Mars had water to support life, Nasa reveals

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Water once drenched the surface of Mars and would have provided the conditions necessary for the evolution of life, scientists at the American space agency Nasa announced last night.

Nasa's robotic rover Opportunity had found the most convincing evidence yet that the Red Planet was once a water-filled world on which life could have thrived, they said after keeping details of the findings a closely guarded secret until a press conference yesterday at Nasa headquarters in Washington. Opportunity, a six-wheeled vehicle the size of a golf buggy, has been exploring a large plain on Mars called Meridiani Planum, which was thought to have been the bed of a huge lake or ocean. In geological terms this would be the best place to search for signs of sedimentary rocks formed by the deposition of material in water.

Nasa scientists, led by the principal investigator, Steven Squyres of Cornell University, said that the Nasa team had found four interlinking pieces of evidence to point to the past presence of water on Mars. "It's hard to avoid the conclusion that water once flowed on Mars," he said.

There is evidence that the Martian rocks were modified as well as being laid down by large bodies of water flowing over the surface over many years. "We think for some considerable time it was a habitable environment," Dr Squyres said.

The Opportunity has for the past few days taken trips out across the plain investigating rocky outcrops that are known to be rich in a mineral called haematite, which could have formed as a result of interaction with oxygen and water.

A microscope on board the rover has also taken pictures of strange spherical objects about the size of small ball bearings embedded in the soil. Scientists had speculated that they could also have formed as a result of interacting with liquid water. Dr Squyres said yesterday that the spherical objects - which have been nicknamed blueberries - were most likely formed by crystals growing in a watery solution.

Both Opportunity and its sister rover Spirit, which landed on the far side of Mars, have also come across a strange "clumpiness" or stickiness in the soil. This could indicate that it contains a mix of concentrated salt in a brine-like solution of water.

Such a salt-laden solution could in theory act as an anti-freeze against the cold temperatures of the Martian night, which at the equator can plunge to below -50C, keeping the water in a liquid state.

Nasa commentators said there had been a "palpable buzz" among scientists at the Jet Propulsion Laboratory in Pasedena, California, where the results have been analysed over the past few days.

Don Savage, a Nasa spokesman, told the Space.Com website before last night's press conference: "It's going to be the most significant science results that we've had from the rovers, and it's bearing on their primary mission [of seeking water]."

The Spirit landed on 4 January in the Gusev Crater, which may once have contained a large lake, and Opportunity landed on 25 January. Both are equipped with cameras, microscopes, spectrometers and other tools for analysing rocks and soil and transmiting the data back to Earth.

Although several missions to Mars have found evidence of frozen water at the poles, and some have hinted at the presence of liquid water, none had provided unequivocal proof of life's most vital ingredient.

* A European mission to land a probe on a comet finally blasted off yesterday from Kourou in French Guiana on board an Ariane-5 launcher, five days late for its 10-year mission. The €1 billion Rosetta mission is due to rendezvous with the comet 67P/ Churymov-Gerasimenko. That will not happen until May 2014. Before that the probe will take a wandering route around the solar system, passing Earth once more and Mars three times.