The unequal distribution of volcanic products between the Earth-facing lunar side and the farside is the result of a complex thermal history. To help unravel the dichotomy, for the first time a lunar ...landing mission (Chang'e-4, CE-4) has targeted the Moon's farside landing on the floor of Von Kármán crater (VK) inside the South Pole-Aitken (SPA). We present the first deep subsurface stratigraphic structure based on data collected by the ground-penetrating radar (GPR) onboard the Yutu-2 rover during the initial nine months exploration phase. The radargram reveals several strata interfaces beneath the surveying path: buried ejecta is overlaid by at least four layers of distinct lava flows that probably occurred during the Imbrium Epoch, with thicknesses ranging from 12 m up to about 100 m, providing direct evidence of multiple lava-infilling events that occurred within the VK crater. The average loss tangent of mare basalts is estimated at 0.0040-0.0061.
On 3 January 2019, the Chang'e‐4 (CE‐4) touched down on the Von Karman crater located inside the South Pole‐Aitken Basin, providing for the first time the opportunity for in situ measurements of the ...lunar regolith at the farside of the Moon. The CE‐4 ground penetrating radar reveals that fine‐grained regolith, coarse impact ejecta, and fractured bedrocks lie beneath the exploration path of the Yutu‐2 rover. The variations of regolith permittivity with depth and the radargrams indicate that the CE‐4 site has a fine‐grained regolith layer thickness of 11.1 m, which is about 1.3–3 times higher than the in situ measurement results at the Apollo and Chang'e‐3 (CE‐3) sites except for Apollo 16, possibly due to a faster weathering rate of ejecta deposits compared with coherent basalt substrates. The penetration depth of CE‐4 is about 2.85 times (in terms of round‐way delay) deeper than CE‐3, probably due to the differences in abundances of ilmenite and rocks in the regolith.
Plain Language Summary
CE‐4 is the first craft in history to land on the lunar farside. Its rover is equipped with a ground‐penetrating radar (GPR), the same as the one mounted on the CE‐3 rover, which uses pulses of electromagnetic energy to reveal the subsurface structure and properties, especially useful to study the lunar soil layer (“regolith”) that mantles most of the lunar surface. The results from the GPR show that the thickness of the regolith at the CE‐4 site is 1.3–3 times higher than the in situ measurements at the Apollo 11,12,14,15, 17, and CE‐3 sites even though the ages of the surfaces of Apollo 11 and Apollo 17 are thought to be comparable with that of the CE‐4 site. It implies a faster regolith growth speed at the CE‐4 site. The mineral mix of the surface materials at the CE‐4 site is different from that at the CE‐3: this results in less radar signal attenuation, thus increasing the detection limit up to the depth of 35 m, 2.85 times deeper than the CE‐3.
Key Points
The LPR measurements at the CE‐4 landing site reveal that the shallow structure comprises of fine‐grained regolith, coarse impact ejecta, and fractured bedrocks
The CE‐4 landing site has a thicker regolith layer (~11 m) compared with the CE‐3, hinting at a longer weathering history
A lower abundance of ilmenite and rocks in the regolith at the CE‐4 site allows 2.85 times the penetration depth compared with CE‐3 site
•CE-4 LPR data of the first 450 m drive reveal a ∼40 m deep subsurface structure.•Four ejecta layers underlying the surface regolith are discontinuous.•The energy map of suggests the cause of ...inconsistencies to be a buried crater.•The rock distribution indicates a brief weathering period of each ejecta layer.•The local evolutionary history is constructed based on the revealed stratigraphy.
The Yutu-2 rover, part of the Chang'e-4 (CE-4) mission to the lunar farside, has been exploring the Von Kármán crater (VK) within the South Pole-Aitken (SPA) gathering data on its geology. The Lunar Penetrating Radar's (LPR) 500 MHz antenna reveals the subsurface structure up to 40 m in depth, which helps to construct models on the evolution of the shallow stratum. This work presents the analysis and interpretation of the data collected during the first twenty lunar days, from January 2019 to July 2020. Below an 11±4-meter surface regolith layer, the radar image reveals well-defined reflectors that are interpreted as discrete depositional layers. These marked density boundaries could indicate a geologically brief time interval between each arrival, which prevented the materials to undergo a deeper homogenization through space weathering. To investigate further, we generated a subsurface rock distribution map using the correlation of dual-channel antennas data from the same channel. Clusters of rocks located at the bottom of each ejecta stratum are revealed, probably sorted by size due to the statistically less frequent occurrence of larger impact events admixing the deeper-seated materials. The bowl-shaped outline discovered in both rock and LPR energy distribution maps is interpreted to represent a 150±30 m wide and 10±5 m deep paleo-crater that was excavated within three thin ejecta layers. The CE-4 LPR reveals a complex geological history within the Von Kármán crater with no fewer than four impact events delivering meters thick ejecta at the CE-4 landing area following the end of the infilling phase.
