Infrared thermal models for Saturn's ring

Infrared (10 and 20 microns) thermal emission data for Saturn's rings are discussed in terms of simple isothermal radiative transfer models of finite optical thickness. Recent brightness temperature measurements, corresponding to essentially maximum ring tilt, indicate that optical single scattering albedos less than 0.75 are required to provide sufficient heating of the ring material. Reconciliation with analyses of the optical scattering properties of the ring requires the backscattering efficiency to be even higher than for a macroscopic sphere. Historical brightness temperature measurements are used to show that no unique isothermal ring model exists. Instead, a temperature gradient perpendicular to the ring plane appears to be present.