The Dusty Plasma Disk around the Janus/Epimetheus Ring

Cassini observations have revealed that the nanometer and micrometer sized charged dust grains are playing an important role in the plasma dynamics near Enceladus and in the E ring. The Ring Grazing orbits are 20 orbits that crosses the ring plane at a distance of 2.5 RS, just outside the F ring and close to where the moons Janus and Epimetheus are orbiting. From December 2016, Cassini has conducted twenty of the ring plane crossing at distances just outside the F ring, the Dust Grazing orbits. We will show the electron, ion, and the dust number densities as well as the electron temperature from these orbits obtained by the Radio & Plasma Wave Science (RPWS) instruments onboard Cassini. The numerous ring passage observations consistently showed that the ion density becomes an order of magnitude larger than the electron density, indicating the existence of the dusty plasma at Z=±0.1RS around the equator. By comparing the electron/ion density differences and the µm sized dust density obtained by the dust impacts by the RPWS antenna we show that the dust size characteristics are different depending on the distance from the equator. On the other hand, the dominant part of the negative charges is carried by the nanometer size small grains throughout the ring.