Search

Dating young lunar surfaces, such as impact ejecta blankets and terrains associated with recent volcanic activities, provides critical information on the recent events that shaped the surface of the Moon. Model age derivation of young or small areas using a crater chronology is typically achieved through manual counting, which requires a lot of small impact craters to be tediously mapped. In this study, we present the use of a Crater Detection Algorithm (CDA) to extract crater populations on Lunar Reconnaissance Orbiter—Narrow Angle Camera (LRO‐NAC) and Kaguya Terrain Camera images. We applied our algorithm to images covering the ejecta blankets of four Copernican impact craters and across four young mare terrains, where manually derived model ages were already published. Across the eight areas, 10 model ages were derived. We assessed the reproducibility of our model using two populations for each site: (a) an unprocessed population and (b) a population adjusted to remove contaminations of secondary and buried craters. The results showed that unprocessed detections led to overestimating crater densities by 12%–48%, but "adjusted" populations produced consistent results within <20% of published values in 80% of cases. Regarding the discrepancies observed, we found no significant error in our detections that could explain the differences with crater densities manually measured. With careful processing, we conclude that a CDA can be used to determine model ages and crater densities for the Moon. We also emphasize that automated crater datasets need to be processed, interpreted and used carefully, in unity with geologic reasoning. The presented approach can offer a consistent and reproducible way to derive model ages. Plain Language Summary: Studying young lunar surfaces, such as impacted areas or volcanic activity, helps us understand recent events that have shaped the Moon's surface. Determining the model age of these areas generally involves manually counting small craters, which is time‐consuming and variable. This study presents a machine‐learning approach to detect craters on images acquired by the Lunar Reconnaissance Orbiter‐Narrow Angle Camera and the Kaguya Terrain Camera. Four impact craters and four young mare terrains were analyzed, where model ages had already been determined manually. When comparing our automatic counts to the manual counts, we observed that our results became more consistent with the published surface ages when we excluded secondary or buried craters from our crater populations. We also outline that automatic crater detection methods can be used to determine the age of lunar surfaces in a reliable and consistent manner when used correctly. Key Points: Automatic crater counting of the Moon was achieved using a Convolutional Neural Network architecture and applied to LRO‐NAC and Kaguya Terrain Camera imagesTesting of the automatic counts against manual counts across the same count areas is required to provide confidence in the resultsSurface ages resulting from automatic crater counts are within acceptable error of model ages for the same area found using manual counts [ABSTRACT FROM AUTHOR]

Impact craters are the most common feature on the Moon's surface. Crater size–frequency distributions provide critical insight into the timing of geological events, surface erosion rates, and impact fluxes. The impact crater size–frequency follows a power law (meter‐sized craters are a few orders of magnitude more numerous than kilometric ones), making it tedious to manually measure all the craters within an area to the smallest sizes. We can bridge this gap by using a machine learning algorithm. We adapted a Crater Detection Algorithm to work on the highest resolution lunar image data set (Lunar Reconnaissance Orbiter‐Narrow‐Angle Camera [NAC] images). We describe the retraining and application of the detection model to preprocessed NAC images and discussed the accuracy of the resulting crater detections. We evaluated the model by assessing the results across six NAC images, each covering a different lunar area at differing lighting conditions. We present the model's average true positive rate for small impact craters (down to 20 m in diameter) is 93%. The model does display a 15% overestimation in calculated crater diameters. The presented crater detection model shows acceptable performance on NAC images with incidence angles ranging between ∼50° and ∼70° and can be applied to many lunar sites independent to morphology. Plain Language Summary: The Moon's surface is covered in impact craters and recording their spatial density gives researchers the ability to study the geological evolution of our satellite. Analyzing craters helps in determining the physical properties of planetary surfaces and how/if impact rates change over time. These analyses rely on recording spatial densities for numerous surfaces, which has been achieved for craters >1–2 km on the Moon. Manually counting the smaller craters, which number in the hundreds of millions, is a daunting task. We adapted a Crater Detection Algorithm and applied it to the highest resolution lunar imagery data set. We describe our method for gathering, reformatting, and detecting craters across lunar images down to 20 m in diameter. The detection model performance was quantitatively evaluated across six different regions, each with different terrain and lighting conditions. Comparison between manually mapped craters and detections from our model allows us to conclude that the model has an acceptable performance in detecting fresh to moderately degraded craters of all sizes, down to 20 m in diameter, when compared to other studies. Automated crater detection complements manual counting methods and aids in unlocking secrets of the Moon's surface. Key Points: Adapted and retrained a Crater Detection Algorithm (using YOLOv3) to work on high‐resolution Lunar Reconnaissance Orbiter‐Narrow‐Angle Camera (NAC) imagesDeveloped a workflow for georeferencing and detecting craters down to 10 pixels in diameter across multiple overlapping NAC imagesEvaluation reveals acceptable performance in detecting craters on diverse terrains, across images with 50–70° incidence angles [ABSTRACT FROM AUTHOR]

