Some meteorites from Mars that have fallen to Earth contain methane, a potential sign that primitive methane-based life may have existed on our planetary neighbor, scientists say.
The finding of methane in the meteorites suggests Mars may have underground habitable environments comparable to some found deep in the Earth, the researchers report in the journal Nature Communications.
While the methane should not be considered hard evidence that life has existed at any time on Mars, it "is an ingredient that could potentially support microbial activity in the Red Planet," says geochemist Nigel Blamey of Brock University in Canada, lead author of the published study.
The researchers, part of a cooperative study involving universities in Scotland, Canada and the U.S., analyzed samples from six meteorites that came to the Earth millions of years ago after being thrown into space from the Martian surface following asteroid impacts.
When the samples were crushed, they released significant amounts of methane and hydrogen, probably from small pockets in the interior of the meteorites, the researchers say.
"The biggest surprise was how large the methane signals were," Blamey says.
While much of the methane in Earth's atmosphere is produced as a byproduct of life, the researchers are quick to point out it can be produced by other means, such as volcanic activity.
Ancient volcanic rocks interacting chemically with the thin atmosphere of Mars could produce methane, they acknowledge.
Still, they say, while the surface of Mars today is probably hostile to any type of life, if methane exists beneath the surface, it could possibly support microbial life, as it does for some bacteria in a range of extreme environments here on Earth.
"We have not found life, but we have found methane that could potentially support microbes in the subsurface," Blamey says.
There have been tantalizing signs that methane may also exist in the Martian atmosphere, with NASA's Curiosity recently detecting a spike in the gas, suggesting it is still being created through some process.
"One of the most exciting developments in the exploration of Mars has been the suggestion of methane in the Martian atmosphere," says John Parnell, a professor at the University of Aberdeen who directed the research.
So far, it's unclear where the methane is coming from or whether the rover's detection was even accurate, he notes.
"However, our research provides a strong indication that rocks on Mars contain a large reservoir of methane," he says, where they could serve as a source of food and energy for rudimentary forms of life.