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P. Helfenstein, P.C. Thomas, J. Veverka, S. Squyres, J. A. Rathbun (Cornell), T. Denk, G. Neukum (Freie.U.Berlin), T. Roatsch, R. Wagner (DLR), J. Perry, E. Turtle, A.S. McEwen (U. of Arizona), T.V. Johnson (JPL), C. Porco (SSI), Cassini ISS Team
Cassini's first year in orbit around Saturn was highlighted by two close flybys of Enceladus that enabled the ISS imaging experiment to map 60 finer spatial resolutions than the best Voyager coverage (< 1km/pixel). Fracturing and tectonic modification of the surface is much more pervasive than previously recognized; tectonic resurfacing has likely played a major role in producing the youthful appearance of Enceladus. Regions that were previously mapped from Voyager as "smooth plains" are now seen at sub-kilometer size-scales to be disrupted by extensive networks of fractures and grooves. The surface is regionally divided by diverse styles of tectonic features that we interpret to include deep rifts, horst-and-graben terrains, folded ridges, braided or vermicular networks of grooves, and an ubiquitous spidery network of sub-parallel, curvilinear, high-angle cracks that appear to dissect topographic structures into vertical slabs. ISS color images of morphologically youthful fractures, including a prominent set over the South Pole, reveal relatively blue fault scarps that may represent exposed wall-outcrops of coarse-grained ice. Possible evidence for past cryovolcanism includes kilometer-scale ridges and linear arrays of rounded domes that appear to have extruded through preexisting surface fractures. Some wrinkled, flow-like features with lobate margins are found near the ridge and dome features, but it is unclear if they are volcanic flows or tectonically folded grooved-terrain. New details of viscously-relaxed craters, first seen by Voyager, include central dome features with structurally breached summits and polygonal craters with lobate, rampart-like rims. Among the most mysterious newly-discovered features are small, sub-kilometer-sized dark spots and circular pits that sometimes cluster in a honeycomb like patterns near faults and scarps. Their origin is unknown, but perhaps the pits and dark spots identify sites of explosive venting of subsurface volatiles through fractures or volcanic conduits.
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Bulletin of the American Astronomical Society, 37 #3
© 2004. The American Astronomical Soceity.