Constraints on the Thickness and Subsurface Characteristics of Europa’s Ice Shell by the Juno Microwave Radiometer

Observations with Juno’s Microwave Radiometer (MWR) provided new constraints on the depth and subsurface structure of Europa’s ice shell.  The observed temperature gradient constrains the thickness of the thermally conductive part of the ice shell, and pores or cracks beneath the surface scatter microwaves, enabling characterization of the size and distribution of the scatterers.  Results assuming an ice shell of pure water ice, are consistent with a conductive ice shell thickness of 29±10 km, with negligible surface reflectivity, volume fraction of scatterers 0.045, scale height of scatterers 219 m, and scatterer size distribution power law index -3.96.  The size, depth, and volume fraction of the scatterers suggest they are not a likely source of carrying nutrients between the ocean and the surface.  Ice salinity of 15 mg/kg would reduce the estimate of the thickness by about 5 km.  A thermally convective layer would increase the total ice shell thickness but only slightly decrease the estimate of the conductive layer.  Recent analysis related to the variation of ice shell thickness and subsurface characteristics will be reported along with the more general results described above.