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L. Dones, H. F. Levison (Southwest Research Institute), J. J. Lissauer (NASA Ames Research Center), R. G. French, C. A. McGhee (Wellesley College)
Saturn's moons Prometheus and Pandora, the putative shepherds of the F Ring, orbit Saturn at rates that differ significantly from the rates at the time of the Voyager flybys in 1980/1981 (C.~A. McGhee et~al., Icarus 152, 282-315, 2001). Specifically, Prometheus is running slow, and Pandora is running fast. Soon after Prometheus' lag was discovered, collisions between Prometheus and the F Ring, occurring every ~19~years when their apses were anti-aligned, were proposed to explain the lag (C.~D. Murray and S.~M. Giuliatti Winter, Nature 380, 139-141, 1996). Pandora's orbital advance cannot be explained in this way, since it does not come as close to the F~Ring as Prometheus does. Instead, chaos is likely to be important for Pandora (F.~Poulet and B. Sicardy, MNRAS 322, 343-355, 2001). The recent discovery that Prometheus and Pandora have nearly equal and opposite longitude anomalies suggests that their motions are coupled (R.~G. French et~al., this meeting). We will present numerical integrations of bodies with orbits similar to those of Prometheus and Pandora, and will discuss ways in which two- and three-body resonances involving Saturn's inner moons might couple the orbits. We thank the NASA Planetary Geology & Geophysics program for grants to LD, HFL, JJL, and RGF, and to STScI for grant GO06806.0195A to RGF.
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