Eric E. Becklin

The diameter and reflectance of Triton

Abstract 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 ( p v ⩾ 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 CH 4 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.

The albedo and diameter of 1862 Apollo

Abstract We report infrared thermal emission measurements of 1862 Apollo, which is the type example of an Earth-crossing asteroid. We derive a geometric albedo of 0.21 ± 0.02 which is within the albedo range of the S class of asteroids. The effective diameter was observed to vary with rotation from 1.2 ± 0.1 to 1.5 ± 0.1 km.

Thermal emission from Saturn's rings at 380 μm

Abstract We have observed the Saturn disk-ring system at a wavelength of 380 μm using the UKIRT 3.8-m telescope. The brightness temperature of the rings was derived using two independent techniques. In our first method we used a wide beam in our observations and compared our results for the disk-ring system with those obtained at an earlier epoch, when the rings were edge-on. Differencing these two measurements then gave a value for the ring contribution. In our second method, we stopped down the field aperture, allowing the ring contribution to be resolved when scanning across the disk-ring plane. The second method, which we believe is inherently more accurate than the first, gives a B-ring brightness temperature 39 ∓ 8°K at 380μm. This temperature is significantly lower than previously reported results at this wavelength. Our results, compared with those obtained at other wavelengths, show that there is a gradual decrease in the observed ring brightness temperature from the infrared into the radio.