The Architecture of the Cassini Division

Details The Architecture of the Cassini Division The Architecture of the Cassini Division

2009-11-12

arxiv.org/abs/0911.2438v2

The Astronomical Journal 139 (2010) 228-251

Astronomy and Astrophysics

Astrophysics

Earth and Planetary Astrophysics

47 pages, 12 figures, accepted for publication in the Astronomical Journal, Some small typographical and wording errors fixed

Scientific paper

10.1088/0004-6256/139/1/228

The Cassini Division in Saturn's rings contains a series of eight named gaps, three of which contain dense ringlets. Observations of stellar occultations by the Visual and Infrared Mapping Spectrometer onboard the Cassini spacecraft have yielded ~40 accurate and precise measurements of the radial position of the edges of all of these gaps and ringlets. These data reveal suggestive patterns in the shapes of many of the gap edges: the outer edges of the 5 gaps without ringlets are circular to within 1 km, while the inner edges of 6 of the gaps are eccentric, with apsidal precession rates consistent with those expected for eccentric orbits near each edge. Intriguingly, the pattern speeds of these eccentric inner gap edges, together with that of the eccentric Huygens ringlet,form a series with a characteristic spacing of 0.06 degrees/day. The two gaps with non-eccentric inner edges lie near first-order Inner Lindblad Resonances (ILRs) with moons. One such edge is close to the 5:4 ILR with Prometheus. The other resonantly confined edge is the outer edge of the B ring, which lies near the 2:1 Mimas ILR. Detailed investigation of the B-ring-edge data confirm the presence of an m=2 perturbation on the B-ring edge, but also suggest that this pattern moves or librates relative to Mimas. The B-ring edge also has an m=1 component that rotates around the planet at a rate close to the expected apsidal precession rate. The pattern speeds of the eccentric edges in the Cassini Division can potentially be generated from various combinations of the pattern speeds of structures observed on the edge of the B ring. We therefore suggest that the locations of most of the gaps in the Cassini Division may be determined by resonances involving a combination of perturbations from Mimas and the massive edge of the B ring.

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