Images suggest water flow on Mars

Liquid water appears to have flowed on Mars within the last seven years, a group of scientists announced yesterday, offering the most tantalizing evidence yet that the planet may be hospitable to life today.

By examining 240,000 photographs snapped by NASA's Mars Global Surveyor satellite since 1999, scientists at Malin Space Science Systems in California discovered debris on two crater walls that appeared to have been left behind by water pouring down them, possibly squirting out from an underground source.

The scientists said the shapes of the deposits are what they would expect to see if sediments were carried by flowing water equivalent to the contents of up to 10 swimming pools. The results were published in the journal Science yesterday.

At a news conference yesterday at NASA headquarters in Washington, D.C., the scientists showed a set of before and after images that documented the emergence of the bright deposits. Pictures taken in 1999 and 2001 showed no debris on the two craters' walls, but images retaken in 2004 and 2005 showed new surface gullies.

"This really opens up the looking for life on another planet," said Jennifer Heldmann, a planetary scientist at NASA's Ames Research Center who was not involved in the study. Scientists believe that liquid water is necessary for life on Mars. The results also hold great significance for US plans to send astronauts to the Red Planet one day. If there is water below the surface, astronauts could possibly tap it.

Until now, there has been no recent evidence of liquid water on the planet. Large volumes of water from millions of years ago appear to have left deltas, shorelines, and evidence of once-drenched rocks.

Researchers have discovered tiny amounts of water vapor in the planet's thin atmosphere and ice at its poles. But while they hypothesized there might be water below the surface, they had little evidence for it.

The scientists said they were intrigued by the bright color of the gullies. Most disturbances on Mars's surface, from rover wheels to meteor craters, leave dark marks behind.

Michael Malin, the report's lead author and principal investigator of the satellite's camera, suggested that water broke out of an underground source and carried debris down the crater wall for less than a mile before freezing or evaporating. He and his team suspect the bright remnants are frost or a salt crust made after the water concentrated salts in surface minerals.

Still, the scientists said, there are a slew of vexing questions about the deposits that they need to study further.

This discovery "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," said Malin. "Future missions may provide the answers."

Other scientists said they were amazed by the scientists' ability to capture such short-term geological events far from Earth. Most planetary science is viewed in the context of million - or even billion - year time frames. To be able to view an event shortly after it happens can help scientists more clearly understand it.

"Any time you can catch a process in the act, it really helps to clarify what is going on," said John Mustard, associate professor of geological sciences at Brown University.

In many ways, the announcement was a fitting good bye for the Mars Global Surveyor, which lost contact with scientists Nov. 2 after being launched 10 years ago. They believe it may be gone for good.

A new orbiter called the Mars Reconnaissance Orbiter, which has far better resolution and ability to examine the planet, slipped into Martian orbit in March. The scientists said yesterday they hoped the new satellite would further study the gullies.

Beth Daley can be reached at bdaley@globe.com.