STRESS AND STRAIN ON SATURN’S ICY MOONS

The Saturnian icy moons of Dione, Enceladus, Rhea, and Tethys each feature abundant evidence of extensional tectonic deformation of their brittle outer shells. This deformation occurs at a range of scales, from lineations, fissures, and single normal faults, through (sets of) graben, to hemisphere-spanning rift systems (chasmata). Numerous mechanisms including non-synchronous rotation, tidal recession, despinning, polar wandering, and global expansion have been proposed to explain this tectonism. Nonetheless, despite differences in the geophysical properties of these bodies, and the varying degrees to which these processes are applicable to a given moon, there are broad similarities in how extensional strains are manifest throughout the Saturnian system. Each moon, for example, shows a concentration of strain at or bordering their trailing hemispheres. And although extension is more broadly distributed on Enceladus than on Dione, Rhea, and Tethys, these latter bodies each have prominent rift systems 70–110 km in width that trend north–northeast at low- to mid-latitudes, subtending at least 90° of arc there—and the chasmata on Dione and Tethys extend farther, to high latitudes (in the south and north, respectively) along trajectories very close to great circles. Further, many of the constituent structures within these rift zones appear relatively pristine, indicating that at least the last phases of localized deformation within each chasma occurred comparatively recently. Here, we are mapping the extensional tectonics of Dione, Rhea, and Tethys by combining the latest Cassini ISS-derived global photogeological and topographic base maps, and recording morphometric data (e.g., length, azimuth, relief, spatial density, and strain) for each mapped landform. The detailed characterization of tectonism on these mid-sized satellites will help test predicted strain patterns for the processes proposed to operate on these and other Saturnian moons and potentially—given the presence of pronounced rift zones on other icy moons like Uranus’ Miranda and Titania—on icy bodies across the Outer Solar System.