Water percolating through the soil once created a friendly environment that would have been ideal for life to flourish on Mars, NASA scientists say.

It is not known how long this environment lasted or if any organisms actually developed, but scientists directing robot rovers prowling the Martian surface said on Tuesday the evidence now is clear that some rocks "were once soaked with liquid water."

"The ground would have been suitable for life," said Steve Squyres of Cornell University, the lead investigator for science instruments on the rover Opportunity. "That doesn't mean life was there. We don't know that."

Mars now is cold and dry and there is no apparent evidence of life on its barren surface.

But Squyres said chemical and geological clues gathered by Opportunity give dramatic proof that at some time in its past, liquid water coursed over the rocks and soils.

Such conditions on Earth, Squyres said at a news conference, "would be capable of supporting life.

"We believe that place on Mars for some period of time was a habitable environment," he said.

Squyres said it is not known how long the environment capable of supporting life lasted, if the water collected in surface pools or underground, and when in the long history of Mars the liquid water existed. Answers to those questions, he said, probably will require missions that scoop up Martian samples and bring them to laboratories on Earth.

NASA researchers from the Jet Propulsion Laboratory in Pasadena, California, who are guiding the exploration of Mars by Opportunity and its twin, Spirit, said the primary goal of the rover mission was to find evidence of Martian water.

That goal was accomplished, they said on Tuesday, when Opportunity used all of its instruments to study a fine, layered rock called El Capitan. The rock is embedded in the wall of the crater where the six-wheeled robot began its journey on Mars.

(Xinhua News Agency March 4, 2004)