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Abstract
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.