Hybrid simulations of jovian plasma interaction with Ganymede's magnetopause

We use a three-dimensional hybrid model of plasma (kinetic ions and charge neutralizing electron fluid) to study the dynamics of the thermal O⁺ and H⁺ ions at Ganymede's magnetopause when Ganymede is inside and outside of the jovian plasma sheet. Our kinetic simulations show that ion velocity distributions at the vicinity of the upstream magnetopause of Ganymede are highly non-Maxwellian where the dominant component of the velocity distribution is parallel to the background magnetic field (i.e., T_ll>T⊥). At the magnetopause, however, ions are substantially heated and the dominant component of the velocity distribution is perpendicular to the background magnetic field (i.e., T_ll<T⊥). We also investigate the energization of the ions interacting with the magnetopause and we find that the energy of those particles on average increases by a factor of 8 and 30 for the O⁺ and H⁺ ions, respectively. The energy of these ions is mostly within 1-100 keV for both species after interaction with the magnetopause, but a few percentage reach to 0.1-1 MeV. Our simulations show that a small fraction (<25%) of the co-rotating Jovian plasma reach the magnetopause, but among those more than 50% cross the high power density regions at the magnetopause and gain energy. Finally, we compare our simulation results with Galileo observations of Ganymede's magnetopause crossings (i.e., G8 and G28 flybys). There is an excellent agreement between our simulations and observations, particularly our simulations fully capture the size of the magnetosphere and reproduce the sharp magnetic transients at the magnetopause crossings.