Juice Mission to Jupiter’s Icy Moons: Hybrid Model Simulations of Ganymede’s Plasma Environment

Sammanfattning

Ganymede is the only moon known to host an intrinsic magnetic field, creating a mini-magnetosphere embedded within Jupiter’s highly variable plasma environment. In the JUICE era, interpreting in-situ and remote-sensing observations requires disentangling local interaction physics from system-scale drivers. Europa Clipper, although focused on Europa habitability, will provide critical contextual measurements during its Jupiter approach, pump--down and tour phases, sampling diverse magnetospheric regions and enabling upstream--in-magnetosphere comparisons that can constrain boundary conditions for Ganymede studies. Ganymede orbits within the co-rotating plasma disk supplied by the Io plasma torus and composition is dominated by heavy ions (notably O+ and S+); particle precipitation sustains sputtering and a tenuous O2 exosphere, while magnetic shielding produces a low-density cavity and polar-cap precipitation linked to auroral emissions. This thesis runs and evaluates 3D quasi-neutral hybrid (HYB) simulations to quantify how upstream Jovian forcing and a simplified near-surface O2+ source shape heavy-ion dynamics and magnetic-field topology relevant to JUICE. A nominal reference case is compared against targeted upstream variations (background-field polarity reversal; expanded/compressed upstream states) and a small source-sensitivity sweep (no-source control; reduced source temperature). Diagnostics include total magnetic-field magnitude |B|, O+ and O2+ density distributions, bulk velocity structure, and traced magnetic field lines. The results show a robust interaction topology across scenarios: upstream field orientation primarily controls asymmetries and field-line geometry via E = -u x B, while upstream expansion/compression mainly modulates the sharpness and amplitude of signatures. The no-source run confirms that structured O+ patterns persist without local production, whereas O2+ remains near-surface and source-controlled; lowering source temperature strengthens this confinement. These findings motivate scenario selection that explicitly samples upstream field orientation and retains no-source controls when assessing source prescriptions for JUICE-era interpretation.