Tidally induced fault motion within Europa's ice shell and implications for subsurface communication development

Abstract

The processes that maintain a subsurface ocean at Europa may also cause geophysical hazards within the overlying ice shell that are important to understand for any subsurface access mission. In this study, we applied 3D finite element models to better constrain the potential magnitude of tidally induced fault motion in the ice shell that a cryobot and communication hardware could experience during a subsurface mission. Models showed that displacement along a fault resulting from a static tidal stress at orbital perijove was <5 cm at the subjovian and ∼ 5–82 cm at Thera Macula, depending on fault orientation, changes in tidal stress with depth, and coefficient of friction. Time-dependent tidal forcing over one tidal cycle resulted in fault displacements of ∼0.50–2.9 m for end-member fault geometries at Thera Macula. The potential strain imposed on a communication tether from the fault movement will depend greatly on the currently unknown adhesion of the tether to the ice as well as potential fault tip propagation, yet these analyses provide first-order approximations for end-member strain conditions using measurements of the motion across a fault for a cryobot at 1 km depth. Results suggest it is important to consider motion throughout a tidal cycle and that certain locations and surface features on Europa may prove to be more challenging for a subsurface mission than others. With NASA's upcoming Europa Clipper and ESA's JUICE missions, fault displacements on Europa could be observed, providing further information on regions or features more/less hazardous to cryobot missions.