This mosaic of four frames shot by the microscopic imager on the robotic arm of NASA's Mars Exploration Rover Opportunity shows a rock target called "Esperance" after some of the rock's surface had been removed by Opportunity's rock abrasion tool, or RAT. The component images were taken on the 3,305th Martian day, or sol, of Opportunity's work on Mars (May 11, 2013). The area shown is about 2.4 inches (6 centimeters) across.