ENCELADUS’S DIVERSE RIDGE TERRAINS

Enceladus’s diverse surface can be divided into 4 unique terrains: cratered terrains, south polar terrain (SPT), and leading and trailing hemisphere terrains (LHT and THT). Ridges are found on the SPT, LHT, and THT; each region displays unique styles of ridge morphology implying the possibility of multiple distinct formation mechanisms. In the central part of the SPT, ridges are curvilinear, relatively small (>10s m high and >10 km long), and display a short topographic wavelength (~400–800 m). The tiger stripes, ~100 m deep troughs with raised ridge flanks on either side, are more prominent with heights of 150–260 m and lengths up to ~130 km. Ridge flank slopes range from 3–23° and average ~9°. The proximal location of the tiger stripes to the jets (Porco et al, 2014) suggests these ridges are related to plume activity. Surrounding the SPT are two regions (centered ~140° and 300° lon) which stand higher than their surroundings and are composed of a series of ridge-and-trough structures that appear to have asymmetric slopes. This evidence suggests those ridges may be formed by thrust faulting and folding. In the northern portion of the LHT are two ridge types, one smaller in amplitude and wavelength, and a second larger amplitude set. The smaller ridges have a spacing of 1–2 km, are ~10s m high, and 1–20 km long. The larger ridges are ~600 m high, 15–35 km long, show a lens-like shape in map view, and in cross-section are broad with flank slopes of 6–30°. The southern LHT is dominated by ridges that are similar in size and shape to the smaller ridges to the north, but this region lacks a larger ridge set. The raised topography and sinuosity suggest that LHT ridges may have formed by a compressional event. On the THT are a series of prominent ridges termed “dorsa.” In map view, they are curvilinear, with branches that intersect other dorsa at near right angles. They can reach lengths of ~50 km and heights of 600–800 m, and they have gentle sloping flanks of ~20° and broad rounded tops that are suggestive of a compressive origin. The orientations of these dorsa suggest simultaneous contractional strain oriented N-S and E-W, where the strain oriented E-W was slightly lesser. Here we explore how the different detailed characteristics of ridge types in each region suggest the tectonized terrains of Enceladus have experienced distinct deformational events.