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In a recent paper, Rogozin and coauthors present a morphologic/seismostratigraphic study of two small lakes, Lake Zapovednoye (LZ) and Lake Peyungda (LP), located 50‒60 km east from the alleged epicenter of the 1908 Tunguska Event (TE), a large explosion believed to have been caused by an extraterrestrial impact. Data presented in that paper suggest a similar (although not specified) origin of these two lakes and Lake Cheko, located close to the TE epicenter. This led Rogozin et al., to question the impact crater origin of Lake Cheko, whose depression was interpreted by Gasperini et al., as caused by the freefall of an extraterrestrial fragment, which survived an atmospheric explosion. We analyze Rogozin et al., data, focusing on similarities and differences between Lake Cheko, LZ and LP, to determine whether their findings are relevant to the TE problem. [ABSTRACT FROM AUTHOR]

This paper aims to study the low-velocity impact (LVI) response and compression after impact (CAI) performance of carbon/aramid hybrid woven composite laminates employed in marine structures subjected to different energy impacts. The study includes a detailed analysis of the typical LVI responses of hybrid woven composite laminates subjected to the impact with three different energies, as well as a comparative analysis of cracks and internal delamination damage within impact craters. Additionally, the influence of different impact energies on the residual compressive strength of hybrid woven composite laminate is investigated through CAI tests and a comparative analysis of internal delamination damage is also conducted. The results indicate that as the impact energy increases, the impact load and CAI strength show a decreasing trend, while impact displacement and impact dent show an increasing trend. The low-velocity impact tests revealed a range of failure modes observed in the hybrid woven composite laminates. Depending on the specific combination of fiber materials and their orientations, the laminates exhibited different failure mechanisms. Buckling failures were observed in the uppermost composite layers of laminates with intermediate modulus systems. In contrast, laminates with higher modulus systems showed early damage in the form of delamination within the top surface layers. [ABSTRACT FROM AUTHOR]

Water ice has been found in the permanently shadowed regions of impact craters around the lunar South Pole, which makes them ideal areas for in situ exploration missions. However, near the rim of impact craters, construction and exploration activities may cause slope instability. As a result, a better understanding of the shear strength of lunar soil under higher stress conditions is required. This paper mainly uses the finite element method to analyze slope stability to determine the position and shape of the slip surface and assess the safety factor. The height and gradient of the slope, the shear strength of lunar soil, and the lunar surface mission all influence the stability of the slope. We also analyze the soil mechanical properties of a soil slope adjacent to the traverse path of the Chang'E-4 Yutu-2 rover. Determining the stability of the slope at the lunar South Pole impact crater under various loading conditions will enhance the implementation of the lunar surface construction program. In this respect, this paper simulates a lunar mission landing at the Shackleton and Shoemaker craters and indicates that areas with higher cohesion lunar soil may be more stable for exploration in the more complex terrain of the South Pole. [ABSTRACT FROM AUTHOR]

Droplet impact is a common occurrence in nature, agriculture, and industry. The research on the multi‐droplet impact is fundamental to understanding the tangled nature of reality. This paper numerically studies the successive oblique impact of dual droplets on the liquid film by building an effective three‐dimensional model. The leading and trailing droplets are set to pass a certain impact point with the same velocity. The main contribution of this paper is the investigation of the effects of Weber number, liquid film thickness, impact angle, and impact time interval on the interface morphology evolution after the droplet impact. Results show that splash pattern conversion of the primary or secondary crown occurs with the change of these factors. Besides, the variations of the maximum crater radius in upstream, lateral, and downstream directions with time are quantitatively analyzed. The crater radius analysis is carried out from three perspectives, the variation during the single droplet impact, the change during the dual droplets impact, and the comparison between them. It is found that the crater of dual droplets impact exhibits shape distortion in the deformation period and appears a marked dimensional increase in the secondary expansion period. [ABSTRACT FROM AUTHOR]

Craters are regarded as significant navigation landmarks during the descent and landing process in small body exploration missions for their universality. Recognizing and matching craters is a crucial prerequisite for visual and LIDAR-based navigation tasks. Compared to traditional algorithms, deep learning-based crater detection algorithms can achieve a higher recognition rate. However, matching crater detection results under various image transformations still poses challenges. To address the problem, a composite feature-matching algorithm that combines geometric descriptors and region descriptors (extracting normalized region pixel gradient features as feature vectors) is proposed. First, the geometric configuration map is constructed based on the crater detection results. Then, geometric descriptors and region descriptors are established within each feature primitive of the map. Subsequently, taking the salience of geometric features into consideration, composite feature descriptors with scale, rotation, and illumination invariance are generated through fusion geometric and region descriptors. Finally, descriptor matching is accomplished by computing the relative distances between descriptors and adhering to the nearest neighbor principle. Experimental results show that the composite feature descriptor proposed in this paper has better matching performance than only using shape descriptors or region descriptors, and can achieve a more than 90% correct matching rate, which can provide technical support for the small body visual navigation task. [ABSTRACT FROM AUTHOR]

A highly resistant mineral, zircon is capable of preserving information about impact processes. The present review paper is aimed at determining the extent to which Raman spectroscopy can be applied to studying shocked zircons from impactites to identify issues and gaps in the usage of Raman spectroscopy, both in order to highlight recent achievements, and to identify the most effective applications. Method: Following PRISMA guidelines, the review is based on peer-reviewed papers indexed in Google Scholar, Scopus and Web of Science databases up to 5 April 2022. Inclusion criteria: application of Raman spectroscopy to the study of shocked zircon from terrestrial and lunar impactites. Results: A total of 25 research papers were selected. Of these, 18 publications studied terrestrial impact craters, while 7 publications focused on lunar breccia samples. Nineteen of the studies were focused on the acquisition of new data on geological structures, while six examined zircon microstructures, their textural and spectroscopic features. Conclusions: The application of Raman spectroscopy to impactite zircons is linked with its application to zircon grains of various terrestrial rocks and the progress of the electron backscatter diffraction (EBSD) technique in the early 2000s. Raman spectroscopy was concluded to be most effective when applied to examining the degree of damage, as well as identifying phases and misorientation in zircon. [ABSTRACT FROM AUTHOR]

