Geologic mapping of the northern leading hemisphere of Europa from Galileosolid-state imaging data

The northern leading hemisphere of Europa was imaged at regional mapping re solution (similar to 230 m/pixel) by the Galileo spacecraft SSI camera. We produced geologic maps from a regional-scale mosaic and a high resolution i nset of this region. Twelve geologic units were sufficient to produce corre lative geologic maps at both regional and local scales. Stratigraphic relat ionships indicate four major episodes in the geologic history of this area: The first episode includes background plains formation and modification, f ollowed by a second period of extensive lineament formation. The third epis ode included extensive chaotic disruption of the surface at low and middle latitudes. The final episode includes the formation of new sets of ridges a nd bands, especially at high latitudes. The low crater density indicates th at all these episodes in Europa's geologic history are geologically recent. The latitudinal distribution of chaos areas broadly matches that of areas of crustal thinning from models of tidal heating. We show that stress direc tions rotated clockwise with time, which is consistent with predictions fro m global stress models involving tidal deformation and nonsynchronous rotat ion of Europa's crust. On the basis of the change in lineament orientation with time, the reconstructed longitudinal positions of the studied area ind icate that Europa's crust completed a full rotation relative to the tidally deformed interior.