The Discontinuous Core of Saturn's F-Ring and Orbit Model

Details The Discontinuous Core of Saturn's F-Ring and Orbit Model The Discontinuous Core of Saturn's F-Ring and Orbit Model

Oct 2010

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010dps....42.2202m&link_type=abstract

American Astronomical Society, DPS meeting #42, #22.02; Bulletin of the American Astronomical Society, Vol. 42, p.988

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Scientific paper

Somewhat surprisingly, in 25 radio occultations of the F-Ring during the Cassini Nominal Mission, it is detectable in only 11. In contrast, the F-Ring was detectable in a single Voyager radio occultation, suggesting time variability. Similar to Voyager, and with one exception, an observed Cassini F-Ring profile is a single strand about 1 km wide and of peak optical depth of few to several tenths. The profiles were reconstructed to remove diffraction effects (few 100 meters resolution). To diffract the radio signals like 1-D structure, the strand must extend azimuthally for several km's (several Fresnel scale). All 11 detections are at both 0.94 and 3.6 cm observation wavelengths, with only 3 detections at 13 cm. The detections imply presence of particle sizes of at least few cm's, possibly extending to few 10's cm's. The sensitivity of the radio signals to these relatively large particle sizes suggests that the observed 1 km wide strand identifies locations where large fraction of the F-Ring mass likely resides, or the "core” of the F-Ring. This radio core can't be azimuthally continuous given the absence of detection on 14 other occultations. In stellar occultations conducted at much shorter wavelengths, the F-Ring core usually refers to a different broader feature 10's of km's wide. Its nondetectability in the Cassini radio observations implies particles of smaller sizes (< 1 mm) likely populate this broad feature. We use the Cassini radio observations of the core to determine parameters of a freely precessing eccentric and inclined Keplerian ellipse model. Results are close to, but measurably different from, those reported based on fitting the broader profiles observed in stellar occultations (Bosh et al., Icarus 157, 57-75, 2002), with RMS fit residual < 7 km compared with almost twice the value if the Bosh-model is directly applied to the radio observations.

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