Powerful evidence that life may still exist on Mars was presented by Nasa last night after the discovery that huge plumes of methane were being spurted into the planet’s atmosphere.

Detection of the gaseous emissions fell short of offering proof of life but indicated to astronomers a distinct possibility that it not only evolved on Mars, but is still there. Most of the gas on earth is created by animals and plants.

Nasa announced the findings at its headquarters in Washington, with Lisa Pratt, of Indiana University, suggesting it was time “to think in terms of present-day life holding on in the subsurface”.

Bursts of methane were first detected by the Nasa team in 2003 and in an analysis of the phenomenon it was concluded that tiny organisms could have been responsible. Microbial organisms are known to exist more than a mile underground in South Africa and would provide a perfect model for similar microscopic life creating methane on Mars, researchers said.

Professor Pratt said the overall quantities of methane were small, so if life exists on Mars it will most likely be in a “thin invisible film”. However, she added: “It’s time to start thinking about active processes as well as extinct processes. It’s such an exciting discovery. We have evidence we need to think about in terms of the possibility of life on Mars.”

Methane was detected using infrared spectrometers in Hawaii but it was impossible to determine whether the gas had been created through biological or geological processes.

Such detailed analysis, said Dr Michael Mumma, of the Goddard Center for Astrobiology, the lead author for the research, will be possible on Mars Science Laboratory mission to the planet which is planned for launch in 2011.

The robotic craft landed on the surface of the planet will be equipped with spectrometers which will allow it to measure the isotopic content of the methane and indicate whether the gas was formed biologically or geologically.

He was also hopeful of using earth-based equipment to seek out other gases in the Martian atmosphere which are associated with biological chemistry.

One point adding weight to hopes of finding life, he said, was that the spectrometers failed to detect sulphur dioxide which would have been expected had the methane been formed during volcanic activity.

Scientists involved in the finds, reported in the journal Science, said that rather than being produced today by live microbes it could have been created by life forms which died millions of years ago. The gas would have been trapped deep underground and only reached the surface recently.

Either way, they maintained, it could indicate life evolved on Mars at some point and that Earth is not unique in developing it.

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