Don't expect little green men, but there really could be life on Mars

FOR centuries, man has gazed into space and wondered: "Are we alone?" Now, following a five-year study of Mars, Nasa has come up with the most compelling evidence yet to suggest we may not be. For deep below the Martian surface, it seems, something might be stirring.

New data released by Nasa last night pinpoints giant plumes of methane emanating from the Red Planet, indicating the possible presence of micro-organisms living within the soil. The alternative, say scientists, is that the methane is the product of volcanic activity, though none has been detected.

The data, which has passed peer review and is published in Science magazine, is considered to be the most solid, irreproachable yet presented relating to the possibility of life on Mars.

But scientists warned that if life does exist it is a far cry from mankind and would make ET, the loveable alien in the 1982 Steven Spielberg film, look positively sophisticated.

"If it (the source of the methane] were biological, it couldn't be the higher life forms that we see on Earth, because the surface of Mars is exposed to harsh ultraviolet light and low-density gases and so on," said Dr Michael Mumma, a planetary scientist and director of Nasa's Goddard Centre for Astrobiology in Maryland, one of the study's lead scientists.

He said: "If this methane is a production of biology, it would be in the form of microbes underground, where they may have access to water and other things needed to live, and where they are protected from the harsh surface environment."

On Earth, 90 per cent of methane – comprising carbon and hydrogen – is created by the breakdown of vegetative materials and is found in the belches and other antisocial emissions of animals, ranging from ants to humans. The other 10 per cent comes from geological activity.

On Mars, which ranges between 36 million and 250 million miles from Earth, it could come from either.

The presence of methane in the Martian atmosphere was first detected by Nasa in 2003, using ground-based telescopes, and confirmed the next year through measurements taken by the orbiting European Space Agency probe, Mars Express.

"That was really exciting, but we knew that if we were to present the data to the scientific community, it would have to be unassailable," said Dr Mumma.

"We would have to demonstrate not only that we were seeing methane, but that there really was no other explanation for it… then it becomes a case of, 'Oh gosh, these guys really have validated their approach. They are getting the right answers, so we can have confidence they have done the right thing'."

There followed a period of intensive and highly technical research, including taking complicated measurements of the Martian atmosphere and calculating how much of the methane recorded was actually emanating from Earth's atmosphere, in order to get the most accurate data to date.

The scientists used infrared spectrometers – instruments that can measure distant gases by analysing the breakdown of light signals – at three high-powered telescopes on a mountain-top in Hawaii to take readings.

Questions remain as to whether the methane may be left over from past Martian life that has become extinct. "Its origin could be ancient, or perhaps recent," Dr Mumma said.

The suggestion of "extremophile" micro-organisms living in colonies below the Martian surface, deriving their energy not from the Sun but from radiolysis – the radioactive breakdown of water molecules, expelling methane in the process – is not alien to scientists.

Such organisms are known to exist on Earth, living in the rock several miles below the surface in deep South African coalmines. "So we know that, on Earth, we have analogues that, if placed on Mars, could in fact prosper," Dr Mumma said.

He added: "We know that every human on Earth wants the answer to the question, 'Where did we come from and are we alone?'.

"I got a lot of pressure from colleagues along the way to 'publish, publish, publish', to write scientific papers announcing what we were finding, and I said, 'You know, we'll publish when we are certain there are no more gremlins to be resolved'.

"Credibility is an important thing," said Dr Mumma. "Credibility can only be lost once."

The odds are good for finding someone else out there

PEOPLE are fascinated by space and the possibility of life off this planet, as well as the prospect of being able to travel in space in the future.

We have seen from science-fiction books and from Hollywood movies what people imagine aliens might look like. They tend to imagine either monsters or aliens like human beings.

But probably the sort of life that develops on most planets would be far more primitive than we have on Earth at the moment. It might be something like slime, or just bacteria that had a chance to get going or even survive until today on a planet like Mars.

It's fascinating to think about life outside Earth. We are living on such a small planet in such a huge universe. Are we unique, or are there many places out there where life got started and developed into complex animals, or even intelligent life? If it turns out that ours is a very rare type of planet, so that we are effectively the only place in the galaxy with life, then we have to be very careful with the planet we have.

There are so many stars out there, and we are finding planets orbiting these stars now. It seems like planets are fairly abundant, so the odds are life does form in other places.

But my bet would be that it would be mainly primitive life forms.

Prof Keith Horne, astronomer at St Andrews University