The plasma density distribution in the inner region of Saturn's magnetosphere

Abstract

Electron density measurements derived from the upper hybrid resonance frequency have been obtained from the Cassini Radio and Plasma Wave Science experiment over a 7 year period from 28 October 2004 through 7 November 2011. Additional density measurements inside the orbit of Enceladus and outside the orbit of Rhea have made it possible to expand a previously published density model to radial distances from 2.6 to 10.0 Saturnian radii (R_S). The distribution of density data is compared to a simple scale height density model for a single-species plasma within 8° of the magnetic equatorial plane. There is a broad peak in the equatorial density distribution between 4 R_S and 5 R_S with the plasma falling off both inward and outward from the peak region. The radial dependence of the equatorial density profile varies as R^4.0 from 2.6 R_S to 4 R_S and as R^-4.8 from 5 R_S to 10 R_S. The plasma distribution outside 5 R_S remains consistent with earlier density models but additional density measurements inside 4 R_S provide information on the plasma distribution in this inner region that will be the focus of the F-Ring and proximal orbits near the end of the Cassini mission.