FRACTURE TRANSPORT OF OCEAN WATER IN EUROPA’S COOLING ICE SHELL

Abstract

The ice shell of Jupiter’s ocean moon Europa, currently under NASA investigation for extraterrestrial life, is covered in pits, domes, and ridges, potentially a result of ∼10 km wide sills of liquid water near the surface. These sills are proposed to form when fractures transport ocean water from the base of the ∼25 km thick shell to a few km depth. Shell-penetrating fractures may also be responsible for observed water vapor eruptions. Previous fracture models are unable to produce such fractures for ice thicker than 10 km, though the coupled dynamic effects of shell cooling and ocean pressurization have not yet been analyzed together. If a viscoelastic ice shell is cooled over time, tensional stresses from thermal contraction and ocean pressurization may be sufficient to crack the shell and transport ocean water near the surface, explaining much of Europa’s surface geology. Surface and Basal fracture stability analysis of stresses from cooling in an ice shell, accounting for deep viscous relaxation and ocean compressibility, reveals that ocean water transport near Europa’s surface is implausible once ice thickness exceeds 3.8 km. If Europa’s surface features and plumes are a result of near surface ocean water, other physical mechanisms are likely at play.