New Global Map of Io's Volcanic Thermal Emission and Discovery of Hemispherical Dichotomies

By combining multiple spacecraft and telescope datasets the first fully global volcanic heat flow map down to spatial resolutions of ~10 km/pixel in Io’s polar regions has been created. Juno Jovian Infrared Auroral Mapper (JIRAM) data have filled coverage gaps in Io’s polar regions and other areas poorly imaged by Galileo instruments. 343 thermal sources are identified in data up to mid-2023. While poor correlations are found between the longitudinal distribution of volcanic thermal emission and radially-integrated end member models of internal heating, the best correlations are found with shallow asthenospheric tidal heating and magma ocean models and negative correlations with the deep mantle heating model. The presence of polar volcanoes supports but does not necessarily confirm the presence of a magma ocean on Io. We find that the number of active volcanoes per unit area in polar regions is no different from that at lower latitudes, but find that Io’s polar volcanoes are smaller, in terms of thermal emission, than those at lower latitudes. Half as much energy is emitted from polar volcanoes than from those at lower latitudes, and the volcanic thermal emission from north polar cap volcanic thermal emission is twice that of the south polar cap. Apparent dichotomies exist between sub- and anti-jovian hemispheres in terms of volcanic advection and resulting power output, between polar regions and lower latitudes, and between the north and south polar regions, possibly due to internal asymmetries or variations in lithospheric thickness.