Crater Size-frequency Distribution Research Articles

Kilometer-scale crater size-frequency distributions on Ceres

This paper presents an investigation of the size-frequency distribution (SFD) of sub-kilometer-sized projectiles in the Main Belt based on the crater distribution on Ceres. Using image data of 35 m/pixel obtained by the Dawn mission with an onboard Framing Camera during the Low Altitude Mapping Orbit (LAMO), we counted craters having diameter larger than 1 km on the entire surface of Ceres. Based on the crater counting, we investigated the crater size-frequency distribution (CSFD) for the entire surface of Ceres and specifically for floors of 15 named impact craters of various ages. Distinct secondary craters were excluded for derivation of the CSFDs for the 15 crater floors. The CSFDs for the entire surface and those for 8 out of the 15 crater floors show good agreement with the crater production function (PF) for the Lunar Derived Model (LDM), which scales the well-investigated lunar cratering record to the impact environment of Ceres. Although the CSFDs for the other 7 crater floors show somewhat deviations from the PF, the deviations are less likely to show projectile information but are more likely to show the contamination with unidentified secondary craters. Our results indicate that the projectile SFDs on Ceres during 220 Ma – 1.9 Ga are invariably consistent with that found for the Moon. On the other hand, the derived SFDs of sub-kilometer-sized projectiles on Ceres are apparently different from those for the Main Belt Asteroids that have been observed telescopically, which might result from subsurface discontinuity or the Yarkovsky effect.

Lunar Crater Detection on Digital Elevation Model: A Complete Workflow Using Deep Learning and Its Application

Impact cratering process is the major geologic activity on the surface of the Moon, and the spatial distribution and size-frequency distribution of lunar craters are indicative to the bombardment history of the Solar System. The substantial efforts on the development of automated crater detection algorithms (CDAs) have been carried out on the images from the remote sensing observations. Recently, CDAs via convolutional neural network (CNN) on digital elevation model (DEM) has been developed as it can combine the discrimination ability of CNN with the robust characteristic of the DEM data. However, most of the existing algorithms adopt a traditional two-stage detection pipeline including an edge segmentation and a template matching step. In this paper, we attempt to reduce the gap between the existing DEM-based CDAs and the advanced CNN methods for object detection, and propose a complete workflow including an end-to-end deep learning pipeline for lunar crater detection, in particular for craters smaller than 50 km in diameter. Based on the workflow, we benchmark nine representative CNN models involving three popular types of detection architectures. Moreover, we elaborate on the practical application of the proposed workflow, and provide an example method to demonstrate the performance advantage in terms of the precision (82.97%) and recall (79.39%). Furthermore, we develop a crater verification tool to manually validate the detection results, and the visualization results show that our detected craters are reasonable and can be used as a supplement to the existing hand-labeled datasets.

Insight into martian crater degradation history based on crater depth and diameter statistics

Impact craters are widely used to investigate the geologic history of planetary surfaces. Their morphology bears clues on past surface processes that affected it such as erosion, sedimentary deposit and volcanic processes and their density is widely used to date planetary surfaces.In this study we propose to combine crater Density and morphology into a single representation, Crater Size and Depth Frequency Distribution (CSDFD) that offers a snapshot not only at the age but also at the obliteration history of the crater population. Using simple models, we interpreted the CSDFD in term of crater obliteration rates. This methods can be applied on any body featuring impact craters. We present here the results obtained on Mars, using a global crater database.The obliteration rates obtained from CSDFD are consistent with known geologic history of Mars. Reaching thousands of m/Gy during Noachian and rapidly dwindling as soon as 3.5 Gy. Moreover, our method highlighted an continuous activity of Northern Lowlands surface during Amazonian we interpret to be linked with the formation of the vastitas borealis formation. This study offer a continuous vision in time and space of Martian obliteration history.

