“Phobos events”: signatures of solar wind dust interaction

In 1989, during its first three elliptical orbits around Mars, the Phobos-2 spacecraft observed significant plasma and magnetic field perturbations near the crossings of the orbit of the Martian moon Phobos. They are commonly considered as indirect evidence for the presence of a dust torus along the Phobos orbit, first predicted by Sloter (CRSR 462, 1971), but not yet observed directly. It is the purpose of this paper to test this hypothesis. To this end, the solar wind interaction with a charged dust column is studied on the basis of a Hall-MHD/fully kinetic plasma description, and the results are compared with observations. The events are suggested to be the signatures of crossings of a fast magnetosonic/whistler Mach cone originating from a dust obstacle with a disk-like cross-section. To reproduce typical features of the observed perturbations, a shift of the obstacle centre from the Phobos orbit radially outwards by about 1000 km and a peak charge density of at least of the order of the solar wind density are required.