In the geological research of the Moon and other celestial bodies, the identification and analysis of impact craters are crucial for understanding the geological history of these bodies. With the rapid increase in the volume of high-resolution imagery data returned from exploration missions, traditional image retrieval methods face dual challenges of efficiency and accuracy when processing lunar complex crater image data. Deep learning techniques offer a potential solution. This paper proposes an image retrieval model for lunar complex craters that integrates visual and depth features ( LC 2 R - Net ) to overcome these difficulties. For depth feature extraction, we employ the Swin Transformer as the core architecture for feature extraction and enhance the recognition capability for key crater features by integrating the Convolutional Block Attention Module with Effective Channel Attention (CBAMwithECA). Furthermore, a triplet loss function is introduced to generate highly discriminative image embeddings, further optimizing the embedding space for similarity retrieval. In terms of visual feature extraction, we utilize Local Binary Patterns (LBP) and Hu moments to extract the texture and shape features of crater images. By performing a weighted fusion of these features and utilizing Principal Component Analysis (PCA) for dimensionality reduction, we effectively combine visual and depth features and optimize retrieval efficiency. Finally, cosine similarity is used to calculate the similarity between query images and images in the database, returning the most similar images as retrieval results. Validation experiments conducted on the lunar complex impact crater dataset constructed in this article demonstrate that LC 2 R - Net achieves a retrieval precision of 83.75%, showcasing superior efficiency. These experimental results confirm the advantages of LC 2 R - Net in handling the task of lunar complex impact crater image retrieval. [ABSTRACT FROM AUTHOR]

This paper introduced automated detection and analysis of lunar craters are crucial for advancing lunar research and facilitating mission planning. This study introduces a comprehensive multi-scale approach for crater detection on the lunar surface using LROC (Lunar Reconnaissance Orbiter Camera) Dataset, enabling the identification of craters across varying scales and enhancing overall detection accuracy and efficiency. The process involves preprocessing lunar imagery to enhance features and delineate potential crater regions, utilizing edge detection algorithms to extract crater boundaries. Clustering techniques are then applied to group similar edge points and isolate potential crater candidates. A thresholding mechanism based on statistical edge intensity analysis refines the detection process. To address multiple detections of the same crater at slightly different diameters, radius criteria are implemented, yielding high diameter accuracy of 84% for mare Imbrium (test site 1) and 80% for mare Nubium (test site 2). Subsequently, a depth-diameter analysis validates crater-like characteristics by combining depth measurements with crater diameter estimation, showcasing the authenticity of potential craters. we compare our diameter and depth with different reference papers and we get high accuracy of R2 =0.99 then other methods. The results highlight the potential of this multi-scale approach for automated lunar crater detection, providing deeper insights into the Moon's surface morphology and history for future lunar exploration missions. [ABSTRACT FROM AUTHOR]

Uniformitarian scientists were surprised to discover channels on Mars like the Channeled Scablands of eastern Washington. Climate models indicate that large-scale Martian floods are impossible. This paper will describe what appear to be flood features on Mars. Three types of channels on Mars are described in this paper: valley networks, outflow channels, and gullies. Like the Solar System's other solid bodies that have not been resurfaced by debris and volcanism, Mars possesses numerous impact craters, some very large, which provide a framework for the planet's history. Secular uniformitarian scientists divide the geologic history of Mars into four main periods which span 4.5 billion years. [ABSTRACT FROM AUTHOR]

During the first year of NASA's Mars 2020 mission, Perseverance rover has investigated the dark crater floor unit of Jezero crater and four samples of this unit have been collected. The focus of this paper is to assess the potential of these samples to calibrate the crater‐based Martian chronology. We first review the previous estimation of crater‐based model age of this unit. Then, we investigate the impact crater density distribution across the floor unit. It reveals that the crater density is heterogeneous from areas which have been exposed to the bombardment during the last 3 Ga to areas very recently exposed to bombardment. It suggests a complex history of exposure to impact cratering. We also display evidence of several remnants of deposits on the top of the dark floor unit across Jezero below which the dark floor unit may have been buried. We propose the following scenario of burying/exhumation: the dark floor unit would have been initially buried below a unit that was a few tens of meters thick. This unit then gradually eroded away due to Aeolian processes from the northeast to the west, resulting in uneven exposure to impact bombardment over 3 Ga. A cratering model reproducing this scenario confirms the feasibility of this hypothesis. Due to the complexity of its exposure history, the Jezero dark crater floor unit will require additional detailed analysis to understand how the Mars 2020 mission samples of the crater floor can be used to inform the Martian cratering chronology. Plain Language Summary: Perseverance rover landed within Jezero crater (Mars) in 2021 and is collecting rocks that will be returned to Earth. In terrestrial state‐of‐the art labs, these rocks will be dated. It will allow to test the method planetary scientists are using to assess the age of Martian surfaces: their impact crater statistics. As impact craters are forming regularly, their statistics are used as a timeline in planetary sciences. The present paper studies the statistic of impacts craters within Jezero crater to reveal that the floor of Jezero has been protected from bombardment during years. These results imply that the collected rocks of the Jezero crater floor will not be ideal to test the method of using impact crater as chronometer of Martian surfaces. Key Points: The dark floor unit of the Jezero crater displays an unusual inhomogeneous crater density, suggesting a complex exhumation historyThe crater density of the dark crater floor unit corresponds to the exposure time post exhumationThe crater density of this unit will not allow the calibration of the Martian crater chronology from return samples [ABSTRACT FROM AUTHOR]

The paper presents the methodology used to digitally document the cavities preserved in the northern city wall of ancient Pompeii, to obtain a detailed documentation of the visible ballistic traces attributed to the impact of Roman artillery during the siege of Sulla in 89 BC, in the area from the Vesuvio to the Ercolano Gate. Building on previous studies by the team, authors intend to illustrate the workflow carried out to analyse the morphological characteristics of the existing traces by means of reality-based 3D digitsl models. These virtual replicas are intended to improve the knowledge of selected case studies due to their high relevance. In addition, some stone projectiles still preserved in the Antiquarium will be analysed. The final objective is to define a suitable approach for quantifying the terminal ballistics of Roman artillery based on conclusive evidence, thus allowing not only the virtual, but also the physical reconstruction of the launching weapons used in the war event. [ABSTRACT FROM AUTHOR]

Crater is a geologic structure in solid bodies (including the terrestrial planets, moons, and asteroids) formed by hyper-speed impact, and the impact process is extremely important to the formation and evolution of these celestial bodies. This paper presents a review of the studies on remote sensing observation, formation mechanism, and scientific application of craters. On the remote sensing study of craters, the topographic characteristics of the micro-craters, simple craters, complex craters, and impact basins are described; the related parameters in the morphological studies of craters are subsequently introduced, and the distribution characteristics of the minerals and rock types during the impact excavation process are analyzed; the methods of crater identification and the crater databases on the Moon, Mars, Ceres, and Vesta are summarized. On the studies of crater formation mechanism, the general formation process of the craters is firstly described, and then the most frequently used methods are presented, and the importance of the empirical equations is also elucidated. On the scientific applications of the craters, the principle and currently utilization of the planetary surface dating method with crater size-frequency distribution are firstly presented, and the applications, including modeling the lunar regolith formation and thickness derivation of both the regolith and basalt, are reviewed. Finally, the future prospects of the formation mechanism study of the craters are discussed. [ABSTRACT FROM AUTHOR]

