Analysis of very-high-resolution Galileo images and implications for resurfacing mechanisms on Europa

The young (<100 Ma) surface of Jupiter's icy satellite Europa raises the key questions: (1) what are the resurfacing mechanisms for creating Europa's young surface, and (2) how have these processes evolved through time? To address these questions we analyze the nine high-resolution frames obtained by the Galileo Solid State Imager (SSI)-eight at 16 m/pixel and one at 8 m/pixel (commonly quoted at the planned 6-12 m/pixel as in Greeley et al., 2000)-during the E12 flyby of Europa in Dec. 1997. This dataset is now two decades old, but it has not been analyzed in detail until this work. Despite the largely different viewing and lighting conditions, we mosaic these high-resolution frames into the 220 m/pixel regional context frame. We then perform geomorphologic mapping of the high-resolution image mosaic and the regional image frame, for comparison, and we also create a structural map of the high-resolution image mosaic. The units in the geomorphologic map are defined by surface texture, landform shape (morphology), dimension, and relative albedo. The structural map units include interpretations from the geomorphologic map units and their interpretation implies potential kinematic processes for the formation of particular structures. Our primary mapping observations include the regular spacing and gentle slopes of the ridge-and-trough terrain, the sharp boundaries and preserved structures of the chaos terrain, and the symmetry but irregular size of double ridges. We then evaluate proposed formation mechanisms for these and other mapped features. The high-resolution images also reveal an abundance of small (<100 m) pits, the presence of a newly identified high-albedo smooth material, and potential tectonic fabric, all of which have possible implications for the surface history. The mapping and structural analyses lead to the key finding that local-scale resurfacing mechanisms have transitioned from distributed deformation expressed by the formation of the ridged plains to discrete deformation characterized by the formation of chaos and isolated fractures. This finding is consistent with simultaneous ice-shell thickening and cooling occurring as the ice-shell deformed.