Effect of a Surficial Porous Brittle Layer on the Dynamics and Equilibrium Thickness of Europa’s Ice Shell

Abstract Tectonic and cryovolcanic features on Europa suggest a dynamically active ice shell with a highly deformable near-surface brittle layer. Shell thickness estimates based on geological interpretation and thermal modeling vary from 10 km to more than 30 km. The surface activity is probably caused by Jupiter’s tidal forces, whose interplay with heat transfer processes still remains poorly understood. We modeled the dynamics and heat transfer of the ice shell, consistently including a variety of ice/ocean crystallization/melting processes and the effect of a superficial brittle porous layer. For tidal heat production corresponding to current orbital eccentricity, we obtained equilibrium thicknesses between 20 and 80 km depending on the assumed reference viscosity values. We show that the presence of a 1–2 km surficial porous layer reduces the average equilibrium thickness by 5–20 km while simultaneously enhancing the convective dynamics, resulting in much steeper near-surface thermal gradients and higher surface heat flux. The 240 K isotherm is predicted to shift closer to the surface, reaching depths of 10–15 km in the presence of a surficial porous layer, favoring the possible generation of eutectic brines at shallow depths and lithospheric breakups. For highly convecting models, the depth of the 240 K isotherms can be as shallow as 3–4 km, with surface heat flux exceeding 70 mW m −2 . We anticipate that any lateral variation in the porous layer thickness should result in significant variations in the overall ice shell thickness and convective dynamics, which could be revealed by future measurements by Europa Clipper and JUICE.