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H. B. Throop, C. C. Porco (SwRI), R. A West (JPL), J. A. Burns (Cornell), M. R. Showalter (ARC), P. D. Nicholson (Cornell)
Cassini's Imaging Science Subsystem (ISS) instrument took nearly 1200 images of the Jupiter ring system during the spacecraft's 6-month encounter with Jupiter. These observations constitute the most complete dataset of the ring taken by a single instrument, both in phase angle (0.5 - 120\deg at seven angles) and wavelength (0.45 - 0.93 \mu\rm{m} through eight filters). The main ring was detected in all targeted exposures; the halo and gossamer rings were too faint to be observed above the planet's stray light. The optical depth and radial profile of the main ring are unchanged from that of previous studies. No evidence for broad asymmetries within the ring were found; we did identify possible evidence for 1000~km-scale clumps within the ring. Cassini observations at a phase angle of 64\deg place an upper limit on the ring's full thickness of 80~km.
We have combined the Cassini ISS and VIMS observations with those from Voyager, HST, Keck, Galileo, Palomar, and IRTF. We have fit the entire suite of data using a photometric model that includes microscopic silicate dust grains as well as larger, long-lived `parent bodies' that engender this dust. Our dust grain model considers a range of spheroidal particle shapes computed using the T-matrix method (Mishchenko & Travis 1998). Our best-fit model to all the data indicates an optical depth of small particles of \taus = 4.7\times 10-6 and large bodies \taul = 1.3\times 10-6. The dust is concentrated about a radius of 15~\mu\rm{m}. The data are fit significantly better using non-spherical rather than spherical dust grains. The parent bodies themselves must be very red from 0.4--2.5~\mu\rm{m} and may have absorption features near 0.9~\mu\rm{m} and 2.2~\mu\rm{m}.
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Bulletin of the American Astronomical Society, 35 #4
© 2003. The American Astronomical Soceity.