From Io's Atmosphere to the Plasma Torus

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AST 0307800FrenchThe objective of this project is to develop a deeper understanding of the dynamics and structure of Saturn's rings, through a comprehensive investigation of dramatic variations in their apparent brightness with ring longitude. This azimuthal brightness asymmetry is generally ascribed to gravitational wakes -- clumps of ring particles attempting to accrete under their mutual gravitation, but frustrated in the attempt by Saturn.s strong tidal influence. Dr. Richard French, at Wellesley College, will compare measurements of the asymmetry from a rich set of hundreds of Hubble Space Telescope images and multiple radar images of the rings from Arecibo Observatory, with the predictions of dynamical models of gravitational wakes. The N-body simulations of the detailed structure of the rings, and the resulting gravitational wakes, show a very strong dependence on the detailed properties of the rings, such as the distribution of particle sizes, the surface mass density, and the elasticity of interparticle collisions. The strength of the resulting asymmetry also varies greatly across the rings, for reasons that are not yet completely understood. This work will quantify the newly-discovered azimuthal asymmetry in the inner B ring, for example. This project will be of general interest to planetary scientists because it combines two complementary, superb quality data sets (a decade of HST observations and several years of Arecibo radar results) with a realistic physical description of the rings. The research will address fundamental characteristics of ring dynamics, such as gravitational instabilities, as well as properties of the ring particles themselves. The observations and analysis will provide a firm foundation for Cassini mission investigation of the rings. The HST and Arecibo data will not be supplanted by Cassini observations, because they have been taken under different viewing geometries and they sample very different parts of the scattering phase function of the particles. The investigator will relate the research to the educational life of Wellesley College, an undergraduate women's college with a history of success in educating women in science. This will be accomplished by supervising honors thesis students and undergraduate summer students, and by incorporating detailed examples of their research in both introductory and advanced courses. Dr. French will continue a successful outreach program by leading several-day seminars to about 25 K-12 teachers each year on the relationship between modern planetary science and terrestrial concerns such as global climate change and the consequences of giant impacts, and he will share the ongoing research under this project with teachers and the general public at a non-technical level. This award is made under the Research at Undergraduate Institutions program at NSF.***