37th DPS Meeting, 4-9 September 2005
Session 66 Planetary Rings III
Oral, Friday, September 9, 2005, 2:00-3:30pm, Music Concert Hall

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[66.03] UV Reflectance of Saturn’s Rings from the Cassini UVIS

H. J. Tollerud, J. E. Colwell, L. W. Esposito (LASP, Univ. of Colorado)

We investigate the composition of Saturn's rings using spatially resolved ultraviolet spectra taken by the Cassini Ultraviolet Imaging Spectrograph (UVIS). UVIS observations span shorter wavelengths (111-191 nm) than near-ultraviolet Hubble observations of the rings. UVIS observations also have higher spectral and spatial resolution than Voyager and IUE UV measurements of the rings. The best spatial resolutions of 150 km occurred during Saturn Orbital Insertion. We have a wide range of phase angles, from 0o to 145o. We observe the water absorption edge at 160 nm, and we see most of our signal at 160-191 nm. We determine the ring reflectance longward of the water absorption edge and then use a radiative transfer model to find the particle albedos. We find a reflectance of 0.11 in the A ring at 180 nm and a phase angle of 10o, compared to 0.18 in the B ring and 0.05 in the Cassini Division. We also observe variations in particle albedo within each ring. These albedo variations indicate varying amounts of dark material mixed in with water ice across the rings. We discuss the UV reflectance and spectra of the rings and their implications for composition and ring evolution.

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Bulletin of the American Astronomical Society, 37 #3
© 2004. The American Astronomical Soceity.