Influence of Europa’s Time-Varying Electromagnetic Environment on Energetic Ion Precipitation

We model energetic and thermal ion dynamics in the perturbed electromagnetic fields at Jupiter’s moon Europa. At the location of its orbit, Europa experiences a periodic variation in background electromagnetic field strength and orientation as well as plasma conditions while Jupiter completes a synodic rotation. We use a hybrid simulation (kinetic ions, fluid electrons) to model field perturbations due to the interaction of the corotating plasma with the ionosphere and induced dipole moment under these varying background conditions. For three cases, (I) Europa at the center of the plasma sheet, (II) Europa at its maximum distance north of the plasma sheet, and (III) Europa at its maximum distance south of the plasma sheet, we calculate surface precipitation maps of energetic magnetospheric ions using a backtracing tool. The effects of the time-varying field perturbations on surface precipitation have not previously been modeled. For three of the dominant ion species (H⁺, O²⁺, and S³⁺), we model the spatial distribution of surface flux over the full range of ion energies observed by the Galileo spacecraft (100 eV to about 10MeV). Our results show that the field perturbations drastically affect surface fluxes. While polar regions receive consistently high particle flux, low-latitude and equatorial regions are partially shielded by draped magnetic field lines close to the moon. These shielded regions migrate in longitude and latitude across Europa’s surface as Jupiter progresses through a full synodic rotation.