TUNA Lunch Talk:

Daniel Jontof-Hutter

University of Maryland

Dynamics in Dusty Rings: Magnetic Field Effects on Orbiting Dust Grains

February 21

12:10PM, Room 230, NRAO, Edgemont Road


The optically thin, dusty ring systems around the outer planets are formed and replenished by impact debris from large ring particles or satellites. As dust grains pick up electric charges from interactions with the plasma environment and sunlight, the motions of grains ranging from micron-scale down to ions, are determined by gravity and electromagnetism.

Following launch at the local Kepler orbital speed, positively-charged dust grains for which EM and gravity are roughly comparable, are immediately unstable to either escape at high speed or collide with the planet in the equatorial plane. Negatively-charged grains remain radially stable. Some positive and negative grains are unstable to vertical perturbations, which cause dust grains to spiral up magnetic field lines to collide with the planet at high latitude. The boundaries between stable and unstable orbits depend only on the charge-to-mass ratio of a dust grain and its radial launch position. For the idealized configuration of a rotating planetary magnetic field aligned and centered with the rotation axis of the planet, a reasonable approximation at Jupiter, but especially applicable at Saturn, we conduct numerical simulations to locate these boundaries, and derive analytical expressions to explain these data, improving upon prior models to provide a complete description of the azimuthal, radial and vertical motions of highly-charged dust grains.

We then test the robustness of our analytical solutions in the idealized case described above with the higher order magnetic field terms of Jupiter's magnetic field. These cause destabilizing Lorentz resonances, which we find numerically and analytically for all charge-to-mass ratios. The resonances provide an escape mechanism for negatively-charged dust grains trapped in the Io plasma torus, the likely source of the high speed dust streams escaping from the Jupiter system.