Thermal ions at Saturn - Plasma parameters and implications

Abstract

Plasma data from the PLS experiment on Voyagers 1 and 2 are analyzed at the Saturn encounters. Measured ion currents are simulated using the full response function of the PLS instrument assuming plasma distributions are isotropic Maxwellians. The plasma velocity, densities, and temperatures which best simulate the observations are determined. Saturn's magnetosphere is found to subcorotate outside of L = 5.5 for Voyager 1 and L = 7 for Voyager 2. Large radial and vertical flows are observed, especially in the outer magnetosphere and on the nightside. Ion temperatures increase with L to a maximum at L = 10, outside of which they vary rapidly. A temperature anisotropy with T-perpendicular greater than T-parallel is necessary to account for the observed temperatures and densities. The ions present are H(+) and O(+); there is no evidence of heavier ions or higher charge states. Calculations of N(L-squared) show an O(+) peak at L = 10 for both encounters, indicating the major O(+) source is at L = 10.