JOVIAN SYSTEM DATA ANALYSIS PROGRAM PROPOSAL SUMMARY

The goal of this proposal is to characterize fully the structure and particle properties of Jupiter's ring system, and to use this information to understand the processes at work. This study will foster comparisons with the numerous similarly faint and dusty rings around all four giant planets, illuminating this entire class of dynamical systems. My primary focus will be on the Galileo SSI and NIMS data. SSI acquired fine-resolution images at a variety of viewing geometries, whereas NIMS measured the ring's reflectance spectrum for the first time. I will also take a fresh look at the earlier Voyager images in the context of the new results, and will use additional data from HST, Keck and Palomar to augment the photometry. Methods to be applied will expand upon my previous studies of dusty rings. My software tools permit the precise determination of image geometry, reconstruction of the 3-D geometry of diffuse clouds of ring material, compensation for faint, smeared, and/or poorly-resolved rings using pixel averaging techniques, and derivation of particle properties by fitting photometry to a vast array of theoretical models. Dusty rings are interesting because they are sculpted by processes that tend to be masked within the denser ring systems. Tiny grains are perturbed by magnetic forces and solar radiation, and are removed from orbit rapidly by drag forces. A family of larger "parent" bodies must be present to replenish the dust continuously, perhaps as ejecta from meteoroid impacts. Depending upon the key processes assumed, dynamical models make specific predictions about the 3-D form of a ring and about the size distribution of its constituent particles. Thus, the analysis proposed will provide unique new information about the Jovian ring system's origin and dynamics. The Jovian ring has three distinct components. (1) The main ring is the brightest and narrowest. The key questions to be addressed are: Where does the dust come from and how is it replenished? What non- gravitational processes are at work? What is the role of the embedded moons Adrastea and Metis? What defines the ring's structure, including its peculiar bending wave? Where are the parent bodies? How did they originate? Careful analysis of the Galileo data will provide answers to many of these questions. (2) The halo begins near the main ring's inner edge and extends half way down to the planet, with a vertical thickness of ~10,000 km. I have developed several processing techniques for extracting the detailed cross-sectional profile of the halo from the images, which I will use to distinguish between the two leading models for halo dynamics. I will also determine the size distribution of the halo dust and will investigate any variations with location, as is predicted by the models. (3) The gossamer ring extends outward from the main ring but is much fainter. Models suggest that it is composed of dust grains ejected from Amalthea and Thebe, which then evolve inward under Poynting-Robertson drag. However, the dust does not appear to respond to Jupiter's magnetic field, suggesting grains are ~10 times larger than expected. I will address this issue by searching more carefully for the distinctive thickness variations expected from magnetic perturbations, and will also use photometry to better determine the dust sizes.