Determining when an impact crater formed is a complex and tedious task. However, this knowledge is crucial to understanding the geological history of planetary bodies and, more specifically, gives information on erosion rate measurements, meteorite ejection location, impact flux evolution and the loss of a magnetic field. The derivation of an individual crater's age is currently performed through manual counting. Because crater size scales as a power law, this method is limited to small (and/or young) surface areas and, in the case of the derivation of crater emplacement age, to a small set of impact craters. Here, we used a Crater Detection Algorithm, specifically retrained to detect small impact craters on large‐ and high‐resolution imagery data set to solve this issue. We applied it to a global, 5 m/pixel resolution mosaic of Mars. Here, we test the use of this data set to date 10 large impact craters. We developed a cluster analysis tool in order to distinguish potential secondary crater clusters from the primary crater population. We then use this, filtered, crater population to date each large impact crater and evaluate our results against literature ages. We found that automated counting filtered through clustering analysis produced similar model ages to manual counts. This technique can now be expanded to much wider crater dating surveys, and by extension to any other kind of Martian surface. We anticipate that this new tool will considerably expand our knowledge of the geological events that have shaped the surface of Mars, their timing and duration. Plain Language Summary: The age of an impact crater on a planetary surface is a crucial constraint in determining erosion rate, the crater source of Martian meteorites and the impact cratering flux evolution. This kind of measurement requires the counting of many impact craters superposed on the ejecta blanket of the considered crater and is therefore limited by human capability. To solve this issue, we adapted an automatic tool to detect small impact craters on the surface of Mars. We also developed an automatic approach to identify and remove clusters of small likely secondary craters detected by our algorithm. We assume these clusters of craters are formed by fragments ejected by an impact that formed a primary crater and need to be removed from crater densities used for age derivations. We applied our technique on 10 large Martian impact craters whose the formation age has been derived using manual counts and reported in the literature. We compared these ages to ours, derived from automatic count and automatic secondary craters filtering. Our results are consistent and indistinguishable from an age inferred from a manual count. For the first time, we demonstrate that an automated approach can deliver geologically meaningful model ages. Key Points: Automatic detection of small craters on ejecta blanket of 10 large Martian cratersIdentification of secondary craters through cluster analysisModel ages from our semi‐automatic approach are similar from manual counts [ABSTRACT FROM AUTHOR]

