As NASA's Mars rover Opportunity travels around the red planet, researchers are using the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) on board the Mars Reconnaissance Orbiter to guide the rover to interesting geology. This is the first time orbital mineral sensing has been used to determine where the rover should go, researchers said at the 2010 AGU Fall Meeting. The Opportunity rover is now near the edge of the 22-kilometer-wide Endeavor crater. CRISM has identified clay minerals in the region. The presence of clay minerals suggests that a less acidic, wet environment existed in the past. Some CRISM observations point to mineral clays that may be types that Opportunity has not investigated before.