Formation of Europas chaotic terrains by porosity compaction without the presence of liquid water
Abstract
The formation mechanisms for chaos terrain on Europa are highly uncertain. The most prominent hypotheses require subsurface melting within a few kilometers or less of the surface over lateral extents of 10s of kilometers or greater. However, the existence of liquid water within the shallow subsurface of Europa implies extremely high thermal gradients and energy fluxes that can heat cryogenic ice and overcome the latent heat of melting, or allow for the injection of deep water from the subsurface ocean. The limited endogenic and tidal energy available at Europa creates conditions where subsurface fluids should rapidly freeze or drain on timescales of less than 103 104 yr, casting into question the high-energy processes that can form or emplace melt. In this study, we propose and investigate a mechanism for chaos formation whereby a porous upper ice shell layer is heated from below, porosity fraction is reduced, the upper ice shell compacts to leave a void, and the upper layer then collapses. We find that adding a small thermal anomaly near the base of the conductive upper ice shell results in the rapid loss of any porosity present because the porous ice warms and relaxes, allowing the porespace to collapse under the overburden pressure. Subsequently, the simplest and most broadly available energy source for chaos formation is the gravitational potential energy of the porous ice shell itself. This gravitational potential energy can be converted into kinetic energy and mechanical deformation by erosion or compaction of the underlaying layers. The mechanism presented here produces chaos terrains by slumping and through forming large, weak cavities that facilitate gravity-driven surface collapse. The porosity compaction mechanism contrasts with previous models that require subsurface melt, which are energetically disfavored. Porous compaction requires minimal added energy, should occur prior to initiation of any melting, and reproduces the deformation at the scales and morphologies expected for Europas chaos terrains.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2021
- Bibcode:
- 2021AGUFM.P51C..04H