Chang'E-1 Research Articles

Validity of a novel device for indoor analysis of cyclists’ drag area

Purpose: Cyclists need to measure aerodynamic resistance accurately and reliably, as well as economically. Devices such as Notio Aerostick, an equipment device that includes one pitot tube, have appeared for this purpose. The aim of this study is, therefore, to test the reliability and degree of agreement in the evaluation of the CdA (coefficient of aerodynamic drag), assessed by means of the Notio Aerostick compared to the Virtual Elevation (VE) and Martin mathematical models. Method: Seventeen professional cyclists rode in a 250-metre-long velodrome covered with a concrete surface with their own time trial bikes. Each cyclist completed three rides of 15 laps at constant speed for the evaluation of the CdA, each of them in a different position [Baseline (B), Change 1 (C1) and Change 2 (C2)]. Results: The differences in CdA between methods were found for Martin in comparison with VE in all positions (p <.001) and with Notio Aerostick in B and C2 (p> .05). About differences of CdA for each method, considering between position changes, the results were the same for VE and Martin, but different for Notio Aerostick. Conclusions: Findings suggest that, notwithstanding Notio Aerostick is valid if we compare CdA values with respect to VE, since the direction of their between-positions CdA changes differs, the results of their aerodynamic evaluation could lead us to recommend different final setups. We need studies that evaluate different units of the Notio Aerostick device as well as the reliability and precision of each sensor that includes Notio Aerostick. Highlights The CdA calculated by the Notio Aerostick and VE, a mathematical model previously validated, can be interchangeable, however the final position recommended by each method may be different, since the changes in the following position are given by the changes of the CdA in the previous position. None of the three methods allowed elite cyclists to measure statistically significant differences between the proposed setups. Although the CdA differences between positions were not significant, they can be decisive in the final result of a time trial competition.

Mineral chemistry and 3D tomography of a Chang’E 5 high-Ti basalt: implication for the lunar thermal evolution history

In December 2020, Chang’E-5 (CE-5), China’s first lunar sample return mission, successfully collected samples totaling 1731 g from the northern Oceanus Procellarum. The landing site was located in a young mare plain, a great distance from those of Apollo and Luna missions. These young mare basalts bear critical scientific significance as they could shed light on the nature of the lunar interior (composition and structure) as well as the recent volcanism on the Moon. In this article, we investigated a CE-5 basalt sample (CE5C0000YJYX065) using a combination of state-of-art techniques, including high resolution X-ray tomographic microscopy (HR-XTM), energy dispersive X-ray spectroscopy (EDS)-based scanning electron microscope (SEM), and electron probe microanalysis (EPMA) to reveal its 3D petrology and minerology. Our results show that this sample has a fine- to medium-grained subophitic texture, with sparse olivine phenocrysts setting in the groundmass of pyroxene, plagioclase, ilmenite and trace amounts of other phases. It has an extremely high ilmenite modal abundance (17.8 vol%) and contains a significant amount (0.5 vol%) of Ca-phosphate grains. The mineral chemistry is in excellent agreement with that of Apollo and Luna high-Ti basalts. The major phase pyroxenes also display strong chemical zoning with compositions following the trends observed in Apollo high-Ti basalts. Based on current data, we came to the conclusion that CE5C0000YJYX065 is a high-Ti mare basalt with a rare earth element (REE) enriched signature. This provides a rigid ground-truth for the geological context at the CE-5 landing site and clarifies the ambiguity inferred from remote sensing surveys.

Trajectory Determination of Chang’E-5 during Landing and Ascending

Chang’E-5 (CE-5) is China’s first lunar sample return mission. This paper focuses on the trajectory determination of the CE-5 lander and ascender during the landing and ascending phases, and the positioning of the CE-5 lander on the Moon. Based on the kinematic statistical orbit determination method using B-spline and polynomial functions, the descent and ascent trajectories of the lander and ascender are determined by using ground-based radiometric ranging, Doppler and interferometry data. The results show that a B-spline function is suitable for a trajectory with complex maneuvers. For a smooth trajectory, B-spline and polynomial functions can reach almost the same solutions. The positioning of the CE-5 lander on the Moon is also investigated here. Using the kinematic statistical positioning method, the landing site of the lander is 43.0590°N, 51.9208°W with an elevation of −2480.26 m, which is less than 200 m different from the LRO (Lunar Reconnaissance Orbiter) image data.

