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  • Exogenic controls on sulfur...
    Dalton, J.B.; Cassidy, T.; Paranicas, C.; Shirley, J.H.; Prockter, L.M.; Kamp, L.W.

    Planetary and space science, March 2013, 2013-03-00, 20130301, Letnik: 77
    Journal Article

    External agents have heavily weathered the visible surface of Europa. Internal and external drivers competing to produce the surface we see include, but are not limited to: aqueous alteration of materials within the icy shell, initial emplacement of endogenic material by geologic activity, implantation of exogenic ions and neutrals from Jupiter's magnetosphere, alteration of surface chemistry by radiolysis and photolysis, impact gardening of upper surface layers, and redeposition of sputtered volatiles. Separating the influences of these processes is critical to understanding the surface and subsurface compositions at Europa. Recent investigations have applied cryogenic reflectance spectroscopy to Galileo Near-Infrared Mapping Spectrometer (NIMS) observations to derive abundances of surface materials including water ice, hydrated sulfuric acid, and hydrated sulfate salts. Here we compare derived sulfuric acid hydrate (H2SO4·nH2O) abundance with weathering patterns and intensities associated with charged particles from Jupiter's magnetosphere. We present models of electron energy, ion energy, and sulfur ion number flux as well as the total combined electron and ion energy flux at the surface to estimate the influence of these processes on surface concentrations, as a function of location. We found that correlations exist linking both electron energy flux (r∼0.75) and sulfur ion flux (r=0.93) with the observed abundance of sulfuric acid hydrate on Europa. Sulfuric acid hydrate production on Europa appears to be limited in some regions by a reduced availability of sulfur ions, and in others by insufficient levels of electron energy. The energy delivered by sulfur and other ions has a much less significant role. Surface deposits in regions of limited exogenic processing are likely to bear closest resemblance to oceanic composition. These results will assist future efforts to separate the relative influence of endogenic and exogenic sources in establishing the surface composition. ► We model distributions of electron and ion flux and sulfuric acid hydrate for Europa. ► We find high correlation between acid hydrate production and sulfur ion flux. ► Electron energy and sulfur ion flux working together dominate acid production. ► Regions of low energy and/or sulfur ion flux exhibit the least radiolytic processing. ► Deposits in these regions are likely to more closely represent ocean composition.