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Thursday, February 15, 2007

More evidence of water on Planet Mars

Life in Mars New images of a craggy, fissure-filled canyon on Mars provide evidence of long-term underground water flows that may have provided a suitable environment for microbial life, scientists said.

''If there are any sort of fossils, these would be good places to look,'' the University of Arizona's Chris Okubo said in a telephone interview yesterday.

While previous NASA probes have found evidence of past and even present-day water on Mars, scientists previously had few clues if the water existed long enough for life to evolve.

The new findings show light-colored features cutting across dark bands in an area known as Candor Chasma. Okubo and his colleagues believe they are looking at places where rock has been chemically altered by water flowing across the fractures.

''Fluids apparently resided within rock long enough to allow geochemical processes to occur,'' Okubo said. ''That's typically very slow.'' In addition, the rock was once underground, providing a safe haven for any microbes from radiation and atmospheric hazards.

''These areas are very good for being an oasis for any sort of biologic activity,'' Okubo said.
Similar terrain exists on Earth, such as in the Colorado plateau.

''It was sort of surprising to see these images from Mars because it's almost exactly like what we see in the field,'' Okubo said.

Scientists say the fractures, which are several hundred yards (meters) long and about four yards (meters) wide, likely existed before any pools of water seeped underground.

''The fractures then acted as nice conduits for the fluids to flow underground, like pipes,'' Okubo said. ''What we're seeing now is an exposure of bedrock that was buried at several kilometers (miles) depth at the time the fluids were present.'' Images of Candor Chasma, one of several large canyons that are part of Mars' sprawling Valles Marineris, were taken during tests last fall of NASA's new Mars Reconnaissance Orbiter. The pictures show fractures stretching hundreds of yards (meters) across bedrock.

Similar features have been found by the Mars rover Opportunity, which currently is perched at the rim of a large crater known as Victoria Crater. Scientists are considering dispatching the rover into the crater for a closer look. The rover already has found evidence of a one-time salty shallow ocean at its landing site.

The discovery was described Friday's issue of the journal Science and at the American Association for the Advancement of Science's annual meeting in San Francisco.



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