Electromagnetic Measurements and Modeling of Rocky and Icy Crust Simulants to Support Planetary Radar Sounder Exploration

Reliable interpretation of orbiting radar sounder observations requires a deep understanding of the electromagnetic behavior of planetary material simulants. Experimental data regarding simulants properties are rather limited, especially for icy materials, and such a lack is often overcome by using mixing models. In this work we performed dielectric and magnetic measurements on rocky granular materials and rocky/icy mixtures to characterize the regolith covering the rocky internal structure of an asteroid and the icy mixtures composing the shallow subsurface of Ganymede at planetary temperatures, and in the frequency range of interest for current and future radar sounder missions (1–100 MHz). We also compared the experimental results with those retrieved using several common mixing formulas to assess the reliability of the electromagnetic models in reproducing the properties of composite materials. Finally, we estimated the attenuation of the radar signal as a function of temperature and rocky grain volume fractions in different subsurface scenarios. Our results suggest that caution should be used in applying mixing formulas to simulate the electromagnetic properties of planetary materials, especially if a non-negligible amount of clay is present in the rocky fraction of the mixtures. Moreover, such results highlight the effect of temperature on the dielectric properties of the icy mixtures which might produce an unexpected behavior in the radar signal attenuation.