Size distributions of circumplanetary dust

Dust rings have been observed around each of the giant planets and may also exist around Mars. The particles comprising these rings have short lifetimes due to a number of processes including exospheric and plasma drag, Poynting-Robertson drag, sputtering, collision with other circumplanetary particles, and the Lorentz force for charged grains. The supply of dust is maintained by collisions between macroscopic ring particles and bombardment of moons and ring particles by interplanetary impactors. All of the processes that act to remove or alter the circumplanetary dust grains are functions of particle size, so the initial size distribution of the grains released from an impact onto a moon or ring particle is modified. The size distribution of the impact ejecta can be described by a power-law of the form n(r)dr ∝r^?qdr where n(r)dr is the number of particles in the size range r,r + dr] and q is the power-law index. For hypervelocity impact excavation, q ≈ 3.5. Drag acts more efficiently on smaller grains resulting in a reduction in q of 1. Other dynamical processes can lead to particle-size dependent collision rates with other circumplanetary objects. These processes can lead to local steepening of the size distribution (increase in q) and to truncation of the dust size distribution to a narrow range of sizes.