astrobiology Institute, which partially supported the research. "If life ever existed on Mars, it's reasonable to think that its metabolism might have involved making methane from Martian atmospheric carbon dioxide."

"We observed and mapped multiple plumes of methane on Mars, one of which released about 19,000 metric tons of methane," said co-author Geronimo Villanueva of the Catholic University of America in Washington. "The plumes were emitted during the warmer seasons, spring and summer, perhaps because ice blocking cracks and fissures vaporized, allowing methane to seep into the Martian air."

The plumes were seen over areas that show evidence of ancient ground ice or flowing water. Plumes appeared over the Martian northern hemisphere regions, such as east of Arabia Terra, the Nili Fossae region, and the southeeast quadrant of Syrtis Major, an ancient volcano about 745 miles across.

The Nili Fossae region is already an MSL landing candidate, but its elevation may be too high for MSL atmospheric entry, descent and landing (EDL) systems.

Meyer said that with an additional two years to plan, the EDL capabilities will be better defined and other sites with methane signatures could be added to the targeting options.