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Dynamical phenomena at the inner edge of the Keeler gap

Status Report From: arXiv.org e-Print archive
Posted: Friday, September 8, 2017

Radwan Tajeddine, Philip D. Nicholson, Matthew S. Tiscareno, Matthew M. Hedman, Joseph A. Burns, Maryame El Moutamid
(Submitted on 6 Sep 2017)

We analyze several thousand Cassini ISS images in order to study the inner edge of the Keeler gap in Saturn's outer A ring. We find strong evidence for an m=32 perturbation with a mean amplitude of radial variation of 4.5 km. Phase analysis yields a pattern speed consistent with the mean motion of Prometheus, indicating that this pattern is generated by the 32:31 Inner Lindblad resonance with Prometheus. In addition, we find evidence of 18-lobed and 20-lobed patterns with amplitudes of ~1.5 km. These patterns, whose rotation rates correspond to resonance locations ~4 km interior to the gap edge, are believed to be normal modes. The former is probably related to the nearby 18:17 (m=18) resonance with Pandora. In addition to these resonant and normal mode patterns, we also observe multiple localized features that appear to move at the local keplerian rate and that persist for only a few months. One hypothesis is that different groups of ring particles at the inner edge of the gap may be reacting differently to the resonance with Prometheus, with local variations in the forced eccentricity and/or pericenter; an alternative hypothesis is the existence of several unseen objects embedded at or near the inner edge of the Keeler gap, similar to those suspected to exist at the outer edges of the A and B rings (Spitale and Porco 2009, 2010). In either case, observations of the ring edge at opposite ansae demonstrate that the localized features must be on eccentric orbits.

Subjects:    Earth and Planetary Astrophysics (astro-ph.EP)
Journal reference:    Icarus, Volume 289, p. 80-93 (2017)
DOI:    10.1016/j.icarus.2017.02.002
Cite as:    arXiv:1709.01974 [astro-ph.EP] (or arXiv:1709.01974v1 [astro-ph.EP] for this version)
Submission history
From: Radwan Tajeddine
[v1] Wed, 6 Sep 2017 19:50:53 GMT (1423kb)
https://arxiv.org/abs/1709.01974

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