The Perseverance rover, Mars 2020 mission, landed on the surface of the Jezero crater, on 18 February 2021. This Martian crater is suspected to have hosted a paleolake as evidenced by the numerous detections of aqueously altered phases and thus is a promising candidate for the search for past Martian life. The SuperCam instrument, a collaboration by a consortium of American and European laboratories, plays a leading role in this investigation, thanks to its highly versatile payload providing rapid, synergistic, fine‐scale mineralogy, chemistry, and color imaging. After its landing, the first measurements of Martian targets with the infrared spectrometer of SuperCam (IRS) showed new instrumental behaviors that had to be characterized and calibrated to derive unbiased science data. The IRS radiometric response has thus been calibrated using periodic observations of the Aluwhite SuperCam Calibration Target (SCCT). Parasitic effects were understood and mitigated, and the instrumental dark and noise are characterized and modeled. The reflectance calibrated data products, provided periodically on the NASA Planetary Data System, are corrected for the main instrumental features. This radiometric calibration allowed us to study the 2.5 μm absorption band, which has been discovered in the Séítah unit and is associated with phyllosilicates‐carbonates mixtures. Plain Language Summary: This paper is an instrumental investigation of the infrared spectrometer (IRS) portion of the SuperCam instrument on the Mars Science Laboratory Perseverance rover. Work performed prior to and during flight operations enabled the derivation of a proper instrumental response suitable for calibration of infrared point spectra of rocks and soils observed along the rover traverse. The paper describes development of a full data reduction pipeline in which the radiometric response, sensitivity of the IRS electronic board to temperature, and electromagnetic interference artifacts were removed. A companion paper (Mandon et al., 2022, https://doi.org/10.1029/2022JE007450) investigates the IRS data set through Sol 379 in more detail. Here, we specifically explore the 2.5 μm band attributed to carbonates in Séítah unit's phyllosilicate‐carbonates mixtures. We found that such mixtures likely have a low carbonate content, which may indicate low amounts of chemical alteration or an alteration by a carbon‐poor fluid. Key Points: The infrared spectrometer of SuperCam on Perseverance has been successfully flight calibrated using the onboard calibration targetsCalibration permitted to study the most challenging long wavelengths and thus to discover an absorption band at 2.5 μmStudy of the 2.3 and 2.5 μm absorption bands showed the Séitah unit has variable clay and carbonate mixtures with low carbonate content [ABSTRACT FROM AUTHOR]

The quest for the parent impact structure for Australasian tektites (AAT) has remained without solution for almost a century. The present paper doubts the plausibility of the recently proposed location of the impact site at the Bolaven volcanic field in Southern Laos by showing problems with most of the presented lines of evidence. The geochemical incompatibility of the AAT composition with a mixture of weathered basalts and Mesozoic sandstones that were proposed as source materials of AAT is demonstrated by a two‐component mixing calculation for major element oxides and the Nd‐Sr isotopic system. Deficiency of the basaltic component as a source of Ni, Co, Cr, and 10Be in AAT and inconsistency with trends observed for O and Pb isotopes are shown. The size of the putative crater, conclusiveness of a gravity anomaly identification, signs of complete crater burial by postimpact lava flows, and identification of proximal ejecta blanket are doubted. Remarks on the shortcomings of the current consensus location of an impact site for AAT in Indochina are presented. [ABSTRACT FROM AUTHOR]

On Mars, the lack of either plate tectonics or a prominent erosional hydrological cycle since the Noachian means geological changes caused by asteroid and comet impact events have been preserved. On Earth, surviving impact‐induced fractures are localized to the relatively few preserved craters on the planet. We estimate that the shell of impact‐fractured rock on Mars (the "impact‐sphere") could provide between 9,200 times the surface area of a Mars radius sphere and up to 100 times this value, depending on the assumptions made, as potential microbially accessible space. Although >93% of craters we consider are smaller than 10 km in diameter, they contribute only about 5% of the total fracture surface area generated by all craters, making complex craters the dominant process for potential habitat formation. Microbiological data from terrestrial impact craters suggest that these fractures could have significantly enhanced local habitability by providing pathways for fluid flow, and thus nutrients and energy. However, unlike on Earth, the geological history of Mars means that pervasive impact fractures may also have provided pathways for Hesperian and Amazonian brines to infiltrate the subsurface and locally reduce habitability. Combining the fracture data with previous microbiological observations provides testable hypotheses for Martian drilling missions. Plain Language Summary: The Martian surface and subsurface is pervasively fractured by asteroid and comet impacts, largely because, compared to Earth, they have not been subducted by plate tectonics or eroded by a vigorous water cycle. In this paper, we estimate the surface area of fractures generated by these impacts. We find that these impact fractures could be 9,200 times the equivalent surface area of a flat Mars‐sized sphere and up to a hundred times this, depending on the assumptions made. On the one hand, these fractures could have provided surfaces for life and improved the flow of nutrients, on the other hand they could have channeled deleterious salty waters into the subsurface, suggesting that habitability of the subsurface is profoundly influenced by impact, but its positive or negative effects depend on the history of water flow and brine formation. This study leads to several testable hypotheses about the subsurface habitability of Mars. Key Points: Impact have fractured the deep subsurface of Mars pervasivelyWe estimate this fracture area to be between 9,200 times the surface area of a Mars radius sphere and up to 100 times this valueThis fracturing has likely profoundly influenced habitability [ABSTRACT FROM AUTHOR]

