Multi-fluid Ten-Moment and Fully Kinetic Modeling of Ganymede's magnetosphere: A Comparative Study

In many magnetospheric processes, non-ideal effects beyond the single-fluid magnetohydrodynamics (MHD) scope are likely to play important roles. For example, in small systems, like Mercury and Ganymede, particle gyroradii are no longer negligible compared to the system variability scale. This introduces nontrivial temporal variations and spatial asymmetries to plasma transport. Such Finite Larmor Radius (FLR) effects, along with the Hall effect, etc., might also be important in other processes, particularly magnetospheric magnetic reconnection, at least locally. Thus it is of high interest to understand the roles of kinetic effects in the global modeling of magnetosphere systems. In this study, we model Ganymede's magnetosphere using two methods: i) the fully kinetic particle-in-cell (PIC) method ii) the multi-fluid ten-moment (10-moment) method. The former retains all kinetic effects but can be prohibitively expensive for full magnetosphere modeling. The latter only retains effects like the FLR effects, the Hall effect, etc., but is computationally more affordable and realistic for continuous modeling of the entire magnetosphere. We will compare the simulation results regarding 1) Reconnection physics, the Flux Transfer Event (FTE) occurrence; 2) Closure of Field-Aligned Current (FAC) system; 3) Plasma entry and circulation patterns; 4) Waves and instabilities in the upstream region due to the subsonic inflow condition; 5) Induction effect due to the electrical conductivity structure within Ganymede. As another comparison study, we will compare Ganymede results and our previously reported Mercury simulation results. We will focus on the similarities and discrepancies introduced by the drastically different upstream conditions and sizes of the magnetosphere, etc. The simulation codes used are VPIC (for PIC) and Gkeyll (for 10-moment).