B. D. Wallis

Thermal phase curves observed in Saturn's main rings by Cassini‐CIRS: Detection of an opposition effect?

[1]xa0We report on thermal phase curve measurements of Saturns main rings by the CIRS infrared spectrometer on-board the CASSINI spacecraft. The extensive data set acquired by Cassini since its insertion in orbit around Saturn provides for the first time spatially resolved temperature measurements over broad phase angle ranges and for different solar elevations. Each of these curves exhibit a nonlinear variation in temperature with phase angle, with pronounced surges at medium to low phase angles that we interpret as an opposition effect in thermal infrared. The transition from a relatively flat linear regime to an exponential behavior in the A and B rings occurs at phase angles of 30° to 40° and is significantly broader in the C ring and Cassini Division. Analytical description of the phase curves is provided to serve as basis for future modeling work. The role played by mutual shadowing as possible origin of the broad thermal surge in thicker ring regions is emphasized. In turn, regolith properties might be inferred from the thermal phase curves in the optically thin ring regions.

Stable, High Quantum Efficiency Silicon Photodiodes For Vacuum-UV Applications

Silicon photodiodes have been developed by defect-free phosphorus diffusion having practically no carrier recombination at the Si-SiO2 interface or in the front diffused region. The quantum efficiency of these photodiodes was found to be around 120% at 100 nm. Unlike the previously tested silicon photodiodes, the developed photodiodes exhibit extremely stable quantum efficiency over extended periods of time. Currently, we are investigating the possibility of using these photodiodes as vacuum ultraviolet detector standards.

Temperature and Thermal Emissivity of the Surface of Neptune's Satellite Triton

Analysis of the preliminary results from the Voyager mission to the Neptune system has provided the scientific community with several methods by which the temperature of Neptunes satellite Triton may be determined. If the 37.5 K surface temperature reported by several Voyager investigations is correct, then the photometry reported by the imaging experiment on Voyager requires that Tritons surface have a remarkably low emissivity. Such a low emissivity is not required in order to explain the photometry from the photopolarimeter experiment on Voyager. A low emissivity would be inconsistent with Triton having a rough surface at the ∼100-�m scale as might be expected given the active renewal processes which appear to dominate Tritons surface.