Radar Attenuation for Subsurface Sounding on Enceladus: Effects of a Thermally Insulating Porous Ice Layer.

Saturn's moon Enceladus is thought to possess habitable conditions due to the presence of a global ocean, potential water‐rock interactions at the ocean's base, and its ocean composition derived from sampling active plumes at the south pole. The thin (< ${< } $35 km) and cold ice shell of this small moon in the outer solar system is expected to allow the direct detection of the ice‐ocean interface using low‐frequency radar sounder instruments. Here we investigate the two‐way radar attenuation in Enceladus' ice shell, focusing on the effect of a porous icy layer generated by Enceladus' jet activity. Our results show that in regions with a thin (or absent) porous surface layer, total ice shell penetration is possible. In regions covered by thick and strongly insulating porous surface layers, however, as little as 2% of the ice shell can be penetrated. Nevertheless, a thick porous surface layer leads to high subsurface temperatures promoting the formation of brines at shallow depth that can be detected by future radar measurements. Plain Language Summary: Saturn's moon Enceladus is a prime target for planetary exploration and for the search of habitable conditions beyond Earth. Beneath its icy surface, this small moon is thought to harbor a global ocean, presumably sampled by active water jets which have been observed at Enceladus' south pole. Moreover, shallow brines may exist within the ice shell. The detection of subsurface water reservoirs (either the ocean or shallow brines) that can be achieved by radar is fundamental in characterizing Enceladus' subsurface environment and its habitability potential. In this study we calculate the attenuation of radar signals through the ice shell in the presence of snow deposits that are believed to exist on the surface of Enceladus due to its water jets activity. While we do identify some scenarios in which the radar is able to reach the ice‐ocean interface, we note that this interface may not be reached by a radar sounding instrument in regions covered by thick snow deposits that act as a blanket and keep the subsurface warm. However, in these regions, due to the high subsurface temperatures, shallow water bodies are likely to exist and could be detected by future radar observations. Key Points: We calculate the two‐way radar attenuation on Enceladus considering a porous thermally insulating surface layerFor regions covered by a thick insulating porous surface layer the detection of the ice‐ocean interface is unlikelyFor the same regions the high subsurface temperatures increase the likelihood that shallow brines are present and can be detected by radar [ABSTRACT FROM AUTHOR]