We demonstrate the capabilities of a published MADNet monocular height estimation network in producing a refined digital terrain model (DTM) mosaic at 50 cm/pixel resolution for the Mars 2020 Perseverance rover landing site in Jezero crater on Mars. Our approach utilizes the publicly available Mars 2020 Terrain Relative Navigation (TRN) High‐Resolution Imaging Science Experiment (HiRISE) Digital Terrain Model (DTM) mosaic, which was originally created by the United States Geological Survey (USGS) Astrogeology Science Centre. Our resultant HiRISE MADNet DTM mosaic is strictly matched with the original HiRISE TRN DTM and orthoimage mosaics. These mosaics are themselves co‐aligned with the USGS TRN Context Camera (CTX) based DTM and orthoimage mosaics, as well as the ESA/DLR/FUB (European Space Agency/German Aerospace Center/Free University Berlin) High Resolution Stereo Camera (HRSC) level 5 DTM and orthoimage mosaics. In this paper, we provide a brief description of the technical details, and present both visual and quantitative assessments of the refined MADNet HiRISE Jezero DTM mosaic product. This DTM product is now publicly available at http://dx.doi.org/10.17169/refubium-38359. Key Points: We demonstrate the capabilities of a published MADNet monocular height estimation network in producing a refined digital terrain model mosaic at 50 cm/pixel resolution for the Mars 2020 Perseverance rover landing site in Jezero crater on MarsThe resultant 50 cm/pixel digital terrain model mosaic demonstrates significant improvements in effective resolution and artifact elimination compared to the publicly available Mars 2020 Terrain Relative Navigation TRN High‐Resolution Imaging Science Experiment digital terrain modelThe resultant digital terrain model mosaic has been made publicly available at http://dx.doi.org/10.17169/refubium-38359 [ABSTRACT FROM AUTHOR]

The network microstructure titanium matrix composites (NMTMCs) exhibit excellent properties but research on its machining remains limited. In this paper, single and continuous pulse electrical discharge machining (EDM) experiments were conducted on the NMTMCs composed of Ti6Al4V matrix combined with 5% vol. network distributed TiB whisker (TiBw). The impact of TiBw on EDM was analyzed in comparison to the machining results of pure Ti6Al4V. The results indicate that the TiBw reinforcements absorbs pulse energy during the machining process, resulting in smaller areas and more complex morphologies for the EDM craters. Based on this, a linear absorption model for pulse energy by reinforcement strips is proposed. Furthermore, in continuous pulse EDM with low capacitance settings, the presence of TiBw tends to generate micro pores on the surface and reduce material removal rate (MRR). However, when using higher capacitance settings, MRR for NMTMCs can surpass that achieved for pure Ti6Al4V. [ABSTRACT FROM AUTHOR]

Impact crater detection is one of the most important and critical studies of the geological history of planetary surfaces. Recent literature on crater identification demonstrates the powerful potential of deep-learning algorithms. However, these methods potentially assumed that the detection is conducted in devices with sufficient computing resources, and used networks with massive learnable parameters to obtain superb performance. In this paper, we proposed a lightweight tensorial convolutional neural network (CNN) for lunar impact crater detection. Specifically, we develop a tensorial you only look once (TYOLO) network by representing the convolutional kernels in tensor train (TT) decomposition. Thus, the parameter redundancy of TYOLO can be greatly reduced. To the best of our knowledge, this is the first work that considers the lightweight CNN model for impact crater detection. We demonstrate the lunar impact crater detection results over the ChangE-2 lunar digital orthophotos model (DOM) and digital evaluated model (DEM). Experimental results show that the proposed TYOLO network can obtain 1.44 × speed up and 39 × compression with 2.4 % improvement in crater detection. Overall, the proposed network demonstrates great potential in spacecraft with emerging computing resource constraints. [ABSTRACT FROM AUTHOR]

This paper investigates the directional distribution of extraterrestrial objects (meteors, fireballs) impacting Earth's surface and forming craters. It also introduces a novel directional statistical mixture model to analyze their falls, validated through rigorous testing. First, we address whether these falls follow non-uniform directional patterns by explicitly employing directional statistical tools for analysing such data. Using projection techniques for longitude and latitude and more importantly, a general spherical statistical approach, we statistically investigate the suitability of the von Mises distribution and its spherical version, the von Mises–Fisher distribution, (a maximum entropy distribution for directional data). Moreover, leveraging extensive data sets encompassing meteor falls, fireball showers, and craters, we propose and validate a novel mixture von Mises–Fisher model for comprehensively analysing extraterrestrial object falls. Our study reveals distinct statistical characteristics across data sets: fireball falls exhibit non-uniformity, while meteor craters suggest a potential for both uniform and von Mises distributions with a preference for the latter after further refinement. Meteor landings deviate from a single-directional maximum entropic distribution; we demonstrate the effectiveness of an optimal 13-component mixture von Mises–Fisher distribution for accurate modelling. Similar analyses resulted in 3- and 6-component partitions for fireball and crater data sets. This research presents valuable insights into the spatial patterns and directional statistical distribution models governing extraterrestrial objects' fall on Earth, useful for various future works. [ABSTRACT FROM AUTHOR]

Impact craters are formed due to the high-speed collisions between small to medium-sized celestial bodies. Impact is the most significant driving force in the evolution of celestial bodies, and the impact craters provide crucial insights into the formation, evolution, and impact history of celestial bodies. In this paper, we present a detailed review of the characteristics of impact craters, impact crater remote sensing data, recognition algorithms, and applications related to impact craters. We first provide a detailed description of the geometric texture, illumination, and morphology characteristics observed in remote sensing data of craters. Then we summarize the remote sensing data and cataloging databases for the four terrestrial planets (i.e., the Moon, Mars, Mercury, and Venus), as well as the impact craters on Ceres. Subsequently, we study the advancement achieved in the traditional methods, machine learning methods, and deep learning methods applied to the classification, segmentation, and recognition of impact craters. Furthermore, based on the analysis results, we discuss the existing challenges in impact crater recognition and suggest some solutions. Finally, we explore the implementation of impact crater detection algorithms and provide a forward-looking perspective. [ABSTRACT FROM AUTHOR]

Impact craters are geomorphological features widely distributed on the lunar surface. Their morphological parameters are crucial for studying the reasons for their formation, the thickness of the lunar regolith at the impact site and the age of the impact crater. However, current research on the extraction of multiple morphological parameters from a large number of impact craters within extensive geographical regions faces several challenges, including issues related to coordinate offsets in heterogeneous data, insufficient interpretation of impact crater profile morphology and incomplete extraction of morphological parameters. To address the aforementioned challenges, this paper proposes an automatic extraction method of morphological parameters based on the digital elevation model (DEM) and impact crater database. It involves the correction of heterogeneous data coordinate offset, simulation of impact crater profile morphology and various impact crater morphological parameter automatic extraction. And the method is designed to handle large numbers of impact craters in a wide range of areas. This makes it particularly useful for studies involving regional‐scale impact crater analysis. Experiments were carried out in geological units of different ages and we analysed the accuracy of this method. The analysis results show that: first, the proposed method has a relatively effective impact crater centre position offset correction. Second, the impact crater profile shape fitting result is relatively accurate. The R‐squared value (R2) is distributed from 0.97 to 1, and the mean absolute percentage error (MAPE) is between 0.032% and 0.568%, which reflects high goodness of fit. Finally, the eight morphological parameters automatically extracted using this method, such as depth, depth–diameter ratio, and internal and external slope, are basically consistent with those extracted manually. By comparing the proposed method with a similar approach, the results demonstrate that it is effective and can provide data support for relevant lunar surface research. [ABSTRACT FROM AUTHOR]

