Ridged plains on Europa reveal a compressive past

Abstract

Europa's young surface implies relatively recent resurfacing. Ridged plains, which make up >50% of Europa's surface, have not yet been fully analyzed for a potential formation mechanism. Because ridged plains dominate Europa's surface, this terrain is key to understanding how Europa has resurfaced and how the resurfacing mechanisms may have evolved through time. In this work, we create a new high-resolution topographic model and a two-layer physical analog model to investigate the formation of ridged plains. We find that the ridged plains most closely resemble the compressional physical analog experiments which generate folds. Specifically, the analog experiments with a brittle layer <1/16th the thickness of the underlying ductile-layer best explain the morphological observations of the ridged plains on Europa. Based on the scaling relationships, we find that at the time of the ridged plains formation, the brittle part of the ice shell of Europa's ice shell was ~200 m thick and the total ice-shell thickness, including both the ductile and brittle parts, was >~3000 m. Compared to the predicted current ice shell thickness, this would imply that Europa's ice-shell has thickened through the visible surface history.