Other
Scientific paper
Sep 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009dps....41.1806n&link_type=abstract
American Astronomical Society, DPS meeting #41, #18.06
Other
Scientific paper
The Cassini Division between Saturn's A and B rings is punctuated by eight nearly empty gaps. It was suggested by Lissauer, Shu & Cuzzi (1981) that each gap contains a small moonlet which holds it open, analogous to the Encke and Keeler gaps in the outer A ring, but to date no such moons have been detected, either directly or indirectly. Based on analysis of 41 high-quality stellar occultation cuts obtained by the Visual and Infrared Mapping Spectrometer (VIMS) onboard the Cassini spacecraft, we propose an alternative explanation. We find that all the gaps which do not contain dense ringlets have nearly circular outer edges, while all the other edges exhibit significant variations in their radial locations. As expected based on previous observations (Porco et al. 1984, Spitale et al. 2006), we find that the outer edge of the B ring has a large m=2 component due to the 2:1 inner Lindblad resonance with Mimas. However, detailed studies of this pattern suggest that the orientation of the B-ring edge slowly drifts or librates relative to Mimas. The inner edge of the Barnard gap exhibits an m=5 component that is likely due to the nearby 5:4 ILR with Prometheus. The inner edges of all the remaining gaps are well-fit by simple precessing ellipses, whose pattern speeds form a quasi-regular series with a spacing of approximately 0.05-0.07 degrees/day. We propose that these eccentric inner edges are all controlled by a type of three-body resonance which involves interacting perturbations from Mimas itself and the librating B-ring edge. The libration provides the observed quasi-regular spacing of the eccentric gap edges, while the m=1 mass anomaly at the inner edge of each gap may lead to a ``shepherding'' affect that repels the nearly circular outer edge and thus may control the width of the gap.
Cassini Vims Team
Hedman Matthew M.
Nicholson Philip D.
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