Io’s polar volcanic thermal emission supports shallow tidal heating and magma ocean models

The distribution of volcanic activity on Io, the most volcanically active object in the Solar System is the result of tidally-induced internal heating. Models predict enhanced heat flow at Io’s poles if tidal heating is deep in the mantle, and at lower latitudes if heating is predominantly in the asthenosphere or a magma ocean is present. We must first understand the distribution and magnitude of Io’s tidal heating in order to determine the current position of Io in the evolving orbital resonance with Europa and Ganymede. However, previous missions did not adequately observe Io’s poles. The desired global measurements of volcanic thermal emission were made possible only when NASA’s Juno mission entered a polar orbit around Jupiter in 2016. Here we show that the distribution of volcanic 4.8-μm spectral radiance supports the shallow tidal heating model. We have created the first global mapping of 4.8-μm spectral radiance from 266 volcanic hot spots identified in Juno Jovian Infrared Auroral Mapper (JIRAM) data. We find 60% more volcanic spectral radiance per unit area at latitudes lower than 60°. Although the numbers of hot spots per unit area are not greatly different, polar volcanoes emit less energy at 4.8 μm than volcanoes at lower latitudes by a factor of more than two. This result is consistent with shallow (aesthenospheric) tidal heating models or the presence of global magma ocean. Our results also show that north polar volcano spectral radiance is more than twice that of south polar volcanoes, suggesting dichotomies in structure and volcanic advection between polar regions.