Impact craters on solar system bodies are used to determine the relative ages of surfaces. The smaller the limiting primary crater size, the higher the spatial resolution in surface/resurfacing age dating. A manually counted database (Robbins & Hynek, 2012, https://doi.org/10.1029/2011JE003966) of >384,000 craters on Mars >1 km in diameter exists. But because crater size scales as a power law, the number of impact craters in the size range 10 m to 1 km is in the tens of millions, a number making precise analysis of local variations of age, over an entire surface, impossible to perform by manual counting. To decode this crater size population at a planetary scale, we developed an automated Crater Detection Algorithm based on the You Only Look Once v3 object detection system. The algorithm was trained by annotating images of the controlled Thermal Emission Imaging System daytime infrared data set. This training data set contains 7,048 craters that the algorithm used as a learning benchmark. The results were validated against the manually counted database as the ground truth data set. We applied our algorithm to the Thermal Emission Imaging System global mosaic between ±65° of latitude, returning a true positive detection rate of 91% and a diameter estimation error (~15%) consistent with typical manual count variation. Importantly, although a number of automated crater counting algorithms have been published, for the first time we demonstrate that automatic counting can be routinely used to derive robust surface ages. Plain Language Summary: Crater counting is the traditional method of determining the surface ages of planets throughout the solar system. This method, up to now, has used data that have been painstakingly counted by hand. The current published database for Mars contains hundreds of thousands of craters for diameters larger than 1 km. If we can count craters smaller than this, we will be able to target specific areas of interest to date. But the rate of impacts on planetary surfaces follows a power law such that the number of small (less than 1 km) craters is exponentially higher than the number of large craters. To count these requires an automated tool. Here we show that we have developed such a tool. We have validated the results against current manual databases. Importantly, and for the first time, we demonstrate that an automated crater counting tool can deliver geologically meaningful ages. Key Points: We built a library of 7,048 craters to train a Crater Detection Algorithm (CDA) that we developed based on a neural network architectureWe applied our algorithm to the Mars global THEMIS mosaic, generating results comparable to manual countingWe applied the CDA to higher‐resolution images generating model ages indistinguishable (within error) from literature ages [ABSTRACT FROM AUTHOR]

Cratering chronologies are used to derive the history of planetary bodies and assume an isotropic flux of impactors over the entire surface of the Moon. The impactor population is largely dominated by near-Earth-objects (NEOs) since ∼3.5 billion years ago. However, lunar impact probabilities from the currently known NEO population show an excess of impacts close to the poles compared to the equator as well as a latitudinal dependency of the approach angle of impactors. This is accompanied by a variation of the impact flux and speed with the distance from the apex due to the synchronicity of the lunar orbit around the Earth. Here, we compute the spatial dependency of the cratering rate produced by such variabilities and recalibrate the lunar chronology. We show that it allows to reconcile the crater density measured at mid-latitudes around the Chang'e-5 landing site with the age of the samples collected by this mission. Our updated chronology leads to differences in model ages of up to 30% compared to other chronology systems. The modeled cratering rate variability is then compared with the distribution of lunar craters younger than ∼1 Ma, 1 Ga and 4 Ga. The general trend of the cratering distribution is consistent with the one obtained from dynamical models of NEOs, thus potentially reflecting a nonuniform distribution of orbital parameters of ancient impactor populations, beyond 3.5 Ga ago, i.e., planetary leftovers and cometary bodies. If the nonuniformity of the cratering rate could be tested elsewhere in the Solar System, the recalibrated lunar chronology, corrected from spatial variations of the impact flux and approach conditions of impactors, could be extrapolated on other terrestrial bodies such as Mercury and Mars, at least over the last 3.5 billion years. The modeled cratering rate presented here has strong implications for interpreting results of the Artemis program, aiming to explore the South Pole of our satellite, in particular when it will come to link the radiometric age of the samples collected in this region and the crater density of the sampled units. • The spatial variability of the lunar cratering rate is computed from the updated NEO population. • The surface located at ±60°N, 90°W is 1.77 more cratered than at the equator and the antapex of motion (0°N, 90°E). • The new lunar chronology leads to differences in model ages of up to ∼30% compared to previous models, depending on location. • The cratering rate variability is in accordance with the distribution of craters formed over the last ∼3.5Ga on the Moon. [ABSTRACT FROM AUTHOR]

