This blink comparison aids evaluation of a drive by NASA's Mars Exploration Rover Spirit during the rover's 2,099th Martian day, or sol (Nov. 28, 2009). A stall by the right-rear wheel ended the drive after the first 1.4 meters (4.6 feet) of wheel movement in a two-step drive that had been planned to include a totla of 5 meters (16.4 feet) of wheel movement. As anticipated, nearly all of the wheel movement was slippage.

The two wide-angle views shown one after the other in this comparison come from the right-side eye of Spirit's front hazard-avoidance camera, one taken on Sol 2095 (Nov. 24) after the last drive prior to Sol 2099, and the other taken after the drive on Sol 2099. The most obvious change is in the position of the shadow of the rover arm, a change unrelated to the rover's movement during the drive. The shadow is farther to the right in the "before" (Sol 2095) image than on the "after" (Sol 2099) image.

The view is looking northward. In the "after" image, the near face of a mound of sand in front of Spirit's left-front wheel has eroded slightly northward. Analysis of data from the drive indicates that the center of the rover moved 0.5 millimeters (0.02 inch) forward, 0.25 millimeters (0.01 inch) to the left and 0.5 millimeters (0.02 inch) downward.

The rover team began commanding extrication drives in November after months of Earthbound testing and analysis to develop a strategy for attempting to drive Spirit out of this soft-soil site, called "Troy." The extrication drives are expected to make slow, if any, progress in coming weeks, and the probability of success in escaping from Troy is uncertain.