Uranian Equinoctial Observations

In December of 2007, the planet Uranus passed through its northern hemisphere spring equinox. The northernmost latitudes of the planet and regular satellites were exposed to sunlight for the first time in 42 years. Unique circumstances during the equinoctial event also concerning the viewing geometries of the rings and satellites provided rare opportunities to determine the physical nature of these elements of the Uranian system and to study the short-term and evolutionary effects of seasonal insolation in the outer solar system. Furthermore, the approaching perspective afforded opportunities to characterize details of surfaces that had not been viewable, even by Voyager 2, since the advent of modern instrumentation. We present preliminary results from these observations made over several nights during the 2006, 2007, and 2008 observing semesters. Our imaging using the Palomar adaptive optics system on the observatory's 200- inch telescope has been used to obtain high-resolution images. These observations have provided constraints on the planet's atmospheric dynamics and structure by monitoring the increasing storm activity and changing large-scale features in the atmosphere, such as the shifting polar collar, and sampling the vertical structure from multiple planetary occultations. These same images also provide unique photometric information regarding the ring-system particles by viewing the system from its dark side, accessible only during the 2007 season. Spectral and spectro-photometric observations of the newly exposed surfaces of the major satellites have also been obtained from the IRTF, the SOAR telescope, and Palomar 200-inch, including observations of some mutual event phenomena. Acknowledgements: These results are based in part on observations obtained at the Hale Telescope, Palomar Observatory, as part of a collaborative agreement between Caltech, JPL and Cornell University. Some observations were also obtained at the Infrared Telescope Facility, which is operated by the University of Hawaii, using the SpeX near-IR spectrometer and at the SOAR telescope, Cerro Pachon, Chile using the OSIRIS camera.