Testing statistical impact crater analysis in permanently shadowed lunar polar regions

This work presents and tests the classical crater size frequency distribution statistical analysis based age estimation for lunar terrains where optical images are not available, e.g. in permanently shadowed polar craters. A comparison of the optical and topographic data based analysis with the joint evaluation of slope maps of about 1° slope resolution together with shadow relief maps, helps to identify craters down to about 300–400 m diameter. Only 2–3% of the craters found in optical WAC images could not be identified on topographic maps. Comparing the size of the same craters measured by these two methods, the difference was also small, usually smaller than 10%, which effect on crater statistics based age estimation was smaller than the error bars. Only one characteristic difference could be identified between these two methods: eroded thus shallow craters could be more difficult to identify with the topographic analysis, however such degraded impact features may not be easy to identify using optical images occasionally. By this method, the plain shaped internal areas of DeGerlache crater floor were found to show 3.8–0.08 + 0.05 and 3.9–0.2 + 0.08 Ga age values, in agreement with the work of Deutsch et al. (2020) using mainly the external and well illuminated ejecta blanket is this crater.

Chronology of the Basalt Units Surrounding Chang’e-4 Landing Area

The Chang’e-4 (CE-4) lunar probe, the first soft landing spacecraft on the far side of the Moon, successfully landed in the Von Kármán crater on 3 January 2019. Geological studies of the landing area have been conducted and more intensive studies will be carried out with the in situ measured data. The chronological study of the maria basalt surrounding the CE-4 landing area is significant to the related studies. Currently, the crater size-frequency distribution (CSFD) technique is the most popular method to derive absolute model ages (AMAs) of geological units where no returned sample is available, and it has been widely used in dating maria basalt on the lunar surface. In this research, we first make a mosaic with multi-orbital Chang’e-2 (CE-2) images as a base map. Coupled with the elevation data and FeO content, nine representative areas of basalt units surrounding the CE-4 landing area are outlined and their AMAs are derived. The dating results of the nine basalt units indicate that the basalts erupted from 3.42 to 2.28 Ga ago in this area, a period much longer than derived by previous studies. The derived chronology of the above basalt units establishes a foundation for geological analysis of the returned CE-4 data.

Chronological and compositional mapping of the Mare Orientale basin using Chandrayaan-1 – M3 and LRO datasets

The lunar multiring mare basins have different ages, compositions and are associated with the diverse unit of mare deposits, providing evidence for the origin and evolution of the lunar crust. The multiring basins offer the opportunity to assess many unknown questions that may reveal the lunar geologic standpoint. The Mare Orientale basin is one of the youngest impact multiring basins on the Moon, which covers about 930 km in diameter and coordinates centered at 200S 950W. In the present study, the compositional, topographical, and chronological studies have been done by using Moon Mineralogy Mapper (M3) from Chandrayaan-1 orbiter and Lunar Reconnaissance Orbiter Camera-Wide Angle Camera (LROC-WAC) image from Lunar Reconnaissance Orbiter (LRO). The M3 data used to map the Optical maturity (OMAT), FeO & TiO2 concentrations of the basin. The Standard Band Ratio (SBR) of the Orientale basin has been prepared to discriminate the different mare and highland lithologies. The 1 μm and 2 μm band depths have been mapped to demarcate the mafic minerals such as olivine and pyroxenes. The age of the Orientale basin mare units was mapped as Orientale event (3.72 Ga - Upper Imbrian), Orientale South West (3.7 Ga), Orientale West unit (3.37 Ga), Lacus Veris North unit- 1, 2, and 3 (3.1 Ga, 2.63 Ga, and 3.3 Ga), Lacus Veris East (2.9 Ga), Lacus Autumni - North (3.1 Ga), Middle (2.01 Ga), South (2.27 Ga) and Kopff crater (mare) (2.92 Ga) by using LROC-WAC data through Crater Size Frequency Distribution (CSFD) technique. Characterization of M3 reflectance spectra profiles was done to map the Orientale basin lithologies like olivine, pyroxene (low calcic and high calcic), plagioclase, ilmenite, Mg-spinel, and olivine – pyroxene mixtures that are present in the anorthositic, basaltic, noritic, and gabbroic rocks. It is revealed that the Orientale basin could have been formed either by global thermal evolution and basin mare volcanic evolution or pressure release melting and associated with secondary convection.

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.

