The thermal emission spectrum of Io and a determination of the heat flux from its hot spots

Abstract

Observations of thermal emission from Io in the near infrared made during an eclipse were combined with unpublished 8‐ to 13‐μm intermediate band photometry and a 16‐ to 22‐μm spectrum to specify Io's emission spectrum from 2.2 to 22 μm. Models were calculated having ‘hot spots’ at several different temperatures superposed on a surface, the major part of which is assumed to be at the solar equilibrium temperature. It was possible to fit the entire composite spectrum with this model. It is argued that the total emission from the hot spots can be equated to the nonsolar energy input into Io. The disk‐averaged heat radiated by the hot spots is found to be 180 ± 60 μW cm −2 = 43 ± 14 μcal cm −2 s −l . A possible bimodal temperature distribution of the hot spots is discussed.