Other
Scientific paper
Dec 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003agufm.p12a1050h&link_type=abstract
American Geophysical Union, Fall Meeting 2003, abstract #P12A-1050
Other
2704 Auroral Phenomena (2407), 2732 Magnetosphere Interactions With Satellites And Rings, 6218 Jovian Satellites, 6297 Instruments And Techniques
Scientific paper
Ultraviolet spectroscopy is an important tool for further understanding of the icy galilean satellites, in addition to Jupiter, Io and the Io torus. In this presen-tation, we explore the past accomplishments using UV spectroscopy in the jovian system, and future meas-urements to be made to increase our knowledge of this exciting environment. The icy Galilean satellites are known to have tenu-ous atmospheres of H, O, O2 and CO2, among other species. A hydrogen corona (121.6 nm) has been de-tected around Ganymede and Callisto. An O2 atmos-phere has been inferred at Europa as a result of HST measurements of oxygen emission features. Observa-tions using an orbiter need to be performed to map out these atmospheric species spatially and temporally to better understand their sources. A very sensitive UV instrument is needed to do limb measurements to de-tect outgassing (particularly at Europa). It is not clear whether the primary source of the tenuous atmospheres is sputtering of the surface ice, sputtering of subli-mated gases, or photolysis. A UV spectrograph on JIMO will be able to map out the atmosphere and cor-relations can be made between abundances of atmos-pheric species and the varying types of sputtering of the surface by charged particles. How thick are the atmospheres, and do they vary across the surface? Is Ganymede's atmosphere relatively thin due to magne-tospheric shielding? Auroral activity has been detected on Ganymede using HST, where the polar regions appear to glow with oxygen emission lines at 130.4 and 135.6 nm. Longitudinal asymmetries appear, however, in the HST data, as do latitudinal and temporal variations that are not understood. The icy satellites of Jupiter are embedded within the magnetosphere and as such, are constantly bom-barded by the charged particles that populate it. The bombardment results in the formation of species that are detectable exclusively at NUV wavelengths (e.g., O3, H2O2, SO2). As such, by imaging these bombard-ment-produced species at UV wavelengths, we can essentially map out the environmental effects on the icy surfaces. Furthermore, UV spectra complement observations from longer wavelengths and have been used to confirm the existence of species detectable in both wavelength ranges. An example is the detection of hydrogen peroxide (H2O2) on Europa. An absorp-tion feature at 3.25 mm measured by the Galileo NIMS was confirmed to be due to H2O2 only after the perox-ide feature was also seen in the UV spectra. The H2O2 UV feature has also been measured on Ganymede and Callisto. Furthermore, ozone (O3), which absorbs at 260 nm, has been detected on Ganymede primarily in the polar regions, suggesting that the source is bom-bardment by electrons travelling along the field lines and impacting the polar ice. The SO2-like UV absorp-tion feature that appears on Europa's trailing hemi-sphere is likely correlated with dark material in re-cently active areas that also causes absorptions in IR spectra [9], and is likely the result of a combination of exogenic and endogenic activities.
Esposito W. L. W. L.
Hansen Camilla Juul
Hendrix Amanda R.
McClintock William E.
Pryor Wayne R.
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