This award will support collaborative research between Dr. William Hubbard, Lunar and Planetary Laboratory, University of Arizona and Drs. Andre Brahic and Bruno Sicardy, Observatory of Paris, Meudon, France. The objective of the project is a joint effort on the reduction and analysis of coordinated observations of stellar occultations by outer solar system bodies, particularly focusing on Saturn and Neptune. These studies will be used to derive new results about the ring systems and the atmospheres of these objects, which will complement and expand the latest information from Voyager encounters. Based on results from the 1989 Neptune encounter, the researchers will plan further coordinated observa- tions of future occultation events, as well as theoretical investigations of ring dynamics and atmospheric structure related to the observational data base. The stellar occultation technique is used to probe the structure of distant atmospheres and rings with a spatial resolution of a few kilometers. With the dearth of spacecraft observations of outer system bodies following Voyager's Neptune encounter, it is particularly important to carry out this work. Neptune's bizarre ring-arcs were first identified by a collaborative effort of these investigators, and the recent confirmation of these structures by the Voyager research has emphasized the value of the proposed research. Also, both groups were highly successful in obtaining recent stellar occultation observations of Saturn's rings and atmosphere, involving a fifth magnitude star, which resulted in data of unusually high quality. Furthermore, the Meudon group obtained the first stellar occultation probe of Saturn's satellite Titan. Because of the diversely located sites at which data are obtained, it is important that these two groups have the continued opportunity to work together closely.
