The South Pole–Aitken (SPA) basin is the oldest and largest impact structure on the Moon, and it gives particular insight on the lunar interior composition1,2,3. However, the surface of the SPA basin has been substantially modified by consequent impacts and basalt flooding. The exploration of the surficial material and the substructure of the SPA basin is one of the main scientific goals of the Chinese spacecraft Chang’E-4 that landed in the Von Kármán crater inside the SPA basin4,5. Here we report the lunar penetrating radar profiles along the track of the lunar rover Yutu-2, which show a three-unit substructure at the landing site. The top unit consists of the ~12-m-thick lunar regolith and ~120 m multilayered ejecta that were delivered from several adjacent craters. The middle unit is the mare basalts filling the Von Kármán crater. The lowest unit is another ejecta layer with a thickness of ≥200 m, likely from the Leibnitz crater. These discoveries fully support the local stratigraphy and geological explanation presented previously6. Our results reveal that the surface materials at the Chang’E-4 landing site are unambiguously dominated by the ejecta from the Finsen crater with a minor contribution from other neighbouring craters. The regolith measured by Yutu-2 is representative of the initial lunar deep interior materials, rather than the later erupted basalts.
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The data used in this work is available on the Science and Application Center for Moon and Deep Space Exploration, Chinese Academy of Sciences (http://moon.bao.ac.cn).
The code for processing the LPR data is available from the corresponding author on request.
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The Chang’E-4 mission was carried out by the Chinese Lunar Exploration Program, and the data were provided by the China National Space Administration. We thank D. Moriarty for helpful suggestions, which greatly improved the clarity and readability of the manuscript. This work was supported by Key Research Program of Frontier Sciences, Chinese Academy of Sciences (QYZDJ-SSW-DQC001) and the National Nature Science Foundation of China (41490631 and 41941002). M.-H.Z. was supported by the Science and Technology Development Fund, Macau (0079/2018/A2) and the pre-research project on Civil Aerospace Technologies No. D020202 funded by China National Space Administration (CNSA). M.-H.Z. acknowledges the iSALE developers. H.S. was supported by the Beijing Municipal Science and Technology Commission (Z181100002918003) and the pre-research project on Civil Aerospace Technologies No. D020201 funded by China National Space Administration (CNSA). We thank the Supercomputing Laboratory of IGGCAS for providing computing resources.
The authors declare no competing interests.
Peer review information Nature Astronomy thanks Gareth Morgan and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.
Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
a, The farside of the Moon; b, Local details in the rectangle in a; c, Local details in the rectangle in b; d, Local details in the rectangle in c. a is obtained by the Lunar Resonant Orbiter (http://lroc.sese. asu.edu/posts/298); b and c are obtained by Chang’E-2 (http://moon.bao.ac.cn); d is obtained by the descending camera under the Chang’E-4 lander.
The landscape images were taken with the panorama camera on the rover Yutu-2 (a) and by the terrain camera on the Chang’E-4 lander (b). The distance between two rows of wheels is ~80 cm.
a, The raw data profile; b, The profile after using a bandpass filter between 10 and 80 MHz for each trace and a 2D median filter using parameters of (3,10). The depth is converted from the travel time using a relative dielectric model shown in Extended Data Fig. 7. The processed data shown in b is exactly the same as that shown in Fig. 2, which is shown here to examine the processing results compared with the original data shown in a.
Extended Data Fig. 5 Local zoom in of original waveforms of low-frequency LPR Channel from 0 to 1.4 μs.
a, The stack of three waveforms at the trace no. 500, 1000, and 1500. b, c, d, The independent waveforms at trace no. 500, 1000, and 1500, respectively. Note that only the waveforms within 0.31 μs (indicated by the orange arrow) have been apparently clipped and the rest are reliable.
a, The same profile as shown in Fig. 2. b, The low-pass eigenimage33 (only keeping eigenvalues from 1 to 10); c, the band-pass eigenimage (only keeping eigenvalues from 11 to 200); d, the high-pass eigenimage (only keeping eigenvalues from 201 to 1973). b~d share the same color scale but is slightly less clipped than a for the convenience of pattern comparison. The singular values are shown in Supplementary Fig. 5.
a, The original LPR profile; b, The migration result. The data are obtained by the high-frequency Channel-2B. The local details in the rectangles are shown in Extended Data Fig. 9.
a–c, The original LPR profiles; d–f, The corresponding migration results of a–c, respectively.
a, Low-frequency channel; b, High-frequency channel. The high-frequency channel can well constrain the subsurface structures within 0.62 μs.
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Zhang, J., Zhou, B., Lin, Y. et al. Lunar regolith and substructure at Chang’E-4 landing site in South Pole–Aitken basin. Nat Astron 5, 25–30 (2021). https://doi.org/10.1038/s41550-020-1197-x
Nature Astronomy (2021)
Nature Astronomy (2021)