Schematic process to calculate depression volumes in this study. (a) Shape model of 81P used in this study. The unexplored side is extrapolated to the fit ellipsoid. (b) Elevation map of 81P. (c) Three defined regions of the explored side: left foot & right foot (orange), Rahe (red), and Hemenway (green). (d) Depressions extracted by the edge detection technique (same as the outermost contours in Fig. 2).