Red/violet contrast reversal on Mars: Significance for eolian sediments - Thomas, P.; Veverka, J. (Elsevier)
Albedo markings on Mars can exhibit reversed contrast with their surroudings when imaged in ''red'' and ''violet'' light. A complete search of Viking Orbiter images shows this phenomenon (on scales less than 300 km) is restricted to specific eolian features: intracrater deposits and wind streaks originating from the deposits. Contrast reversal is not found between features (such as lava flows of different ages) that might expose different materials without a largely eolian influence. Laboratory simulations suggest that iron oxides are the most likely materials involved in contrast reversal on the Martian surface. Red/violet contrast reversal is achieved easily (but not exclusively) between samples from which very fine particles (〈5 μm) in diameter) have been removed, and corresponding samples in which larger grains are coated by such fine particles. Substantial particle-size-dependent albedo and color viriations exist for material which can be carried in suspension on Mars (〈100 μm). Thus, all fine-grained eolian deposits on Mars need not be the same as the brighter parts of Arabia, which have colors and albedos similar to the fine (〈10 μm) component of Martian dust storms. The observed contrast reversal characteristics and colors of the intracrater dunes and related sediments can be explained readily if they are essentially free of adhering dust, as would be the case if such eolian features were subject toactive saltation.
http://dx.doi.org/10.1016/0019-1035(86)90005-9
Keywords: U