Showing signs of wear after more than seven years driving across the plains of Mars, NASA's Opportunity rover is investigating a broad impact crater unlike any place ever visited on the Red Planet, effectively beginning a new mission for the celebrated robot, scientists said Thursday.

Opportunity captured this mosaic of Endeavour crater on Aug. 6. Credit: NASA/JPL-Caltech
 
"This has the potential to be the most revealing destination ever explored by Opportunity," said Dave Lavery, the mission's program executive at NASA headquarters. "This region is substantially different than anything we've seen before. We are looking at this next phase of Opportunity's exploration as a whole new mission, entering an area that is significantly different in the geologic context than anything we have seen with the rovers."

Opportunity arrived at the 13.7-mile-wide Endeavour crater in early August after a 13-mile drive since climbing out of the much smaller Victoria crater in August 2008. The three-year journey across the Martian plains stretched Opportunity's odometer to 21 miles since the rover touched down on Mars in January 2004.

Designed for a 90-day mission, Opportunity has weathered harsh winds and extreme temperatures for more than 2,700 Martian days, or sols.

Engineers battled high currents in one of the rover's wheels and minimized movements of its actuators and joints during the journey to Endeavour crater, said John Callas, the rover's project manager at the Jet Propulsion Laboratory.

"All in all, we have a very senior rover that's showing her age," Callas said. "She has some arthritis and some other issues, but generally, she's in good health, she's sleeping well at night, her cholesterol levels are excellent and so we look forward to productive scientific exploration for the period ahead."

Callas said engineers expect Opportunity will have enough electrical power to keep operating during the next Martian winter. Dust on the rover's solar panels, which is always a concern on Mars, should not prohibit continued scientific research throughout the winter, according to Callas.

Opportunity extends its robot arm to study a block of rock named Tisdale 2. Credit: NASA/JPL-Caltech
 
Since Opportunity landed in 2004, its radioisotope heaters have decayed and lost efficiency, its robot arm is locked in front of the rover, and it runs on more advanced software than at the start of its mission, making the craft "significantly different" than when it arrived on Mars, Lavery said.

"We're treating every extra day of exploration as an unexpected gift in recognition that Opportunity's mission could end at any time," Lavery said.

Steve Squyres, the rover's chief scientist from Cornell University, said Opportunity's first observations at Endeavour crater "feels like the beginning of a new mission" for the automated robot.

"It's pretty much pure exploration at this point," Squyres said.

Endeavour crater harbors older rocks than in areas visited by Opportunity so far. Instead of layered sandstone sedimentary material that coalesced on the floors of ancient Martian lakes, the impact that formed Endeavour exposed rocks that could date from the planet's early history, according to Ray Arvidson, the rover's deputy principal investigator from Washington University in St. Louis.

"We've got some strange stuff going on, but we're not really ready yet to draw any firm conclusions from it," Squyres said. "Instead, what you should think of is you're coming along with us to a brand new geologic field site."

Opportunity's first scientific subject at the new research site was named Tisdale 2, a block of rock blasted out of a smaller impact basin at the rim of Endeavour. The five-foot-wide rock showed signs of high zinc content, a feature Squyres said could be a clue that the area was once home to a hot spring or other hydrothermal activity.

This color image shows Tisdale 2, Opportunity's first research subject at Endeavour crater. Credit: NASA/JPL-Caltech/Cornell/ASU
 
"This rock has a huge amount of zinc in it, way more zinc than anything we have ever seen in any other Martian rock," Squyres said.

Opportunity's microscopic imager captured up-close views of Tisdale 2, revealing the rock is a breccia, or an agglomeration of smaller rocks that assembled during the intense heat and pressure of a meteor impact event.

Breccia-type rocks are common on the moon, but they're believed to be rare on Mars.

"The bottom line is we are seeing a rock type here that is different than anything we've ever seen before," Squyres said.

"Mars is a very complex planet, a very diverse place with lots of different things going on," Squyres said. "And we're seeing some of that diversity here."

Next up for Opportunity is to drive northeast in search of smoother bedrock to analyze with its grinding tool and other sensitive instrumentation. Then the rover could move south along the crater's rim to a more dramatic 250-foot-tall outcrop called Cape Tribulation, where satellite data indicate clay minerals may exist.

"We'll be looking for other evidence of water activity," Squyres said. "Stay tuned is basically the message."