On January 3rd 2019, the Chang’e-4 mission successfully landed in the Von Kármán Crater inside the South Pole-Aitken (SPA) basin and achieved the first soft landing on the farside of the Moon. Lunar ...penetrating radar (LPR) equipped on the rover measured the shallow subsurface structure along the motion path for more than 700 m. LPR data could be used to obtain the dielectric properties of the materials beneath the exploration area, providing important clues as to the composition and source of the materials. Although the properties of the upper fine-grained regolith have been studied using various methods, the underlying coarse-grained materials still lack investigation. Therefore, this paper intends to estimate the loss tangent of the coarse-grained materials at depth ranges of ~12 and ~28 m. Stochastic media models with different rock distributions for the LPR finite-difference time-domain (FDTD) simulation are built to evaluate the feasibility of the estimation method. Our results show that the average loss tangent value of coarse-grained materials is 0.0104±0.0027, and the abundance of FeOT+TiO2 is 20.08 wt.%, which is much higher than the overlying fine-grained regolith, indicating different sources.
The observable lunar surface is represented by a ubiquitous layer of fine‐grained materials produced by billions of years of hypervelocity pounding of its crustal layer. The data from the Lunar ...Penetrating Radar onboard Chang'e‐4 (CE‐4) rover (Yutu‐2), which is exploring the Von Kármán Crater on the lunar farside, are helping to peel back the upper layer of finely comminuted materials, interpreted as a thick layer of ejecta from the neighboring Finsen crater, to reveal a complex paleo‐surface morphology. During the rover’s 560 m journey, from depths of 7–20 m, distinct variations in the returned signal characteristics reveal a possible 270 ± 10 m buried crater with an estimated age of less than 100 m.y. A smooth surface depression that lies to the southwest of the Yutu‐2 rover’s travel path might not be the remnant of a degraded crater but a related surface expression of the hidden structure.
Plain Language Summary
The absence of an atmosphere and substantial resurfacing events in the last couple of billion years means that the Moon's surface has journeyed through space exposed to anything that travels through it and, unlike the Earth, most of these “encounters” have left a mark. Thus, the good news for scientists is that the lunar surface represents a record of astrophysical phenomena within the Solar System that is no longer available on its larger companion: our planet. However, the larger impacts have indeed contributed to modify its surface hiding some of its old terrains. The Lunar Penetrating Radar (LPR) onboard Chang'e‐4 (CE‐4) rover (Yutu‐2) can see below the surface as it makes its way across the lunar ground, revealing the ancient lunar surface (paleo‐surface) at the depth of ∼12 m. It has mapped its elevation profile, which now we can see that it has been substantially modified following its formation some 3.1 billion years ago. Notably, the LPR has discovered a 270 m sized buried crater corresponding to a large ground depression seen on the surface, a first achievement for lunar radar sounding.
Key Points
The CE‐4 LPR reveals the paleo‐surface of the lunar farside at a depth between 7 and 20 m
The LPR has mapped a 270 m sized buried crater probably related to a larger circular depression on the lunar surface
The geomorphology, the subsurface structure, the impact melt deposits, and the exposure time of the buried crater, are analyzed
Impact craters are extensively researched geological features that contribute to various aspects of lunar science, such as evaluating the model age, regolith thickness, etc. The method for ...identifying impact craters has gradually transitioned from manual counting to automated identification. Automatic crater detection based on the digital elevation model (DEM) is commonly used to detect larger craters. However, using only DEM has limitations in discerning smaller craters (diameter < ~1 km). This study utilizes an improved Faster R-CNN algorithm and the Kaguya Terrain Camera (TC) morning map to detect small impact craters in the Chang’e-5 (CE-5) landing site. It uses model fusion to improve the precision of small crater identification. The results show a recall rate of 96.33% and a precision value of 90.19% for craters with diameters exceeding 200 m. The model found a total of 187,101 impact craters in the CE-5 region. The spatial distribution density of impact craters with diameters ranging from 100 m to 200 m is approximately 2.5706/km2. For craters with diameters ranging from 200 m to 1 km, the average spatial distribution density is about 0.9016/km2. By the unbiased impact crater density of chronological analysis, the model age of the Im2 and Em4 geological units in the CE-5 region is 3.78 Ga and 2.07 Ga, respectively.
