Perched on the edge of "Endurance Crater," NASA's Mars Exploration Rover Opportunity prepares to roll all six wheels in and then back out to the rim as an engineering test to ensure that the slope and rock surface meet expectations. The rover executed the maneuver successfully and proceeded farther into the crater the following day. This image was taken by the rover's front hazard-avoidance camera during Opportunity's 133rd martian day, or sol, on June 8, 2004.