Constraining the Thickness of the Conductive Portion of Europa's Ice Shell Using Sparse Radar Echoes

Ice penetrating radar sounding is the primary geophysical technique for imaging the subsurface of planetary ice shells and has the potential to directly detect the ice-ocean interface. However, many sounding measurements may lack laterally extensive features that would aid their physical interpretation. In this scenario, the detection of sparse echoes can also provide rich information on ice shell properties. To explore and demonstrate this possibility, we consider three cases of isolated radar signatures: pore-curing, eutectic melt, and unattributed echoes. We show that through detection of unattributed sparse echoes, the thickness of the conductive portion of Europa's ice shell can be constrained. These constraints can be improved by attributing sparse echoes to thermally diagnostic signatures such as pore-curing and eutectic melt. Notably, this approach to radar sounding echo analysis is particularly compatible with joint inversions with other planetary geophysical observations such as tidal deformation, magnetic induction, and rotation state. Upcoming missions to explore Europa, the icy moon of Jupiter, include ice penetrating radar sounders as part of their instrument payloads. One of the primary goals of these instruments is to investigate the subsurface structure and thickness of Europa's ice shell. It's possible that the radar profiles returned by these instruments will include imagery of the ice-ocean interface across much of the moon, providing a direct measurement of ice-shell thickness. However, we show that, even in the absence of such imagery, a small number of isolated radar echoes can be used to measure the thickness and structure of the ice shell. These echoes include scattering from porous ice near the moon's surface and pockets of melt water within the shell. Radar-detectable interfaces from the subsurface of Europa's ice shell can be thermally diagnostic The thickness of the conductive portion of Europa's ice shell can be constrained without direct detection of the ice-ocean interface The detection of sparse echoes places a lower bound on conductive ice shell thickness based on the two-way integrated radar attenuation