The Likely Thickness of Europa’s Icy Shell

Abstract

Abstract The icy outer shell of Jupiter's moon Europa is believed to be geologically active, and geological processes within the ice may be key to sustaining chemical disequilibria and potentially habitable environments within the icy shell and ocean. Currently, there are insufficient observational data to determine the thickness of the icy shell, obfuscating crucial aspects of interior processes. Although a range of icy shell thicknesses (∼10−1–102 km) have been proposed, not all are equally likely given the current knowledge of Europa. In this study, I construct a probability density distribution for Europa's present-day mean icy shell thickness using a heat flux balance, assuming a simple two-layered model consisting of a partially porous conductive upper layer, and a ductile interior layer that may be experiencing solid-state convection. Current best estimate (CBE) values and uncertainties for ∼20 key parameters are propagated through this steady-state heat flux balance to construct ∼107 independent simulations. Additionally, I estimate present-day values for the icy shell layer thicknesses, the rocky interior and icy heat fluxes, icy shell thermal properties, and convective ice viscosity. I predict Europa’s total icy thickness to be ∼23–47 km, with a CBE thickness of 24.3 − 1.5 + 22.8 km . This result is highly skewed; icy shells many tens of kilometers thick are much more probable than icy shells <10 km thick. The resulting distributions have key implications for future spaceborne, landed, and subsurface exploration of Europa, as well as studies of icy shell processes, thermal and mechanical state, and habitability across the icy ocean worlds.