Composite materials in association with metal sheets or ceramic coatings have found a variety of applications, especially as load-bearing components in composite structures. Their disassembly for recycling or maintenance has therefore become more complex. The magnetic pulse technique, usually dedicated to dynamic forming and welding processes, can be used to separate composite materials of a laminate structure of their recyclable adjacent materials. This technology profits from Lorentz forces appearing in electrically conductive materials placed in the vicinity of conductors in which high-intensity electrical discharges are performed. These body forces act locally during the fast energy discharge, from which a stress wave propagates in the structure. The propagation of this stress wave can be used to generate interfacial tensile stress in laminate structures or assemblies. Especially, this technique can be used for evaluating the dynamic bond strength of an interface. This works aims at determining the required conditions for disassembling a laminate structure using a magnetic pulse imposed on one side of the assembly, without significantly damaging the debonded layers. Ideally, the generated interfacial tensile stress should be greater than the interfacial bond strength. In this paper, a one-dimensional analytical analysis is performed in linear elastodynamics on a tri-layered laminate structure, infinite in transverse directions, based on the method of characteristics. An optimisation problem is defined, maximising the interfacial stress between the first two layers, whose solution requires to study various configurations of the assembly involving different sets of characteristics in the laminate, associated with different areas of the domain of feasibility spanned by the unknown vector. Some assumptions and introduced simplifications of the optimisation problem allows to follow a simple two-stage solution procedure, first with respect to the thickness of the first layer for a given stress pulse, then with respect to material impedances of all layers. Several configurations of the assembly are shown to create a sufficiently large interfacial tensile stress to reach the crack initiation and propagation, and a maximum tensile interface stress of twice the maximum applied pressure is obtained in the asymptotic limit. • 1D analytical analysis in of a laminate using the method of characteristics • Linear elastodynamics behavior of a tri-layered infinite in transverse direction. • An optimisation problem is defined to maximise the interfacial tensile stress. • Various configurations are studied considering different sets of characteristics. • The solution of the optimisation problem follows a two-stage solution procedure. • Optimal asymptotic interfacial tensile stress is twice the maximum applied pressure. [ABSTRACT FROM AUTHOR]

Introduction: The Moon's cratered surface and lack of significant geological activity makes it suitable record for the solar systems chaotic past. The craters scattered across the lunar surface can be mapped and measured giving a relative chronology [1]. Furthermore, the spatial densities of those craters, when linked with radiometric measurements from collected samples, provide absolute model ages [1]. The various sample sites from the Apollo and Luna missions have greatly increased our understanding of the Moon's and Earth's geological evolution [2]. Looking onward to the most recent sample return mission, Chang'e 5 (2022) which brought back 1,731g of material from northeastern Oceanus Procellarum, the in-situ lunar samples host a range of radiometric ages [3,4]. This momentous mission was the first sample return in 44 years, which returned samples from the youngest Mare region on the Moon dated to 1963±57 Ma [3]. Many of the Lunar samples, including those from CE-5, contain clasts that suggest that they have been transported by impacts [4]. This raises questions about where the lunar material originates from, and what can we determine about those areas from the collected sample material. During an impact, a significant amount of material is ejected, and without of atmosphere or strong gravity, this material can travel great distances [5]. This material falls back down to the surface forming a network of secondary craters and debris. Looking at secondary crater clusters around the sample sites, which are typically small (<1km) and number in the several millions [5,6], researchers can determine potential trajectory and distance lunar material has traveled. Specifically for the CE-5 material, probable source locations have been identified through crater mapping and numerical modeling [4]. To aid the time-consuming process of mapping secondary craters we propose using a machine learning algorithm to automatically detect small lunar craters across high-resolution image datasets [7,8,9]. Identifying secondary craters at ultimate resolutions can provide the source of the exogenic material contained in CE-5 samples, and more generally for other lunar samples. Image Datasets: Our team have utilized two high-resolution lunar image datasets for this project. The first was the Lunar Reconnaissance orbiter - Narrow Angle Camera (LRO-NAC), offering a resolution of 0.5-2 m/px [10]; and the second was the Kaguya Terrain Camera (TC), offering a resolution of ~10m/px [11]. This allows us to compile automatic crater detections over across multiple geographical scales. Crater Counting Algorithm: The Crater Detection Algorithm (CDA) is a machine learning image-based Convolutional Neural Network (CNN) that has been specialized to detect craters over high-resolution satellite imagery [7,8,9]. Our CNN uses 'You Only Look Once version 5' (YOLOv5) as the network's architecture. We have two crater detection models, each focusing on a different image dataset (NAC and Kaguya). The NAC model has been trained and validated across 247 square image tiles (416 pixels in length/width) with a detection accuracy of ~92% [9]. The Kaguya model was trained and validated on ~420 tiles and has a detection accuracy of ~94%. All the training image tiles have afternoon/morning lighting conditions, to facilitate impact crater recognition. Before running the detection model across the dataset, they are processed and converted into GeoTiffs through USGS ISIS3 and GDAL, respectively. The CDA is then run across the image datasets, detecting millions of craters at the 10m to 100m scale, magnitudes faster than manual methods. Chang'e 5 Secondary Clusters: The preliminary results over the Chang'e 5 landing site and surrounding areas show multiple secondary clusters (>10) cross cutting the region. At the Kaguya-scale (10m/px), we analyzed a ~800km by ~800km region and found considerable secondary clusters that crosscut the landing region from Aristarchus crater. At the NAC-scale (2m/px), we analyzed a ~450km by ~275km area and located a significant secondary cluster less that 10km from the landing site, originating from Rümke E crater. We also mapped a series of north-west and eastwest trending clusters. Acknowledgments: This work is supported by the resources provided by the Pawsey Supercomputing Centre with funding from the Australian Government, Curtin University, and the Government of Western Australia. [ABSTRACT FROM AUTHOR]

