Tenuous Ring of Captured Dust at Saturn

We use numerical simulations to predict the existence of a faint ring of dust particles in retrograde orbits about Saturn. Small dust particles, less than 300 nm in radius, on orbits with low eccentricity and small inclinations are captured from the interplanetary medium. The code uses the Z3 model for the magnetic field and plasma parameters provided by Richardson [1995]. It includes solar radiation pressure, planetary oblateness, and sputtering of the dust grains in the magnetosphere. We conduct both long and short term integrations to study the ring. Short term integrations show that the ratio of retrograde to prograde captured particles is around 2:1 and that the capture efficiency for particles with sizes between 5 and 300 nm is ≈ 0.7 %. Long term integrations are used to calculate the equilibrium dust distribution orbiting Saturn. Particles are injected into the system at a steady rate and the simulations continue until an equilibrium number of dust particles has been reached. The major loss mechanism is through ejection from the system by the corotational electric field. This typically occurs when the grain has sputtered down to 50 nm. The predicted ring has a peak density of ≈ 3 x 10^-18 cm^-3 and extends from just outside the main ring to about 12 planetary radii (R_S) and is ≈ 3 R_S thick at its widest point. These predictions will be verified by the Cassini spacecraft?s dust detector.