The Chronology of Pythagoras and Sharp B Craters in the Adjacent Highlands of the Chang'E-5 Landing Site

Introduction: The Chang’E-5 (CE-5) was successfully launched on November 23 2020. The spacecraft landed in the northeastern of Oceanus Procellarum (43.0576° N, 308.0839° E). The CE-5 is the first lunar sample mission in years after Apollo 17 and Luna 24. It has returned about 1731 g lunar regolith samples. The CE-5 mission will contribute more diverse lunar samples, which would complement the existing lunar samples collected by the Apollo and Luna missions. The CE-5 samples are of great significance to the interpretation of lunar geological history. The CE-5 landing site is located in the young mare unit within the northeastern Oceanus Procellarum. The Oceanus Procellarum is the largest basalt-filled depression on the Moon. According to previous studies based on terrestrial observation and remote sensing data, mare volcanism within this region actived from 3.93 to 1.2 Ga[1]. The CE-5 landing site is located within young P58 unit (1.33Ga) [2], which is among the youngest mare units on the Moon. The CE-5 landing site has been contaminated by ejecta from the adjacent highlands. The regolith developed on the mare plains of CE-5 site were mixed by the distantly sourced particles ejected from highland craters, such as the Pythagoras, Aristarchus, Copernicus, Sharp B, Harpalus, Robertson, Hausen, Philolaus and Carpenter[3]. These highland materials probably were collected by CE-5 mission. Both the ages of mare basalt and highland eject fragments could be measured by laboratory radiometric dating in future study. These materials would also provide new calibration points for lunar crater chronology in this region. Among above craters, the absolute model ages (AMAs) of Pythogaras and Sharp B craters are poorly investigated (Figure 1). Here we performed crater size-frequency distributions (CSFD) for the two crater to determine their AMAs and N(1) values (i.e., the cumulative number of craters with diameters >1 km) using recent orbital data. Data and Methods: Both Lunar Reconaissance Orbiter (LRO) Narrow Angle Camera (NAC) images and Kaguya Terrain Camera (TC) were used to identify small craters in this study. We used the CraterTools to determine the size of craters and perform crater counting. CraterTools is an extension of ArcGIS and can automatically adjust for map-projection distortions to prevent mismeasurement of crater diameters and count area [4]. The CSFDs were plotted using Craterstats[5]. The AMAs were obtained using a cumulative fit and the production and chronology function [6]. Figure 1 Pythagoras crater and Sharp B crater (red