Engineers at the Jet Propulsion Laboratory in Pasadena, Calif., have been working to free NASA's Spirit rover from a soft patch of Mars soil for more than two weeks now, but progress in the struggle has been hard to come by. After a series of attempted extraction moves, Spirit has budged, but not by much. By the end of a drive on November 28, which ended prematurely when one of the rover's wheels stalled, Spirit had spun its wheels a linear distance of 9.5 meters but had moved forward only 16 millimeters. (It had also sunk five millimeters downward.)

The robotic explorer became embedded in soft soil more than seven months ago, and its operators carefully weighed escape options before commencing drive attempts on November 17. The plan is to move Spirit forward, retracing its path so as to avoid breaking new ground. (The rover had been driving backward for years because of a front wheel failure.)

Mission managers have cautioned that Spirit may never extricate itself from Troy, as the troublesome area of Mars has become known. But the rover, along with its more mobile twin Opportunity, has long outlived its original assignment. Tapped for three-month missions on the Red Planet, both Spirit and Opportunity will mark their six-year anniversaries of reaching Mars early next year.