China's first Mars rover, Zhurong, has carried out an exploration mission in southern Utopian Planitia. As rocks and their three‐dimensional (3D) morphology are essential for studying the geological characteristics of the Martian surface, this paper presents an approach for automatically extracting 3D rocks from stereo rover images. With our approach, 6,185 cm‐scale rocks are extracted using the Zhurong NaTeCam images, with the F1‐score achieving 91.86%. Approximate 3D morphological features are then calculated for each rock, and the statistical result shows that small rocks in centimeters make up the majority. Comparative morphological analyses of rocks in different areas show that landscape type affects the number of rocks but has no clear relationship to the proportions of rocks of different sizes. The outcrops of sedimentary rocks, the predominant type of rocks in the Zhurong landing area, and the float rocks are distributed differently regarding all morphological features, making the size‐frequency distribution of rocks around craters significantly different from other areas. Further comparative analysis with the Bonneville crater ejecta rocks extracted from the Spirit rover data is also conducted. Some similarities between the Zhurong outcrop rocks and the Bonneville crater ejecta rocks are found in 2D compactness. Meanwhile, the Bonneville crater ejecta rocks have a more scattered distribution in sphericity than both the float and outcrop rocks in the Zhurong landing area, indicating that the shapes of the Bonneville crater ejecta rocks may be more diverse. In addition, the sphericity is found to converge with height for rocks in both landing areas. Plain Language Summary: Rocks on the Martian surface and their three‐dimensional (3D) morphology record the geological evolution of Mars and its interaction history with outer space. Currently, China's Zhurong Mars rover has traveled nearly 2 km on Mars and collected a wealth of images, allowing the fine‐scale measurement and 3D morphological analysis of Martian rocks with statistical significance. We therefore propose an automatic approach for extracting individual 3D rocks from the stereo images and apply it to the Zhurong NaTeCam images to facilitate fine‐scale morphological analyses of the Martian rocks in the Zhurong landing area. Our morphological analyses lead to several remarkable findings about the interior relations between Martian rocks and geomorphology, giving new clues about the topographical and geomorphic evolution of Mars. Key Points: We extracted 6,185 three‐dimensional rocks at centimeter‐scale in the Zhurong landing area and computed their morphological featuresWe analyzed the morphology of the rocks and revealed the relationships between the rocks and landscape type of the Martian surfaceCompared to the rocks from the Spirit data, we found morphological similarity and difference for the outcrop and float rocks, respectively [ABSTRACT FROM AUTHOR]

The Mars 2020 Perseverance rover landed in Jezero crater on 18 February 2021. After a 100‐sol period of commissioning and the Ingenuity Helicopter technology demonstration, Perseverance began its first science campaign to explore the enigmatic Jezero crater floor, whose igneous or sedimentary origins have been much debated in the scientific community. This paper describes the campaign plan developed to explore the crater floor's Máaz and Séítah formations and summarizes the results of the campaign between sols 100–379. By the end of the campaign, Perseverance had traversed more than 5 km, created seven abrasion patches, and sealed nine samples and a witness tube. Analysis of remote and proximity science observations show that the Máaz and Séítah formations are igneous in origin and composed of five and two geologic members, respectively. The Séítah formation represents the olivine‐rich cumulate formed from differentiation of a slowly cooling melt or magma body, and the Máaz formation likely represents a separate series of lava flows emplaced after Séítah. The Máaz and Séítah rocks also preserve evidence of multiple episodes of aqueous alteration in secondary minerals like carbonate, Fe/Mg phyllosilicates, sulfates, and perchlorate, and surficial coatings. Post‐emplacement processes tilted the rocks near the Máaz‐Séítah contact and substantial erosion modified the crater floor rocks to their present‐day expressions. Results from this crater floor campaign, including those obtained upon return of the collected samples, will help to build the geologic history of events that occurred in Jezero crater and provide time constraints on the formation of the Jezero delta. Plain Language Summary: The Mars 2020 Perseverance rover, along with the Ingenuity Helicopter technology demonstration, landed in Jezero crater, Mars on 18 February 2021. Here, we detail results from the first science campaign of the mission, the purpose of which was to explore the enigmatic Jezero crater floor. By the end of the campaign, Perseverance traversed more than 5 km, created seven abrasion patches, and sealed a total of nine samples and a witness tube for return to Earth. Analysis of the rocks in the crater floor revealed two distinct geologic formations, named the Máaz and Séítah formations. Both formations were determined to be igneous in origin, the former likely from a series of lava flows and the latter formed from a slowly cooling melt or magma body. The composition of the Máaz and Séítah formation rocks also indicate that they experienced significant alteration from water in the past, consistent with Jezero crater having once been filled with water. Results from Perseverance's Jezero crater floor campaign, including those obtained upon return of the collected samples to Earth, will help build the geologic history of Jezero crater and reveal its past habitability. Key Points: The Máaz and Séítah formations are igneous, with Séítah representing olivine‐rich cumulates and Máaz representing separate lava flowsCrater floor rocks have been variably altered to produce carbonates and other alteration minerals during multiple aqueous episodesPost‐emplacement processes tilted these rocks near the Máaz‐Séítah contact, and erosion produced varied textures and olivine‐rich regolith [ABSTRACT FROM AUTHOR]

This paper gives an insight to formation of ablation craters on float glass samples due to irradiation by high energetic nanosecond laser pulses and its optimisation for laser-induced breakdown spectroscopy (LIBS) analysis. Use of such lasers is less common for material processing, therefore ablation and eventual degradation of the samples has not been in the focus technical studies. Meanwhile high energy pulses can be optimal for certain applications, such as LIBS. Here the properties of ablation craters on common float glass samples after high energetic laser pulse irradiation were investigated. LIBS spectra were obtained and their quality was compared against the irradiation parameters such as wavelength and focusing conditions. It was found that these have a significant effect on crater formation, but parameters can be set to allow ablation without major degradation of the sample. [ABSTRACT FROM AUTHOR]

