Albedo, internal heat, and energy balance of Jupiter: Preliminary results of the Voyager Infrared Investigation

Abstract

Full disk measurements recorded 31 days before the Voyager 1 encounter with Jupiter by the radiometer (0.4–1.7 µm) of the infrared instrument Iris indicate a geometric albedo of 0.274±0.013. The given error is an estimate of systematic effects and therefore quite uncertain; the random error in the radiometer measurement is negligible. Combining this measurement with the Pioneer‐derived phase integral of 1.25 of Tomasko et al. (1978) and our error estimate of 0.1 yields a Jovian Bond albedo of 0.343±0.032. Infrared spectra recorded at the same time by the Michelson interferometer (4–55 µm), along with a model extrapolation to low wave numbers not covered by the instrument, yield a thermal emission of 1.359±0.014 × 10−3 W cm−2. This corresponds to an equivalent blackbody temperature of 124.4±0.3 K, in agreement with results of Ingersoll et al. (1975) and Erickson et al. (1978) but lower than all other previous estimates. As in the case of the albedo measurement the quoted errors in the emission measurement reflect estimates of systematic effects and are uncertain, while the random component is negligible. From these measurements the internal heat flux of Jupiter is estimated to be 5.444±0.425 × 10−4 W cm−2, and the energy balance defined as the ratio of emitted thermal to absorbed solar energy is 1.668±0.085.