Investigating the mathematical and geometric principles embedded in ancient classic architecture is a significant tradition in the history of architectural development. Drawing inspiration from the ...modular design and creative ideology based on the geometric proportions of squareness and roundness in ancient Chinese architecture, we propose a new mode of squareness and roundness composition based on scale proportion specifically for the design of multi-story buildings. Taking Yingxian Wooden Pagoda as the case study, we not only re-evaluate the modular system and proportional rules followed in the design of the entire pagoda, but also reveal the technical approaches and geometric rules for effectively controlling the form of multi-story buildings. In particular, the mode of squareness and roundness composition based on scale proportion, utilizing a modular grid combined with squareness and roundness drawings as decision-making tools, can control the scale and proportion of buildings across different design dimensions and organically coordinate the design of multi-story buildings’ plans and elevations. Thus, it can achieve an effective balance of multi-story architectural forms. This study has potential applications in the creation of traditional multi-story buildings and heritage restoration projects, and offers valuable insights for future research on ancient multi-story buildings.
Abstract
The landing site of China’s Chang’e-4 (CE-4) probe is located on the mare basalts on the floor of the Von Kármán crater on the lunar far side. The Von Kármán crater is inside the ancient and ...highly cratered South Pole–Aitken basin, which has experienced complex emplacement sequences of both near and distant ejecta materials. These issues complicated the interpretation of the CE-4 surface in situ measurements of the visible and near-infrared spectrometer and the lunar penetrating radar (LPR) onboard Yutu-2 rover. To evaluate the sources and amounts of all principle foreign materials at the CE-4 landing site, we thoroughly examine the ejecta delivered by crater-forming events that occurred later than the formation of the mare basalts at the CE-4 landing site. We found a total of 16 craters that may have delivered ejecta thicker than 10 cm level superposed on the mare basalts at the CE-4 landing site. Crater Finsen, Von Kármán L, Von Kármán L′, and Maksutov are the top four major foreign material sources, and each of them contributed ejecta thicker than 1 m. Our surveys confirm that the ejecta from Finsen crater are the most dominant foreign materials in the uppermost few meters at the CE-4 landing site and the total impact ejecta deposited upon the mare basalts at the landing site is estimated to be thinner than 30 m. We found that the estimations from Pike’s model are the most consistent with the Yutu-2 LPR observations.
The Chang'e-5 (CE-5) mission marks China's first lunar sample return endeavor, with its landing site (43.06°N, 51.92°W) situated in the Mons Rümker region of the northern Oceanus Procellarum on the ...Moon. This region hosts some of the youngest mare basalts of the Moon and contains a relatively youthful geologic unit characterized by crater's equilibrium diameters slightly over 100 m. By refining the Faster Region-based Convolutional Neural Network (Faster R-CNN) algorithm and leveraging high-resolution imagery to create training samples, accurate identification of lunar craters can be achieved. In this study, we enhance the algorithm in aspects such as anchor boxes and Region of Interest alignment. Additionally, we have utilized high-resolution images for training, and identify and statistics craters within the CE-5 landing area. Ultimately, our model attains a validation set Recall of 90%, Precision of 69%, and an Average Precision score of 0.83. Notably, in certain scales, such as for the crater larger than 400 m, recognition results reach Precision of 88% and Recall of 89%. The findings of this study are mapped into a crater catalog. Furthermore, we predict crater density and integrate it with geochronological functions to estimate the absolute model age of nine major geologic units within the CE-5 landing area. The results are generally in agreement with those of other studies who have used manual methods for crater counting, and verify the correctness of our automatic crater identification results.
•Enhanced small crater recognition in deep learning: sub-kilometer scale precision.•Employed three strategies to improve Faster RCNN in identifying lunar craters.•Created a crater catalog and estimated model age for the Chang'E-5 area.
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