Juno Microwave Radiometer Observations of Europa’s Subsurface Ice Shell

Juno flew less than 360 km from the surface of Jupiter’s moon Europa on 29 September, 2022, and mapped part of the ice shell with the Microwave Radiometer (MWR) at frequencies of 0.6, 1.2, 2.5, 4.8, 9.6, and 22 GHz.  The partial map covers a latitude range from ~20^oS to ~50^oN and a longitude range from 70^oW to 50^oE.  At these frequencies, the emission originates well beneath the nearly-transparent surface, probing from as deep as 28 km (at 0.6 GHz) and less than 20 m (at 22 GHz), depending on the purity of the ice.  Microwave reflection plays an important role, and MWR data suggest the presence of small (radius a few cm) scatterers at depths of many meters.  Spatial variation is dominated by reflection, especially for the higher-frequency channels, and correlates with terrain type.  We present analysis of the data and discuss the implications.