Enceladus' global geology as seen by Cassini ISS

Abstract

Enceladus, one of Saturn's medium-sized icy moons, was the target of three close Cassini flybys in 2005. The first two revealed a world more tectonically active than previously known based on Voyager data. The "smooth plains" regions that were mapped then have now resolved themselves into terrains filled with networks of parallel to sub-parallel sets of ridge-and-trough morphology. Also seen are cracks, deep rift systems, chevron and curvilinear fractures, curvilinear ridges, heavily cratered terrain, and tectonically modified craters. Several of the impact craters have been modified by cracks, the orientations of which appear to have a radial component, indicating that the extensional stress field that caused the fractures was influenced by stresses due to the craters themselves. Mapping of the locations of these craters and other, undeflected, fractures yields information about variations in the stress field across the satellite. The third Cassini flyby revealed the youngest surface on Enceladus, the south polar area. With the images from all three flybys and Voyager data, we can characterize the global geology. Firstly, measurements of the spacing in various regions of ridge-and-trough terrain yield information on the lithospheric thickness. Further, the heavily cratered terrains appear to be distributed systematically on the surface. Finally, while the south pole appears to be young, the north pole is more heavily cratered. It also displays some tectonic deformation, but no evidence of a tectonic ring like that seen in the south.