Pioneer 11 Infrared Radiometer Experiment: The Global Heat Balance of Jupiter

Abstract
Data obtained by the infrared radiometers on the Pioneer 10 and Pioneer 11 spacecraft, over a large range of emission angles, have indicated an effective temperature for Jupiter of 125° ± 3°K. The implied ratio of planetary thermal emission to solar energy absorbed is 1.9±0.2, a value not significantly different from the earth-based estimate of 2.5±0.5.