Color changes at the Viking landing sites over the course of a Mars year

Abstract

There have been significant color changes at both Viking landing sites over the past Mars year. Both sites exhibited an increase in the red to blue ratio of the soil, in addition to a loss of contrast between soil units and a general brightening. These changes are due to the accumulation of a thin layer of bright red dust from the two global dust storms that were observed over the past Mars year. The dust layer appears to be thicker and more continuous at the Viking Lander 2 site, perhaps because condensation of CO2 and H2O around soil nuclei significantly increased the probability of depositing soil particles onto the surface. Such an interpretation is consistent with the reddish tint exhibited by the condensates seen at Viking Lander 2. Generation of bright areas on Mars appears to occur by blanketing with a thin layer of bright red dust. Formation of dark areas by stripping of bright dust layers would appear to be controlled in part by the distribution of roughness elements capable of disturbing the atmospheric flow field. Such an interpretation is supported by the lander observations before the dust storm activity, which show a number of isolated bright red drifts that may be regions where material deposited during previous storms was protected from wind erosion. Finally, both aeolian erosion and deposition of material not directly connected with the global dust storms have been observed over the past Mars year. Thus aeolian processes are operative at times other than during global storms.