Introduction: The geological record of the formation and differentiation of our planet has been destroyed by its subsequent evolution, but extremely rare clues may be obtained from other terrestrial planets. Mars provides a unique and accessible example of an early evolutionary path corresponding to that, inaccessible, of our own world. We can investigate it with spacecraft, and samples are available for in-depth analysis on Earth in the form of martian meteorites. So far, the only available martian samples that appear to have recorded the early conditions and the evolution of the planet until the present time are Northwest Africa (NWA) 7034 and its paired stones, nicknamed "Black Beauty". This regolith breccia has been ejected a few million years ago by the formation of a large impact crater, and contains the oldest martian igneous material ever dated: ~4.5 Ga old [1-4]. However, its source and geological context have so far remained unknown. and with it, a region where the earliest geological records of the planet [1-4] are exposed on the surface. Knowing this source region would provide insights into early Mars geological history and crustal extraction [1-4]. This source region may therefore become a high-priority target for detailed orbital analyses and in-situ exploration [5]. Constraints on the meteorite launch site: Following a hypervelocity impact, ejecta materials moving faster than the escape velocity (5 km/s) may get through the martian atmosphere and continue their course into interplanetary space to become martian meteorites [6]. Slower debris fall back on the surface in a radial pattern or ray around the primary crater, forming secondary craters. The presence of 100 meter-size secondaries attests to the freshness of their associated primary craters [7]. Using the size and spatial distribution of more than 90 million impact craters >50 m (both primaries and secondaries) detected using a Crater Detection Algorithm (CDA) [7-8] on the whole surface of Mars from the global Context Camera (CTX) mosaic [9], a previous work [7] identified ray systems of secondary craters <150 m associated with 19 large primary craters, potential source of the ejection of martian meteorites. Here we compare the abundance of K and Th [10-11] as well as the magnetic field intensity and the magnetization of the surface of Mars derived from orbital measurements [12] at the immediate vicinity of each crater candidate with those of the breccia. We also compare the geological context of each of the crater candidates with the chronology and the lithology of the meteorite [e.g. 1-3, 13-14]. The ejection site for Black Beauty: Among the 19 crater candidates investigated, we found that only one match with the characteristics of the meteorite: a 10 km crater located in the north-east of the Terra Cimeria - Sirenum (TCTS) region, between Hesperia Planum and the Tharsis bulge. Our work suggests that clasts contained in the regolith breccia are representative of the TCTS province, making this region a relic of the early crustal processes on Mars [e.g. 15], and thus, a region of high interest for future missions. Details on the identification of the crater source of this unique meteorite, as well a its geological context and broader implications for early crustal processes on Mars will be presented at the conference. [ABSTRACT FROM AUTHOR]

