Far ultraviolet spectral properties of Saturn's rings from Cassini UVIS

    Authors

    E. T. Bradley; J. E. Colwell; L. W. Esposito; J. N. Cuzzi; H. Tollerud;L. Chambers

    Comments

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    Abbreviated Journal Title

    Icarus

    Keywords

    Saturn, Rings; Ices, UV spectroscopy; Ultraviolet observations; BIDIRECTIONAL REFLECTANCE SPECTROSCOPY; MAIN RINGS; PHOTOMETRY; SCATTERING; SURFACES; COLOR; Astronomy & Astrophysics

    Abstract

    Spectra taken by the Cassini Ultraviolet Imaging Spectrograph (UVIS) of Saturn's C ring, B ring, Cassini Division, and A ring have been analyzed in order to characterize ring particle surface properties and water ice abundance in the rings. UVIS spectra sense the outer few microns of the ring particles. Spectra of the normalized reflectance (I/F) in all four regions show a characteristic water ice absorption feature near 165 nm. Our analysis shows that the fractional abundance of surface water ice is largest in the outer B ring and decreases by over a factor of 2 across the inner C ring. We calculate the mean path length of UV photons through icy ring particle regolith and the scattering asymmetry parameter using a Hapke reflectance model and a Shkuratov reflectance model to match the location of the water ice absorption edge in the data. Both models give similar retrieved values of the photon mean length, however the retrieved asymmetry (g) values are different. The photon mean path lengths are nearly uniform across the B and A rings. Shortward of 165 nm the rings exhibit a slope that turns up towards shorter wavelengths, while the UV slope of 180/150 nm (reflectance outside the water absorption ratioed to that inside the absorption band) tracks I/F with maxima in the outer B ring and in the central A ring. Retrieved values of the scattering asymmetry parameter show the regolith grains to be highly backscattering in the FUV spectral regime. (C) 2009 Elsevier Inc. All rights reserved.

    Journal Title

    Icarus

    Volume

    206

    Issue/Number

    2

    Publication Date

    1-1-2010

    Document Type

    Article; Proceedings Paper

    Language

    English

    First Page

    458

    Last Page

    466

    WOS Identifier

    WOS:000275847600008

    ISSN

    0019-1035

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