Data underlying the publication: Callisto's atmosphere: First evidence for H2 and constraints on H2O

We explore the parameter space for the contribution to Callisto's H corona observed by the Hubble Space Telescope (Roth et al. 2017a) from sublimated H2O and radiolytically produced H2 using the Direct Simulation Monte Carlo (DSMC) method. The spatial morphology of this corona produced via photo- and magnetospheric electron impact-induced dissociation is described by tracking the motion of and simulating collisions between the hot H atoms and thermal molecules including a near-surface O2 component. Our results indicate that sublimated H2O produced from the surface ice, whether assumed to be intimately mixed with or distinctly segregated from the dark non-ice or ice-poor regolith, cannot explain the observed structure of the H corona. On the other hand, a global H2 component can reproduce the observation, and is also consistent with enhanced electron densities observed at high altitudes by Galileo's plasma-wave instrument (Gurnett et al. 1997, 2000), providing the first evidence of H2 in...