• Semi-automatic dating of 521 impact craters on Mars. • Statistical assessment of the lunar and terrestrial cratering rate. • Plate tectonic reconstruction of the formation location of terrestrial craters. • Coupling between the impact flux of small and large impactors. • The impact flux is constant over the last 600 Ma in the inner Solar System. The impact flux over the last 3 Ga in the inner Solar System is commonly assumed to be constant through time due to insufficient data to warrant a different choice for this range of time. However, asteroid break-up events in the main belt may have been responsible for cratering spikes over the last ∼2 Ga on the Earth-Moon system. Due to its proximity with the main asteroid belt, i.e., the main impactors reservoir, Mars is at the outpost of these events with respect to the other inner planets. We investigate here, from automatic crater identification, the possible variations of the size frequency distributions of impactors from the record of small craters of 521 impact craters larger than 20 km in diameter. We show that 49 craters (out of the 521) correspond to the complete crater population of this size formed over the last 600 Ma. Our results on Mars show that the flux of both small (> 5 m) and large asteroids (> 1 km) are coupled, does not vary between each other over the last 600 Ma. Existing data sets for large craters on the Earth and the Moon are analyzed and compared to our results on Mars. On Earth, we infer the formation location of a set of impact craters thanks to plate tectonic reconstruction and show that a cluster of craters formed during the Ordovician period, about 470 Ma ago, appears to be a preservation bias. On the Moon, the late increase seen in the crater age signal can be due to the uncertain calibration method used to date those impacts (i.e. rock abundance in lunar impact ejecta), and other calibrations are consistent with a constant crater production rate. We conclude to a coupling of the crater production rate between kilometer-size craters (∼100 m asteroids) and down to ∼100 m in diameter (∼5 m asteroids) in the inner Solar System. This is consistent with the traditional model for delivering asteroids to planet-crossing obits: the Yarkovsky effect slowly pushes the large debris from asteroid break-ups towards orbital resonances while smaller debris are grinded through collisional cascades. This suggests that the long-term impact flux of asteroids > 5 m is most likely constant over the last 600 Ma, and that the influence of past asteroid break-ups in the cratering rate for D > 100 m is limited or inexistent. [ABSTRACT FROM AUTHOR]

Ages of geological units of planetary bodies are determined from impact crater counts on their surface. These ages are model-dependent, and several models largely used in the community assume a constant production function and a constant cratering rate over the last 3 Ga. We have mapped the population of small impact craters (>200 m in diameter) formed over a population of large impact craters (>5 km in diameter) with layered ejecta on Acidalia Planitia, Mars. We have deduced the age of each large impact crater under the assumption of a constant impact rate and constant production function. The impact rate inferred from this set of ages is, however, not constant and show a significant increasing during the last ~1 Ga compared to chronology models commonly used. We interpret this inconsistency as an evidence for temporal variations in the size-frequency distribution (SFD) of impactors in the main belt, consistent with recent studies argued for a late increasing of the large impactor flux on Earth and the Moon. • We measured the age of a set of Martian craters >5km using the small craters on their ejecta and a constant rate. • The impact rate inferred from this set of ages is inconsistent with the constant impact rate model commonly assumed. • This inconsistency is interpreted as the result of variations in the large impactor frequency distribution over the last 2Ga. • The variation in the size frequency distribution of large impactors could be the result of recent asteroid break-ups. [ABSTRACT FROM AUTHOR]

