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M.C. Wong (JPL/NRC), R.W. Carlson (JPL), R.E. Johnson (Univ. of Virginia)
Europa's tenuous atmosphere is thought to be produced from sputtering of surface species (predominantly H2O ice ) by heavy ions in the Jovian magnetosphere. Because of its low residence time at Europa's surface temperature, O2, a stable decomposition product of H2O, has been predicted to exist in a significant amount in Europa's atmosphere [Johnson et al. 1982, Eviatar et al. 1985, Johnson 1990]. Recent HST observations have confirmed that and suggested an O2 atmospheric column of ~1015 cm-2 on Europa [Hall et al. 1995]. Recent theoretical studies applied to modeling of pure oxygen atmospheres on Europa [Ip et al. 1996, Saur et al. 1998, Shematovich and Johnson 2000] have produced results that are consistent with the above scenerio. In addition to water products, recent observations from Galileo NIMS instruments have suggested the existence of hydrated salt minerals and sulfuric acid on Europa's surface [McCord et al. 1999, Carlson et al. 1999]. Therefore, it is expected that decomposition of these materials by magnetospheric ions can produce volatile species such as H2S, SO2, CO2 and Na in Europa's atmosphere. In fact, Na has been identified in the extended atmosphere of Europa [Brown and Hill, 1996]. In this paper, we will use a kinetic model to study the fate and abundance of these volatile species in addition to simulating the formation of an oxygen atmosphere on Europa.
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