Photos show evidence of recent water on Mars

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Photos show evidence of recent water on Mars
POSTED: 1:25 p.m. EST, December 6, 2006

Story Highlights• Photos suggests liquid water flowed on Mars as recently as several years ago
• Strongest evidence yet that water even now sometimes flows on red planet
• Scientists: Images of gullies and trenches carved by fast-moving water
• NASA lost contact with Mars probe last month
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LOS ANGELES, California (AP) -- A provocative new study of photographs taken from orbit suggests that liquid water flowed on the surface of Mars as recently as several years ago, raising the possibility that the red planet could harbor an environment favorable to life.

The crisp images taken by the Mars Global Surveyor do not directly show water. Rather, they show apparently recent changes in surface features that provide the strongest evidence yet that water even now sometimes flows on the dusty, frigid world. Water and a stable heat source are considered keys for life to emerge.

Until now, the question of liquid water has focused on ancient Mars, and on the Martian north pole, where water ice has been detected. Scientists have long noted Martian features that appear to have been scoured by water or look like shorelines, and have tried to prove that the red planet had liquid water eons ago.

"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."

The new findings were published Wednesday in the journal Science and NASA scheduled a news conference for Wednesday afternoon to announce the results.

Oded Aharonson, an assistant professor of planetary science at the California Institute of Technology, said that while the interpretation of recent water activity on Mars was "compelling," it's just one possible explanation. Aharonson said further study is needed to determine whether the deposit could have been left there by the flow of dust rather than water.

The latest research emerged when the Global Surveyor spotted gullies and trenches that scientists believed were geologically young and carved by fast-moving water coursing down cliffs and steep crater walls.

Scientists at the San Diego-based Malin Space Science Systems, who operate a camera aboard the spacecraft, decided to retake photos of thousands of gullies in search of evidence of recent water activity.

Two gullies that were originally photographed in 1999 and 2001 and re-imaged in 2004 and 2005 showed changes consistent with water flowing down the crater walls, according to the study.

In both cases, scientists found bright, light-colored deposits in the gullies that weren't present in the original photos. They concluded the deposits -- possibly mud, salt or frost -- were left there when water recently cascaded through the channels.

The Global Surveyor, managed by NASA's Jet Propulsion Laboratory, abruptly lost radio contact with Earth last month. Attempts to locate the spacecraft, which has mapped Mars since 1996, have failed and scientists fear it is unusable. (Full story)

NASA's durable Mars rovers have sent scientists strong evidence that the planet once had liquid water at or near the surface, based on observations of alterations in ancient rocks.

"We're now realizing Mars is more active than we previously thought and that the mid-latitude section seems to be where all the action is," said Arizona State University scientist Phil Christensen, who was not part of the current research.

Mars formed more than 4.5 billion years ago and scientists generally believe it went through an early wet and warm era that ended after 1.5 billion to 2.5 billion years, leaving the planet extremely dry and cold.

Water cannot remain a liquid for long because of subzero surface temperatures and low atmospheric pressure that would turn water into ice or gas.

But some studies have pointed to the possibility of liquid water flowing briefly on the surface through a possible underground water source that periodically shoots up like an aquifer.