December 11, 2006

Photos Suggest Water May Still Flow on Mars, Scientists Say

By ALICIA CHANG Associated Press writer

LOS ANGELES -- For decades, scientists have scoured Mars in search of water, a basic ingredient for primitive life.

But the best clues were always tied to the ancient past when the Red Planet was warmer and wetter. On Wednesday, scientists made the startling announcement that water may still course through the frigid surface.

Crisp photographs taken by NASA's old Mars Global Surveyor before it lost contact with Earth last month do not actually show flowing water. But scientists said before and after pictures of two gullies showing feature changes provide the strongest signs yet that water flowed through them as recently as several years ago, and is perhaps doing so even now.

"This is a squirting gun for water on Mars," declared Kenneth Edgett, a scientist at San Diego-based Malin Space Science Systems, which operates a camera on the Global Surveyor, one of six spacecraft focused on Mars.

The discovery excited scientists who hunt for extraterrestrial life. If the finding is confirmed, they say, all the ingredients favorable for life on Mars are in place: liquid water and a stable heat source.

In all of its Mars exploration missions, NASA has pursued a "follow the water" strategy to determine if the planet once contained life or could support it now.

Spacecraft missions previously detected water in the forms of vapor and ice on the planet, and scientists believe ancient Mars was once awash with pools of water. But evidence of present-day bursts of liquid has been scant.

"This underscores the importance of searching for life on Mars, either present or past," said Bruce Jakosky, an astrobiologist at the University of Colorado at Boulder, who had no role in the study. "It's one more reason to think that life could be there."

Some researchers were skeptical that liquid water was responsible for the surface feature changes seen by the spacecraft. They said other materials such as sand or dust can flow like a liquid and produce similar results.

"Nothing in the images, no matter how cool they are, proves that the flows were wet, or that they were anything more exciting than avalanches of sand and dust," Allan Treiman, a geologist at the Lunar and Planetary Institute in Houston said in an e-mail.

The findings will appear in Friday's issue of the journal Science.

The Global Surveyor previously spotted tens of thousands of gullies that scientists believed were geologically young and carved by fast-moving water coursing down cliffs and steep crater walls. Scientists decided to retake photos of thousands of gullies in a search for evidence of recent water activity.

Two craters in the southern hemisphere that were originally photographed in 1999 and 2001 were examined again in 2004 and 2005, and the images yielded changes consistent with water flowing down the crater walls, according to the study.

Scientists said five to 10 pools of water rushed down the craters in each case. In both craters, scientists found bright, light- colored deposits several hundred yards long in gullies that weren't present in the original photos. They concluded that the deposits -- possibly mud, salt or frost -- were left there when water recently cascaded through.

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