PASADENA, Calif. - NASA is sending its Opportunity rover looping around a gaping crater rimmed with rocky cliffs that may have formed long ago in a salty extraterrestrial ocean.
Opportunity will spend the next several weeks carefully circumnavigating Endurance along a counterclockwise route and photographing its gaping interior from multiple angles.
Eventually, scientists may send the rover skidding into the crater, if they determine it's safe to do.
The crater is 430 feet across and up to 66 feet deep, its bottom carpeted in a patchwork of dunes. Walls of rock line portions of the hole, punched out by an asteroid or comet.
"There are cliffs the rover could roll off and die if we're not careful," rover driver Brian Cooper said of the route around the rim.
A newly produced panorama of the crater showed the cliffs stand 16 to 33 feet tall in places.
"It's the most spectacular view we've seen of the Martian surface, for the scientific value of it but also for the sheer beauty of it," said Cornell University astronomer Steve Squyres, the mission's main scientist.
The bulk of the bedrock is deeper below the surface, and therefore older, than a far smaller outcrop a half-mile away that Opportunity previously revealed to have formed in a wet environment suitable for life.
Scientists know the older rocks now exposed at Endurance crater are different but cannot say yet what conditions were like when they originally formed.
The now-dry region could have been permanently covered by a deep body of water, periodically flooded by a shallow swamp, capped in ice or even scattered with shifting dunes later turned to stone.
Sending Opportunity even part of the way into the crater, named for the ship that carried Ernest Shackleton's 1914 expedition to Antarctica, would enable the robotic geologist to study the rocks up close, determine their origin and learn if water played a role in its history.
But the slope and dry soil inside the crater combined could make it slippery enough to prevent the six-wheeled Opportunity from rolling back out again.
Scientists on the $835 million mission said the potential scientific payoff could justify consigning the rover to a crater it couldn't escape. Opportunity and its twin, Spirit, are expected to last at least through September.
If not, Opportunity could "toe-dip" into the crater and then roll off investigate other sites on the surrounding plains it previously studied only briefly or missed altogether.
Opportunity arrived at Endurance crater after a six-week trek from its landing site at the far smaller Eagle crater.
Both craters have given scientists glimpses below the otherwise flat terrain at the Meridiani Planum site.
Halfway around Mars, Spirit was several weeks away from a cluster of hills that could represent a scientific bonanza in its own right. The hills may have formed in an environment where water played a role, scientists said.
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