Geologic map of Selk crater, Titan
Photoclinometry (determining shape from shading) reveals that the crater's rim is in the middle of the optically bright area, making Selk somewhat larger in diameter (about 90 kilometers) than is obvious from photos. Its interior walls are terraced, typical for craters of this diameter on large icy bodies. Its exterior is cut by drainage channels (blue lines), and the crater may be superposed on ancient, degraded craters (yellow circles). The shape of the crater rim is polygonal, indicating some possible planes of weakness within the crust (black arrows).