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L. Dones, H.F. Levison (SwRI), J.J. Lissauer (NASA Ames), R.G. French, C.A. McGhee (Wellesley)
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). Prometheus's eccentricity now appears to be smaller than previously thought, implying that it does not enter the F Ring (M.~W.~Evans, Ph.~D.~thesis, Queen Mary College, 2001; R.~G.~French et~al., this meeting). Furthermore, Pandora's orbital advance cannot be explained by interactions with the F~Ring, since it does not come as close to the ring as Prometheus does. Instead, chaos is likely to be important for Pandora (F.~Poulet and B.~Sicardy, MNRAS 322, 343--355, 2001). The orbital anomalies of Prometheus and Pandora are anticorrelated, suggesting that their motions are coupled. This conclusion is strengthened by the even more deviant odyssey they both embarked upon in 2001 (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 their motions might be coupled, possibly through the action of mass distributed in the ``F Ring region'' between them. We thank the NASA Planetary Geology & Geophysics program for grants to LD, HFL, JJL, and RGF, and to STScI for a grant to RGF.
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Bulletin of the American Astronomical Society, 34, #3
© 2002. The American Astronomical Society.