DIAMETER AND REFLECTANCE OF TRITON

New image-tube spectra of Triton are analyzed for a determination of the reflectance of the satellite between 0.32 and 0.74 μm. Comparison of the violet reflectance of Triton with that of terrestrial minerals, lunar samples, and meteorites, gives evidence that the satellite surface is composed largely of rocky material having the same sources of violet opacity (mineral charge transfer and crystal field transitions). New radiometric observations set a stringent upper limit to the satellite radius (r ≤ 2600 km) and a lower limit to the geometric albedo (pv ≥ 0.19). The albedo can be somewhat higher and still within the range allowed by a rocky surface. No useful constraints can be put on the mean density of Triton because of remaining uncertainties in the radius and the mass. The image-tube spectra show no evidence of gaseous absorption in the methane bands, though a stronger band has been found in the infrared at 2.3 μm (Cruikshank and Silvaggio, 1979, in press; the near-infrared photometric colors may be affected by the CH4 band. Rayleigh scattering computations of a potential inert atmospheric component of Triton appear to preclude the presence of large quantities of nitrogen and the noble gases. © 1979.