Planetary Rings: An Update on Structure and Properties

Over the last several years there has been steady progress in several areas related to the structure and composition of planetary rings. Much of the progress was related to Saturn's rings: new observations by Hubble Space Telescope (HST) and NASA's Infrared Telescope Facility (IRTF), theoretical modeling of the vertical structure of, and particle properties in the rings, discovery of intriguing structural/spectral variations on small spatial scales, new observations and analysis of thermal emission from the rings, theoretical and observational constraints on the quadrupole brightness asymmetry at visual and microwave wavelengths, and new studies of "clumps" in and near the F ring. In addition, new observations were obtained of Jupiter's rings by Cassini, and new models were put forth to explain the narrow edges and apse alignment of the Uranian rings (and presumably other narrow eccentric rings).