DPS Meeting, Madison, October 1998
Session 17. Rings II
Contributed Oral Parallel Session, Tuesday, October 13, 1998, 10:30-11:30am, Madison Ballroom C

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[17.05] Saturn's ``Gossamer'' Ring: The F Ring's Inner Sheet

M. R. Showalter (Stanford), J. A. Burns (Cornell), D. P. Hamilton (U. Maryland)

Recent Galileo and Earth-based images have revealed for the first time that Jupiter's ``gossamer'' ring is actually composed of two rings, one bounded at the outer edge by Amalthea and the other bounded by Thebe. Dynamical models suggest that these rings are composed of dust grains ejected off the surfaces of the two moons, which then evolve inward under Poynting-Robertson drag. A very faint sheet of material filling the region between Saturn's A and F~Rings reported by Burns et al. ({\it BAAS} {\bf 15}, 1013--1014, 1983) may be a dynamically analogous system, in which dust escapes from the F~Ring and evolves inward to the A~Ring. Unlike Jupiter's gossamer rings, however, the inner sheet of Saturn's F~Ring has been well observed from a large range of phase angles and visual wavelengths by Voyager.

Voyager images reveal that this faint ring shows a tenfold increase in brightness between phase angles of 125\circ and 165\circ, indicating that it is composed of fine dust microns in size. Preliminary estimates of the normal optical depth fall in the range 1--2\times10-4, depending on the dust size distribution assumed. Initial spectrophotometry reveals that the ring is neutral in color. The ring is uniform in brightness over the entire region between the two rings, with no evidence for internal structure associated with Prometheus and Atlas, suggesting that neither of these embedded moons acts as either a source or a sink. We will refine the aforementioned measurements and develop photometric models to better constrain the properties of the dust in this ring. This will enable us to relate the dust population to that in the F~Ring proper, and to better explore the dynamical processes at work.

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