Galileo Plasma Observations of the Europa Plume: Comparison with Simulation Results

Hubble Space Telescope observations [e.g. Sparks et al., 2017] and modeling of Galileo magnetometer and wave measurements during the E12 flyby [Jia et al., 2018] have provided strong evidence for Europa plume activity in the region of thermal anomaly on Europa. The Galileo spacecraft was active at Jupiter from December 1995 to September 2003, carrying the Galileo Plasma Science Instrument (PLS), an electrostatic analyzer with three spherical-segment plates which directed energy selected particles into one of seven electron sensors or seven ion channels with field-of-views which combined to cover 80% of the 4pi-sr unit sphere. While Galileo accomplished most of its primary scientific objectives, the mission did not reach its full potential due to a failed high-gain antenna deployment, which severely limited the available bandwidth for data transmission. Consequently, the PLS was only able to collect data with high temporal and energy resolution for short periods of time, primarily during moon flybys. We have written a new analysis code to process data from the Galileo PLS instrument, in particular in this presentation we compare ion velocity derived from PLS data with MHD simulation results from Jia et al. (2018) of the Europa plasma environment with an active plume during the E12 flyby as well as results from other flybys to explore whether there is any additional evidence for plume activity.