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The paper presents the results of model calculations of impact craters ejecta thickness variations in the south polar region of the Moon from the south pole to 70° S for craters of Nectarian, Imbrian, Eratosthenian, and Copernican ages. This work does not consider pre-Nectarian craters since younger deposits often hide the boundaries of their ejecta. Housen, Sharpton and Fassett models were chosen to estimate the power. The first was used for craters larger than 45 km in diameter, the second for smaller craters (from 3 to 45 km), and the third for the Mare Orientale basin. During estimation, the mixing factor of ejecta with the underlying regolith (factor μ) was considered. As a result, maps of ejecta thicknesses were produced for the Moon's south polar region. They provide an opportunity for quantitative estimation of the various aged impact events' contribution to the formation of polar regolith and, accordingly, to determine the dominant source (sources) of material in a particular area, not least in the proposed landing sites. [ABSTRACT FROM AUTHOR]

The paper considers the geochemical effects of impact processing of the polar regolith of the Moon. It contains an admixture of water ice, which can (should?) provide conditions for possible chemical reactions. To date, only one geochemical effect was reliably found—the formation of hematite Fe2O3, which is uncharacteristic for relatively low selenographic latitudes. In the work, a thermodynamic analysis of the conditions required for the formation of hematite is carried out. It is shown that this requires the presence of free oxygen, which (this is a possible option) can accumulate during the dissipation into outer space of hydrogen formed during water decomposition. The specific process or processes of hematite formation require further study. It is very likely that impact processing of polar regolith also leads to hydration of silicate glasses and to the formation of heavy hydrocarbons. The dissipation of free hydrogen into outer space, which, apparently, is formed in these processes, should lead to an increase in the deuterium content in the remaining hydrogen. The Н2О ice of the polar regolith likely contains a significant amount of heavy water. Future investigations in the polar regions of the Moon, especially with the delivery of samples to Earth, should confirm or refute these conclusions and assumptions. [ABSTRACT FROM AUTHOR]

Venus' thick atmosphere is capable of destroying kilometer-sized bodies such as asteroids, creating various types of traces on the surface. While larger cosmic bodies are able to reach the surface, creating impact craters or crater dispersion fields, smaller bodies effectively transfer the initial kinetic energy into the atmosphere, resulting in an "atmospheric explosion" at some altitude. In these cases, the most visible marks on the surface of Venus are created by atmospheric shock waves and the flow of gas behind the shock fronts reflected from the solid surface. The transitional sizes of impactors that break up in the atmosphere but reach the surface give rise to clusters of craters. The paper presents the first results of three-dimensional calculations of the destruction of rocky asteroids in the atmosphere of Venus, indicating significant differences from simple two-dimensional axisymmetric calculations. [ABSTRACT FROM AUTHOR]

On August 11, 2023, the Luna-25 spacecraft was launched with the task of landing in the southern polar region of the Moon and conducting research on the soil and near-surface exosphere. It flew safely to the Moon vicinity and settled into the orbit of Moon satellite. The landing of the spacecraft was scheduled for August 21. In accordance with the flight program, on August 19, a braking impulse was issued to form a pre-landing orbit. But the braking engine worked longer than planned, and the spacecraft crashed into the lunar surface. The team of the LROC television camera of the Lunar Reconnaissance Orbiter, having received information from Roscosmos about the crash site of Luna-25, photographed this site and on August 24 received an image showing a morphologically fresh crater with a diameter of about 10 m, which was not present in previous images of this site. The paper describes the regional topographic and geological characteristics of the site. A photogeological analysis of LROC images of the impact site was performed. An estimate has been made of the expected diameter of the crater formed as a result of the impact of Luna-25. From our examination, it follows that the 10-meter crater described in the NASA message appears to have actually been formed as a result of the impact of Luna-25. Its size corresponds to estimates calculated from impact parameters. The absence of a bright halo of emissions, typical of very young lunar craters, is likely due to the fact that the impact was relatively low-velocity, and in this case the crater is more likely an indentation depression and/or due to the fact that there was about half a ton of unspent fuel in the spacecraft "smeared" the surface near the crater. [ABSTRACT FROM AUTHOR]

The impact crater is the most dominant geomorphic structural units over the planetary surface and its accurate extraction is of great significance to investigate the evolution of the Moon, the impact history of the solar system and the space environment. Through the impact crater's identification, especially small-scale, and their spatial distribution characteristics, the impact flux, morphological characteristics, age of impact craters and surface degradation can be revealed. Therefore, this paper presents an automatic method for the impact crater detection, especially small-scale ones, using anchor-free deep learning. Due to the limitation of traditional object proposals for detecting different types of impact craters, we retrain the anchor-free CenterNet model using a transfer learning strategy, where the detection task of impact crater is formulated into the detection of its center point and regression of its property (i.e., size) without non-maximal suppression. We select the stacked Hourglass network as backbone to aggregate different levels of feature for enhancing the capability of estimating the impact crater centers. Moreover, we find the center points of impact craters on the image features' heatmap only based on their locations, instead of box overlap, which allows us to detect different types of impact craters, even the impact craters that contain other impact craters. The model is trained in an end-to-end manner and applied to detect the impact craters on the lunar images between ±50° of latitude, with the spatial resolution of 100 m/pixel, from Wide Angle Camera (WAC) onboard Lunar Reconnaissance Orbiter (LRO) mission. The obtained results are compared relative to an existing crater database both qualitatively and quantitatively that suggests the reliability and robustness of the developed method in the automatic detection of small-scale impact craters, where the smallest one is 500 m. Moreover, the developed method is capable to detect different types of impact craters, including dispersal and connective ones, with the recall of 73.66% and precision of 78.27% compared with an existing crater database. The code is publicly available at https://github.com/ShuoweiZhang/crater_detection. [ABSTRACT FROM AUTHOR]

