Reactive scattering of water group ions on ice surfaces with relevance to Saturn's icy moons

Collisions of hyperthermal water group ions with ices are known to occur in astrophysical environments, for example, solar wind-comet interactions and moon-magnetosphere (at Saturn Jupiter), yet their effect on surface gaseous composition is little understood. Here, we report molecular dynamics simulations water-group molecules impacting water-ice surfaces using the ReaxFF reactive force fields describe bond breaking forming processes dynamically during collision events. Simulation conditions chosen relevance Saturn's moons Dione Rhea. At impact velocities 10–35 kms−1 (8 102 eV O), find that projectiles undergo Eley-Rideal reactions ice form O2, HO2, H2O2. a 45o angle incidence OO bonded products tend embed within few layers surface. Smaller angles lead formation some oxygen promptly rebounds from ~3 kinetic energy. Impact velocity, incidence, hydrogenation impactor strongly influence O2 formation, yield peaking at 19% atomic impactors 20 kms−1. Notably, this reaction relatively temperature independent proceeds hydrogen rich pristine ice, where radiolysis hindered. This mechanism production low energy impacts may contribute exospheres Jupiter's icy moons, ion fluxes large.