Pits, Uplifts and Small Chaos Features on Europa: Morphologic and Morphometric Evidence for Intrusive Upwelling and Lower Limits to Ice Shell Thickness

TL;DR

This study analyzes Europa's surface features to estimate the ice shell thickness, suggesting a lower limit of 3-8 km based on geomorphological evidence of pits, uplifts, and chaos features.

Contribution

It provides new morphological and morphometric evidence supporting intrusive upwelling models and constrains Europa's ice shell thickness using detailed feature analysis.

Findings

Largest features are around 5-6 km in diameter

No pits smaller than 3.3 km in high-resolution images

Supports intracrustal sill models over melt-through models

Abstract

One of the clearest but unresolved questions for Europa is the thickness of its icy shell. Europa's surface is resplendent with geological features that bear on this question, and ultimately on its interior, geological history, and astrobiological potential. We characterize the size and topographic expression of circular and subcircular features created by endogenic thermal and tectonic disturbances on Europa: pits, uplifts, and small, subcircular chaos. We utilize the medium-resolution Galileo regional maps (RegMaps), as well as high-resolution regions, digital elevation models derived from albedo-controlled photoclinometry, and in some cases stereo-controlled photoclinometry. While limited in extent, the high-resolution images are extremely valuable for detecting smaller features and for overall geomorphological analysis. A peak in the size-distribution for all features is found at ~5-6 km in diameter and no pits smaller than 3.3 km in diameter were found in high resolution images. Additionally, there is a trend for larger pits to be deeper, and larger uplifts to be higher. Our data support a diapiric or intracrustal sill interpretation (as opposed to purely non-intrusive, melt-through models) and place a lower limit on ice shell thickness at the time of feature formation of 3-to-8 km, assuming isostasy and depending on the composition of the ice and underlying ocean.