Impact cratering is one of the most important processes shaping planetary surfaces, offering valuable clues about the target body's geologic history and composition. However, crater mapping has historically been done manually, a process that has proven to be both arduous and time consuming. This paper outlines a machine learning crater mapping approach for bodies with limited elevation data available (Digital Elevation Models). We applied a Convolutional Neural Network for the detection and morphometry of impact craters on Saturn's moon Enceladus using light‐shadow labels trained on data from the Cassini Imaging Science Subsystem. Our algorithm identified a total of 5,240 features which were used to quantify crater distribution; this included the highest number of small craters (<1–2 km in diameter) recorded on Enceladus by any previous published study. The pool of features was later down‐selected to craters between 0 and 30°N (latitude) imaged at high incidence (>60°) and phase angles (>26°). The down selection was necessary to accurately perform diameter measurements and derive depths from shadow estimation techniques to calculate depth–diameter ratios (d/D); a well‐studied relationship used to constrain planetary surface properties. Results show that the d/D ratio of craters in the equatorial region of Enceladus range from ∼0.06 to 0.37, with a median of 0.19. Our results will inform efforts to constrain the surface properties of this region of Enceladus, potentially also supporting future mission concept design for the Saturnian moon. Future work will explore the simple‐to‐complex crater transition and differences between this area's d/D and Enceladus' northern and southern latitudes. Plain Language Summary: Saturn's moon Enceladus epitomizes the statement "tiny but mighty." A mere ∼500 km in diameter, this body boasts a remarkable array of diverse terrains, a subsurface ocean, and is a strong candidate in the search for extraterrestrial life. As such, it is no surprise that it was named a top research priority in the 2023–2032 Planetary Decadal Survey. The study of impact craters is regarded as one of the most important tools in the study of planetary surfaces, providing insights into the history of celestial bodies. However, traditional manual approaches have proven to be arduous and time intensive. Motivated by the abundance of Cassini mission imagery, the lack of updated studies of Enceladus' cratered terrains and seeking a method to avoid intensive hand‐mapping, we developed a machine learning approach for crater identification and morphometry determination on Enceladus. This approach recorded more smaller craters (<1–2 km in diameter) on Enceladus than any previous published study and supports a history of intense geologic activity and heat flow in the leading and trailing hemispheres. Our method also allowed us to calculate the depth‐diameter relationship for craters in the equatorial region, a relationship that will inform the community's knowledge of the geological characteristics of the region. Key Points: Crater counting and identification provides information about a planet's history and properties, but is time‐consuming when done by handWe used a machine learning approach to map over 5,000 craters on the surface of Enceladus, using highlight‐shadow labelsWe present the depth–diameter ratio for craters on Enceladus' equator to aid future efforts to constrain surface properties of the region [ABSTRACT FROM AUTHOR]

Crater recognition on Mars is of paramount importance for many space science applications, such as accurate planetary surface age dating and geological mapping. Such recognition is achieved by means of various image-processing techniques employing traditional CNNs (convolutional neural networks), which typically suffer from slow convergence and relatively low accuracy. In this paper, we propose a novel CNN, referred to as MC-UNet (Martian Crater U-Net), wherein classical U-Net is employed as the backbone for accurate identification of Martian craters at semantic and instance levels from thermal-emission-imaging-system (THEMIS) daytime infrared images. Compared with classical U-Net, the depth of the layers of MC-UNet is expanded to six, while the maximum number of channels is decreased to one-fourth, thereby making the proposed CNN-based architecture computationally efficient while maintaining a high recognition rate of impact craters on Mars. For enhancing the operation of MC-UNet, we adopt average pooling and embed channel attention into the skip-connection process between the encoder and decoder layers at the same network depth so that large-sized Martian craters can be more accurately recognized. The proposed MC-UNet is adequately trained using 2∼32 km radii Martian craters from THEMIS daytime infrared annotated images. For the predicted Martian crater rim pixels, template matching is subsequently used to recognize Martian craters at the instance level. The experimental results indicate that MC-UNet has the potential to recognize Martian craters with a maximum radius of 31.28 km (136 pixels) with a recall of 0.7916 and F 1 -score of 0.8355. The promising performance shows that the proposed MC-UNet is on par with or even better than other classical CNN architectures, such as U-Net and Crater U-Net. [ABSTRACT FROM AUTHOR]

Crater degradation and erosion control the lifetime of craters in the meter‐to‐kilometer diameter range on the lunar surface. A consequence of this crater degradation process is that meter‐scale craters survive for a comparatively short time on the lunar surface in geologic terms. Here, we derive crater lifetimes for craters of <∼200 m in diameter by analyzing existing functional expressions for crater population equilibrium and production. These lifetimes allow us to constrain the topographic degradation needed at different scales to explain when craters become undetectable on equilibrium surfaces. We show how topographic degradation can be treated as a process of anomalous (scale‐dependent) topographic diffusion and find large differences in effective diffusivities at different scales, consistent with a wide range of evidence besides equilibrium behavior. Understanding the range of morphology of meter‐scale craters is particularly relevant for future exploration of the lunar surface with rovers. We illustrate expectations for the d/D distribution of small lunar craters on surfaces with negligible regional‐scale slopes. Our results imply that if volatiles are found in preserved <4 m craters and were delivered after crater formation, the volatiles must have been emplaced in the last ∼50 Ma. Given the rates of surface evolution we infer, the most likely emplacement time for any volatiles discovered at or near the surface in the interior of fresh, small craters may be much younger than this upper limit. Plain Language Summary: Impact craters are the most common landform on the Moon and form across a range of sizes and at vastly different rates. Small, meter‐sized craters form much more frequently than large, kilometer‐sized craters. After crater formation, craters start to widen, fill in, and their topographic relief is reduced due to their exposure to the lunar environment. Eventually, this infilling process is sufficient to render craters unrecognizable on the surface. The time over which this occurs is the crater lifetime, which is a function of crater diameter. This paper quantifies the crater lifetime. As suggested by some earlier workers, we show that, for 10–100 m craters, lifetime increases as a function of diameter to a power p of ∼1.1–1.3. This diverges from what would be expected for one model for how regolith on the Moon is transported ("classical diffusion"), which would have p = 2, and supports a different model ("anomalous diffusion") that implies the rate of infilling depends on the scale being considered. In this study, we also show that this model for surface evolution implies that any volatiles that end up being discovered within small fresh craters on the Moon must have gotten there recently. Key Points: The crater population in equilibrium can be combined with a production model to directly constrain crater lifetime for <∼200‐m diameter cratersWith known initial crater shapes and erasure thresholds, the effective diffusivity compatible with these crater lifetimes can be inferredIf volatiles are found in small (<4‐m) craters and were delivered after crater formation, the volatiles are <∼50 Ma old [ABSTRACT FROM AUTHOR]

The Sirente main crater is a ≈ 130 m wide, in plan view droplet-shaped depression with an elevated rim, surrounded by 30 smaller depressions. It was proposed to be of meteorite impact origin. Given the age of formation in the 3rd to 5th centuries A.D., the inferred catastrophic origin was related to the celestial sign ("Chi Rho") said to have been seen by Emperor Constantine in 312 A.D. and suggested to have changed the course of both Roman and Christian history. However, the meteoritic origin is not yet confirmed. This paper presents new results from synthetic modelling of Electric Resistivity Tomography field data collected at the Sirente main crater which provide further clues around the controversy of its origin. This study arises from the need to validate the observed structural features which include possible upturned strata (i.e., overturning of strata below impact crater rims) and compaction-fissure-like features below and just outside the crater rim, well-developed "breccia lens", as well as an ejecta layer, and provide key indicators for objective and quantitative interpretation of the measured resistivity pattern. The results from this study are consistent with the hypothesis of a small impact crater in a low-strength target, with a relatively shallow apparent crater and do not support other proposed mechanisms of formation such as karst, mud volcano or merely anthropogenic origin. [ABSTRACT FROM AUTHOR]