An arid-semiarid climate during the Noachian-Hesperian transition in the Huygens region, Mars: Evidence from morphological studies of valley networks

Fluvial activities play important roles in the geologic evolution of early Mars. As one of the most ancient fluvial features on Mars, the widely distributed valley networks (VNs) provide clues for understanding the early martian climate. Our study focuses on the morphological and hydrological features of VNs around the Huygens basin in the ancient southern highland. A total of 198 VNs are identified in the Huygens region with a total length of 23,991.6 km, among which 83 VNs are firstly identified. VNs possess drainage patterns of dendritic to parallel, and show average stream order of 2.45 with a maximum of 5, suggesting a simple branching morphology. Sinuosity indexes of mainstreams range from 1.02 to 1.98 with an average of 1.15, exhibiting a straight to winding form. Two types of VN channels are observed with distinct elevational distribution, headwater morphology, and longitudinal profile shape, and are considered to be sapping-related and surface runoff-related, respectively. Age estimations from crater size-frequency distribution measurements suggest that VN activities at the basin rim mainly started around the Noachian/Hesperian boundary at ~3.7 Ga, and decayed near the Early/Late Hesperian boundary. VNs at the basin floor show a younger age of ~3.5 Ga, which supports a potential short-lived lake inside the basin during the Noachian-Hesperian transition. A combined effect of rainfall and groundwater is considered as the dominant water sources of VNs in the Huygens region, with the climate condition characterized by transient warm and arid-semiarid periods under a possibly cold and arid environment.

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.

New Evidence to Support Zephyria Tholus as a Composite Volcano on Mars

Zephyria Tholus has been proposed to be a composite volcano, however, detailed geomorphological study was not carried out due to limited high-resolution remote sensing data. Here we use MOLA, THEMIS, CTX and HiRISE data to conduct topographical and geomorphological analysis of Zephyria Tholus. We identify extensive valleys and troughs on the flank, which are sector collapse or glacio-fluvial in origin. The valleys and troughs indicate coexistence of different erosion resistance materials, along with the observed solid lava outcrops. There are also layered materials identified on the wall of the largest valley. In addition, perched craters are identified on the top depression and flanks of Zephyria Tholus, indicating the presence of ice-rich layer. We conducted crater size-frequency distribution of the caldera and found the absolute model age is 3.74 (+0.03, −0.04) Ga. The geomorphology evidence and chronology result support the composite volcano nature of Zephyria Tholus, and indicate the magma volatile content in the Aeolis region in Noachian is more than 0.15 wt% if the atmosphere paleo-pressure was similar to present Mars.

Pluto and Charon Impact Crater Populations: Reconciling Different Results

Abstract The size–frequency distribution (SFD) of objects across the solar system is influenced by their formation and dynamic evolution. Bodies in different areas of the solar system—especially the inner versus outer—have likely experienced different histories, so measuring that SFD across orders of magnitude of solar distance can elucidate those different pasts. Accurate measurement of the SFD is greatly assisted by impact craters, formed from the smaller bodies that strike much larger ones, and it is often easier to measure impact craters’ SFDs than the smaller impactors themselves. One of the main results from New Horizons’ Pluto–Charon encounter was the crater SFD measurement, which illustrated an unexpected SFD with a distinct change in slope near ≈10–15 km diameter features. However, different methods of reporting these impact craters have resulted in some questions in the community about what the SFD actually is of Pluto's and Charon's crater population and therefore what the SFD is of the impactors that formed them. We have performed new crater population studies on both bodies, compared them with previously published work, and demonstrated that there is no ambiguity with respect to whether there is a transition to a shallower SFD population near ≈10–15 km. We find that this shallower slope is approximately −1.7 ± 0.2, while the steeper slope for larger craters is approximately −3.8 ± 0.6, though both of these uncertainties must be considered absolute minima based on fit sensitivity to the exact parameters and craters used. These values are consistent with previously reported results.

