The light and dark areas of Mars

Abstract

The origin of the light and dark areas on Mars has long been the subject of controversy, upon which the Mariner IV photographs have shed some indirect light. Evidence provided by Mariner, together with evidence from other sources, indicates that the bulk of the surface material in light areas is probably pulverized Martian crustal rock. Where this material has been exposed on the surface for long periods of time, even the tenuous Martian atmosphere is expected to produce surficial chemical weathering. A review of the various hypotheses which have been advanced to explain the origin of the dark areas indicates that both organic and nonorganic hypotheses are consistent with the observations. It is suggested that internal water might play an important role in the creation of dark areas, through either organic or nonorganic means. It appears, lacking conclusive evidence for any darkening mechanism, that still more alternative hypothesis might usefully be sought.