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S.M. Brooks, L.E. Esposito (LASP - Univ. of Colorado), M.R. Showalter (NASA Ames Research Center), H.B. Throop (LASP - Univ. of Colorado)
During Galileo's third orbit at Jupiter, the Solid State Imaging Experiment (SSI) took high-resolution images of Jupiter's ring system through its clear filter at phase angles between ~176-179~degrees. The Near Infrared Mapping Spectrometer (NIMS) also recorded one observation of Jupiter's main ring during the same pass at wavelengths between 0.7 and 5.2 microns. The broad wavelength coverage of the NIMS data means that it is more sensitive to larger particles than the SSI observations. Although the NIMS data cube suffers from low spatial resolution, low signal-to-noise (especially at the longest wavelengths), and a faulty detector, its spectral coverage provides an excellent complement to the SSI images. Combining the two sets of data provides strong constraints on the ring particles' size distribution.
Showalter et al.\  (Icarus, 69, 458-498) analyzed Voyager imaging data, finding the ring particle size distribution to be a power-law with an index of 2.5 ± 0.5. They also found that ratios of the main ring's brightness through orange and violet filters suggest a power-law index of 2.2 ± 0.2. McMuldroch et al.\  (Icarus, 146, 1-11) analyzed the C3 NIMS observation of the Jovian main ring and concluded that the size distribution of the ring particles is the sum of a power-law distribution with an index of 3.9 ± 0.2 and a log-normal distribution centered at 4.5 microns. Our analysis of both the SSI and NIMS ring observations yields a particle size distribution which may reconcile the disparate results of Showalter et al.\ and McMuldroch et al. Specifically, smaller particles can be described by a shallower distribution similar to those determined by Showalter et al.\ , whereas the larger particles require a steeper power-law distribution. We will discuss the implications for the creation and evolution of the ring system.