The inner magnetosphere of Saturn: Cassini RPWS cold plasma results from the first encounter

We present new results from the inner magnetosphere of Saturn obtained by the Radio and Plasma Wave Science (RPWS) investigation onboard Cassini around the period of the Saturn orbit injection (July 1, 2004). Plasma wave electric field emissions, voltage sweeps by the Langmuir probe (LP) and radio sounder data were used to infer the cold plasma (<100 eV) characteristics within 20 R_S of Saturn. A dense (<150 cm^-3) and cold (<7 eV) plasma torus was found just outside the visible F-ring. This torus of partly dusty plasma does not perfectly co-rotate with Saturn, which suggests the cold plasma is electro-dynamically coupled to the charged ring-dust particles. The spacecraft potential was a few volts negative above the E- and G-rings, indicating the dust-particles were likewise negatively charged. The cold ion characteristics changed near the magnetically conjugate position of Dione, indicating release of volatile material from this icy moon.