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

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. Plain Language Summary: As the closest Galilean moon of Jupiter, Io is strongly influenced by high energy ions from Jupiter's magnetosphere. The collisions between these high energy ions and background atmospheric particles can produce considerable high energy atmospheric recoils. A large portion of these particles are able to escape to space when their kinetic energies exceed local escape energy. Such a phenomenon is named atmospheric sputtering. In this study, we simulate this process on Io with the aid of parameters from laboratory measurements and a Monte Carlo model. Our calculations show that sputtering is the most important process driving atmospheric loss at Io. We also analyze the effects of various incident plasma populations and model setups on the atmospheric sputtering at Io. Key Points: Atmospheric sputtering is the most important mechanism driving atmosphere escape at IoOur calculations suggest a total escape rate of 3 × 1029 atom s−1 on IoSputtering yields vary substantially with incident plasma and atmospheric conditions, yet are insensitive to proton precipitation and inelastic process [ABSTRACT FROM AUTHOR]