Photochemistry of SO2in the atmosphere of Io and implications on atmospheric escape

Abstract

Photochemical models of Io's atmosphere are presented with the assumption that SO2is the major gas and that the SO2surface pressure is controlled by vapor‐pressure equilibrium at the surface. Photolysis of SO2leads to efficient production of SO, O2, S, and O. Of these products, O and S are likely to be the dominant constituents in the upper atmosphere, and the atmospheric escape is expected to be in atomic form. Nonthermal escape processes are necessary to populate the plasma torus. SO2surface densities greater than 1011cm−3are needed on the dayside to supply the required amounts of S and O to maintain the torus. Surface chemistry presents an interesting possibility, namely, the conversion of O to O2, in which case O2will be the dominant constituent throughout the nightside and over the polar caps with a surface O2density of 1010cm−3.