Dayside/nightside asymmetry of ion densities and velocities in Saturn's inner magnetosphere

Abstract

We present Radio and Plasma Wave Science Langmuir probe measurements from 129 Cassini orbits, which show a day/night asymmetry in both ion density and ion velocity in the radial region 4-6 R_S (1 R_S = 60,268 km) from the center of Saturn. The ion densities n_i vary from an average of ∼35 cm^-3 around noon up to ∼70 cm^-3 around midnight. The ion velocities v_i,θ vary from ∼28-32 km/s at the lowest dayside values to ∼36-40 km/s at the highest nightside values. The day/night asymmetry is suggested to be due to the radiation pressure force acting on negatively charged nanometer-sized dust of the E ring. This force will introduce an extra grain and ion drift component equivalent to the force of an additional electric field of 0.1-2 mV/m for 10-50 nm sized grains.