Modeling Fracture Hazards at Europa for Cryobot Tunneling and Communication

Abstract:

The potential habitability of Europa’s subsurface ocean makes it an ideal candidate for future exploration. However, a probe would need to drill or melt through the potentially tens of kilometers thick ice shell and be able to navigate cryotectonic hazards to reach the ocean. Communications will likely be dependent on a tether extending from the probe to the surface, so it is necessary to understand the potential hazards that the probe and tether could experience within the ice shell. A finite element modeling program, FRANC2d, was used to determine the stresses that a probe and tether could experience when pre-existing fractures are proximal to the tunneling probe at a depth of 1 km. We designed a 2-dimensional model for a melting probe that is 5.2 m long and 0.5 m wide; these dimensions were based on probe designs described in the 2019 “Compass Final Report: Europa Tunnelbot.” A 0.5-meter-wide column represents the refrozen melt column in the model, which extends from the top of the probe to the surface. We are exploring the effects of changes to the material properties within the refrozen column due to the solidification rate, microstructure and composition of the melt water within the column. When applying homogeneous material values to the entire ice shell, tensile stresses at the base of the probe and at the surface, where tunneling was initiated, were observed when a fracture was within 500 meters of the probe’s tunnel at the surface. The presence of an additional fracture on the opposite side of the probe (also within 500 m) resulted in tensile stresses at the surface but compressive stresses around the probe. These results indicate that a new fracture could form at the surface as a result of tunneling when one or more fractures are proximal to the probe because the tensile stresses exceed the tensile strength of ice (10⁴-10⁶ Pa). The compressive stresses around the probe when two fractures are present show it is less likely that a fracture would form at the base of the probe in this scenario. Future models will determine the effects of the potentially induced fractures on the probe, communications tether, and the surrounding environment.