Statistics – Applications
Scientific paper
Dec 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufmsm11c..05j&link_type=abstract
American Geophysical Union, Fall Meeting 2009, abstract #SM11C-05
Statistics
Applications
[0343] Atmospheric Composition And Structure / Planetary Atmospheres, [5470] Planetary Sciences: Solid Surface Planets / Surface Materials And Properties
Scientific paper
Europa and Ganymede are imbedded in the Jovian magnetospheric plasma. This plasma alters their surfaces producing tenuous surface boundary-layer atmospheres (Johnson, 2002). That is, the interactions of the desorbed neutrals with the surface determine the composition and morphology of their atmospheres (Cassidy et al. 2009; Cipriani et al. 2009). Those neutrals that escape the satellite remain gravitationally bound to Jupiter in a toroidal-shaped cloud until they are ionized and contribute to the ambient plasma. Since gas-phase species are readily identified, the gravitationally bound and toroidal components are of interest as extensions of the satellite’s surface. If these atmospheres were only populated by thermal desorption, they would have a small subsolar water component (Shematovich et al. 2005) and the trace volatiles would be rapidly depleted. However, Europa and Ganymede orbit in a region of the Jovian magnetosphere in which the trapped plasma density and temperature are relatively high. This plasma and the solar EUV flux chemically alter and erode their surfaces, processes often lumped together as sputtering. Early laboratory results were used to predict the principal atmospheric component, O2, and its average column density (Johnson et al. 1982). Since loss of H2 accompanies the formation and ejection of O2 from ice (Johnson and Quickenden 1997), and, since H2 escapes more readily than the heavier species, hydrogen is a principal species in the neutral torus (Smyth and Marconi 2006) and a primary source of protons for the Jovian magnetosphere. Atmospheric simulations using models for the surface composition, data on the radiation flux, and laboratory data have been used in to interpret the available observations and to suggest which trace species might be detectable by an orbiting spacecraft. Models for the atmospheres of Europa and Ganymede and their relation to the plasma-weathered surfaces will be described in which redistribution and loss to the surface compete with loss due to ionization and pick-up, direct escape, and dissociation. Our interest is the relationship of the morphology and composition of the atmosphere and to its surface properties and the possibility of detection of atmospheric species (Johnson et al. 2009). References: Cassidy, T.A., et al, Trace constituents of Europa's atmosphere, Icarus (2009) Cipriani, F., et al, Exospheric signatures of alkali abundances in Europa's regolith, GRL 36, 2009 Johnson, R.E., et al. Planetary applications of ion-induced erosion of condensed-gas-frost.NuclInstrMethods 198, 147-157, 1982. Johnson, R.E., T.I.Quickenden, Photolysis & Radiolysis of Ice on Outer Solar System Bodies, JGR 102, 10985, 1997. Johnson, R.E., Surface Boundary Layer Atmospheres, in Atmospheres in the Solar System: Comparative Aeronomy Geophys.Mono. 130, 203-219 (2002) Johnson, R.E., et al."Composition and Detection of Europa's Sputter-Induced Atmosphere", in Europa, Eds. R. Pappalardo et al. (2009) in press. Shematovich, V.I., et al "Surface-bounded Atmosphere of Europa", Icarus 173, 480-498 (2005). Smyth W.H.,M.L. Marconi, Europa's atmosphere, gas tori, and magnetospheric implications, 181, 2, 510-526, 2006
Cassidy Timothy A.
Cipriani Fabio
Cooper John F.
Hendrix Amanda R.
Johnson Robert E.
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