Particle motion on Mars inferred from the Viking Lander cameras

Abstract

The cameras of the Viking landers have uncovered several lines of evidence for fine particle mobility on the Martian surface, including particulate drifts, rock-associated raised streaks, and probable ventifacts. Inferred peak wind directions in both Chryse and Utopia are roughly the same and are consistent with peak winds inferred by orbiter photography. A 24° systematic offset between the direction of rock-associated streaks in the Viking 1 landing site and Mariner 9 and Viking observations of crater-associated streaks is consistent in both sign and magnitude with a Coriolis acceleration of particles entrained by high-velocity winds in the course of the production of crater-associated streaks. If a significant fraction of the impact energy upon collision goes into deformation, strain, and rupture, there should be a preferential destruction of the most easily saltated grains, which are here called kamikaze particles, and a depletion of 150-μm-diameter grains. Observations of fine particulates dumped on the VL-1 grid indicate that major saltation events occurred between sols 96 and 207 and were caused by winds of >50 m s−1, normalized to the top of the velocity boundary layer. This is the first observation of saltation on another planet and a rough confirmation of the usual Bagnold saltation theory applied to another planet.