DPS 2001 meeting, November 2001
Session 32. Rings II
Oral, Chair: H. Throop, Thursday, November 29, 2001, 2:40-3:30pm, Regency GH

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[32.02] Determining the Size Distribution of Jupiter's Main Ring with Galileo SSI and NIMS Imaging

S.M. Brooks, L.W. Esposito (LASP - Univ. of Colorado), M.R. Showalter (Stanford University), H.B. Throop (Southwest Research Institute)

Galileo's Solid State Imaging experiment (SSI) photographed Jupiter's ring system at visible wavelengths and at a variety of phase angles. We analyzed the high phase angle images of the main ring obtained during Galileo's third orbit. The Near Infrared Mapping Spectrometer (NIMS) recorded an observation of Jupiter's main ring during the same orbit at wavelengths from 0.7 to 5.2 microns.

Showalter et al. (1987, Icarus, 69, 458-498) produced a phase curve for the main ring using Voyager images. Modeling that phase curve, they concluded that the ring particles' size distribution is best described as a power law with an index of 2.5 ± 0.5. Showalter et al. also found that ratios of the main ring's brightness at different wavelengths suggest an index of 2.2 ± 0.2. From their analysis of the NIMS observation, McMuldroch et al. (2000, Icarus, 146, 1-11) argued that the size distribution is a log-normal distribution centered at 4.5 microns superposed on a power-law with an index of 3.9 ± 0.2.

We will report on our modeling of the SSI and NIMS data. Producing a phase curve for the main ring with SSI images requires the careful subtraction of any ring halo contributions. Our analysis of this phase curve and the NIMS data suggests the ring particles' size distribution is a broken power-law, where particles smaller than ~ 13~microns have a power-law index of 1.6 ± 0.3 and larger particles have an index of 4.8 ± 0.8. This distribution is steep like McMuldroch et al.'s for the larger particles. Yet, it is similar to the Showalter et al. distribution for the smaller particles, which were highlighted at Voyager's viewing geometry. This could indicate that ring particle production rates and/or lifetimes vary with size and may relate to the physical processes that control their evolution.

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