Physical Processes on Circumplanetary Dust

Abstract

AbstractThe life cycles of grains in circumplanetary space are governed by various physical processes that alter sizes and modify orbits. Lifetimes are quite short, perhaps 102-104years for typical circumplanetary grains of 1 micron radius. Thus particles must be continually supplied to the circumplanetary complex, probably by the grinding down of larger parent bodies in collisions. Dust is eroded gradually through sublimation and through sputtering by the magnetospheric plasma but also is catastrophically destroyed through hypervelocity impacts with interplanetary micrometeoroids. Orbits evolve through momentum transfer (light drag, plasma or Coulomb drag, and atmospheric drag), and through resonant gravitational and electromagnetic forces. Plasma drag is generally the most effective evolution mechanism, with the possible exceptions of exospheric drag at Uranus and of electromagnetic schemes for some conditions. Since grains become charged (with typical electric potentials of a few volts), they undergo associated orbital perturbations: variable electromagnetic forces can cause the systematic drain of energy (orbital collapse) or, at specific (resonant) orbital locations can force large orbital inclinations/eccentricities. Solar radiation induces a periodic orbital eccentricity that can reach substantial values for 1 micron particles distant from the giant planets.