The Role of Jupiter's Magnetospheric Plasma in Europa's Plasma Interaction

We have developed a multi-fluid MHD model for Europa's interaction with Jupiter's magnetosphere. The model self-consistently solves for the bulk properties of 3 ion fluids (magnetospheric O⁺ and ionospheric O⁺, O₂⁺), an electron fluid, and the electromagnetic fields in the vicinity of the moon. We model the magnetospheric O⁺ as a separate fluid to understand how this relatively cold component of Jupiter's magnetospheric plasma penetrates Europa's ionosphere and reaches the icy surface, where the plasma then contributes to the sputtering process that replenishes Europa's neutral atmosphere. We use Galileo magnetometer and plasma observations to constrain simulations of various Galileo flybys. Our results show that less than 20% of the upstream magnetospheric plasma reaches Europa's surface because the ionosphere acts as a partial barrier that diverts much of the cold magnetospheric plasma around the moon. We repeat our simulations while varying the column density of Europa's neutral atmosphere to assess how effectively different neutral atmospheres limit the access of cold magnetospheric plasma to Europa's surface.