Throop, H. and Porco, C. (2001). "Cassini Observations of Jupiter's Rings." American Astronomical Society, DPS meeting #33, #32.03.


Abstract
Nearly 600 visible-light images of the Jovian main ring over a broad range of wavelengths and viewing geometries were obtained with the ISS (Imaging Science Subsystem) during Cassini's December 2000 -- January 2001 flyby of Jupiter. This data set represents the most comprehensive coverage in spectrum and phase ever collected by one instrument on the Jupiter ring. Our observations focused on a) determining the nature of the small particles in the main ring, b) searching for structure and/or temporal variation in the ring, c) searching for material outward of the known rings, and d) measuring the vertical structure of the ring. Cassini obtained observations of the main ring over large range of phase angles (α = 0-120o). At each phase angle we imaged the ring in nine colors (UV to near-IR) and at three polarizations. Analysis of the wavelength-dependent phase curve allows constraint of particle sizes in the main ring, and in turn their lifetimes and histories. Observations of the polarized nature of the scattered light yields insight into the surface structure of the particles and the processes acting upon them in the ring. Observations by Cassini just after it passed through the planet's equator, at a distance of 137 {RJ}, yielded our best spatial resolution of 58 km/pixel. Our observations followed both ring ansae at a spacecraft latitude of ~ 1'. We have not detected the halo and gossamer rings (τ ~ 10-6 - 10-7) in the Cassini images, as a result of their intrinsic faintness and significant scattered light from Jupiter. We also searched for material in faint gossamer rings (τ ~ 10-7) out to 6 {RJ}, well beyond the locations of the known Thebe and Amalthea gossamer rings, but have not yet detected new material. Finally, Cassini obtained 40-hour, 150-exposure movies of the main ring on both the inbound (α ~ 3o) and outbound (α ~ 120o) segments. We have not yet found evidence for any temporal variation in the ring, or any `clumps' of material larger than our spatial resolution of 50-120 km.