Voyager 2 stellar occultation probe of the Uranian rings: A detailed comparison of UVS and PPS results

Abstract

We conducted a detailed study and comparative analysis of the Voyager UVS and PPS stellar occultations of the Uranian ring system. The primary objective of this study was the determination of the constraints on the sizes of the ring particles. The Voyager UVS and PPS occultations probed the epsilon and delta rings at significantly shorter wavelengths (0.11 μm and 0.27 μm, respectively) and at substantially different viewing geometries than a large number of existing Earth-based occultations. These differences combine to produce a unique mutual sensitivity among the UVS, PPS and Earth-based observations to the particle properties of the rings. Our results yield slight, but significant differences between PPS and UVS optical depths. We interpret these differences as wavelength dependent scattering due to a population of small particles in the mm to cm size range in epsilon and delta rings. The size distribution of particles in epsilon and delta rings were found to be similar, the main difference being the total number of particles. In contrast to studies at longer wavelengths, our results imply a relatively steep particle size distribution characterized by a power law of index 3 or greater.