Geologic History and Crater Morphology of Asteroid (162173) Ryugu

AbstractCrater morphology and surface age of asteroid (162173) Ryugu are characterized using the high‐resolution images obtained by the Hayabusa2 spacecraft. Our observations reveal that the abundant boulders on and under the surface of the rubble‐pile asteroid affect crater morphology. Most of the craters on Ryugu exhibit well‐defined circular depressions, unlike those observed on asteroid Itokawa. The craters are typically outlined by boulders remaining on the rim. Large craters (diameter > 100 m) host abundant and sometimes unproportionally large boulders on their floors. Small craters (<20 m) are characterized by smooth circular floors distinguishable from the boulder‐rich exterior. Such small craters tend to have dark centers of unclear origin. The correlation between crater size and boulder number density suggests that some processes sort the size of boulders in the shallow (<30 m) subsurface. Furthermore, the crater size‐frequency distributions (CSFDs) of different regions on Ryugu record multiple geologic events, revealing the diverse geologic history on this 1‐km asteroid. Our crater‐counting analyses indicate that the equatorial ridge is the oldest structure of Ryugu and was formed 23–30 Myr ago. Then, Ryugu was partially resurfaced, possibly by the impact that formed the Urashima crater 5–12 Myr ago. Subsequently, a large‐scale resurfacing event formed the western bulge and the fossae 2–9 Myr ago. Following this process, the spin of Ryugu slowed down plausibly due to the YORP effect. The transition of isochrons in a CSFD suggests that Ryugu was decoupled from the main belt and transferred to a near‐Earth orbit 0.2–7 Myr ago.

Geology and history of the Malea Planum region: A new view of Mars’ oldest large volcanic province

Geology and history of the Malea Planum region: A new view of Mars’ oldest large volcanic province

Maria Basalts Chronology of the Chang’E-5 Sampling Site

Chang’E-5 is the first lunar sample return mission of China. The spacecraft was landed in the northwest of the Procellarum KREEP Terrane (43.0576°N, 308.0839°E) on 1 December 2020 and returned 1731 g samples from a previously unvisited region. The landing area has been proposed as one of the youngest mare basalt units of the Moon and holds important information of lunar thermal evolution and chronology. However, the absolute model ages estimated in previous studies are quite different, ranging from 2.07 Ga to 1.21 Ga. Such significant difference may be caused by (1) different crater counting areas, (2) different crater diameter ranges, (3) effects of secondary craters, and (4) biases in crater identification. Moreover, the accurate landing site was unknown and the ages were estimated over the Eratosthenian-aged mare unit (Em4) instead. In light of the above unsatisfactory conditions, this study seeks to establish a standard crater size-frequency distribution of the CE-5 landing site. We derived the concentrations of FeO and TiO2 to map out the pure basaltic areas where external ejecta deposits are negligible and thus secondary craters are rare. Based on the geochemistry of basaltic ejecta excavated by fresh craters in the mare unit, the FeO concentration threshold for mapping pure basaltic areas is 17.2 wt.%. The morphologically flat subunits in the pure basaltic areas were selected for crater identification and age dating to exclude the contamination of external ejecta to the best as we could. In the Chang’E-5 sampling site subunit, we detected 313 craters with a diameter greater than 100 m and derived the absolute model age as 1.49−0.084+0.084 Ga. The craters identified in all pure basaltic subunits of Em4 gave the model age of 1.41−0.028+0.027 Ga. As least affected by secondary craters, the crater size-frequency distribution of the sample-collected pure basaltic subunit can provide important constraints for lunar cratering chronology function in combination with isotopic age of returned samples.

Ina Lunar Irregular Mare Patch Mission Concepts: Distinguishing between Ancient and Modern Volcanism Models

Abstract The Ina irregular mare patch, an ∼2 × 3 km summit depression on an ancient ∼22 km diameter shield volcano, displays two very enigmatic units: (1) dozens of dark convex-upward mounds and (2) a very rough, optically immature floor unit with very sharp morphologic contacts between the two. Controversy surrounds the age interpretation of Ina; superposed impact crater size–frequency distributions (CSFDs) suggest an age of ∼33 Ma, consistent with the presence of sharp contacts between the units and indicating that mare volcanism continues to today. Models of the terminal stages of volcano summit pit crater activity suggest an age coincident with the building of the shield, ∼3.5 Ga; these models interpret the CSFD age and sharp contacts to be due to an extremely porous lava lake floor and extrusion and solidification of magmatic foams. We present robotic–human exploration mission concepts designed to resolve this critical issue for lunar thermal evolution.

