Distribution of Sub-surface Heating on Io

We report on new results analyzing Io’s upwelling thermal emission over the range of 0.6 to 22 GHz acquired with the Juno Microwave Radiometer (MWR) in December 2023 and February 2024.  The microwave emission spectrum from the surface of Io is retrieved from the MWR calibrated brightness temperatures and represents the vertical temperature gradient in the upper 10s of meters of Io.  A large spectral slope (>20K) is observed at all latitudes in the lowest frequency MWR channels suggesting significant endogenic near-surface heating. The spectral slope increases toward the north pole. We compare two end-member model fits to the MWR spectra; a conductive model and a model comprising cooling lava flows.  The conductive model implies heat flows ranging from 1-3 W/m².  The alternative model of relatively fresh lava flows or heat vents covered by a cold, highly insulating crusts fits the MWR spectra with flows covering about 10% of the surface with a 3-8m thick crust.  We show the regional distribution of sub-surface temperature anomalies with depth, comparing to previously catalogued hot spots, flow units and volcanic centers. We will discuss how model assumptions, such as the microwave loss tangent of the crust material and magma temperature, impact the results.