A large Martian crater that once featured running water and now has a three-mile high mountain in the middle of it was selected as the landing site for the Mars Science Laboratory rover Curiosity, NASA officials said Friday.

The long-debated decision was based on the wide range of features the rover can explore in Gale Crater — ranging from a fan that was likely once a river delta, to layers of clay and additional areas where minerals were created in the presence of water.

In addition, the rover — which can travel as far as 14 miles — will explore what may well have once been a river gorge like the Grand Canyon and will climb hundreds of yards up the central mountain.

“At Gale, we’ll be able to see a long history of ancient Martian environments,” said Dawn Sumner of the University of California at Davis and co-chair of the committee that selected Gale Crater out of 160 other possible sites. “It has so many environments that could once have been habitable.”

The Mars rover, which is scheduled to launch in November, was described Friday as the first astrobiology mission to Mars since the Viking landers went there in 1976.

While the mission is not designed to look for life, per se, the 10 major instruments on the rover will search for the kind of organic material needed for life as we know it, and will assess whether Mars once had features that made it “habitable.” It will also try to determine if the makeup of the planet would allow for remnants of ancient life to be preserved.

Although the surface of Mars is now very cold and dry, NASA and European missions over the past decade have collected information that strongly suggest the planet was once wet and considerably warmer. These findings have led scientists to conclude that Mars may once have supported life, and that remnant microbes may still be alive deep below the surface.

The Mars Science Lab, with its rover the size of a small car, is scheduled to land on Mars in August 2012. Twice as long and five times heavier than any previous Mars rover, and considerably more sophisticated , it will be placed down using a unique method. With its mother spacecraft hovering over the surface, the rover will be lowered with the help of straps that will allow for a soft landing.

The announcement was made at the Smithsonian’s National Air and Space Museum on the occasion of its annual “Mars Day,” but the timing could not have been better for NASA. With the final landing of a space shuttle Thursday, many have doubted the agency’s plans for an innovative future. As several speakers remarked, the Mars Science Laboratory shows that NASA is continuing to conduct dramatic and scientifically important missions.

In further explaining their decision, mission project scientist John Grotzinger of the California Institute of Technology said: “One fascination with Gale is that it’s a huge crater sitting in a very-low-elevation position on Mars, and we all know that water runs downhill.”

“Follow the water” has long been NASA’s motto for Mars exploration because water is seen as essential for life. The rover will also have instruments that can test for organic carbon — which is also present in all life as we know it. But even finding ancient organic carbon on Earth is difficult, so the scientists were cautious in their predictions.

“Gale gives us attractive possibilities for finding organics, but that is still a long shot,” said Michael Meyer, lead scientist for NASA’s Mars Exploration Program at agency headquarters.

“What adds to Gale’s appeal is that, organics or not, the site holds a diversity of features and layers for investigating changing environmental conditions, some of which could inform a broader understanding of habitability on ancient Mars,” he said.

When the Viking missions flew to Mars 35 years ago, their mission controllers had to search for a landing site as they approached because NASA didn’t have the satellite capability to map out and really understand the Martian surface. Now it does, and the scientists today said all four of the finalists as landing sites were approved by engineers as suitable.

The Viking missions went to Mars with great anticipation that life would be found, and some early tests appeared to support that hypothesis. Over time, however, the Viking team generally concluded they had not detected life, although the principle investigator of one of the experiments has fought ever since to convince his colleagues that microbial life had indeed been detected.

The upcoming mission will not be directly testing for life, but rather for signs that life could have once existed on Mars.

The rover Curiosity and other pars of the MSL spacecraft are undergoing final testing. The mission is targeted to launch from Cape Canaveral between Nov. 25 and Dec. 18.