Peering into the Sub-surface of Jovian Moons with Microwave Radiometry: Latest Findings from the Juno Extended Mission

The Juno Extended Mission (EM) included close fly-bys of Jupiter’s moons Ganymede, Europa and Io between 2021 – 2024. Juno carries a 6-channel microwave radiometer (MWR) operating between 0.6-22 GHz. The broad frequency range of the MWR probes successively deeper into the sub-surface of these bodies with the 0.6GHz channel probing the deepest.  For Ganymede and Europa, the MWR is sensitive to the temperature from the surface to 10s of km into the ice shell over the six frequencies.  For Io, the penetration is much shallower, on the order of 10s of meters maximum depth.  The sub-surface temperature, dielectric and surface roughness properties are encoded in the spectra obtained by the MWR. We will provide an overview of the latest analysis of data from each moon, focusing on the new information gained from this unique planetary instrument.  This includes ice shell thickness, surface/sub-surface composition and heat flow for the icy moons.  For Io, the MWR data provide the latitudinal dependence of the temperature below the diurnal layer and the spectra indicate significant endogenic heating in the upper 10-20 meters that increases with latitude.  The MWR was designed for observing the deep atmosphere of Jupiter but has now demonstrated unique capability for observing the sub-surface of terrestrial planets and planetary moons.  From lessons learned analyzing Juno MWR data, we will discuss how future instruments could be configured specifically for targeting icy or rocky solar system bodies.