Plumes of methane in the atmosphere of Mars provide evidence of the possible existence of microbes living below the Martian surface that produce the gas as some do on Earth, US scientists said on Thursday.

The methane likely was produced either by water reacting with hot rock below the surface or by living microorganisms as a waste product, they said during a NASA news briefing. The scientists said the evidence does not suggest the methane was brought to Mars by an object like a comet.

"This is exciting because we have evidence that we need to think about in terms of the possibilities of life on Mars," Indiana University scientist Lisa Pratt said.

"It's prudent that we begin to explore Mars looking for the possibility of a life form that's exhaling methane."

Scientists have been eager to determine whether Mars, the fourth planet from the sun and Earth's neighbor, had conditions in the past or present to support life. The new observations, made by using telescopes in Hawaii, did not directly detect life but found tantalizing evidence suggesting it was possible.

The scientists said if methane is coming from microbes, they likely live far below the frigid surface at depths warm enough for liquid water to exist. Liquid water is considered one of the essential ingredients for life. Water is known to exist on Mars. Robot rovers have sampled ice from the surface.

The scientists found substantial plumes of methane in the northern hemisphere of Mars in 2003 and called it the first definitive detection of the gas on the Red Planet.

'A very large amount'

Michael Mumma of NASA's Goddard Space Flight Center in Greenbelt, Maryland, said there were three regions slowly releasing "a very large amount" of methane. The regions all showed evidence of ancient ground ice or flowing water.

There was no sign of gases expected if methane was produced by volcanoes, particularly sulfur dioxide, Mumma said.

In mid-summer, methane is being released there at a rate similar to that of a massive hydrocarbon seep at Coal Oil Point in Santa Barbara, California, Mumma said.

Living organisms release much of Earth's methane as they digest nutrients, but strictly geological processes such as oxidation of iron also yield the gas.

Michael Meyer, lead scientist for NASA's Mars program, said the methane indicates "that Mars is active. Now, whether or not it's because of geology or biology or both, we don't know."

Methane is composed of four atoms of hydrogen bound to a carbon atom, and is the main component of natural gas.

On Earth, methane is known as swamp gas and made by decaying plants or found in the burps, belches and other emissions of animals from termites to cattle and people.

Agencies

(China Daily 01/17/2009 page11)