Passing the Baton: HST Observations of Pandora and Prometheus on the Eve of Cassini

Abstract

For nearly a decade, the Hubble Space Telescope has provided stunning
views of the Saturn system, including hundreds of images of Pandora and
Prometheus, two small moons that straddle the F ring. In spite of
technological advances in large ground-based telescopes since the launch
of the HST, Hubble's WFPC2 is the only near-Earth instrument capable of
routine observations of these and other tiny satellites lying just
outside of the bright A ring. From earlier HST images, we have shown
that Pandora and Prometheus are interacting dynamically (French et al.
2002 Icarus 162, 143-170). Goldreich and Rappaport (2003 Icarus 162,
391-399; 166, 320-327) have demonstrated that their orbits are chaotic,
due to interactions associated with the 121:118 mean motion resonance,
with particularly strong perturbations at closest approach during the
6.2 year precessional cycle. We have continued to monitor the wanderings
of these satellites with the HST, with additional observations scheduled
for late March 2004. Not until April of 2004 will the Cassini
spacecraft's cameras finally surpass the HST in angular resolution, just
before the start of a four year orbital tour of Saturn. We will present
a summary of a survey of ten years of HST astrometric observations of
Saturn's satellites. This work was supported in part by the NASA PGG
program and the Massachusetts Space Grant Consortium. Our results are
based on observations with the NASA/ESA Hubble Space Telescope, obtained
at the STScI, which is operated by AURU under NASA Contract NAS5-26555.