for National Geographic News
New images of Mars reveal a drier planet than many scientists had hoped, throwing a wet blanket over previous geologic signs of liquid water near the planet's surface.
"It has always been highly unlikely, because it would be hard to maintain liquid water [in the Martian environment]," said Alfred McEwen at the University of Arizona in Tucson.
"Now it appears even less likely."
McEwen led one of several studies on Martian geology that appear in the current issue of the journal Science.
His team's paper analyzes high-resolution images from the Mars Reconnaissance Orbiter (MRO), a NASA satellite placed into Martian orbit last year.
"The [new MRO data] will help to determine where to focus future exploration, where to send landers, and where to pursue the search for life on Mars," McEwen said.
In recent years scientists have found frozen water beneath the Martian surface and locked up in the planet's polar ice caps (see images of Mars).
But liquid water—a key ingredient for life as we know it—has proven elusive on the frigid planet.
Topographical features like gullies and ravines have offered some of the best evidence so far for recent flows of liquid water on the Martian surface.
Now MRO's latest images are casting doubt on some once-promising locales.
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