Magnetospheric effects on micrometeoroid fluxes

The planets, and their moons and rings, are bombarded by a population of interplanetary and interstellar micrometeoroids. This bombardment affects the evolution of planetary rings and electron densities in ionospheres. It also generates and overturns regolith on planetary satellites and ring particles. The impacting flux is enhanced by the planet's gravity, but the magnetosphere can also affect the flux for micrometeoroids near 1 mu m in radius. We present calculations for micrometeoroids hitting Jupiter which show the magnetosphere shields the planet from impactors smaller than about 0.1 mu m in radius, and enhances the flux of impactors by a factor of up to about 4 for grains near 0.5 mu m in radius. Thus, in addition to the gravitational focusing factor, there is a size-dependent electromagnetic focusing factor active up to about 1.0 mu m. In addition, we find that after 1 (Earth) year, significant numbers of small particles still orbit Jupiter. The fate of these particles may represent an additional enhancement of the flux of micrometeoroids onto the planet.