The Effect of Gas-Surface Interaction on the Abundance and Composition of Io's Atmosphere.

M.C. Wong, W.H. Smyth (AER)

Recent dynamic models of Io atmosphere (Wong and Johnson, JGR 101, 23243-23254, 1996) showed the abundances and spatial distributions of various gaseous species depend strongly on their interaction with the surface (i.e., condensibility/sticking coefficient [ tex2html_wrap_inline15 ]). In this study, we have employed the numerical fluid model to examine scenarios with different source rates of SO tex2html_wrap_inline17 at the surface, and with variable gas-surface interaction condition (0 tex2html_wrap_inline19 1) for SO tex2html_wrap_inline17 and other minor species. Emphasis has been placed on the effect of such variations on the day-night asymmetry of the atmospheric abundance, composition, and the extend of the exobase. The results provide constraints on the supply rates of neutrals for the corona, and for escape from the satellite. Since Na is known to exist as a trace species and its population in the corona has been well-studied, Na bearing compounds (NaX) are included in our multi-species fluid model and the abundance of Na at the exobase is determined. Model calculations illustrating different scenarios will be presented.