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F. Namouni, C. Porco (Southwest Research Institute)
The outer edge of the B-ring is located within the 2:1 mean motion resonance with the satellite Mimas. A detailed kinematic fit of the edge (Porco et al. 1984, Icarus 60, 17) shows that a two-lobed distortion characteristic of 2:1 resonance with Mimas dominates its shape, and that the ring edge's pattern speed is consistent with Mimas' mean motion. However, a number of features remain unexplained. First, the edge does not fall exactly at the location of the resonance. Instead, the edge semi-major axis is offset by 24 km outside the resonance location. Taken alone, this is not necessarily an issue since ring particle libration is possible away from the resonance location. However and secondly, since the ring extends outside the resonance, it is expected that ring particles encounter Mimas at apochrone. Instead, Mimas is aligned with the edge's two radial minima. The third unexplained feature is that the amplitude of the edge radial distortion is approximately 75 km when the maximum radial amplitude that the disk can support before nearby streamlines cross is 20 km. To explain these features, we explore the possibility of exciting standing density waves between the resonance location and the ring's sharp edge by improving on earlier models of wave propagation in dense rings (Borderies et al. 1985, 63, 406).
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Bulletin of the American Astronomical Society, 34, #3< br> © 2002. The American Astronomical Soceity.