On the density of the dust halo around Mars

This paper provides an estimate of the average number density of dust particles accumulated around Mars. As investigated earlier, submicron‐sized grains ( a < 1 μm) are perturbed by electromagnetic forces and solar radiation pressure so that they do not stay close to the Keplerian orbit of the ejecting satellite. The lifetime of these particles in the vicinity of Mars ranges from a few days to a few hundred days. Their trajectories are contained in an approximately spherical volume. For larger grains (1 μm < a ≲ 7 μm), solar radiation pressure is the major loss mechanism and these particles fill a disklike volume. The corresponding lifetime due to this perturbation ranges from a few tens of days to half a Martian year. Dust grains with a ≳ 7 μm have relatively stable orbit forming a disk/torus around Mars, and their lifetime is determined by collisions with the satellite since they stay close to its orbit. Despite the short lifetime of submicron‐sized particles and the relatively large volume which contains their trajectories, their number density is comparable with that of particles whose size is between 7 and 50 μm. This is due to the fact that submicron‐sized grains are thought to dominate the number of escaping particles. We conclude that particles with sizes a < 0.5 μm and 7 μm ≲ a ≲ 50 μm will be the most abundant in the Martian dust environment.