Cassini-VIMS Observations of Stellar Occultations by Saturn's Rings

Details Cassini-VIMS Observations of Stellar Occultations by Saturn's Rings Cassini-VIMS Observations of Stellar Occultations by Saturn's Rings

Jul 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007dda....38.1205n&link_type=abstract

American Astronomical Society, DDA meeting #38, #12.05

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Scientific paper

Since entering orbit around Saturn in July 2004, the VIMS instrument on the Cassini spacecraft has observed 15 stellar occultations by Saturn's rings, at incidence angles ranging from 3.5 to 51 degrees. The radial resolution of the resulting optical depth profiles varies from 200 meters to 4 km. We will present selected results from these observations, concentrating on the narrow, kinky, multistranded and eccentric F ring. An initial series of grazing occultations of the long-period variable star, o Ceti yielded eight high S/N profiles of the F ring, revealing a dense central strand of FWHM 25-45 km flanked by inner and outer strands which are variable both in normal optical depth (0.005-0.035) and radial separation from the core (250-465 km). All three strands are embedded in a broad `skirt' of diffuse material which is at least 1200 km wide. These results are qualitatively consistent with Cassini imaging observations (Porco etal. 2005). Despite local radial distortions of up to 50 km, the measured radii of the F ring's core are found to be remarkably consistent with the model developed by Bosh etal. (2002) - based on Voyager and Earth-based occultation data - of an eccentric, inclined keplerian orbit precessing under the influence of Saturn's oblate figure. Our measured radii of the fainter flanking strands, on the other hand, do not appear to support the one-armed trailing spiral model developed by Charnoz etal. (2005). One VIMS profile across the F ring shows evidence for a dense embedded clump, approximately 1 km in diameter, which may correspond to one of the bright pointlike features seen in several Cassini images. This clump was also seen in simultaneous observations by the UVIS instrument (Esposito
etal. 2007), where it is clearly seen to be partially transparent (ie., it is not an embedded moonlet).

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