The Geological History of the Chang’e-5 Sample Return Region

Chang’e-5 (CE-5), China’s first sample-return mission, has successfully landed in Oceanus Procellarum near Mons Rümker. It is important to have a detailed study of the geological evolution of the CE-5 sample return region. This work aims to study the geological background, topography, geomorphology, major chemical composition, mineralogy, and chronology of the landing site region. First, we used the map of topography obtained by the Kaguya TC merged Digital Terrain Model (DTM) to analyze the topographic characteristics. Then, we used the Kaguya Multiband Imager (MI) reflectance data to derive FeO and TiO2 abundance and the hyperspectral data of the Moon Mineralogy Mapper (M3) onboard the Chandrayaan-1 spacecraft to study the mineralogy of the landing site region. Later, we defined and dated the geological units of the landing area using the crater size–frequency distribution (CSFD) method. Finally, we conducted a detailed analysis of the volcanism and tectonism that occurred in the CE-5 landing area. The study region has experienced multi-stage magmatic activities (~3.36 Ga to ~1.22 Ga) and formed multiple mare units with different chemical and mineral compositions. The relationship between the wrinkle ridges cut by small impact craters suggests that the U7/Em5 has experienced Copernican aged tectonism recently ~320 Ma. The U7/Em5 unit where the Chang’e-5 sample return mission landed is dominantly composed of mature pyroxene and the basalts are mainly high-iron and mid-titanium basalts. Additionally, the analysis of pure basalt in the U7/Em5 suggests that the samples returned by the CE-5 mission may contain the ejecta and ray materials of young craters, including sharp B, Harding, Copernicus, and Aristarchus.

Investigation on unexpected variations of differential phase delay of Chang’E-3

Abstract The Chinese lunar spacecraft Chang’E-3 (CE3) was launched on December 1, 2013, and it kept transmitting differential one-way range (DOR) signals during the whole mission. Differential phase delays calculated from those DOR signals are examined. An interesting phenomenon is that differential phase delays of different frequency pairs change in similar patterns before CE3′s landing on the Moon, whereas they change differently after the landing. Moreover, differential phase delays and signals’ power experience sudden and large-amplitude variations from time to time. Our analysis shows that, before the landing, signal reflection mainly happened on the spacecraft surface while CE3 was moving in space. Thus, the delay of reflected signals was a few nanoseconds with amplitude variation much larger than 0.12 ns, causing differential phase delays to vary in similar patterns. However, after CE3′s landing, reflected signals from lunar surface were received by ground stations when CE3 was sitting still on the Moon. Accordingly, the delay of reflected signals was more than 20 ns and with amplitude variation within a few tens of picoseconds, causing differential phase delays to change in different patterns. Further investigation reveals that those sudden, large-amplitude variations in differential phase delays and signals’ power were caused by CE3 maneuvers and onboard device movements.

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

AbstractThe 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.

Dynamic dual-target VLBI correlator technology

The dynamic dual-target very long baseline interferometry (VLBI) processing technology applied to the CVNScorr software processor is introduced. Chang’e 5 (CE-5) has achieved China’s first sample return mission from an extraterrestrial body. The characteristics of VLBI are that there are several target probes and the telemetry tracking and command (TT&C) technical requirements are high in CE-5. In the rendezvous and docking process, a real-time in-beam VLBI technology is required to perform the high-precision orbit measurement of two dynamic targets, the orbiter and the ascender. In addition, the VLBI correlator (CVNScorr) should tackle two-phase centers from two probes simultaneously. In the special power flight phases such as rendezvous and docking, near-moon braking, powered descending, and lunar takeoff, the VLBI high-precision delay model cannot be derived owing to the low accuracy of the predicted orbit. If the conventional data processing method is adopted, the VLBI fringe cannot be obtained. Therefore, the VLBI correlator should have the function of real-time dual-target fringe search and delay model reconstruction. CVNscorr adopts the principle of FX-type software correlation and has the function of dual-target correlation module, multibeacon fringe search, and delay model reconstruction. By taking advantage of the characteristics of TT&C signals from different probes, multiple beacons fringes are automatically searched and the delay values of the two targets are obtained simultaneously to reconstruct the high-precision delay models. CVNScorr uses MPI, GPU, and other technologies to realize parallel computing, and it is run on a CPU+GPU parallel cluster platform. In the CE-5 mission, the real-time processing capability is up to four stations of the Chinese VLBI Network and the postprocessing capability is up to six stations. The real-time data rate reaches 128 Mbps per station, the VLBI delay accuracy reaches 0.4 ns, and the real-time performance is better than 25 s.

