Mars rover to explore crater for more clues

— -- NASA launches the Mars rover "Curiosity" on Saturday, a daring bid to find clues that the Red Planet has the essential chemical ingredients needed for life.

Despite that goal, space agency officials behind the $2.5 billion rover, formally known as the Mars Science Laboratory, downplayed expectations that the rover's chemical sensors would detect Martians, even in the form of microbes.

"We're on the hot seat here. We don't want to promise more than we can deliver," mission scientist John Grotzinger of the California Institute of Technology in Pasadena, Calif., said at a briefing Tuesday.

Still, Grotzinger said, "I would be surprised if we didn't find something that looks like a formerly habitable environment."

Weather permitting, Curiosity will lift off Saturday at 10:02 a.m. ET aboard an Atlas V rocket on an eight-month trip to Mars.

The 1,982-pound rover is the size of a small car. It will explore the 96-mile-wide Gale Crater, which is a suspected former lake bed with a 3-mile-high mound in its center.

"Looking for signs of life on Mars has been a 40-year mission," NASA astrobiology chief Mary Voytek said as she noted the Viking lander missions of the mid-1970s.

In 2004, the rover Opportunity discovered crater layers left by water, an ingredient for life that has since been seen by other orbiters and landers.

"We're now looking for other conditions necessary for life," Voytek said.

Curiosity will explore Gale Crater's basin for the first 98 weeks of its mission, equal to a Martian year. It will examine clay layers likely left behind by a lake several billion years ago.

The rover will blast and analyze rock samples with a chemistry-sensing laser, "like an arm that can reach out 20 feet away," says David Blake of NASA's Ames Research Center in Moffett Field, Calif. A drill-equipped robot arm will deliver closer samples to the chemistry lab inside the rover for analysis.

Although only the first two years of the mission have been approved, Curiosity will roam Mars powered by a nuclear battery rated to last at least 14 years. Like previous NASA deep-space missions, the rover battery has been tested for impact in the event of a launch disaster.

Following that mission, the rover will likely ascend the 3-mile-high mound at the crater's center, moving at about a half-mile an hour on six wheels, looking for sulfur-rich sands left behind by receding lake levels. "All in one place, probably the entire early history of Mars" resides inside Gale Crater, said NASA's Ashwin Vasavada.

Some scientists held out hope for Martians. If a "creature came up and banged us on the head, we don't want to ignore it," said chemist Steven Benner of the Foundation for Applied Molecular Evolution in Gainesville, Fla., who spoke at the NASA rover briefing on Tuesday.

"But that is pretty far down on the likely list."