Astronomy and Astrophysics – Astrophysics
Scientific paper
Dec 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002agufm.p61a0342s&link_type=abstract
American Geophysical Union, Fall Meeting 2002, abstract #P61A-0342
Astronomy and Astrophysics
Astrophysics
0343 Planetary Atmospheres (5405, 5407, 5409, 5704, 5705, 5707), 6062 Satellites, 6218 Jovian Satellites
Scientific paper
The very tenuous O2 atmosphere of Europa is a near-surface (or surface-bounded) atmosphere [1]. It is produced by the radiolysis of Europa's surface due to exposure to solar ultraviolet radiation and energetic magnetospheric plasma ions and electrons. Earlier we developed a collisional Monte Carlo model of Europa's atmosphere [2] accounting for adsorption, thermalization and re-emission of condensed O2, a stable decomposition product of H2O radiolysis. Dissociation and ionization by magnetospheric electron and solar UV-photon impact, and collisional ejection from the atmosphere by the low energy plasma were also taken into account. It was found that to account for the production of oxygen emission observed by HST [3] larger surface fluxes of O2 are required than those assumed in earlier work from measured fluxes of magnetospheric particles [4]. This has since been shown to be due to the fact that radiolysis is occurring in a regolith and not on a laboratory surface [5]. In this report we present the results of an expanded Monte Carlo model of Europa's atmosphere. In this model the sublimation and sputtering sources of H2O molecules and their molecular fragments are also included. Therefore, we account for water and oxygen photochemistry in the near surface atmospheric region and for adsorption-desorption of radiolytic water products onto the satellite surface. This expanded model allowed us to emphasize the important role of chemical exchange in the atmosphere-surface interface of Europa. The numerical modeling of chemical composition in both the near-surface gas-phase boundary region and the satellite surface provides a more complete accounting of the chemical pathways occurring in the icy satellite surface material following decomposition by the solar ultraviolet radiation and the energetic magnetospheric plasma. The model will eventually be expanded to include the effect of the release of trace amounts of SO2 and CO2 that are trapped in the surface ice. [1] Johnson, R.E., 2002, in Atmospheres in the Solar System: Comparative Aeronomy Geophy. Mono. AGU, p. 203. [2] Shematovich and Johnson, 2001, Adv. Space Res., v.27, 1881. [3] Hall et al., 1998, Astrophys. J., v.499, 475. [4] Cooper et al., 2001, Icarus, v.149, 133. [5] Johnson et al., 2003, In Jupiter: Satellites, Atmosphere, Magnetosphere. Ed. by F. Bagenal, Univ. of Arizona Press, 2003.
Cooper John F.
Johnson Robert E.
Shematovich Valery I.
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