Subsurface radar evidence of cryovolcanic resurfacing on the Jovian moon Ganymede: RIME detectability analysis

Abstract

Smooth bright terrains represent the stratigraphically youngest geological units on Ganymede. One plausible theory explaining their unusual smoothness is based on cryo-volcanic eruptions of low-viscosity water-ice lava, flooding the pre-existing rough terrain to an equipotential flat surface [1]. The cryo-volcanic resurfacing hypothesis is interesting since it implies the presence of local melting or liquid water in the shallow crust of Ganymede. However, due to lack of concrete evidence of source vents of cryo-magma, the theories of cryovolcanic origins of the bright terrain are debatable.

These ambiguities can be resolved by directly imaging the subsurface using low-frequency ice-penetrating radar sounders. This is the case of the Radar for Icy Moon Exploration (RIME) [2] on board the ESA’s Jupiter Icy Moons Explorer (JUICE). RIME is designed to achieve a penetration up to 9 km through the ice crust, by operating at a central frequency of 9 MHz with a programmable bandwidth (high-resolution 2.8 MHz, low-resolution 1 MHz). In order to understand the RIME capability in resolving the possible evidence of cryovolcanic resurfacing, it is necessary to model the radar response using radar sounder simulations.

The goal of this analysis is to model the geo-electrical hypotheses of cryovolcanic resurfacing on Ganymede and simulate the corresponding RIME radargrams. One of the main challenges to accomplish this task is the limited availability of high-resolution topographic data over the potential cryovolcanic targets required for generating the simulation inputs. This might be partially mitigated using manually sketched models, flexible enough for tuning the topographic parameters. However, the process is subjective, and manually generated models are a simplified approximation of reality. To address this limitation, in this paper we propose automatic modelling of the target, coupled with a simulation approach, which is described in the next section.