Mars: the blue planet

Parts of Mars were once drenched in water which would have made the red planet suitable for life, Nasa scientists said last night.

But the Mars rover, Opportunity, has yet to uncover any direct traces of living organisms, researchers added.

'Opportunity has landed in an area of Mars where water once drenched the surface,' Nasa chief Edward Weiler said. 'This area would have been a good, habitable environment.'

A study of rocks by the rover found evidence of sulphates and minerals which form in the presence of water.

'Nasa launched the Mars exploration mission to check whether at least one part of the planet had a persistently wet environment that could have been hospitable to life,' the agency said in a statement. 'Today, we have strong evidence for an exciting answer: Yes.' Lead scientist Steve Squyres said rock formations near the landing site showed water once flowed there, changing the rocks' chemistry and composition. 'We've been able to read the tell-tale clues the water left behind, giving us confidence,' he added.

More studies will determine if the rocks were laid down by minerals formed in a salt lake or sea.

A second member of the team said the rover had found 'an astounding amount of salt' both on the surface and in bore samples taken from rocks.

Opportunity and its twin rover, Spirit, landed one week apart in the middle of January and are controlled by a team of scientists based in California.