Rock Fragments in Shallow Lunar Regolith: Constraints by the Lunar Penetrating Radar Onboard the Chang'E‐4 Mission

Abstract

The surface of the Moon is almost entirely covered by a layer of fine-grained debris (i.e., regolith) that is formed by repeated impact cratering and space weathering (McKay et al., 1991). Regolith grains are mostly

Heterogeneous Weathering Process of Lunar Regolith Revealed by Polarimetric Attributes Analysis of Chang’E‐4 Lunar Penetrating Radar Data Acquired During the Yutu‐2 Turnings

“…These modifications probably lasted for a long time and simultaneously flattened the lunar surface. Most coarse ejecta materials filled in the degraded crater survive the gardening on the lunar surface resulting in its unique properties compared to both the materials of the underlying and overlying regolith. Stage (e and f): the distal impact events delivered rock fragments to the surface of the landing zone, some of which formed small and fresh secondary craters (Ding et al., 2020, 2021). These events also produce melt welded impact breccia in the near‐surface of fine‐grained regolith and resulting in the horizontal heterogeneity of the lunar surface.…”

“…Although the 0–10 m is convinced to be the fine‐grained Finsen ejecta, the 0–2 m region presents distinct lower maturities than the 2–10 m region. A possible reason is that the surface of the CE‐4 landing area may consist of lithic material from secondary cratering whereas the 2–10 m region below consists mainly of native materials which experienced longer time weathering (Ding et al., 2021). Besides, both maturities of near‐surface and coarse ejecta regions have significant spatial differences whereas that of the fine‐grained regolith layer is generally of higher degrees and lower variations.…”

“…The regions with high maturities are likely to experience more impacting events whereas the regions with low maturities or high dielectric constants may compose of fresh ejecta from local impact or dense materials like melt-bearing impact breccias. Besides, the distal impact events can also deliver rock fragments to the region (Melosh, H. J., 1989), some of which formed small and fresh secondary craters and increased the roughness of the lunar surface (Ding et al, 2020(Ding et al, , 2021Gou et al, 2019;Lin et al, 2020). These events can also produce melt welded impact breccia in the near-surface of fine-grained regolith and resulting in the horizontal heterogeneity of the lunar surface (Ding et al, 2020(Ding et al, , 2021.…”

“…Besides, the distal impact events can also deliver rock fragments to the region (Melosh, H. J., 1989), some of which formed small and fresh secondary craters and increased the roughness of the lunar surface (Ding et al, 2020(Ding et al, , 2021Gou et al, 2019;Lin et al, 2020). These events can also produce melt welded impact breccia in the near-surface of fine-grained regolith and resulting in the horizontal heterogeneity of the lunar surface (Ding et al, 2020(Ding et al, , 2021.…”

“…5. Stage (e and f): the distal impact events delivered rock fragments to the surface of the landing zone, some of which formed small and fresh secondary craters (Ding et al, 2020(Ding et al, , 2021. These events also produce melt welded impact breccia in the near-surface of fine-grained regolith and resulting in the horizontal heterogeneity of the lunar surface.…”