Small spherical objects fill the field in this mosaic combining four images from the Microscopic Imager on NASA's Mars Exploration Rover Opportunity. The view covers an area about 2.4 inches (6 centimeters) across, at an outcrop called "Kirkwood" in the Cape York segment of the western rim of Endeavour Crater. The individual spherules are up to about 0.125 inch (3 millimeters) in diameter. // Image credit: NASA/JPL-Caltech/Cornell Univ./ USGS/Modesto Junior College