IRAS survey-mode observations of Pluto-Charon

Radiometric observations of Pluto and its moon, Charon, by the Infrared Ast ronomical Satellite (IRAS) in 1983 marked the first detection of the system at thermal wavelengths. Reexamination of the IRAS observations prove that Pluto-Charon was detected several times during the all-sky survey in additi on to the pointed observations that targeted the system. Pluto-Charon exhib its thermal lightcurve variations that can be explained by the known variat ion in hemispherically averaged geometric albedo with sub-Earth longitude. Changes in albedo, however, are not sufficient to explain the lower than ex pected fluxes observed at microwave wavelengths. (C) 1999 Academic Press.