Extraction and Analysis of Three-Dimensional Morphological Features of Centimeter-Scale Rocks in Zhurong Landing Region

China's first Mars rover, Zhurong, has carried out an exploration mission in southern Utopian Planitia. As rocks and their three-dimensional (3D) morphology are essential for studying the geological characteristics of the Martian surface, this paper presents an approach for automatically extracting 3D rocks from stereo rover images. With our approach, 6,185 cm-scale rocks are extracted using the Zhurong NaTeCam images, with the F-1-score achieving 91.86%. Approximate 3D morphological features are then calculated for each rock, and the statistical result shows that small rocks in centimeters make up the majority. Comparative morphological analyses of rocks in different areas show that landscape type affects the number of rocks but has no clear relationship to the proportions of rocks of different sizes. The outcrops of sedimentary rocks, the predominant type of rocks in the Zhurong landing area, and the float rocks are distributed differently regarding all morphological features, making the size-frequency distribution of rocks around craters significantly different from other areas. Further comparative analysis with the Bonneville crater ejecta rocks extracted from the Spirit rover data is also conducted. Some similarities between the Zhurong outcrop rocks and the Bonneville crater ejecta rocks are found in 2D compactness. Meanwhile, the Bonneville crater ejecta rocks have a more scattered distribution in sphericity than both the float and outcrop rocks in the Zhurong landing area, indicating that the shapes of the Bonneville crater ejecta rocks may be more diverse. In addition, the sphericity is found to converge with height for rocks in both landing areas. Plain Language Summary Rocks on the Martian surface and their three-dimensional (3D) morphology record the geological evolution of Mars and its interaction history with outer space. Currently, China's Zhurong Mars rover has traveled nearly 2 km on Mars and collected a wealth of images, allowing the fine-scale measurement and 3D morphological analysis of Martian rocks with statistical significance. We therefore propose an automatic approach for extracting individual 3D rocks from the stereo images and apply it to the Zhurong NaTeCam images to facilitate fine-scale morphological analyses of the Martian rocks in the Zhurong landing area. Our morphological analyses lead to several remarkable findings about the interior relations between Martian rocks and geomorphology, giving new clues about the topographical and geomorphic evolution of Mars.