Analyses of landforms on Rhea are used to define three physiographic provinces (cratered terrain 1 undifferentiated, cratered terrain 1 lineated, cratered terrain 2) for which stratigraphic relationships are derived and examined in relation to major impact basins and tectonic features. The formation of multiringed basins may have caused, or at least controlled, the locations of major resurfacing and mantling events. The diameters of central peaks relative to impact crater diameters are significantly larger than those within craters on the moon and Mercury. Rim segments of polygonal craters have preferential orientations. Both crater and noncrater lineaments show regional orientations that do not fit current global or regional stress models. Superposition relationships of provinces and associated features imply the following postaccretional sequence for the geological evolution of Rhea's surface. Cratered terrain 1 undifferentiated formed first. Then linear troughs and chains of coalescing pits developed extensively on cratered terrain 1 lineated. A resurfacing event emplaced cratered terrain 2, on which small craters, scarps, and ridges formed. Small grooves on cratered terrain 1 undifferentiated are tentatively assigned a young age, based on their susceptibility to impact erosion. This geologic history is generally consistent with theoretical models for Rhea's evolution. |