Modeling of sputtering of the ice surfaces under impact of H+ ions: Redistribution of the h and o isotopes applied to the satellites of Jupiter

Abstract

Using computer modeling, the current models for sputtering coefficient calculation of the ice surfaces under the impact of H+ ions are statistically analyzed and the sputtering coefficients and their confidence intervals are calculated over a wide range of ion energies. It was established that the approximation model (Fama et al., 2008) with a calculated confidence interval of ±20% is less sensitive to the variable parameters. The sputtering coefficients of water ice p = 0.94, T = 80 K) are calculated under the impact of H+ ions for energies from several eV to 10 keV and the results are verified with experimental data. The maximum sputtering coefficient is 0.9 H2O/ion at the energy of the incident H+ ions of 200 eV. The modeling of the sputtering coefficients dependence of H2O molecules from the ice surface temperature showed that they weakly vary in the temperature range of 40–100 K and increase with an increase in the surface temperature. At maximum of distribution under T = 40–100 K, the sputtering coefficient Y(E = 200 eV) is 0.9 H2O/ion at T = 200 K — 1.1 H2O/ion. The distribution by kinetic energy of the dispersed H2O molecules and H and O atoms are modeled for the energy of 1–100 keV of the incident H+ ions. These results may be applied for modeling of variable isotopic compositions of the exosphere of the Jupiter’s satellites in the course of sputtering. The calculated ratios of the sputtering coefficients of H, D, 18O, and 16O from the surface for the Jupiter’s satellites (Europe, Ganymede, Callisto) under the impact of H+ ions for energy from several eV to 10 keV are (1.7 ± 0.3) × 10−5 and 0.18 ± 0.03, respectively. These ratios are distinct from the initial isotope ratios on the surface of the Jupiter’s satellites. This significant difference may lead to the redistribution of isotopes on the surface of the Jupiter’s satellites. The variation in the D/H ratio on the surface of the Jupiter’s satellites depends on the flux density of the radiated ions.