The 16- to 38-micron spectrum of Callisto

The emission spectrum of Callisto was measured between 16 and 38 microns with a spectral resolution of 1/30 of a wavelength, using the NASA Kuiper Airborne Observatory on the night of October 30-31, 1975. Within the errors, the observed spectrum is like that of a 155 K blackbody, in both shape and absolute intensity. The infrared emission and diameter of Callisto indicate a bolometric Bond albedo of 0.05 + or - 0.14, which is consistent with heating of the surface by absorbed sunlight.