Saturn's E ring: A dynamical approach

Abstract

Dust particles in Saturn's faint E ring are expected to exhibit complex single‐particle dynamics. The optical depth in this region is very low; hence collective effects (dust‐dust collisions, waves, and self‐gravity) are negligible. There are four embedded moons in this ring that can serve as sources (ejecta generation via bombardment) and sinks (dust‐moon collision) of dust. Grains exposed to magnetospheric plasmas swiftly erode owing to sputtering, and because of their electrostatic charging, their motion is determined by electrodynamic forces, in addition to radiation pressure, drag, and gravity. As grains erode, their charge‐to‐mass ratio is increasing; hence the importance of electromagnetic forces steadily grows through the lifetime of a grain. The particles and fields environment plays a fundamental role in shaping the E ring. Here we present a detailed dynamical model of the motion of charged dust particles. We combine a large number of single‐particle orbits as a function of six free parameters (the radii of smallest and largest grains escaping any of the moons, the relative dust flux from each of the moons, and the exponent of the assumed power law size distribution of the grains generated in impacts onto the moons). Using a Monte Carlo approach, we determine the best combination of these parameters to match the ground‐based observations. The fit provides an excellent agreement between our computer model and several other ground‐based and spaceborne observations. The model will be tested in situ by the Cassini Cosmic Dust Analyzer instrument, due to arrive at Saturn in 2004.