The characterization and distribution of polygonal impact craters on Ceres and their implications for the Cerean crust
Michael F. Zeilnhofer, Nadine G. Barlow
In Press, Journal Pre-proof, Available online 16 June 2021
• A polygonal crater database for Ceres was created in this study.
• 1466 polygonal impact craters (PICs) are identified in the study.
• Hexagonal craters were the most prominent shape.
• The average angle for PICs on Ceres is 121. 99° ± 0.25°.
• Four categories of PICs were identified.”
“Polygonal impact craters (PICs) are supposed to form as a result of impacts into structure systems within the target. The structure systems are an umbrella term which encompass faults, joints, fractures, lithographic boundaries, and other planes of weakness. These impact craters are defined as having at least two linear rim segments with a recognizable angle between the segments. PICs have been reported on both rocky and icy bodies including Ceres. Using a near-global Cerean crater database, PICs were categorized into four different categories: (1) polygonal craters not related to visible structure systems (PICNVS), (2) polygonal craters related to visible structure systems outside of the crater (PICVSO), (3) polygonal craters related to visible structure systems inside of the crater (PICVSI), and (4) polygonal craters related to visible structure systems inside and outside of the crater (PICVSIO). Measurements of the number of linear rim segments, the angle between linear rim segments, mean angle between linear rim segments for the crater, length of linear rim segments, and the mean length of the linear rim segments for the crater were reported for each category. Additionally, the angle between nearby structure systems and the linear rim segments are determined, along with the crater’s cardinal direction with relation to the structure system. The most frequent type of PIC is those not related to structure systems. Hexagonal craters are the most prominent polygon shape observed, which is consistent with the observed shape of PICs throughout the solar system. The visible structure systems which displayed the highest number of PICs related to them were the Junina and Samhain Catenae. The average angle between linear rim segments for PICs on Ceres is 121.99° ± 0.25° which is similar to the average angle between linear rim segments reported for PICs on Rhea and Dione. Polygonal craters are found in different degradation states, indicating structure systems have influenced the formation of PICs throughout much of Ceres’ history. The observation of greater concentrations of PICs in the northern hemisphere may indicate target strength differences and support the idea of crustal heterogeneity across Ceres; however, the lack of PICs in the southern hemisphere may be due to the younger and larger impact basins (Urvara and Yalode) erasing these craters creating an observational bias.”