We study the interaction between the Moon and the solar wind using a three-dimensional hybrid plasma solver. The proton fluxes and electromagnetical fields are presented for typical solar wind conditions with different magnetic field directions. We find two different wake structures for an interplanetary magnetic field that is perpendicular to the solar wind flow, and for one that is parallell to the flow. The wake for intermediate magnetic field directions will be a mix of these two extreme conditions. Several features are consistent with a fluid interaction, e.g., the presence of a rarefaction cone, and an increased magnetic field in the wake. There are however several kinetic features of the interaction. We find kinks in the magnetic field at the wake boundary. There are also density and magnetic field variations in the far wake, maybe from an ion beam instability related to the wake refill. The results are compared to observations by the WIND spacecraft during a wake crossing. The model magnetic field and ion velocities are in agreement with the measurements. The density and the electron temperature in the central wake are not as well captured by the model, probably from the lack of electron physics in the hybrid model.

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.

Ganymede possesses strong surface brightness asymmetries both between its polar cap and equatorial regions and between its leading and trailing hemispheres. Here we test the hypothesis that these asymmetries are due to differential Jovian plasma and energetic particle precipitation to the surface with the combination of a hybrid plasma model (kinetic ions and fluid electrons) and a particle tracing model. We describe the hybrid model, the first of its kind applied to Ganymede, and compare the results to both Galileo observations and previous MHD and MHD‐EPIC models of Ganymede. We calculate spatially resolved precipitating Jovian ion fluxes to the surface of Ganymede for energies 1 < E < 104 keV and find (1) precipitating fluxes peak near 100 keV and (2) excellent correlation between the precipitating flux and Ganymede's surface brightness variations. Thus, we conclude that precipitating energetic particle fluxes are the primary driver for altering the surface brightness of Ganymede.

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