A One-Dimensional Model of Atmospheric Sputtering at Io Driven by S++ and O+

Abstract

Io, the closest of Jupiter's four Galilean moons, suffers from intense ion bombardment from Jupiter's magnetosphere. The constant atmospheric erosion by energetic ion precipitation, referred to atmospheric sputtering, serves as an important mechanism of Io's atmospheric escape. This study is devoted to a state-of-the-art study of atmospheric sputtering at Io, with the aid of constantly accumulated understandings of Io's space environment and atmospheric photochemistry, as well as the updated laboratory measurements. A Monte Carlo model is constructed to track the energy degradation of incident S⁺⁺ and O⁺ and atmospheric recoils from which the sputtering yields of different atmospheric species are determined. Our calculations suggest a total escape rate of 3 × 10²⁹ atom s⁻¹ on Io, and SO₂ is the dominant sputtered species. Further investigations reveal that S⁺⁺ is the most efficient species for atmospheric sputtering on Io, and sputtering yields increase substantially with increasing incident ion mass, energy, and incidence angle. The model sensitivity to different influence factors is also discussed, including scattering angle distribution, atmospheric column density, proton precipitation, inelastic process, and surface sputtering, of which the former two dominate.