Self-Secondaries Formed by Cold Spot Craters on the Moon

Self-secondaries are a population of background secondaries, and they have been observed on top of impact melt and ballistically emplaced ejecta deposits on various planetary bodies. Self-secondaries are formed by impacts of sub-vertically launched ejecta, but the launch mechanism is not confirmed. The potential threat of self-secondaries to the theoretical and applicable reliability of crater chronology has been noted, but not constrained. Hitherto discovered self-secondaries were located around complex impact craters, but their potential existence around simple craters has not been discovered. Here we report the first discovery of self-secondaries around lunar cold spot craters, which are an extremely young population of simple craters formed within the past ~1 million years on the Moon. Self-secondaries are widespread on layers of cascading flow-like ejecta deposits around cold spot craters. The spatial density of self-secondaries dwarfs that of potential primary craters. The spatial distribution of self-secondaries is highly heterogeneous across the ejecta deposits. With respect to the impactor trajectory that formed cold spot craters, self-secondaries formed at the downrange of the ejecta deposits have the largest spatial density, while those at the uprange have the smallest density. This density pattern holds for all cold spot craters that were formed by non-vertical impacts, but self-secondaries do not exhibit other systematic density variations at different radial distances or at other azimuths with respect to the impactor trajectory. Among known mechanics of ejecting materials to the exterior of impact craters, impact spallation is the most likely scenario to account for the required large ejection velocities and angles to form self-secondaries. The production population of self-secondaries is estimated based on the highly diverse crater size-frequency distributions across the ejecta deposits of cold spot craters. For a better understanding of the impact history on the Moon, a systematic investigation for the effect of self-secondaries on lunar crater chronology is required.

Possible polyphase periglaciation and glaciation adjacent to the Moreux impact-crater, Mars

The cyclicity and temporal succession of glacial-periglacial periods or epochs are keynotes of cold-climate geology on Earth. Relatively recent work within the Mars community has begun to dissect the mid- to higher-latitudinal terrain of Mars for analogical evidence of similar cold-climate cyclicity and succession.Here, we carry on with this work by focusing on the terrain immediately to the north of the Moreux impact-crater (40–44° N, 43–47° E). The crater is located in northern Arabia Terra, to the south of Protonilus Mensae. It lies astride of and postdates Mars' crustal-dichotomy. The latter is a global geological-boundary that separates the ancient southern-highlands from the relatively younger northern-lowland plains.Using cross-cutting relationships, relative stratigraphy and crater-size frequency distributions (CSFDs) we identify three glacial and two periglacial periods that are temporally intertwined and differentiated by a suite of features unique to each of these periods. For example, we report and discuss clusters of pingo-like mounds amidst ridge and trough terrain or “brain terrain”. On Earth, the former are the work of freeze-thaw cycling; on Mars, the latter are thought to be glacial remnants. In turn, the brain terrain is underlain by small-sized polygons possibly formed by thermal contraction cracking and with margins underlain by degraded ice-wedges. Age estimates derived of CSFDs suggest that the polygonised terrain could as much as ~100 Ma, whereas the brain terrain and pingo-like mounds are thought to be ~1–~10 Ma. Possible terminal-moraines that intercept brain-terrain fragments point to an even more recent period of glaciation.If the CSFD age-estimates are valid, then the polygons that underlie the brain terrain and incise the basin floors of our study zone could be an order of magnitude older than most of the age estimates associated with polygonised terrain at other locations on Mars. The fact that there are two distinct periods of polygonization and periglacial activity with a wide offset of time within one relatively small study zone also highlights the extent to which the freeze-thaw cycling of water might be rooted as iteratively and as deeply in Mars' geological history as is its glaciation.

Ages and chemistry of mare basaltic units in the Grimaldi basin on the nearside of the Moon: Implications for the volcanic history of the basin

