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Rover Perched on Mars Crater

Posted on: Saturday, 8 May 2004, 06:00 CDT

Opportunity, the robotic Mars rover, is perched on the lip of a huge Martian crater whose layered rocks could reveal millions of years of the Red Planet's history -- but descending the crater's steep sides could doom the six-wheeled vehicle.

The layers of ancient bedrock many feet thick and towering above the crater's sandy and dune-marked bottom are giving the rover team "the most spectacular view we've seen yet of the Martian surface," the mission's chief scientist, Steven Squyres, told reporters Thursday.

But before committing the rover to a perilous descent into the pit, mission planner Brian Cooper said engineers will send the rover around the crater's entire quarter-mile periphery to seek a safe slope down.

That voyage alone could take several weeks. Along the way, Squyres said, Opportunity may encounter chunks of that same bedrock, which were blasted out of the planet's interior by the impact of a crater-forming meteor or comet unknown eons ago.

The thick, horizontal layers of rock on the crater wall look very much like sandstone, perhaps laid down as "a wonderful record of water in a past salty sea," Squyres said. But they might also be layers of basalt -- a record of ancient volcanic eruptions in a region already known to be volcanic in origin, he added.

The crater has been named Endurance, after the storm-ravaged ship that explorer Ernest Shackleton took on a 1914 voyage to Antarctica.

Stippling the edge of Endurance crater, Squyres said, are rocky patches of hematite, the iron oxide mineral that on Earth typically precipitates out in water, as well as abundant clusters of the tiny round pebbles the Mars scientists call "blueberries," which may well have once formed in flowing water.

"This is all fundamentally different from anything we've seen before," Squyres told reporters during a Webcast from mission control at NASA's Jet Propulsion Laboratory in Pasadena, Calif. "But to get down in the crater we'll have to seek safe access, because it's at least a 20-degree slope, and the rover could fall over and die."

It's possible, though, that the scientific rewards of exploring the crater's bedrock layers at close range could appear so enticing that Squyres and his team might risk sending Opportunity down, even though the rover's wheels would never be able to climb back up the slippery slope's loose rocks, he said.

"I can imagine circumstances where we might balance the risks and going in with no chance of ever coming out, if the science is really worth it," he said.

But another intriguing target for Opportunity to explore now lies about 600 feet away: the spot where the rover's blazing protective heat shield fell after it detached from the plunging rover just before the Jan. 24 landing. "It dug a big hole there," Squyres said, "and we need to get a look at the sides of that hole."

On the other side of the planet in Gusev Crater, Spirit, the first Mars rover that landed Jan. 3, was faring exceedingly well Thursday, said Amy Knudsen of the Spirit science team. The vehicle is now heading toward a region called the Columbia Hills, named to honor the space shuttle Columbia's crew, which perished when its craft crashed on Feb. 1, 2003.

The terrain along the route, Knudsen said, bears "hints of horizontal structures, perhaps of glacial or lacustrine origin," meaning that the region bears the marks of an ancient glacier or an equally ancient lake. "We're finding fabulous and wonderful things," she said.

Both rovers have exceeded the three months that mission scientists originally said was the expected life of the $830 million mission, but both are proving so sturdy and productive that their scientific teams predict they will continue to function for weeks or months.

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