Earth and Planetary Science Letters | 2019
On the electrical properties of meridianiite and implications for radar sounding of icy satellites
Abstract
Abstract Salts are important secondary components of the icy shells of outer-planet satellites. Salt hydrates formed from freezing brines may influence reflectivity and absorption of surface-penetrating radars. We compare new measurements of frozen mixtures of water and magnesium sulfate with those made by Pettinelli et al. (2016) and Grimm et al. (2008) . We find a high-frequency real dielectric constant of the hydrate endmember (meridianiite) of 4.9 ± 0.3 at −85\xa0°C, within the error bounds derived by Pettinelli and colleagues. We confirm the existence of a dielectric relaxation in meridianiite, similar to the well-known response of ice but at higher frequency and with lower amplitude. However, the meridianiite relaxation is evident only at supereutectic concentrations and for a freezing history that maximizes annealing and partitioning of soluble impurities into the lattice. Dielectric relaxation is nonetheless important for radar sounding of Europa because it controls absorptive loss. Chloride is the most abundant ice-soluble impurity on Europa and will have the greatest impact on radar absorption, whether in ice or hydrates. Salt hydrates may generate reflectivity contrasts in surface-penetrating radar but are unlikely to be uniquely identified.