Abstract
Chang’E-5 is the first lunar sample return mission of China. The spacecraft was landed in the northwest of the Procellarum KREEP Terrane (43.0576°N, 308.0839°E) on 1 December 2020 and returned 1731 g samples from a previously unvisited region. The landing area has been proposed as one of the youngest mare basalt units of the Moon and holds important information of lunar thermal evolution and chronology. However, the absolute model ages estimated in previous studies are quite different, ranging from 2.07 Ga to 1.21 Ga. Such significant difference may be caused by (1) different crater counting areas, (2) different crater diameter ranges, (3) effects of secondary craters, and (4) biases in crater identification. Moreover, the accurate landing site was unknown and the ages were estimated over the Eratosthenian-aged mare unit (Em4) instead. In light of the above unsatisfactory conditions, this study seeks to establish a standard crater size-frequency distribution of the CE-5 landing site. We derived the concentrations of FeO and TiO2 to map out the pure basaltic areas where external ejecta deposits are negligible and thus secondary craters are rare. Based on the geochemistry of basaltic ejecta excavated by fresh craters in the mare unit, the FeO concentration threshold for mapping pure basaltic areas is 17.2 wt.%. The morphologically flat subunits in the pure basaltic areas were selected for crater identification and age dating to exclude the contamination of external ejecta to the best as we could. In the Chang’E-5 sampling site subunit, we detected 313 craters with a diameter greater than 100 m and derived the absolute model age as 1.49−0.084+0.084 Ga. The craters identified in all pure basaltic subunits of Em4 gave the model age of 1.41−0.028+0.027 Ga. As least affected by secondary craters, the crater size-frequency distribution of the sample-collected pure basaltic subunit can provide important constraints for lunar cratering chronology function in combination with isotopic age of returned samples.
Highlights
IntroductionOn 1 December 2020, China’s first lunar sample return mission, Chang’E-5 (CE-5), successfully landed in the northwest of lunar Procellarum KREEP Terrane (PKT) [1]
Introduction published maps and institutional affilOn 1 December 2020, China’s first lunar sample return mission, Chang’E-5 (CE-5), successfully landed in the northwest of lunar Procellarum KREEP Terrane (PKT) [1]
Hiesinger et al [3,4] dated the lunar near-side mare basalt units using the crater size-frequency distribution (CSFD) model [5,6,7], and the results show that some mare units are younger than 2.0 Ga in the PKT region and that the CE-5 landing area can be dated to 1.33 Ga
Summary
On 1 December 2020, China’s first lunar sample return mission, Chang’E-5 (CE-5), successfully landed in the northwest of lunar Procellarum KREEP Terrane (PKT) [1]. The ages of all lunar basaltic samples returned by previous missions are older than 2.93 Ga [2]. Hiesinger et al [3,4] dated the lunar near-side mare basalt units using the crater size-frequency distribution (CSFD) model [5,6,7], and the results show that some mare units are younger than 2.0 Ga in the PKT region and that the CE-5 landing area (unit P58) can be dated to 1.33 Ga. the location and age of the mare basalt of the CE-5 landing site were very different from previous sample return missions. The absolute model age (AMA) and CSFD of the landing iations
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