Saturn's Rings: 3-mm Low-Inclination Observations and Derived Properties.
AEROSPACE CORP EL SEGUNDO CA ELECTRONICS RESEARCH LAB
Pagination or Media Count:
We have combined 3-mm observations of Saturn at low ring inclinations with our previous observations to determine a much more precise brightness temperature for Saturns rings. Allowing for uncertainties in the optical depth and uniformity of the A and B rings and for ambiguities due to the C ring, but assuming the ring brightness to remain approximately constant with inclination, we determine a mean brightness temperature for the A and B rings of 17 or - 4 K. The portion of this brightness attributed to ring particle thermal emission is 11 or - 5 K. The disk temperature of Saturn without the rings would be 156 or - 6 K, relative to absolutely calibrated disk temperature for Jupiter. Assuming that the ring particles are pure water ice, a simple slab emission model leads to an estimate of typical particle sizes of approx 0.3 m. A multiple scattering model gives a ring particle effective isotropic single-scattering albedo of 0.85 or - 0.05. This albedo has been compared with theoretical Mie calculations of average albedo for various combinations of particle size distribution and refractive indices. If the maximum particle radius approx 5 m deduced from Voyager bistatic radar observations Marouf et al., 1982 is correct, our results indicate either a a particle distribution between 1 cm and several meters radius of the form r-s with 3.3 or approx s or approx 3.6, or b a material absorption coefficient between 3 and 10 times lower than that of pure water ice Ih at 85 K, or both.