Various active and passive orbital measurements have provided evidence for surficial water ice within some lunar permanently shadowed regions (PSRs), especially from near-infrared observations by the M³ instrument. However, radar identification of lunar ice has so far remained ambiguous. Here, we examine the radar-inferred dielectric properties of lunar PSRs and illuminated craters to investigate the potential for ice. We show that the dielectric permittivity of proposed surficial ice-bearing PSRs is lower and has a different distribution than illuminated crater floors of the same diameter range. This difference is confirmed via polarimetric analysis. However, we find that regions with fewer or greater numbers of M³ detections do not have meaningfully different dielectric properties. The lack of correlation with M³ detections suggests the differences in radar properties are likely due to a smoother surface at the wavelength scale, perhaps as a consequence of the presence of deeper ice, as suggested by prior studies.

A growing number of satellites in the outer solar system likely have global oceans beneath their outer icy shells. While the presence of liquid water makes these ocean worlds compelling astrobiological targets, the exchange of heat and materials between the deep interior and the surface also plays a critical role in promoting habitable environments. In this article, we combine geophysical, geochemical, and geological observations of the Jovian satellites Europa, Ganymede, and Callisto as well as the Saturnian satellites Enceladus and Titan to summarize our current state of understanding of their interiors and surface exchange processes. Potential mechanisms for driving exchange processes upward from the ocean floor and downward from the satellite surface are then reviewed, which are primarily based on numerical models of ice shell and ocean dynamics and complemented by terrestrial analog studies. Future missions to explore these exo-oceans will further revolutionize our understanding of ice-ocean exchange processes and their implications for the habitability of these worlds.