The Colors of Mars (3)

Color is of considerable geologic interest because it allows remote detection of chemical and mineralogical differences. Only the upper few millimeters of the surface contribute to the color and on Mars this layer may be mostly wind blown debris. The bright materials that dominate the north equatorial zone are apparently aeolian deposits. Two units have been recognized. The upper unit is discontinuous, very red, and among the brightest of materials exposed at the planet's surface. The lower unit is darker and less red. The boundary between the two is generally serrated and has no relief. In the southern e equatorial belt, the color variations are apparently related to local bedrock and not to randomly dispersed aeolian debris. The dark highland region (0° to 40° S and 60° W to 30° E) is divided into (a) dark red ancient crater rims, rugged plateaus, mostly riddled with small channels , and graben; and (b) dark "blue" volcanic flows intermediate in age, and show very few channel networks. The large volcanic constructs in the Tharsis region and volcanic centers in the southern highlands northeast of Hellas are both very dark and very red.

In this image, all three color components have received the same contrast e enhancement, which approaches saturation in the brightest areas. Because Mars is by a factor of two to three more reflective in the red than in the violet, the red component is predominant-giving the planet its classic rusty appearance. Some artifacts of the processing remain in the image, for example, diagonal streaks running from upper left to lower right.