THE strongest evidence yet that life could exist on Mars has been discovered by scientists, in the form of a sea of ice near the planet’s equator.

The ice sheet detected by the European Mars Express spacecraft appears to have bubbled up from a subterranean aquatic layer, which researchers believe may harbour the right conditions for primitive microbes to have evolved.

As the frozen sea is certainly of geologically recent origin, the find makes it more probable than ever that any life that might once have emerged on the Red Planet could still survive there.

Any such lifeforms would be microscopic creatures, similar to bacteria. They would have been brought to the surface by the geyser-like spring that burst through fissures in the rock to form the ice sea in the Elysium region, and could be preserved there.

The findings, which are published today in the journal Nature, suggest that Elysium is the best place on Mars where scientists might look for evidence for life, and mark it out as an early candidate site for the next landings planned by the European Space Agency and Nasa.

John Murray, of the Open University, one of the leaders of the high-resolution stereo camera team that made the discovery, said he had been happy to believe that traces of past life might have been found in the rocks on Mars, although he would not have imagined finding life there. “But it’s a possibility now,” he added.

“If there are organisms, we will be looking at the organisms themselves, rather than fossils. Europe is sending the ExoMars lander in 2011 and Nasa the Mars Science Laboratory at about the same time. I would say Elysium is by far the most likely place for finding life on Mars, and that’s where we should be going.

“I would never have thought it possible before that life could exist today, and now I believe it is very possible.”

The frozen sea measures about 560 miles (900km) by 500 miles, and was formed approximately five million years ago.

Water from a liquid layer between four and six miles beneath the surface is thought to have erupted through a fault in the rock 125 miles away and spilled on to the planet’s surface.

The high pressure of the water prevented it from freezing instantly, but allowed it to flow over this large area and form the sea before it became ice.

“It’s like opening a bottle of champagne,” Professor Murray said. “The water is under enormous pressure, with millions of tonnes of rock on top. It should freeze when it comes out, but it doesn’t have time to freeze immediately because of the high pressure, so much of it, the vast majority, remains as liquid that settles flat and freezes slowly.”

Many important prerequisites for life — liquid water, carbon and a heat source from volcanic activity — are known to have existed on Mars either now or in the past. Professor Murray said that the sea’s relatively young age also made it much more likely that any organisms that did evolve might survive.

If the Elysium region does harbour life, it could explain high levels of methane detected there by another Mars Express instrument, the planetary Fourier spectrometer. Methane can be generated either by living things or by volcanic activity.

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