Characteristics of the lunar samples returned by the Chang'E-5 mission.

Forty-five years after the Apollo and Luna missions returned lunar samples, China's Chang’E-5 (CE-5) mission collected new samples from the mid-latitude region in the northeastern Oceanus Procellarum of the Moon. Our study shows that 95% of CE-5 lunar soil sizes are found to be within the range of 1.40–9.35 μm, while 95% of the soils by mass are within the size range of 4.84–432.27 μm. The bulk density, true density and specific surface area of CE-5 soils are 1.2387 g/cm3, 3.1952 g/cm3 and 0.56 m2/g, respectively. Fragments from the CE-5 regolith are classified into igneous clasts (mostly basalt), agglutinate and glass. A few breccias were also found. The minerals and compositions of CE-5 soils are consistent with mare basalts and can be classified as low-Ti/low-Al/low-K type with lower rare-earth-element contents than materials rich in potassium, rare earth element and phosphorus. CE-5 soils have high FeO and low Mg index, which could represent a new class of basalt.

Absolute model ages of three craters in the vicinity of the Chang'E-5 landing site and their geologic implications

The Chang'E-5 (CE-5) mission has successfully collected lunar regolith samples from the northern Oceanus Procellarum. The Eratosthenian-aged mare units where the CE-5 landed on, might have been contaminated by distant ejecta delivered by several craters, such as Pythagoras, Sharp B, Harpalus, Copernicus, and other craters. Laboratory dating of distant ejecta in the CE-5 regolith can provide the formation ages of these craters. Therefore, these ejecta materials, the same as local young mare basalts, would serve as new calibration points for lunar chronology curve. Among above craters, the absolute model ages (AMAs) of Pythagoras, Sharp B and Harpalus are not well constrained. Here we used the Crater Size Frequency distribution (CSFD) method to yield their formation ages and the crater density values (N(1)/(km−2)). Using high resolution images, craters on the selected counting areas of their floors, ejecta blankets were identified. Our results indicate that Pythagoras is an Eratosthenian-age crater with an AMA of 2.13 ± 0.16 Ga and a N(1) =1.79 × 10−3 km−2. The Sharp B and Harpalus are both Copernican. The AMA of Sharp B crater is 1.01 ± 0.12 Ga with a N(1) of 8.46 × 10−4 km−2 while the AMA of Harpalus is 1.10 ± 0.04 Ga with a N(1) of 9.22 × 10−4 km−2. The ejecta from Sharp B and Harpalus as well as local mare basalt of the CE-5 site may be served as calibration points for lunar chronology curve, which will fill the age gaps of lunar chronology curve. Based on the estimated ages, we interpreted that Pythagoras ejecta might be beneath the young CE-5 mare unit, while the Sharp B and Harpalus ejecta should overlie the surface of the CE-5 site.

The Identification and Analysis of Gas-Related Volcanic Features within Chang’e-5 Landing Region

Chang’e-5 (CE-5) successfully landed on the young basalts area in the northeastern Oceanus Procellarum on 1 December 2020. Recent studies on the CE-5 landing area have shown that the lack of gas-related volcanic morphology indicates that the volatile elements captured in the interior of the Moon within late-stage magma is relatively low. Typical lunar gas-related volcanic features include dark mantle deposits, volcanic pits, irregular mare patches and so on. Based on orbital images, topography, and spectral data obtained from multiple missions restricted by the morphologic and compositional characteristics of typical volcanic explosive features, this study investigated the morphological characteristics of the volcanic features in detail and found that there are three dark mantle deposits (DMDs) near the source area of Rima Mairan that have unusually low albedo and abnormally high titanium and iron content than those of the surrounding material. Combined with M3 spectral analysis, it is shown that DMDs contain some volcanic glass components, which indicates a gas-rich explosive eruption process. In addition to DMDs, irregular mare patches (IMPs) and a volcanic depression/pit have been recognized in this area, both of which indicate a history of gas-related volcanic eruptions. Based on this study and combined with past studies, we determined the volcanic history in the source area of Rima Mairan, including both effusive and explosive volcanic activities.

