Small variations in ice composition and layer thickness explain bright reflections below martian polar cap without liquid water.

Abnormally bright radar reflections below the Martian south polar layered deposit were originally interpreted as evidence of subglacial liquid water. However, unlike on Earth, conditions beneath the Martian ice are too cold to create or maintain meltwater. In this work, we use radar reflectivity simulations to show that the strong reflections can instead be caused by constructive interference between dusty ice layers that are more closely spaced than the radar resolution. Unlike previous hypotheses, interference does not require anomalous subsurface conditions or exotic materials to be present beneath the ice. In addition, interference between thin layers can explain the variable power of radar returns beneath the entire ice sheet and does not require different mechanisms to be responsible for reflections in different regions.

Surface properties of the seas of Titan as revealed by Cassini mission bistatic radar experiments.

Saturn's moon Titan was explored by the Cassini spacecraft from 2004 to 2017. While Cassini revealed a lot about this Earth-like world, its radar observations could only provide limited information about Titan's liquid hydrocarbons seas Kraken, Ligeia and Punga Mare. Here, we show the results of the analysis of the Cassini mission bistatic radar experiments data of Titan's polar seas. The dual-polarized nature of bistatic radar observations allow independent estimates of effective relative dielectric constant and small-scale roughness of sea surface, which were not possible via monostatic radar data. We find statistically significant variations in effective dielectric constant (i.e., liquid composition), consistent with a latitudinal dependence in the methane-ethane mixing-ratio. The results on estuaries suggest lower values than the open seas, compatible with methane-rich rivers entering seas with higher ethane content. We estimate small-scale roughness of a few millimeters from the almost purely coherent scattering from the sea surface, hinting at the presence of capillary waves. This roughness is concentrated near estuaries and inter-basin straits, perhaps indicating active tidal currents.