This blink comparison aids evaluation of a drive by NASA's Mars Exploration Rover Spirit during the rover's 2,092nd Martian day, or sol (Nov. 21, 2009). This was the third drive commanded by the rover team in an effort to extricate Spirit from loose sand where the rover became embedded in April 2009.

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 2090 (Nov. 17) after the last drive prior to Sol 2092, and the other taken after the drive on Sol 2092. 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 left in the "before" (Sol 2090) image than on the "after" (Sol 2092) 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, and some of the material that slid down that face can be seen slumped against the front of the wheel. Spirit experienced a wheel stall with the right rear wheel during the second step of the two-step drive on Sol 2092.

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.