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The presence of polygonal-shaped craters, i.e., craters with complete or incomplete polygonal rims along with circular or elliptical outlines, on the surface of celestial bodies has been known for nearly a century. However, many investigations on their distribution and formation have not been carried out, until recently. Scientists have proposed that the polygonal shapes of the crater rims owe their origin to the pre-existing structurally weak planes like faults/fractures in the area adjacent to the impact. The present study area is the southern part of Margaritifer Terra, Mars; a mid-Noachian terrain, which has craters of different morphologies, including the polygonal impact craters (PICs). The study focuses on the reason for the development of PICs by identification and mapping of a population of 50 selected polygonal craters along with morphotectonic features namely grabens, wrinkle ridges, and lobate scarps. The analysis of orientations of the straight segments of polygonal crater rims shows marked resemblance with orientations of these morphotectonic features conforming to their control on the rim geometries. Research highlights: Structural mapping of the southern Margaritifer Terra region, Mars. Generating rose diagrams and line graphs for the orientation of the straight edges of polygonal craters and the morphotectonic features within the southern Margaritifer Terra region. Conducting statistical F-test to find out the bearing of weak planes on the formation of PICs. Finding out the presence of buried weak planes by comparing the rose diagrams and spike graphs. [ABSTRACT FROM AUTHOR]

On the Moon, impact craters and basins expose a wide range of crustal and mantle rocks that provide excellent opportunity for sampling them, understanding their origins and reconstructing spatial and temporal evolution of lunar interior. The previous studies detected olivine-bearing mantle rocks in and around large impact craters and basins. The Japanese SLIM mission landed on the ejecta of a ∼ 280-m-diameter Shioli crater that was emplaced on the ejecta blanket of ∼ 103-km-diameter Theophilus crater, for characterizing potential mantle-derived olivine in the Shioli crater ejecta boulders. To test this hypothesis, we studied the geological setting of Shioli crater, host Theophilus crater and Nectaris multi-ring basin using the orbiter data from Chandrayaan-1 and 2, Lunar Reconnaissance Orbiter, and Kaguya missions and the earth-based Arecibo radar observation. The asymmetrically distributed secondary craters and impact melt ponds around Theophilus crater suggests that a northeast-directed oblique impact produced this crater. Composition of Theophilus crater and surrounding region indicates that the crater excavated a heterogeneous target composed of a thin layer of high-Al olivine basalt (Mare Nectaris) underlain by anorthositic highland rocks possibly intruded by Mg-suite plutons; layers of Cyrillus crater ejecta blanket and Nectaris basin materials (both ejecta and impact melt sheets) were also present beneath the mare basalt flows. Hence, the Theophilus ejecta blanket is a mixture of all these materials. Our dating of Theophilus crater suggests that it is a ∼ 2 Ga Eratosthenian crater. Shioli is a fresh simple crater that was formed at ∼ 1 Ma on the uprange ejecta blanket of Theophilus, where the Arecibo radar data indicated the presence of abundant buried Theophilus ejecta boulders. An ESE-directed hypervelocity oblique impact event produced the elongated Shioli crater and its asymmetrically distributed bright ejecta. Shioli is a primary impact crater indicating the role of impact spallation processes associated with this hyper-velocity impact in producing thousands of ejecta (or spall) boulders around Shioli crater, displaying their asymmetric dispersal pattern and spatial variation of boulder sizes and shapes. The larger and elongated boulders are concentrated near the crater rim, while their size and axial ratio gradually decreases outward from the crater rim. The SLIM mission landed on a thin downrange ejecta of Shioli crater, where fewer large-size boulders are present. Our compositional study suggests that the Shioli ejecta boulders are composed of olivine basalt (Mare Nectaris) mixed with highland anorthositic fragments, including the reworked Cyrillus ejecta and Nectaris basin materials. The Shioli ejecta boulders were produced by complex impact fragmentation of already existing, buried Theophilus ejecta boulders. The regional crustal structure of Nectaris basin and its petrological composition suggest that both Nectaris basin and Theophilus crater did not excavate the lunar mantle. Therefore, the Shioli ejecta boulders are of crustal origin, including the olivine minerals present in them. Our results have important implications for the origin of olivine in the Shioli crater boulders being investigated by the SLIM mission. • A NE-directed oblique impact produced Theophilus crater, asymmetric distribution of secondary craters and impact melt ponds • Theophilus excavated a thin layer of high-Al olivine mare basalt underlain by Cyrillus ejecta and highland anorthositic rocks • An east-southeast directed oblique impact produced Shioli crater and its asymmetrically distributed ejecta and spall boulders • A hypervelocity impact (16 km/s) is responsible for the observed size and shape variation in the Shioli crater spall boulders • The Shioli boulders are mixtures of olivine basalt and highland materials, produced from Theophilus ejecta boulders [ABSTRACT FROM AUTHOR]