Saturn's F Ring Core: Calm in the Midst of Chaos
Abstract
Saturn’s F Ring, or more specifically its stable, narrow, optically thick but clumpy core (Bosh et al 2002 Icarus 157, 57; Murray et al 2012, DDA #43, 4.08) is often described as “shepherded”, or confined in its present location, by Pandora and Prometheus much as the Uranian epsilon ring is shepherded by Cordelia and Ophelia. However, the F Ring is closer to the more massive Prometheus, inconsistent with the shepherding principle of torque balance (Showalter and Burns 1982 Icarus, 52, 526). Moreover, orbital calculations show that test particles throughout the F ring region tend to have chaotic orbits caused by the densely spaced resonances of Prometheus and Pandora (Scargle et al 1983 DPS 25, #26.04, Winter et al 2007 MNRAS 380, L54 and 2010 A&A 523, A67). We have developed a simple physical model and performed Bulirsch-Stoer orbital integrations containing all the classical satellites and named, close-in ringmoons as gravitational perturbers. We follow thousands of nongravitating test particles for over >30 years (>20000 orbits), covering selected swaths of the F ring region (139500-141500km) at high radial resolution. We find that narrow radial regions of orbital stability, which we term antiresonances, arise midway between first order resonances where these are clearly isolated. In this talk we summarize the situation, and present a simple physical impulse model for the presence of antiresonances. We show time histories of eccentricity and semimajor axis from realistic orbital integrations (perturbed by the gravity of all known moons) that illustrate chaotic behavior in general, with properties consistent with the behavior of S/2004S6 and other sizeable objects in the region. We also show examples of highly stable behavior in a few, very narrow, locations. At these specific locations, particle eccentricities and semimajor axes are largely invariant over periods of at least decades (Whizin et al., this meeting).
- Publication:
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AAS/Division for Planetary Sciences Meeting Abstracts #44
- Pub Date:
- October 2012
- Bibcode:
- 2012DPS....4451301C