NASA shows new evidence of water on Mars - San Francisco Chronicle

Scientists have detected the first clear signs that water may be flowing on Mars right now, apparently coursing down thousands of slopes inside one of the planet's younger craters.

The water - if it is water - appears to be extremely salty and is running inside narrow channels along the inner walls of a small crater called Newton that lies in the planet's southern hemisphere.

The new evidence comes from extremely high-resolution images taken by a powerful camera called HiRISE aboard NASA's Mars Reconnaissance Orbiter, which has been orbiting the planet for five years.

Rapid successions of images sent by the orbiter show long dark streaks somewhat like fingers starting late every Martian spring at rocky outcrops inside the crater's walls facing the planet's equator. The dark features run within narrow channels called lineae - 18 inches to 15 feet wide - for hundreds of yards. They lengthen at up to 60 feet a day during full summer until they fade away in the winter.

The HiRISE scientists have detected as many 1,000 of the possible watercourses at 39 separate sites, they say.

"This is the most compelling evidence yet for liquid water on Mars; it's not proof, but it's compelling," said Scott Murchie, a physicist at Johns Hopkins University's Applied Physics Laboratory and a scientist on the orbiter team.

"It's the best evidence of water flowing on Mars to date," said Philip Christensen of Arizona State University, who led a team gathering images transmitted by an earlier orbiter called Mars Global Surveyor that operated for a decade until its transmissions ended five years ago.

A detailed paper on the Orbiter's findings appears today in the journal Science.

"We haven't found any good way to explain what we're seeing without water," said lead author Alfred McEwan of the University of Arizona during a press briefing Thursday.

A lower-resolution instrument aboard the orbiter called CRISM - Compact Reconnaissance Imaging Spectrometer for Mars - so far has not seen any sign of what the HiRISE team is reporting, said Murchie.

There has already been overwhelming evidence that water was abundant on Mars millions of years ago. One sign is the deep Martian canyons that only water could have carved; another is the broad and sinuous surface webs that could only have been river beds once upon a time.

The Mars rovers Opportunity and Spirit have identified all kinds of chemicals in rocks and rounded pebbles on the planet's surface that on Earth are only formed in water.

The Orbiter scientists reason that any water on Mars today must be extremely salty - a kind of brine - because normal water would freeze solid permanently at Martian winter temperatures.

But salts can lower the freezing point of water so brines remain liquid even at the lowest temperatures recorded during Martian winters. There are plenty of salts like chlorides and sulfates in rocks and sandy plains all over the planet's surface.

E-mail David Perlman at dperlman@sfchronicle.com.

This article appeared on page A - 11 of the San Francisco Chronicle