Magnetospheric Ion Bombardment of Europa’s Surface

Jupiter’s moon Europa is exposed to constant bombardment by magnetospheric charged particles, which are expected to be a major source of physical and chemical surface modification. Here we have investigated the flux of magnetospheric ions at Europa’s surface by carrying out single particle tracing within realistic electromagnetic fields from multifluid magnetohydrodynamic simulations of the moon’s interaction with Jupiter’s magnetosphere. We find that magnetic field line draping and pileup leads to shielding and drastically reduced flux at low latitudes across Europa’s trailing (upstream) hemisphere. Furthermore, we find that magnetic induction within Europa’s subsurface ocean leads to additional shielding when the moon is located at high magnetic latitudes in Jupiter’s magnetosphere. Overall, we find that the high-latitude and polar regions on Europa receive the largest flux of magnetospheric ions. Both spacecraft and ground-based observations have previously identified a non–water ice surface species concentrated at Europa’s trailing (upstream) hemisphere, possibly hydrated sulfuric acid formed from radiolysis of water ice with implanted S ions. Our results demonstrate that the S ion flux across Europa’s equatorial trailing (upstream) hemisphere is strongly reduced, possibly indicating that the formation of the observed non–water ice species is controlled primarily by energy input from magnetospheric electrons, rather than the flux of S ions. We find that that O and S ions at >1 MeV energies have nearly uniform access to the surface, while energetic protons in this energy range are constrained to a “bull’s-eye” centered on the trailing (upstream) hemisphere.