Bright blue marks a deposit of chloride (salt) minerals in the southern highlands of Mars in this THEMIS false-color image which highlights mineral composition differences. Using THEMIS, researchers have found more than 200 such features. These deposits typically lie within topographic depressions and suggest that Mars was much wetter long ago. The black rectangle shows the outline of a closeup view in the image below.
NASA/JPL/Arizona State University/University of Hawaii