Astronomy and Astrophysics – Astronomy
Scientific paper
May 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009dda....40.0302n&link_type=abstract
American Astronomical Society, DDA meeting #40, #3.02; Bulletin of the American Astronomical Society, Vol. 41, p.896
Astronomy and Astrophysics
Astronomy
Scientific paper
The Cassini Division between Saturn's A and B rings consists of ring material with an optical depth of around 0.10, punctuated by eight nearly empty gaps. Thus far, the only published explanation for the existence of these gaps is a suggestion by Lissauer, Shu & Cuzzi (1981) that each one contains a small moonlet which holds open the gap in a manner analogous to the Encke and Keeler gaps in the outer A ring, which are maintained by Pan and Daphnis. However, no such moons have yet been directly or indirectly detected in any of the Cassini Division gaps. Based on analysis of occultation data obtained by the Visual and Infrared Mapping Spectrometer (VIMS) onboard the Cassini spacecraft, as described in the accompanying abstract by Hedman et al., we propose an alternative explanation, whereby the six gaps not maintained by resonances with external satellites are indirectly established by perturbations from the nearby, resonantly-controlled edge of the massive B ring. Specifically, we argue that the eccentric inner edges of most of the gaps in the Cassini Division may be generated by a type of three-body resonance involving interacting perturbations from Mimas itself and the B-ring edge. A libration of the m=2 distortion of the B ring edge with a period of approximately 16 years provides the observed quasi-regular spacing in the pattern speeds of the eccentric gap edges. The resulting m=1 mass anomaly at the inner edge of each gap may lead in turn to a ``shepherding'' effect that controls the nearly circular outer edge and thus the width of the gap.
Cassini Vims Team
Hedman Matthew M.
Nicholson Philip D.
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