![]() The units in the geomorphologic map are defined by surface texture, landform shape (morphology), dimension, and relative albedo. 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. Despite the largely different viewing and lighting conditions, we mosaic these high-resolution frames into the 220 m/pixel regional context frame. This dataset is now two decades old, but it has not been analyzed in detail until this work. 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. ![]() ![]() ![]() As the ice shell thinned, the NSR stresses were enhanced, making fracturing more likely after a smaller amount of NSR compared to the previous fracturing episode. An apparent decreasing angular separation between consecutive fracture sets that formed in the south polar region suggests an ice shell that has weakened in strength over the course of its recent geologic history this could be a result of increased heating, thinning of the ice shell, or a combination of the two. If the ice shell is rotating at a constant rate, the tiger stripes would thus be up to ∼100,000 years old. Our modeled NSR stress magnitudes and orientations suggests a NSR period on the order of 1 Myr and advocate that the tiger stripes have rotated ∼45° clockwise about the south pole since their initial formation in response to NSR of the ice shell. The difference in ice shell thickness, and resultant NSR stress, can help explain the activity in the south, but relative quiescence in the north. However, the thicker ice to the north reduces the NSR stress to less than 2 MPa making fracturing less likely. The thinner ice around the south pole permits NSR tensile stresses of ∼5 MPa, enough to fracture the ice. The difference is most likely due to the elevated energy flux at the south pole, compared to the regions to the north, resulting in a warmer and thinner ice shell in the south polar region. We suggest the brittle layer in the south polar region is 2–4 km thick whereas in the more northern regions, it is 6–8 km. Using the tidal stress calculation program SatStressGUI, we demonstrate the dependence of the magnitude of the NSR stress on the thickness of the ice shell, particularly the brittle outer layer of the ice shell. We suggest nonsynchronous rotation (NSR) stresses, induced by a freely rotating ice shell over a global ocean, are large enough to overcome the tensile strength of the ice shell and initiate fracturing on Enceladus. However, due to their small magnitude (10–100 kPa), diurnal stresses alone are unable to completely explain the initial formation of the tiger stripes and the many additional fractures in the region. Numerous studies of the south polar region of Saturn's moon Enceladus have focused on the four main fractures (the tiger stripes), their associated water plume, and the effects of diurnal tidal stresses on these fractures. Surface fracturing, if a consequence of tidal deformation, places important constraints on the orbital evolution of Europa. Stresses due to orbital eccentricit could have produced tension cracks near the anti-Jove point only if tensile failure occurred either prior to the accumulation of orbital recession stresses or after they had relaxed. If cuspate ridges are compressional features, their orientations and distribution suggest that they formed in response to combined orbital recession and a decrease in planetary volume. ![]() Long, arcuate dark band and triple bands peripheral to the anti-Jove point orientations which suggest that they are strike-slip faults which formed in response to orbital recession. If short, reticulate dark band nnear the anti-Jove point are tension cracks which formed in response to tidal distortion, they could only have been produced by orbital eccentricity. The hypothesis that lineaments on Europa are fractures produced by tidal distortion and planetary volume change is examined by comparing the orientations of dark bands, triple bands, and cuspate ridges to fracture patterns predicted for tidal distortion due to orbital recession and orbital eccentricity. ![]()
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