Dust grains in planetary magnetospheres

Micrometeoroid impacts on small moons or ring particles generate dusty debris of all sizes. Grains launched from parent bodies on Kepler orbits become electrically charged due to interactions with the plasma environment and solar photons. The tenuous dusty rings are essentially collisionless systems and hence sub-micron grains, released and charged in the rotating magnetic field of their host planet, follow trajectories under the combined forces of electromagnetism and gravity. Depending on their launch distance and charge-to-mass ratio, some grains can be unstable to either radial perturbations (positively-charged grains only), or vertical perturbations (both positive and negative charges). These instabilities act on short timescales and cause grains to collide with the planet or escape in less than an orbit. [5] compiled numerical data and analytical solutions to the boundaries between stable and unstable trajectories, for the idealized case of a planet with an aligned dipolar magnetic field. The effect of a vertically offset or moderately tilted dipolar magneticfield configuration increases the class of grains that are vertically unstable, but has little effect on the short-term radial instability. We present numerical stability maps for each of the giant planets.