Reconciling the Infrared and Microwave Observations of the Lunar South Pole: A Study on Subsurface Temperature and Regolith Density

AbstractThe Diviner Lunar Radiometer Experiment on the Lunar Reconnaissance Orbiter and the Microwave Radiometer (MRM) onboard Chang'e‐2 (CE‐2) orbiter performed nearly coincident measurements of the lunar south polar region in 2010–2011. In this study, we reconcile infrared data from Diviner and microwave data from MRM to reveal thermal behavior of lunar regolith at very low temperatures. Assuming a uniform density structure and dielectric properties across the polar region, we retrieve a relative apparent thermal‐gradient map based on radiative transfer model. The result shows apparent thermal gradients in the permanently shadowed regions (PSRs) are much larger than that in non‐PSRs, which implies a systematic difference in thermal conductivity and/or density of lunar regolith in PSRs. We also model surface temperature and microwave brightness temperature over time in PSR and non‐PSR locations. The modeling results at these representative locations and the thermal gradient map confirm that the regolith in the PSRs is consistent with a much lower thermal conductivity and higher porosity than non‐PSRs.

General Scheme and Key Technology of Long March 5 Launch Vehicle

Long March 5 (LM-5) is a new generation of heavy-lift launch vehicle developed by China. It has successfully completed the first Mars exploration of China and the 3rd phase of China lunar exploration program of Chang’E 5 (CE-5). LM-5 experienced 30 years of key technology research and engineering development. During this period, a lot of engineering technical problems were conquered, rich experience in the development of large cryogenic launch vehicle was accumulated, and the development of the new generation launch vehicle system was constructed. The research capability and foundation of carrier rockets have been greatly improved. This paper describes the development background of LM-5. Based on the overall rocket technical scheme and technical innovation, this paper discusses the development thinking of the rocket, the modular configuration scheme, the overall optimization design technology of the whole rocket and the structure technology of the large diameter and large concentrated load rocket body, and probes into the key technical problems of the LM-5 for the deep space exploration mission, specifically, the orbit design and optimization technology for deep space exploration mission, and narrow window multi-orbit launch technology. LM-5 is a landmark project of China’s new generation of launch vehicle, representing the highest level of launch vehicle technology of China, and is a significant symbol for China’s transformation from a major player in space to major power in space.

Integration of very long baseline interferometry data acquisition, recording, and transmission with multichannel and multibit for CE-5 mission

<p indent="0mm">Real-time signal acquisition, recording, and transmission are the important functions of very long baseline interferometry (VLBI). In the Chang’e-5 (CE-5) mission, a VLBI backend is required to connect the telemetry, track and command (TT&amp;C) beacons, data signals from multiple probes, such as the orbiter, ascender, and lander, and signals from the extragalactic radio source in time. Due to the multiple frequency points, large dynamic range, and complex spectrum form of the probe signals, existing VLBI astronomical backends do not meet the requirements of lunar exploration and deep space exploration. According to the characteristics of the beacon of CE-5 probes, we researched the integration technology of multichannel and multibit signal acquisition, recording, and transmission. This paper proposes a frequency tunable polyphase-filter bank algorithm, which can flexibly set frequency and obtain flat amplitude and linear phase characteristics in a wide band. The novel integrated VLBI backend developed by this technology contains 16 channels, which can sample and record all the TT&amp;C and data signals from CE-5 probes in real time and transmit the VLBI data to the VLBI center through the network. It ensures successful VLBI measurement in the complex electromagnetic environment of CE-5 multi beacons. Compared with the previous astronomical backends, the real-time performance, measurement accuracy, and reliability of the novel integrated VLBI backend are greatly improved, which support the successful completion of China’s first lunar sampling return mission of CE-5. The novel integrated VLBI backend also has the function of multibit quantization to meet the needs of wide and narrow observation of future radio sources and probes.

