Permalink : http://hdl.handle.net/2115/49076

JaLCDOI : 10.14943/gbhu.75.133

We statistically investigated the ion bulk speeds in the equatorial region of the Saturn’s inner magnetosphere using the Langmuir Probe (LP) onboard the Cassini spacecraft. The LP observations showed that the ion speeds are about 60% of the ideal co-rotation speed at 5 RS and the ions have between co-rotation and Keplerian speed. Beyond 7 RS the ion speeds are spread to be a larger speed and become close to the ideal co-rotation speed. It is suggested that the sub-micron sized negatively charged E ring dust contributes to the plasma dynamics in the plasma disk. We also calculated the ion speeds using the three components MHD equations, which include the interaction with dusts to investigate the effect of the ion-dust coulomb collision and the massloadings, and the magnetosphere-ionosphere coupling. Our model shows that the ion speeds can be significantly reduced by the magnetospheric electric fields generated by the collisions between ions and dusts. It is also indicated that the coulomb and/or direct collisions between ions and dusts can be effective around Enceladus.