'Recent' flowing water points to life on Mars

Scientists have found the strongest evidence yet that liquid water flows on Mars, raising the prospects that there may be simple microbial life still living on the red planet.

The US National Aeronautics and Space Administration (Nasa) said satellite photographs of craters on Mars show the unequivocal signs that water has flowed down them within the past seven years. Two photographs of the same crater, one taken in August 1999 and one taken in September 2005, show the appearance of a lightly-shaded patch that has all the hallmarks of being caused by water bubbling up from under the Martian surface and running down the 30 degree slope.

"These observations give the strongest evidence to date that water still flows occasionally on the surface of Mars," said Michael Meyer, the lead scientist for Nasa's Mars exploration programme.

The surface of Mars is too cold for water to remain liquid for long without freezing but there was always the possibility that liquid water may exist underground. Michael Malin, one of the scientists involved in the study, said the latest images support the idea of water occasionally coming out of the ground.

"The shapes of these deposits are what you would expect to see if the material were carried by flowing water," Dr Meyer said. "They have finger-like branches at the downhill end and easily diverted around small obstacles."

When Nasa announced the discovery of gullies on Mars in 2000, which it said were caused by running water, other scientists were sceptical, saying they could have been caused by downhill avalanches of dry dust. However, Professor Colin Pillinger of the Open University said last night the latest images are far more impressive than anything seen before and very strong evidence for running water. "They are on to something that is really, really significant. If you've got liquid water, and not just ice, you're starting to believe there can be life there now," he said.

The latest pictures were taken by a special high-resolution camera on board Nasa's Mars Global Surveyor, an orbiting spacecraft that took the images of the water deposits in 2004 and 2005.

Photographs show deposits that extend for several hundred metres down the inner slope of a crater caused by the impact of a massive object many years ago that could have broken open the crust enough to allow water to seep through on occasions.

Dr Malin said: "These fresh deposits suggest that at some places and times on present-day Mars, liquid water is emerging from beneath the ground and briefly flowing down the slopes. This possibility raises questions about how the water would stay melted below ground, how widespread it might be, and whether there's a below-ground wet habitat conducive to life. Future missions may provide the answers."