The Provenance of Regolith at the Chang'e‐5 Candidate Landing Region

Abstract

The upcoming lunar Chang'e-5 mission is scheduled to land near Mons Rümker, in northern Oceanus Procellarum, and return samples with masses up to 2 kg from depths up to~2 m. A clear understanding of the regolith components in the candidate landing region is crucial to both the selection of sampling sites and the interpretation of the geological affinities for the returned samples. We quantitatively estimate the abundance of distantly sourced particles (DSPs) in the regolith at the landing region using an updated ballistic sedimentation model. Our results suggest that older units have a higher abundance of DSPs. In the targeted landing area, the total abundance of DSPs on the surface of the regolith varies from approximately 12% to 20%, and most of the DSPs on the surface are ejecta from the Pythagoras (~5%) and/or Aristarchus (~7%) craters. The youngest geological unit, which is located in the easternmost sector of the landing region, possesses the least DSPs in the regolith. Therefore, sampling the eastern unit has a higher potential of revealing both the petrological characteristics and age of the youngest mare basalt, which are fundamentally important to improve both the lunar crater chronology and the understanding of late-stage evolution of the Moon. Our results also indicate that the anorthositic material within the shallow regolith is most likely ejected from the Pythagoras and Aristarchus craters, which could further improve the understanding of lunar geology and chronology.Plain Language Summary Chang'e-5 will be the first lunar sample return mission since the 1976 Luna 24 mission. It will return surface and core samples with masses up to 2 kg from depths up to~2 m from northern Oceanus Procellarum. Most of the returned samples are expected to be lunar regolith. A better understanding of the regolith components in the candidate landing region is therefore helpful to both select sampling sites and interpret the samples that will be returned in the future. Here, we estimate the abundance of distantly sourced particles (DSPs) in the regolith within the proposed landing region. We find that older units are more enriched in DSPs, and the total surface abundance of DSPs varies from approximately 12% to 20%. Most DSPs on the surface are ejecta from the Pythagoras (~5%) and/or Aristarchus (~7%) craters. Our results support that the youngest mare unit is most suitable for sample return because of the low abundance of DSPs. Furthermore, core samples from this unit contain not only local basaltic materials and the several major sources of distant ejecta in the regolith but also both pristine highland anorthosites and pyroclastic deposits.

Thermophysical Features of the Rümker Region in Northern Oceanus Procellarum: Insights from CE-2 CELMS Data

“…Campbell et al [25] analyzed the surface properties of Mons Rümker with Earth-based radar data and found it likely to be covered with rock-poor, fine-grained pyroclastic materials. Xie et al [26] quantitatively estimated the abundance variations of distantly sourced particles with depth using an updated ballistic sedimentation model, concluding that most of the extraneous materials are derived from Pythagoras (~5%) and Aristarchus craters (~7%). Qian et al [27] and Yue et al [28] studied the regolith thickness of the region, and found that the Imbrian-aged mare basalts have thicker regolith than the Eratosthenian-aged and that over 99% of the Rümker region has a regolith thickness larger than 2 m (the length of the core drill).…”

“…The FeO and TiO 2 abundance maps ( Figure 8) show that Em4 has the highest FeO and TiO 2 abundances, followed by Im1, Em1, and Em3 units, and Im2 has the lowest values. Linear anomalies distributed along northwest and northeast directions indicate the presence of secondary craters and rays formed by foreign materials excavated by distant craters and laterally delivered to the region [2,26].…”

“…rays formed by foreign materials excavated by distant craters and laterally delivered to the region [2,26].…”

“…Different authors have mapped the geological units in the Rümker region using different datasets, e.g., Clementine UVVIS data [14,16,23] and Kaguya MI data [1,2]. However, all of the previous studies rely on optical reflectance for subdividing geological units, which inevitably ignores the internal structure of a geological unit [26]. The CE-2 CELMS TB (Figure 3), nTB (Figures 4 and 5), and dTB data ( Figure 6) provide a new opportunity to gain insight into the geological units in the region, and these data and implications for the units are discussed below.…”

“…The Chang'e-5 (CE-5) mission is China's first lunar sample return mission, with a goal of returning samples from the Rümker region [4] (Figure 1). Detailed geological investigations of the area have been conducted recently by different researchers to assess its potential scientific value [1,2,22,26,27,[63][64][65][66]. Within these analysis, 18 sampling sites or zones have been proposed and their scientific value evaluated [1,2,26,64,65,67] (Figure 13).…”