Thermal and Energetic Ion Dynamics in Ganymede's Magnetosphere

Abstract Ganymede is the solar system's only known moon with an intrinsic, global magnetic field. This field is strong enough to stand off the incident Jovian magnetospheric flow to form a small, complex magnetosphere around the satellite. Ganymede's magnetosphere is thought to be responsible for variable surface weathering patterns, the production of a neutral exosphere, and the generation of UV aurorae near Ganymede's open‐closed field line boundaries; however, the exact details and underlying mechanisms are poorly understood. We use results from three‐dimensional hybrid models of Ganymede's magnetosphere and a three‐dimensional particle tracing model to quantify the dynamics of thermal and energetic Jovian ions as they interact with Ganymede's magnetosphere and precipitate to the surface. We identify the formation of quasi‐trapped ionic radiation belts in the model and variable surface weathering. Most of the particle precipitation occurs in Ganymede's polar caps, yet ions also precipitate onto Ganymede's equatorial region in lesser amounts due to particle shadowing of quasi‐trapped ions in Ganymede's ionic radiation belts. Model results predict that within Jupiter's central plasma sheet, total ion fluxes to Ganymede's polar, leading, and trailing hemispheres are 50 × 10 6 , 10 × 10 6 , and 0.06 × 10 6 cm −2 · s −1 , respectively. Finally, convolution of incident ions fluxes with neutral sputtering yields for icy bodies predicts neutral sputtered fluxes in Ganymede's polar, leading, and trailing hemispheres of 1.3 × 10 9 , 4.8 × 10 8 , and 1.2 × 10 8 neutrals cm −2 · s −1 , respectively. Together, we estimate that Ganymede loses 7.5 × 10 26 neutral particles per second, or assuming a mean mass of 18 amu, approximately 23 kg/s, half that estimated for Europa.