The surface of Mars 3. Light and dark markings

The Mariner 6 and 7 pictures have provided significant clues to the nature of the light and dark markings on Mars, but do not yet provide an adequate foundation for any complete explanation of the phenomena. They display detail never before seen or photographed and demonstrate that there is no network of dark lines (i.e. canals) on the planet. A variety of shapes and of boundaries between major markings are recorded in the pictures. No substantial correlation of albedo markings with cratered or chaotic terrain has been recognized; featureless terrain conceivably may be genetically related to light areas. Within and surrounding the dark area Meridiani Sinus there is evidence of local topographic control of albedo markings; light material is found in locally low areas. Also, characteristic patterns of local albedo markings are exhibited by craters there. Aeolian transportation of light material with deposition locally in low areas is suggested as an explanation of these markings and may be useful as a working hypothesis for subsequent exploration. Across some light/dark boundaries crater morphologies are unchanged; across others craters in the light area appear smoother. If there is a relationship between cratered terrain modification and surface albedo it is an indirect one.