Tharsis is the largest volcanic province on Mars and in the solar system. This region includes major volcanoes (Olympus Mons, Alba Mons, Arsia Mons, Pavonis Mons, and Ascraeus Montes) and hundreds of small volcanic cones and vents, whose origin is not yet fully understood. Although the main Tharsis' edifices plumbing system has been extensively studied, smaller volcanoes' origin remains unknown. The formation of those minor volcanic landforms may be related to the large volcanic edifices' evolution, and/or controlled by the fault systems through which magma migrates towards the Martian surface. In this study, we analyzed the central part of the Tharsis volcanic province using satellite images with a resolution of ~6 m/px from the Context Camera onboard the Mars Reconnaissance Orbiter (CTX/MRO). We identified and mapped 659 volcanic edifices >1 km in diameter. We analyzed (1) their spatial distribution, (2) alignment of summit craters, and (3) surface model ages derived from crater counting. We found that volcanic edifices are unevenly distributed across the Tharsis province and proposed that their formation is controlled by at least six individual magma-plumbing systems associated with major edifices: Olympus Mons, Alba Mons, Arsia Mons, Pavonis Mons, Ascraeus Mons, and Uranius Mons. Their summit alignment orientations indicate they were controlled by radial and circumferential dikes originated from magma sources beneath the six central volcanoes, either magma chambers in the crust or other magmatic underplates at the base of the crust. Volcano flanks of distributed volcanoes are of similar age or younger than the summit calderas of the associated central volcano indicating a common magmatic system. Magma migration and eruptions from distributed volcanoes may thus extend beyond the magma waxing periods when magma supply was high enough to sustain summit eruptions. The relatively young age of documented volcanic activity within the Tharsis province may imply recently active hydrothermal systems triggered by magma-water interaction. • Tharsis on Mars hosts at least 659 distributed volcanoes. • Our crater count dating shows most volcanoes are < 200 Ma. • The 659 volcanic edifices were classified into 6 subprovinces of central volcanoes. • They are supplied by systems of radial and circumferential dikes. • The dikes are controlled by central volcanoes' magmatic systems. [ABSTRACT FROM AUTHOR]

Over the last decades, a significant number of small asteroids (diameter < 10 km) having a satellite in orbit around them have been discovered. This population of binary asteroids has very specific properties (secondary-to-primary diameter ratio of about 0.3, semi-major axis to primary diameter ratio around 2 and an obliquity of the system close to either 0 ∘ or 180 ∘) pointing at formation by YORP-induced spin-up and rotational fission. When impacting the surface of terrestrial bodies, those exotic objects lead to the formation of binary craters, exhibiting various morphologies depending on the configuration of the system at the moment of the impact. Planetary surfaces constitutes therefore the best (if not the only one) record of binary asteroid population through time. In contrast to the Moon or Mercury, a large fraction of impact craters on Mars exhibits thick ejecta layers due to the presence of volatile material at the moment of the impact (e.g., water ice). The martian surface represents thus the ideal case to survey for the existence of binary craters, as the ejecta morphology can attest of a synchronous impact. From a survey of 87% of Mars surface, we identify 150 binary craters (0.5% of the total), likely formed by the impact of binary asteroids. The properties of these craters contrast with those of the population of binary asteroids: size ratio close to unity, large separation, and isotropic orientation on the surface. We run numerical simulations of impacts to test whether tidal effects on the impact trajectory can explain these discrepancies. Our results suggest that a population of similarly-sized and well-separated binary asteroids with non-zero obliquity remains to be observed. [Display omitted] • First database of Martian binary craters with 150 entries compiled from a survey over 87% of the surface. • Comparison between properties of the binary craters and the population of binary asteroid systems. • Mismatch between observed and simulated properties of binary craters on Mars. • Unobserved population of binary asteroids suspected with large separation, near-similar size, and non-zero obliquity. [ABSTRACT FROM AUTHOR]

