\Thermal transport in Saturn\u27s B ring inferred from Cassini CIRS

We examine the heat budget of Saturn\u27s B ring using all of the data from Cassini\u27s Composite Infra Red Spectrometer (CIRS) taken during one Saturn season, together with a detailed numerical calculation of the incident flux. We find that at all times 30-40% of the energy incident on the sunlit side finds its way through the ring to be emitted on the unlit side, and that the specific fraction of heat throughput from the lit to unlit side of the ring varies inversely with the normal optical thickness as f similar to 0.41-0.024 tau. From this we derive a high effective conductivity of the ring, on the order of 0.5 W m(-1) K-1, together with a heat flux through the midplane of the rings that is about 1.5 W m(-2) at high solar elevations. The derived conductivity is at the high end of plausible values for the ring, but the flux rate can easily be met by particle diffusion across the midplane of the rings. While the integrated normal flux from the B ring varies linearly with sin B\u27 as expected, an important finding is that it is dominated for by isotropic emission both on the lit and unlit sides. On the lit side there is an additional emission from a low-phase hot spot with an angular width of 500 that accounts for approximately 2-10% of the total emission. Accounting for wake orientation affects only the inner B Ring, decreasing the absorbed incident radiation by 5-10% there. The numerical model uses only a scalar albedo to parameterize the absorption. It requires a low albedo of A similar to 0.3 to be brought into agreement with ring emission, which is expected if there is enhanced radiance absorption over the single scattered estimates, due to multiple scattering within the ring. (C) 2015 Elsevier Inc. All rights reserved