Semi-Supervised Deep Learning for Lunar Crater Detection Using CE-2 DOM

Lunar craters are very important for estimating the geological age of the Moon, studying the evolution of the Moon, and for landing site selection. Due to a lack of labeled samples, processing times due to high-resolution imagery, the small number of suitable detection models, and the influence of solar illumination, Crater Detection Algorithms (CDAs) based on Digital Orthophoto Maps (DOMs) have not yet been well-developed. In this paper, a large number of training data are labeled manually in the Highland and Maria regions, using the Chang’E-2 (CE-2) DOM; however, the labeled data cannot cover all kinds of crater types. To solve the problem of small crater detection, a new crater detection model (Crater R-CNN) is proposed, which can effectively extract the spatial and semantic information of craters from DOM data. As incomplete labeled samples are not conducive for model training, the Two-Teachers Self-training with Noise (TTSN) method is used to train the Crater R-CNN model, thus constructing a new model—called Crater R-CNN with TTSN—which can achieve state-of-the-art performance. To evaluate the accuracy of the model, three other detection models (Mask R-CNN, no-Mask R-CNN, and Crater R-CNN) based on semi-supervised deep learning were used to detect craters in the Highland and Maria regions. The results indicate that Crater R-CNN with TTSN achieved the highest precision (of 91.4% and 88.5%, respectively) in the Highland and Maria regions, even obtaining the highest recall and F1 score. Compared with Mask R-CNN, no-Mask R-CNN, and Crater R-CNN, Crater R-CNN with TTSN had strong robustness and better generalization ability for crater detection within 1 km in different terrains, making it possible to detect small craters with high accuracy when using DOM data.

Regolith Properties in the Chang'E‐5 Landing Region of the Moon: Results From Multi‐Source Remote Sensing Observations

AbstractIn December 2020, China's Chang'E‐5 (CE‐5) spacecraft successfully collected 1.731 kg samples from Oceanus Procellarum on the Moon's nearside, becoming the first lunar sample return mission since Luna 24 in 1976. These samples, collected from one of the youngest mare basalt units within the Procellarum KREEP Terrain, are critical to deciphering several fundamental questions of the Moon. In order to provide geologic context for interpreting the returned samples, we conducted a comprehensive analysis of regolith properties in the landing region using optical, topographic, multispectral, thermal, and radar observations. The CE‐5 landing site is within a flat, young mare basalt unit with intermediate titanium. A ballistic sedimentation model suggests that ∼98% of the surface regolith are local materials. The dielectric permittivity of the regolith is estimated to be 2.96 + i0.03 based on its composition and porosity. Morphologies of small fresh craters identified in high‐resolution optical images show that regolith thickness varies from ∼1.5 to ∼8 m with a median value of ∼5 m, implying a large mean regolith growth rate over the landing region. A comparison between radar image and Lunar Reconnaissance Orbiter Diviner surface rock abundance (RA) map indicates that subsurface rocks play a significant role in producing the observed radar backscatter. Further analysis of the radar echo suggests that subsurface RA is ∼0.47%–0.88% if the effective size is 3 cm, which can explain the shallow sampling depth of the CE‐5 drilling device. All these results provide valuable information for understanding the geological context and properties of the returned regolith samples.

Evaluating the Thickness and Stratigraphy of Ejecta Materials at the Chang’e-4 Landing Site

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.

Effect of Lunar Complex Illumination on In Situ Measurements Obtained Using Visible and Near-Infrared Imaging Spectrometer of Chang’E-4

In-situ measurements of the spectral information on the lunar surface are of significance to study the geological evolution of the Moon. China’s Chang’E-4 (CE-4) Yutu-2 rover has conducted several in-situ spectral explorations on the Moon. The visible and near-infrared imaging spectrometer (VNIS) onboard the rover has acquired a series of in-situ spectra of the regolith at the landing site. In general, the mineralogical research of the lunar surface relies on the accuracy of the in-situ data. However, the spectral measurements of the Yutu-2 rover may be affected by shadows and stray illumination. In this study, we analyzed 106 CE-4 VNIS spectra acquired in the first 24 lunar days of the mission and noted that six of these spectra were affected by the shadows of the rover. Therefore, a method was established to correct the effects of the rover shadow on the spectral measurements. After shadow correction, the FeO content in the affected area is corrected to 14.46 wt.%, which was similar to the result calculated in the normal regolith. Furthermore, according to the visible images, certain areas of the explored sites were noted to be unusually bright. Considering the reflectance, geometric information, and shining patterns of the multi-layer insulation (MLI), we examined the influence of the specular reflection of the MLI on the bright spot regionsd, and found that the five sets of data were likely not affected by the specular reflection of the MLI. The results indicated that the complex illumination considerably influences the in situ spectral data. This study can provide a basis to analyze the VNIS scientific data and help enhance the accuracy of interpretation of the composition at CE-4 landing sites.

