Operators of NASA's Mars Exploration Rover Opportunity have determined that a proposed route eastward out of "Endurance Crater" is not passable, so the rover will backtrack to leave the crater by a southward route, perhaps by retracing its entry path.

Opportunity captured this view from the base of "Burns Cliff" during the rover's 280th martian day (Nov. 6). This cliff in the inner wall of "Endurance Crater" displays multiple layers of bedrock for the rover to examine with its panoramic camera and miniature thermal emission spectrometer. The rover team has decided that the farthest Opportunity can safely advance along the base of the cliff is close to the squarish white rock near the center of this image. Credit: NASA/JPL Download a larger version here

"We've done a careful analysis of the ground in front of Opportunity and decided to turn around," said Jim Erickson, rover project manager at NASA's Jet Propulsion Laboratory, Pasadena, Calif. "To the right, the slope is too steep -- more than 30 degrees. To the left, there are sandy areas we can't be sure we could get across."

Before turning around, Opportunity will spend a few days examining the rock layers in scarp about 10 meters (33 feet) high, dubbed "Burns Cliff." From its location at the western foot of the cliff, the rover will use its panoramic camera and miniature thermal emission spectrometer to collect information from which scientists hope to determine whether some of the layers were deposited by wind, rather than by water. The rover will not reach an area about 15 meters (50 feet) farther east where two layers at different angles meet at the base of the cliff.

"We have pushed the vehicle right to the edge of its capabilities, and we've finally reached a spot where we may be able to answer questions we've been asking about this site for months," said Dr. Steve Squyres, rover principal investigator at Cornell University, Ithaca, N.Y. "But after we're done here, it'll be time to turn around. Going any farther could cut off our line of retreat from the crater, and that's not something anybody on the team wants to do."

Opportunity entered the stadium-size crater on June 8 at a site called "Karatepe" along the crater's southern rim. Inside the crater, it has found and examined multiple layers of rocks that show evidence of a wet environment in the area's distant past.

Opportunity and its twin, Spirit, successfully completed their primary three-month missions on Mars in April. NASA has extended their missions twice, most recently on Oct. 1, because the rovers have remained in good condition to continue exploring Mars longer than anticipated.

Engineers have finished troubleshooting an indication of a problem with steering brakes on Spirit. The brakes are designed to keep the rover wheels from being bumped off course while driving. Spirit has intermittently sent information in recent weeks that the brakes on two wheels were not releasing properly when the rover received commands to set a new course. Testing and analysis indicate that the mechanism for detecting whether the brakes are released is probably sending a false indication. The rover team will disregard that signal and presume the brakes have actually released properly when commanded to do so. This anomaly has not been observed on the Opportunity rover.

"We're going back to using the full steering capabilities of Spirit," Erickson said.

JPL, a division of the California Institute of Technology in Pasadena, manages the Mars Exploration Rover project for NASA's Science Mission Directorate, Washington, D.C.