The E-ring Asymmetry and Saturn's Noon-to-midnight Electric Field

The E ring, the diffuse ring occupies almost the entire magnetosphere of Saturn, is populated by micron-sized ice particles originated from Enceladus. The dynamics of microscopic E ring grains are shaped by various perturbing forces, which manifest in the configuration of the ring. Cassini measurements provide three-dimensional information about the E ring structure and reveal a day-night asymmetry in both remote sensing and in situ dataset. Here we suggest that the observed asymmetry is caused by the large-scale noon-to-midnight electric field in Saturn's magnetosphere. The perturbation caused by this electric field depends on the charge-to-mass ratio of dust particles, which is a function of particle sizes. For negatively charged E ring particles, the effect of such electric field competes with the solar radiation pressure force, leading to a dichotomously distributed orbital configuration depending on particle sizes. Observational evidences and long-term E ring dynamics simulation results will be presented and compared to support the hypothesis. The effects of such electric field on the E ring particle deposition patterns on Saturn's icy moons will also be discussed.