A Complex Paleo‐Surface Revealed by the Yutu‐2 Rover at the Lunar Farside

Abstract

Impact craters represent the most salient geomorphological characteristic of the lunar surface and are a key to a better understanding of the geology of our satellite. Crater chronology, a dating methodology derived from returned lunar samples, remains the sole remote sensing methodology for estimating absolute surface ages across the solar system. The geomorphology of craters can constrain their age and shed light on the regional stratigraphy, set constraints on the thickness of lunar regolith, and assist in estimating the depth of the basalt layers. The impact events also exhume materials from depth granting access to analysis. However, the relentless reworking of the surface, from the micro to the macro level, remodels the lunar surface through a process of destruction and burial (Carrier et al., 1991). Gravity field variations interpreted from the GRAIL data (Evans et al., 2016;Sood et al., 2017) have revealed tens to hundreds of km sized craters hidden below the lunar maria. Ground Penetrating Radars (GPR) can reveal the shallow subsurface stratigraphy, including buried craters, and they have been deployed on Earth, Mars, and the Moon. On our planet, the scientific yield has been modest probably due to the high attenuation of GPR signals in moist environments and interferences caused by vegetation and human activities (Heggy & Paillou, 2006). On Mars, the dense data coverage of the Shallow Radar (SHARAD) sounder in the polar region enables a three-dimensional view of hidden structures and reveals a couple of km-scale buried craters (Putzig et al., 2018).

From Schrödinger to Von Kármán: An Intriguing New Geological Structure Revealed by the Chang'e‐4 Lunar Penetrating Radar

“…Since C is presumably closer to 35 m using ɛ = 5.8 (Lai et al, 2021), larger than the value shown in Figure 2 which uses the uniform ɛ of 6.5. If the variation of ε for Strata C and D is considered, the fluctuations of the bottom of Stratum D will be reduced.…”

“…The reflector at the bottom of Stratum D also rises at the distance between 300 and 600 m. This could represent the change of the average permittivity caused by the insertion of Stratum C, see Equation . The ɛ of the ejecta deposits is smaller than the basalt of Stratum D , so the real thickness of Stratum C is presumably closer to 35 m using ɛ = 5.8 (Lai et al., 2021), larger than the value shown in Figure 2 which uses the uniform ɛ of 6.5. If the variation of ε for Strata C and D is considered, the fluctuations of the bottom of Stratum D will be reduced.…”

Exploring the Lunar Regolith's Thickness and Dielectric Properties Using Band‐Limited Impedance at Chang’E‐4 Landing Site

“…To compare the influences of diverse dielectric constants, two of them (i.e., $${\varepsilon }_{r}^{\prime }=4.3$$ in Lai et al. (2021) and $${\varepsilon }_{\mathit{r}}^{\prime }=3.52$$ in Li et al. (2020)) were used to estimate the regolith thickness.…”

“…In this regard, when using the same LPR low frequency data (60 MHz), some reported a penetration depth of ∼360 m (Zhang et al, 2020) while others reported ∼500 m (Zhang et al, 2021). In studies of thickness estimation, modelers have typically applied a singular dielectric constant for regolith, for example, 𝐴𝐴 𝐴𝐴 ′ 𝑟𝑟 = 3 in Fa et al (2015) and Lai et al (2021), and calculated the thickness by multiplying half of the observed round-trip time at the stratigraphic interface and the propagation velocity of radar wave in a medium with the corresponding dielectric constant. If the round-trip time at the stratigraphic interface is very short, then an average dielectric constant ( 𝐴𝐴 𝐴𝐴 ′ 𝑟𝑟 = 3 ) based on Apollo samples was considered appropriate (Krupenio & Kroupenio, 1973;Muhleman et al, 1969); otherwise, the influence of variation in the dielectric constant of the deep material should be investigated.…”

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

“…In other studies, the LPR data are applied to the analysis of subsurface properties and rock quantity in the regolith (Dong et al., 2020; Lai et al., 2021a, 2021b; Zhang, Xu et al., 2021; Zhou, Feng, Ding, et al., 2021). However, the rock localization using LPR data mainly depends on the reflection signals from the subsurface and the results in previous works cannot determine whether these signals are from horizontally distributed rocks or continuous geological interfaces (Zhou, Feng, Ding, et al., 2021) because the regolith maturity over the full depth has not been obtained.…”