Particle pressure, inertial force, and ring current density profiles in the magnetosphere of Saturn, based on Cassini measurements

We report initial results on the particle pressure distribution and its contribution to ring current density in the equatorial magnetosphere of Saturn, as measured by the Magnetospheric Imaging Instrument (MIMI) and the Cassini Plasma Spectrometer (CAPS) onboard the Cassini spacecraft. Data were obtained from September 2005 to May 2006, within +/- 0.5 R-S from the nominal magnetic equator in the range 6 to 15 RS. The analysis of particle and magnetic field measurements, the latter provided by the Cassini magnetometer (MAG), allows the calculation of average radial profiles for various pressure components in Saturn's magnetosphere. The radial gradient of the total particle pressure is compared to the inertial body force to determine their relative contribution to the Saturnian ring current, and an average radial profile of the azimuthal current intensity is deduced. The results show that: ( 1) Thermal pressure dominates from 6 to 9 RS, while thermal and suprathermal pressures are comparable outside 9 RS with the latter becoming larger outside 12 RS. ( 2) The plasma beta (particle/magnetic pressure) remains >= 1 outside 8 RS, maximizing (similar to 3 to similar to 10) between 11 and 14 RS. ( 3) The inertial body force and the pressure gradient are similar at 9-10 R-S, but the gradient becomes larger >= 11 R-S. ( 4) The azimuthal ring current intensity develops a maximum between approximately 8 and 12 RS, reaching values of 100-150 pA/m(2). Outside this region, it drops with radial distance faster than the 1/r rate assumed by typical disk current models even though the total current is not much different to the model results.