Radar Subsurface Exploration of Icy Moons: Understanding Radar Wave Propagation Through Europa, Ganymede and Callisto

Orbital low frequency ice penetrating radars are proposed as a unique tool to probe the first 10 km of the subsurface icy crust of the Jovian satellites, Europa, Ganymede and Callisto. The main objective of our study is to characterize the radar response to the potential presence of aquifers, global ocean and ice tectonic structural elements associated to the moons thermal evolution. We performed a parametric detectability study of the above-mentioned features using the Finite Difference Time Domain (FDTD) method. The forward propagation were performed for a central frequency of 9 MHz, as suggested for future sounding experiments. Simulations were performed for several geoelectrical models that in turn represent different geological hypothesis of Europa, Ganymede and Callisto. We investigated the radar detectability and identification of three main subsurface features: brine aquifers, brittle-ductile interfaces and shallow faults. For each of them we studied the effect of their structural and dielectric properties on their identification considering different geological and geophysical scenarios. In particular we studied the effect of surface clutter and volume scattering on the detectability of the above-mentioned features. The amplitude and losses of the backscattered electromagnetic field of the incident radar pulse were evaluated as a function of the radar range time. Our simulations suggest that aquifer detectability is compromised by its depth, ice impurities content and by the surface and volume scattering. Aquifers are detectable between 7 and 25 dB above the 65 dB galactic noise level at depths ranging respectively from 4 to 2 km. Beyond 4 km of depth and considering the validity of the topographic and dielectric parameters used in our modeling, aquifers could be more challenging for a non ambiguous detection. For the brittle-ductile interface our simulation results suggests that it is identifiable between 2 and 3 km even under highly fractured subsurface conditions. Additionally the depth variation of the brittle ductile interface can be assessed from radar sounding. On contrary, detectability of faults on Ganymede is highly dependent on the dielectric properties of their inner fill materials that is yet to be characterized by our ongoing laboratory characterization of icy moon analog materials.