TRITONS SURFACE-PROPERTIES - A PRELIMINARY-ANALYSIS FROM GROUND-BASED, VOYAGER PHOTOPOLARIMETER SUBSYSTEM, AND LABORATORY MEASUREMENTS

The surface properties of Triton have been determined from a threefold approach involving analysis of ground-based and Voyager photopolarimeter subsystem observations of its phase curve, theoretical modeling, and laboratory measurements of the phase functions of a wide variety of materials. The physical parameters derived include the single-scattering albedo, the single-particle phase function, the compaction state of the optically active portion of the regolith, and the degree of macroscopic roughness. We find that Triton has a high single-scattering albedo (0.96 +/- 0.01 at 0.75-mu-m) and an unusually compacted surface possibly similar to that of Europa. Preliminary results suggest that Triton's single-particle phase function and the macroscopically rough character of its surface are similar to those of most other icy satellites. Laboratory measurements of the phase curve of a sample of a high-albedo, compact volatile-contaminant analogue are in reasonable agreement with Triton's phase curve and provide evidence that the model parameters derived for Triton's surface are physically realistic.