This blink comparison documents very slight forward movement of NASA's Mars Exploration Rover Spirit during a drive on the rover's 2,090th Martian day, or sol (Nov. 19, 2009).

The two wide-angle views are from the right-side eye of Spirit's front hazard-avoidance camera, one taken on Sol 2088 (Nov. 17) and the other after the drive on Sol 2090. 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 on the "before" (Sol 2088) image than on the "after" (Sol 2090) image.

In the "after" image, Spirit's left-front wheel has become slightly less buried in the soft soil in which the rover had become embedded about six months ago. The right-front wheel, which has not been usable for driving since 2006, has been pushed perceptibly forward by the drive. The amount of forward motion is less than one percent of the distance that would have been covered on firm ground by the amount of wheel rotation commanded in the drive.

The Sol 2090 drive was the second drive commanded after the rover team spent months using Earthbound testing and analysis to develop a strategy for attempting to drive Spirit out of this soft-soil site, called "Troy." Extrication drives are expected to make slow, if any, progress in coming weeks, and the probability of success in escaping from Troy is uncertain.