Properties of Lunar Regolith on the Moon's Farside Unveiled by Chang'E‐4 Lunar Penetrating Radar

AbstractThe complex thermal history of the Moon leads to an unequal distribution of volcanic products between the lunar nearside and the farside. So far, no lunar materials have been sampled from the Moon's farside and no detailed properties of lunar regolith on the farside have been detected before. On January 3, 2019, Chang'E‐4 (CE‐4) touched down onto the Von Kármán crater on the Moon's farside. CE‐4 Lunar Penetrating Radar (LPR) onboard the Yutu‐2 rover is the first surface radar on the Moon's farside. Here we show the subsurface structure and properties of regolith materials at the landing region with LPR data during the first five lunar days. The thickness of lunar regolith is constrained as ∼12 m, much thicker than that at Chang'E‐3 (CE‐3) landing site, which is expected since CE‐3 landed on lunar maria. The relative permittivity of lunar surface (&lt;30 cm) at CE‐4 landing region is identified to be 2.35 0.20. The loss tangent and TiO2 + FeO content of the regolith materials layer (0–∼12 m) are constrained to be and wt.%, respectively, much lower than those at CE‐3 landing site. It indicates that local surface materials possess less attenuation for radiowave, in accordance with the greater penetrating depth of CE‐4 LPR than that of CE‐3 LPR. Furthermore, the results also prove that the growth rate of lunar weathered regolith successively declines over time and the growth rate of lunar regolith on the Moon's farside may well be higher than that on the nearside due to the more frequent meteorite impacts.

The Long Sinuous Rille System in Northern Oceanus Procellarum and Its Relation to the Chang'e‐5 Returned Samples

AbstractChina's Chang'e‐5 (CE‐5) mission recently returned samples from a young intermediate‐Ti mare unit (Em4/P58, ∼1.5 Ga) in Northern Oceanus Procellarum. Rima Sharp, previously mapped as the longest lunar sinuous rille, is the most prominent volcanic feature associated with the landing region. Our analysis shows that Rima Sharp is not a single rille, but instead is composed of two separate rilles (Rima Sharp, originating from the North Vent, and Rima Mairan from the South Vent), meeting at ∼40.40°N, 48.38°W. Both vent have characteristics suggesting relatively low magma volatile contents. Rima Mairan and associated lavas (southeast of Em4/P58), embay and are slightly younger than Rima Sharp. Rille formation is largely influenced by pre‐existing topography (earlier mare surface, proto‐wrinkle ridges, highlands); rilles and deposits experienced post‐formation deformation (wrinkle ridges, mare subsidence). CE‐5 samples probably originate mainly from Rima Sharp's source vent, but may represent deposits from both rilles.

Analysis of plume–lunar surface interaction and soil erosion during the Chang’E-4 landing process

When the lander approaches the lunar surface, the rocket exhaust will erode the surface and eject massive high-speed dust, which could damage the payloads on the lander or interfere with subsequent surface operations. This process also provides a unique opportunity to study the plume–dust interaction and the wind erosion on the surface of airless body such as the Moon. Previously, limited knowledge was obtained from Apollo landing images and a simplified erosion model is built to study the erosion process. With high-quality data acquired in the landing process of Chang’E-4 (CE-4) mission, for the first time, we aim to quantify the dust ejection angle and erosion depth for a low-thrust lander, test the effectiveness of the current erosion model, and provide reference information for future landing missions. We use image measurement methods to extract key parameters such as dust ejection angle and erosion depth from the landing image of CE-4. For comparison with the observation, we also employ an erosion model to estimate the erosion thickness. The dust appears at about 7 s before the lander touch the surface, with a height of 13 m above the surface. When the nozzle altitude was about 0.6 m, the dust ejection angle is measured to be above 7°, while the dust ejection angle calculated by the particle trajectory method is less than 4.3°for particle sizes smaller than 1 mm. For the first time, an average erosion depth of 0.7 cm is measured between 1.12 m and 2 m from the nozzle centerline for a low-thrust lander. The measurement corresponds to an erosion time duration from 1.1 s before landing to 0.4 s after landing. The measured erosion range using CE-4 data is much larger than the estimated erosion radius given by the previous erosion model. It indicates that the dust’s angular distribution, local topography of the landing area, and other factors are important in improving the precision of the erosion model.