Close-Up of 'Cheyenne'

As NASA's Mars Exploration Rover Opportunity is traversing southward toward "Victoria Crater," it is periodically stopping to characterize exposed bedrock, using the contact instrument suite on the robotic arm. Between Martian days (sols) 818 and 821 of the mission (May 13 to May 16), one such characterization was carried out on a rock target called "Cheyenne." The target was brushed by the rock abrasion tool, analyzed by the alpha particle X-ray spectrometer and Moessbauer spectrometer, and photographed by the microscopic imager.

This image is a mosaic of four frames taken by the microscopic imager after the brush had removed dust and sand grains from most of the area shown, exposing the underlying bedrock. The resolution is 30 microns per pixel and the entire mosaic is 6 centimeters (2.4 inches) square. Opportunity acquired the images on Sol 819 (May 14, 2006) while the target was fully shadowed.

This rock surface exhibits relatively small spherical concretions compared to those observed in the vicinity of "Eagle Crater" and "Endurance Crater." Such small concretions, and in places apparent absence of concretions, have characterized the outcrops south of "Vostok Crater." Also visible in this image are small pits and grooves in the rock surface, including narrow, elongated void spaces different from any previously observed by Opportunity. Crystal-shaped and elongated void spaces that were seen in the vicinity of Eagle and Endurance Craters are interpreted as spaces left by dissolving of soluble salts. However, these features at Cheyenne have a significantly different appearance and the science team is considering a number of alternative hypotheses for their origin.