Dr. Mark Showalter

December 21, 2006

“Planetary Rings: Observation and Interpretation”

NNG05GL48G

This project addresses some of the fundamental open questions related to the dynamics and origins of planetary ring systems. We employ a variety of state-of-the-art techniques in image analysis and photometric modeling to glean untapped new information from the best existing spacecraft- and Earth-based data sets. The three systems to be studied encompass the full range of physical processes at work in planetary rings. (1) Continuing studies of the Voyager images of Saturn's F Ring will illuminate the dynamical processes behind its clumps, kinks and so-called "braids," providing context for recent Cassini results. We will study recently-identified brightness variations that appear to be an indicator of the clumps' collisional origins. We will also study periodicities and kinks in the ring to better define the role of nearby Prometheus and to search more thoroughly for the effects of Pandora and perhaps other nearby bodies. (2) We will take a new look at the question of whether unseen "shepherding" moons confine the rings of Uranus. We will use the best Voyager images to search for evidence of moons down to ~ 5 km in size, well below Voyager's widely quoted detection limit. We will also seek rotating modes and patterns in the rings, which could provide additional evidence for the resonant effects of nearby shepherds. (3) We will study the dynamics of dust in the Jovian ring system, using image analysis techniques that reveal more clearly the three-dimensional structure and photometric properties of the system. Analysis of Galileo, Voyager and Earth-based data, combined with dynamical simulations, will reveal the roles of non-gravitational processes including Poynting-Robertson drag and Lorentz resonances, and will help us to distinguish between rival models for dust evolution through the system. Key observations to explain are a newly-discovered ringlet of dust sharing its orbit with Amalthea and a discrepancy between the locations of dust and source bodies in the main ring.