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

Ice penetrating radars are intuitively appealing for probing ice shells because it is perceived as a way to directly imaging the ice/ocean interface or as a way to "picture" and interpret visually the structural  cross-section of the ice. While this approach is significant and can lead to substantial discoveries, it's also likely that many radar sounding measurements will not exhibit these obvious, intuitive features. Here, we address the potential of more subtle radar echoes (or the absence thereof) in providing valuable information. These echoes can impose constraints on ice temperature and thickness, offering insights similar to those obtained from other planetary geophysical methods like gravity science or magnetic induction measurements. In our study, we examine four potential radar signatures: pore-closure, eutectic melt, isolated echo detection, and attenuation horizons. We demonstrate that each of these signatures, by providing observational constraints on either the temperature or the integrated two-way attenuation at a given depth, can help determine the thickness of the conductive portion of Europa's ice shell. By integrating these findings with other geophysical approaches (e.g., gravity, magnetics), radar sounding data can significantly enhance studies and models of the ice-shell interior, even without the direct detection of the ice/ocean interface.