A SOURCE of methane gas has been identified by scientists probing the atmosphere of Mars, showing for the first time a possible location for life on the red planet.

The gas, thought to be produced by underground colonies of microbes, has been detected at high levels in Meridiani Planum, a low-lying region near the equator thought to have been covered once by an ocean.

Scientists say the only other possible source of the gas would be volcanoes but, while this has not been ruled out, most evidence suggests there has been no volcanic activity on Mars for millions of years.

Jim Garvin, head of Mars exploration at the National Aeronautics and Space Administration (Nasa), said the results were “very impressive”. He added: “This has sharply raised the chances of finding life on Mars. It is too early to be sure but the most likely source of this gas is life.”

He made the announcement of the find last week at an international astronomy conference in Iceland attended by more than 200 scientists.

The significance of methane lies in the fact that it is quickly destroyed by radiation from the Sun. This means it could exist on Mars only if there was an active and constant source to replenish what was being lost.

The only likely place for life on Mars is underground, where bacteria could be protected from solar radiation. On Earth, methane is produced by volcanic activity but the main sources are biological, especially bacteria that break down organic matter.

The discovery is the latest of several indicators suggesting that Mars may have — or have had — the ability to support life. In March, Nasa’s Opportunity rover confirmed earlier evidence that oceans may have covered much of Mars.

This was also supported by the European Space Agency’s Mars Express, from which Britain’s ill-fated Beagle 2 rover was launched. Such evidence suggests that water, probably in the form of ice, is still hidden underground all over the planet.

Meridiani Planum is thought to be one of the most likely sites for life to have evolved because of its wet past and because it may also have large reserves of underground ice. Nasa’s orbiting Odyssey spacecraft has sent back spectacular pictures from the surface of Mars showing channels and scouring probably caused by water flows.

Nasa is already exploring the Meridiani area with Opportunity, but the rover has no instruments capable of measuring methane levels.

The emissions were measured from Earth using telescopes equipped with an infrared spectrometer which can analyse light reflected from Mars and pick out the unique signature of methane molecules. Nasa has found methane in all parts of the Martian atmosphere but with particularly high levels around Meridiani.

Professor Michael Mumma, who heads Nasa’s astrobiology research programme at Goddard Space Flight Center in Maryland, oversaw the project. He said that frequent strong winds on Mars meant gases in its atmosphere tended to be swiftly mixed together.

“It means that if we find relatively high concentrations, then there must be a local source,” he said.

“The levels we are finding around Meridiani are powerful evidence that there is something emitting it at a steady rate. There is no evidence of vulcanism or tectonic plate movements, so it does favour the conclusion that this methane is of biological origin.”

The location of the discovery fits in with theories about Martian evolution, which suggest that the red planet may once have been lush and green and that its history has been marked by huge climatic swings.

As the climate enters a warmer phase, the underground ice may melt and emerge. Meridiani Planum is thought to have once been covered by a sea hundreds of metres deep.

Methane has also been detected on Mars by other researchers. Earlier this year scientists at the European Space Agency announced that its Mars Express probe had spotted the telltale signature of methane in the atmosphere.

Now both agencies plan to return to Mars with spacecraft able to drill into the soil and analyse the atmosphere directly. Mumma said: “The clear implication is that these emissions are a sign of life on Mars but we need to go there again to find out for sure.”

Researchers think it highly likely that if evidence of bacteria is found in one place then they must exist elsewhere, too, so the scientists are planning to survey the whole planet. oNasa spacecraft may have carried bacteria to the Moon, Mars and across the solar system, a senior official with the organisation has admitted.

The lunar Surveyor spacecraft, which landed on the Moon in 1967, was examined by astronauts from the subsequent Apollo 12 mission in 1969. The samples they brought back were contaminated with streptococcus bacteria, said John Rummel, Nasa’s planetary protection officer.

At the Iceland conference last week he also confirmed that the Nasa craft now surveying Mars, including the rovers, had not been sterilised and were carrying microbes.

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