Research ArticleASTRONOMY

The Moon’s farside shallow subsurface structure unveiled by Chang’E-4 Lunar Penetrating Radar

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Science Advances  26 Feb 2020:
Vol. 6, no. 9, eaay6898
DOI: 10.1126/sciadv.aay6898
  • Fig. 1 The CE-4 landing region and the Yutu-2 rover route.

    (A) CE-4 landed in the eastern floor of Von Kármán crater (44.45°S, 176.3°E; diameter ~186.3 km), as indicated by the white cross (177.5991°E, 45.4446°S) on a bright ejecta blanket. The yellow and green lines show the ejecta direction from Finsen (12) and Von Kármán L, respectively. The image is CE-2 7-m resolution Digital Orthophoto Map (DOM). (B) Yutu-2 rover route during the first two lunar days. Two red lines show the tracks of the left and right wheels on the Yutu-2 rover. The LPR performed observation along the ~106-m route from exploration points A to LE210. The background image is mosaicked from images obtained during the landing process, where the spatial resolution is 5 cm.

  • Fig. 2 LPR data at 500 MHz.

    (A) LPR 500-MHz radargram represented in standard seismic colors after applying Dewow, background subtraction, and spherical and exponential compensation (SEC) gain and migration. The x axis is the rover distance (top, starting point on the left) and the exploration points (bottom), and the y axis indicates the two-way travel time and depth; the depth is calculated on the basis of the average electromagnetic wave velocity of 0.16 m/ns. (B) Tomographic reconstruction of the radar data, where red represents high reflectivity (large electromagnetic contrast) and blue is low reflectivity (small electromagnetic contrast). (C) Schematic of the stratigraphic sequence highlighting the contacts between units and the relevant thicknesses based on the radargram (A) and the tomographic reconstruction (B). Gray tone indicates finer (light gray) or coarser (dark gray) materials.

  • Fig. 3 Schematic representation of the subsurface geological structure at the CE-4 landing site inferred from LPR observations.

    The subsurface can be divided into three units: Unit 1 (up to 12 m) consists of lunar regolith, unit 2 (depth range, 12 to 24 m) consists of coarser materials with embedded rocks, and unit 3 (depth range, 24 to 40 m) contains alternating layers of coarse and fine materials.

Supplementary Materials

  • Supplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/6/9/eaay6898/DC1

    Fig. S1. CE-4 landing site.

    Fig. S2. Data processing procedure of LPR high frequency.

    Fig. S3. Comparison of high-frequency LPR data between CE-3 and CE-4.

    Fig. S4. Velocity estimation using point targets.

    Fig. S5. Bulk density versus depth in the first 8 m.

    Fig. S6. Joint probability density function of loss tangent as a function of bulk density and oxide content.

    Fig. S7. Estimation of the ejecta thickness using DHCs and non-DHCs.

    Fig. S8. Geological context and topography at CE-4 landing site.

    Table S1. Estimated ejecta thickness at the CE-4 landing site from Finsen, Von Kármán L, and Von Kármán L’ craters.

    Table S2. The data IDs for the images used in the figures.

  • Supplementary Materials

    This PDF file includes:

    • Fig. S1. CE-4 landing site.
    • Fig. S2. Data processing procedure of LPR high frequency.
    • Fig. S3. Comparison of high-frequency LPR data between CE-3 and CE-4.
    • Fig. S4. Velocity estimation using point targets.
    • Fig. S5. Bulk density versus depth in the first 8 m.
    • Fig. S6. Joint probability density function of loss tangent as a function of bulk density and oxide content.
    • Fig. S7. Estimation of the ejecta thickness using DHCs and non-DHCs.
    • Fig. S8. Geological context and topography at CE-4 landing site.
    • Table S1. Estimated ejecta thickness at the CE-4 landing site from Finsen, Von Kármán L, and Von Kármán L’ craters.
    • Table S2. The data IDs for the images used in the figures.

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