HR: 13:55h
AN: P43B-02    [Abstracts]
TI: Ultraviolet Observations of Icy Saturnian Satellites from Cassini
AU: * Hendrix, A R
EM: hendrix@jpl.nasa.gov
AF: Jet Propulsion Laboratory/CalTech, 4800 Oak Grove Dr., Pasadena, CA 91109 United States
AU: Hansen, C J
EM: candice.j.hansen@jpl.nasa.gov
AF: Jet Propulsion Laboratory/CalTech, 4800 Oak Grove Dr., Pasadena, CA 91109 United States
AU: Esposito, L W
EM: esposito@lasp.colorado.edu
AF: Laboratory for Atmospheric and Space Physics/U. Colorado, 1234 Innovation Dr., Boulder, CO 80303 United States
AU: Shemansky, D E
EM: dons@hippolyta.usc.edu
AF: University of Southern California, 854 W. 36th Pl., Los Angeles, CA 90089 United States
AB: We present results from the Ultraviolet Imaging Spectrograph (UVIS) measurements of Phoebe during the Cassini flyby on June 11, 2004. Cassini UVIS mapped the illuminated side of Phoebe at resolutions on the order of 5-10 km/pixel. Phoebe is known to be dark and spectrally flat at all visible wavelengths, similar to C-type asteroids. Unresolved Earth-based observations have detected the presence of water ice. We find that the normal albedo of Phoebe is very low (<0.05) at far-UV wavelengths (110-190 nm), similar to carbonaceous chondrites. Phoebe's FUV spectral albedo, however, is not flat like such meteorites, suggesting that another species strongly affects the FUV spectrum. We investigate candidate species, and study albedo and spectral variations across the surface, to map distributions of species. We also present Phoebe's UV lightcurve, measured during both the inbound and outbound portions of the flyby. In addition to the reflectance studies we investigate the presence of any emissions from gaseous species. Phoebe's spectrum does not display any strong emission features, suggesting that gaseous species are not present and/or that the density of solar wind electrons in Phoebe's environment is too low to produce detectable excitation emission features. We also report on the disk-integrated observations of Iapetus throughout October, 2004, at ranges between 1 and 2 million km. The FUV spectra of Iapetus will be compared with the Phoebe data to investigate a possible relationship between these two satellites. On October 28, 2004 UVIS will obtain disk-resolved measurements of Tethys from a range of 255,000 km. Tethys represents an icy body that orbits well within Saturn's magnetosphere and the E-ring; we will compare and contrast FUV spectra of Tethys with those of the outer satellites to look for effects of different exogenic processes.
DE: 6008 Composition
DE: 6025 Interactions with solar wind plasma and fields
DE: 6280 Saturnian satellites
SC: Planetary Sciences [P]
MN: 2004 AGU Fall Meeting