On June 19, 2020 at 20:05:07 UTC, a fireball lasting 5.5s was observed above Western Australia by three Desert Fireball Network observatories. The meteoroid entered the atmosphere with a speed of 14.00±0.17 km s‐1 and followed a 58° slope trajectory from a height of 75 km down to 18.6 km. Despite the poor angle of triangulated planes between observatories (29°) and the large distance from the observatories, a well‐constrained kilo‐size main mass was predicted to have fallen just south of Madura in Western Australia. However, the search area was predicted to be large due to the trajectory uncertainties. Fortunately, the rock was rapidly recovered along the access track during a reconnaissance trip. The 1.072 kg meteorite called Madura Cave was classified as an L5 ordinary chondrite. The calculated orbit is of Aten type (mostly contained within the Earth's orbit), only the second time a meteorite was observed on such an orbit, after Bunburra Rockhole. Dynamical modeling shows that Madura Cave has been in near‐Earth space for a very long time. The dynamical lifetime in near‐Earth space for the progenitor meteoroid is predicted to be ~87 Myr. This peculiar orbit also points to a delivery from the main asteroid belt via the ν6 resonance, and therefore an origin in the inner belt. This result contributes to drawing a picture for the existence of a present‐day L chondrite parent body in the inner belt. [ABSTRACT FROM AUTHOR]

The article presents a study exploring genomic deciphering of sex determination and unique immune system of a potential model species rare minnow (Gobiocypris rarus). It mentions that Gobiocypris rarus as sensitive to environmental pollution, especially to heavy metal and grass carp reovirus and has potential utility as a biological monitor.

Tharsis volcanic province on Mars (15˚ S to 45˚ N, and 90-140˚ W) hosts hundreds of smallvolcanic cones and vents in addition to the giant volcanoes: Olympus Mons, Alba Mons andthe three Tharsis Montes (Arsia Mons, Pavonis Mons, and Ascraeus Montes). The genesisof the small volcanic cones in this area is not yet fully explained. Their genesismay be related to the evolution of the large volcanic edifices, or controlled by thefractures of fault systems. Characterizing the system of small volcanic cones interms of space and time is essential to understand the Tharsis magmatic plumbingcomplex. In this study, we mapped the small volcanic cones of Tharsis (1-65 km in diameter),determined the orientation of their elongated craters or central fissure vents, and dated flanksof six volcanoes. For mapping we used ArcMap and combined the Thermal EmissionImaging System (THEMIS) of Mars Odyssey (MO) (spatial resolution of ∼100 m/pixel) withthe Context Camera (CTX) of Mars Reconnaissance Orbiter (MRO) (6 m/pixel). The sixvolcanoes were dated using crater counting (&#x003E;100 m in diameter) with the ArcGIS extensionCraterTools2.1 on a CTX mosaic. Crater statistics and derivation of crater model ages,including errors, was carried out with CraterStats II by applying the Hartmann&#x2019;s (2005)chronology system. We identified and mapped 302 parasitic cones. They are unevenly distributed across theTharsis province. Based on volcano geographic distribution and measured orientations ofelongated summit craters and central fissure vents, we distinguish three major cone groupsrelated to 1) Olympus Mons (with orientations of ∼N100) 2) Tharsis Montes (∼N055), and3) Alba Mons (∼N005). The three identified groups represent distinct episodes of volcanismassociated with various giant volcanoes. To support our hypothesis, we dated six parasitic cones in the identified groups andcompared with the ages of Olympus Mons, the Tharsis Montes, and Alba Mons. Interestingly,parasitic cones always show slightly younger age compared to the nearby feeding volcanoes.For example, the age of the last activity for Olympus Mons is 64±30 Ma, whereas forparasitic cones we dated ∼52±12 Ma. Similarly, ages determined for parasitic cones(107±28 Ma and 115±13 Ma) in Tharsis Montes correspond well to the last activity of theArsia Mons (126±6 Ma) and Pavonis Mons (138±13 Ma). The latest Alba Mons activity(110±30 Ma) might be also linked with parasitic cones (62±9 Ma and 70±20 Ma) situated inCeraunius Fossae. The spatial distribution of parasitic cones, along with their alignment and relatively youngages allowed us to distinguish three distinct plumbing systems related to the largest Tharsisvolcanoes, perhaps currently dormant. Furthermore, our results indicate that the smallvolcanoes may have formed 10-20 Ma after the extinction of the last eruptive activity at thenearby giant volcano, which might be related to the smaller pressure needed to feedthese parasitic cones compared to the pressure needed to feed summit calderas. [ABSTRACT FROM AUTHOR]