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Douglas P. Hamilton (U. Maryland), Jospeh A. Burns, Philip D. Nicholson (Cornell U.), Mark R. Showalter (Stanford U.), Imke de Pater (U.C. Berkeley)
The faint and diffuse jovian ring system, as imaged by Voyager, consisted of three separate components: 1) A thin dusty ring located between about 1.71 and 1.81 jovian radii (RJ), 2) a ~0.1 RJ thick halo interior to 1.71RJ, and 3) an extremely faint ``Gossamer ring'' located between 1.81RJ and 3.1RJ. Spectacular new Galileo and Keck images of the Gossamer ring change this picture somewhat, in particular showing that there are actually two separate Gossamer rings, each extending inward from a small source satellite. This has a number of important implications for the dynamical evolution of the Gossamer rings.
First, the new images strongly imply that drag forces cause dust orbits to decay inward toward the planet rather than to edge outward. This is rather unexpected since in the Gossamer ring Poynting-Robertson drag (which acts inward) was estimated to be a few orders of magnitude less effective than plasma drag (which acts outward). Clearly there are huge uncertainties in our understanding of the near-Jupiter plasma environment. The direction of orbital evolution is especially important in determining the effects of the numerous electromagnetic (Lorentz) resonances in the two Gossamer rings. These resonances are very powerful and important at Jupiter; a vertical Lorentz resonance, for example, is believed to cause the transition between the main jovian ring and its halo.
We have analytically and numerically modeled dust grains of various sizes evolving inward through the Gossamer rings under the action of planetary and satellite gravity, the electromagnetic force, radiation pressure, and Poynting-Robertson drag. Our new findings include:\\ ......1) Trapping of dust into stable orbits with large inclinations.\\ ......2) An unusual cluster of resonances near synchronous orbit (2.23 RJ).\\ ......3) Calculations of the strengths of relevant Lorentz resonances.\\ ......4) Stability of dust on tadpole and horseshoe orbits.\\ One of our more interesting predictions is that each of the Gossamer rings should have a faint vertically-extended halo associated with it. The dynamical connection between each Gossamer ring and its halo is similar to the relationship between the main ring and its halo.
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