AbstractLunar mare basalts represent flood volcanism between ~4.0 and 1.2 Ga, therefore, providing insights into the thermal and volcanic history of the Moon. The present study investigates the spectral and chemical characteristics as well as ages of the nearside mare basaltic units from the Grimaldi basin, namely Mare Grimaldi and Mare Riccioli, using a wealth of orbital remote sensing data. This study delineated distinct basaltic units of varying albedo, mineralogy, and titanium contents in both Mare Grimaldi and Mare Riccioli. The crater size–frequency distribution technique revealed that at least two phases of basaltic magmatism spanning ~3.5 to 1.5 Ga (Late Imbrian–Eratosthenian) have occurred in the Grimaldi basin. High‐Ti olivine basalts dated at 2.05 Ga are found to be surrounded by the Late Imbrian (~3.47 Ga) low‐ to intermediate‐Ti basalts in Mare Grimaldi. Low‐ to intermediate‐Ti basalts observed in Mare Riccioli date back to two different volcanic events at ~3.5 Ga and ~3.2 billion years, while patches of basalts having remarkably higher titanium content within the Mare Riccioli record the youngest age of ~1.5 Ga. The chemical trend of the pyroxenes from distinct basaltic units also revealed that multiple events of volcanism have occurred in the Grimaldi basin. The high‐Ti basalts in the Mare Grimaldi crystallized from an Fe‐enriched late‐stage magma while the low‐Ti basalts crystallized from an Mg‐ and Ca‐rich initial magma that experienced an ultra‐late stage quenching. The low‐ to intermediate‐Ti basaltic magma erupted in both the units was derived by partial melting of early cumulate materials from the hybrid source region in the post‐overturn upper mantle and made its way to the surface through dikes that propagated by excess pressures accumulated in the diapirs stalled at the base of the crust due to buoyancy trap. The high‐Ti magma erupted in the Mare Grimaldi was generated by a hot plume ascended from deeper clinopyroxene–ilmenite‐rich cumulate layer near the core–mantle boundary. However, the Eratosthenian (~1.5 Ga) intermediate‐Ti volcanic activity in the Mare Riccioli rather sourced from the ilmenite–clinopyroxene cumulate materials that remained in the upper mantle after mantle overturn. The new results suggest that volcanism had not ceased in the Grimaldi basin at 3.27 Ga, rather it was active and fed by different mantle sources until 1.5 Ga for a period spanning ~2 billion years.

Geological evolution of the Sinus Iridum basin

As a semi-enclosed crater basin on the northwest rim of Imbrium basin, Sinus Iridum is a key site to investigate the geological characteristics at the intersection of two basins. For this reason, we focused on model age determination in Sinus Iridum basin using Chang’E−2 high-resolution images coupled with compositional maps from the Clementine data sets, as well as with digital elevation models (DEMs) from the Lunar Orbiter Laser Altimeter (LOLA) onboard the Lunar Reconnaissance Orbiter (LRO). With these datasets we identified different geologic units onto which we performed model age determinations based on crater counting. This systematic analysis of the Sinus Iridum basin shows that the age of the oldest exposed basaltic unit is 3.37 ​Ga (Imbrian age), while the youngest, a mare basalt unit that enters the basin from Imbrium basin, is 1.24 ​Ga (late Eratosthenian). In general, the ages of the geologic units inside the Sinus Iridum basin gradually decrease from the northeast to the southwest, with the only exception of the young units being located in the north-eastern area. We conclude that the crater size-frequency distributions (CSFD) reflect a multi-layer sequence, suggesting multiple resurfacing events inside Sinus Iridum. The model age determinations identify several infilling events of basalts ranging from 3.37 ​Ga to 1.24 ​Ga, which are all derived mare basalt flows from the Imbrium basin.

Multi-scale morphologic investigation of craters in the Chang'e-4 landing area

China's Chang'e-4 (CE-4) rover landed in Von Kármán crater on January 3, 2019, and has acquired a large amount of data of the landing site. Craters are an important landform in lunar surface and the analysis of craters at the landing site with high-resolution images is of great significance for both scientific study and engineering safety. In this study, multi-sources data, including Lunar Reconnaissance Orbiter Camera Narrow Angle Camera (NAC) images, NAC digital elevation model (DEM), Chang'e-2 (CE-2) digital orthophoto map (DOM), SLDEM2015 and stereo images from panoramic cameras onboard the CE-4 rover, are involved to reveal the crater morphologic features at the landing site. The diameter, depth, spatial density and depth/diameter ratio (d/D) of the mapped craters have been investigated. Randomness analysis and the size-frequency distributions of craters in two scales are conducted to thoroughly elaborate the crater distribution in the landing area. The multi-scale crater investigation establishes a foundation for subsequent in-depth studies, e.g., crater evolution and degradation of lunar farside and CE-4 landing area dating.