Non‐Thermal Escape of Sulfur and Oxygen on Io Driven by Photochemistry

Abstract

AbstractIo, the closest of Jupiter's four Galileo moons, experiences intense volcanic activity that is induced by Jupiter's powerful tidal forces. The active volcanisms consequently create a tenuous SO2‐dominated atmosphere on Io, from which energetic particles can be easily lost due to the weak gravity field. The photolysis of SO2 triggers a complicated network of chemical reactions, which may be a significant source of atmospheric escape on Io. This study, for the first time, is devoted to evaluating the role of the chemically induced escape of S‐ and O‐containing species on Io by combining previous photochemical results and Monte Carlo model calculations. Different atmospheric conditions are compared, including high‐density volcanic and low‐density quiet scenarios, in which various chemical channels are considered. Our calculations suggest that the escape rates driven by photochemistry on Io are (1.1 − 2.0) × 1027 s−1 for total O and (1.5 − 6.7) × 1026 s−1 for total S, occurring mainly in the atomic form. The escape rates are found to vary extensively with the atmospheric conditions, especially in terms of the intensity of volcanic eruption. In general, photochemical escape is more important than Jeans escape for both atomic O and S for the quiet atmosphere scenario, whereas for the volcanic scenario, it is likely important for atomic S only.