Mars rover Opportunity found "strong evidence" that a salty sea once existed on the Red Planet, NASA's Jet Propulsion Laboratory (JPL) announced Tuesday.  

The finding appears to be the best evidence to date that conditions which could have supported life once existed on the now-frozen planet.

JPL announced three weeks ago that the six-wheeled rover -- which landed in a shallow crater on Mars' Meridiani Planum on Jan.24 -- had found evidence that water once "drenched" the area.

At that time, scientists presented evidence "that the rocks at Meridiani Planum had once had water seep slowly through them," said Steve Squyres of Cornell University, principal investigator for the Mars Exploration Rover project.

"What's happened since then is we have found what I believe to be strong evidence that the rocks themselves are sediments that were laid down in liquid water," Squyres said. "It's a fundamental distinction -- like the difference between the water you can draw from a well and water you can swim in."

Squyres said the evidence indicates that Opportunity "is now parked on what was once the shoreline of a salty sea on Mars."

NASA's Ed Weiler, associate administrator for space science, described the finding as a "profound discovery" that has profound implications for astro-biology.

The aim of the US$820-million mission -- which also involves a twin rover named "Spirit" -- was to determine if there ever were life-supporting conditions -- such as abundant water -- on the planet.

Scientists say that so far, neither Opportunity, nor its twin six-wheeled rover, Spirit, have found direct signs of living organisms on Mars.

US rover finds evidence of salty sea on Mars surface

US rover Opportunity has found evidence that salty sea once existed on the surface of Mars, scientists at US space agency NASA said on Tuesday.

The rover has demonstrated some rocks on Mars probably formed as deposits at the bottom of a body of gently flowing saltwater, scientists told a press conference held at NASA headquarters in Washington, DC.

"We think Opportunity is parked on what was once the shoreline of a salty sea on Mars," said Dr. Steve Squyres of Cornell University, the principal investigator for Opportunity and its twin rover Spirit.

According to Dr. John Grotzinger, a member of the rover science team, bedding patterns in some finely layered rocks at Opportunity's landing site indicated that the sand-sized grains of sediment that eventually bonded together were shaped into ripples by water at least five centimeters deep, possibly much deeper.

The water might be flowing at a speed of 10 to 50 centimeters per second, Grotzinger said.

The scientists noted that clues gathered so far by Opportunity do not tell how long or how long ago liquid water covered the area.

However, the latest discovery raised the possibility that Mars was wet and warm in history and might have supported life.

"This dramatic confirmation of standing water in Mars' history builds on a progression of discoveries about that most earthlike of alien planets," said Ed Weiler, NASA associate administrator for space science.

"This result gives us impetus to expand our ambitious program of exploring Mars to learn whether microbes have ever lived there and, ultimately, whether we can," he said.

(Xinhua News Agency March 24, 2004)