Summary: The aim of the scientific community, towards the investigation of solutions able to favor a futuristic human settlement on Mars, also concerns ad hoc communication systems and wireless networks to be deployed over the "Red planet." However, the state‐of‐the‐art appears to be missing of realistic and replicable models for understanding the radio propagation over precise Martian locations. This means that performing solid simulations, rather than roughly approximated ones, is really a tough task. Thus, this paper describes the design of a 3D ray‐tracing simulator based on high‐resolution digital elevation models (DEMs) for the evaluation of Martian large‐scale and small‐scale phenomena in the S and EHF bands. First, by taking advantage of the Cole–Cole equations, we computed the complex permittivity of the JSC Mars‐1 Martian regolith simulant. Then, we developed a 3D tile‐based structure of the Gale crater, thanks to its DEM, and finally, we implemented a ray‐tracing algorithm for outdoor environments able to trace the line of sight (LOS), the first and second reflections of a radio frequency (RF) signal between a transmitter (TX) and a receiver (RX) over the 3D structure. The results focus on estimating path losses, shadowing values, outage probability, and on the parametrization of multipath channels for selected areas and subareas, presenting heavily different morphological features, of the Gale crater. Moreover, some brief considerations about dust storms and atmosphere harmful effects on propagation will be drawn. [ABSTRACT FROM AUTHOR]

Copyright of Experimental Technology & Management is the property of Experimental Technology & Management Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

At present, the selection of lunar landing areas is mostly determined by experts' argumentation and experience. Generally, it is artificially limited to a small zone, and there are few effective quantitative models for landing areas. Under the premise that big data, artificial intelligence, and other technologies are becoming increasingly mature, with in-depth analysis and the mining of lunar-related digital data, it is possible to automatically optimize the landing zones in the whole moon. Factors such as engineering constraints, scientific goals, and resource requirements are comprehensively considered. This paper proposes a new method that strategically applies the weights of evidence (WoE) and fractals to optimize the landing area of the detector in the whole moon. The method takes the thickness of the lunar crust, roughness, slope, digital elevation model, gravity gradient, iron oxide distribution, and lunar soil optical maturity as evidence layers, and known landing sites as the target layer. After all moon data are divided into grids, the prior probability of each evidence factor, the in-cell weight of each evidence factor, and the Bayesian posterior probability are calculated. According to the semi-parabolic distribution in the fuzzy distribution, the fuzzy membership degree of the impact crater radius is presented and the complexity of the number of impact craters in a cell is calculated. The distribution complexity of impact craters in each cell is calculated according to the fractal. The result of the weights of evidence is further constrained by the complexity of the number of cells and the complexity of the distribution, and the posterior probability map of suitable landings is finally obtained. When comparing and analyzing the posterior probability map of the landing zones with the known landing points and the artificially preferred landing zones, it is found that 84% and 82.6% fall within the suitable landing zones, respectively. Among them, the first gradient is 58% and 58.7%, and the second gradient is 26% and 23.9%. The results at different resolutions are relatively stable and are consistent with the distribution of craters or basins in the lunar mantle and the spatial distribution of olivine, which proves the effectiveness and feasibility of this method. This method is a typical application of lunar big-data-driven knowledge discovery and will help promote the transformation of lunar landing area selection from traditional qualitative analyses to automated intelligence optimization. [ABSTRACT FROM AUTHOR]

The landing camera (LCAM) of Chang'e-4 lander provides a series of low (46 cm/pixel) to high (2.3 cm/pixel) resolution images, which are suitable for centimeter-scale craters. In this paper, we analyze the degradation of those small-sized craters to provide detailed information on the local geological evolution of the lunar surface. From the mosaicked descent image, 6316 craters were extracted and classified into four degradation levels based on their morphology on the image: fresh, slightly degraded, moderately degraded, and severely degraded. The ground terrain camera (TCAM) image and the DEM of the Yutu-2 panoramic camera (PCAM) validate the crater degradation levels from a qualitative and quantitative perspective, respectively. The results show that the smaller the size of the craters, the more easily they are degraded. The crater populations in equilibrium in the four study areas indicate that the cumulative size–frequency distribution (SFD) slope is different from previous research results, and the smaller the craters, the more difficult to reach an equilibrium state (for craters smaller than a given size, the production rate is exactly balanced by the removal rate), which may be due to secondary cratering and surface resurfacing caused by the burial of ejecta from neighboring craters. [ABSTRACT FROM AUTHOR]

Context. The YORP effect is the thermal torque generated by radiation from the surface of an asteroid. The effect is sensitive to surface topology, including small-scale roughness, boulders, and craters. Aims. The aim of this paper is to develop a computationally efficient semi-analytical model for the crater-induced YORP (CYORP) effect that can be used to investigate the functional dependence of this effect. Methods. This study linearizes the thermal radiation term as a function of the temperature in the boundary condition of the heat conductivity, and obtains the temperature field in a crater over a rotational period in the form of a Fourier series, accounting for the effects of self-sheltering, self-radiation, and self-scattering. By comparison with a numerical model, we find that this semi-analytical model for the CYORP effect works well for K > 0.1 Wm−1 K−1. This semi-analytical model is computationally three-orders-of-magnitude more efficient than the numerical approach. Results. We obtain the temperature field of a crater, accounting for the thermal inertia, crater shape, and crater location. We then find that the CYORP effect is negligible when the depth-to-diameter ratio is smaller than 0.05. In this case, it is reasonable to assume a convex shape for YORP calculations. Varying the thermal conductivity yields a consistent value of approximately 0.01 for the spin component of the CYORP coefficient, while the obliquity component is inversely related to thermal inertia, declining from 0.004 in basalt to 0.001 in metal. The CYORP spin component peaks at an obliquity of 0°, 90°, or 180°, while the obliquity component peaks at an obliquity of around 45° or 135°. For a z-axis symmetric shape, the CYORP spin component vanishes, while the obliquity component persists. Our model confirms that the total YORP torque is damped by a few tens of percent by uniformly distributed small-scale surface roughness. Furthermore, for the first time, we calculate the change in the YORP torque at each impact on the surface of an asteroid explicitly and compute the resulting stochastic spin evolution more precisely. Conclusions. This study shows that the CYORP effect due to small-scale surface roughness and impact craters is significant during the history of asteroids. The semi-analytical method that we developed, which benefits from fast computation, offers new perspectives for future investigations of the YORP modeling of real asteroids and for the complete rotational and orbital evolution of asteroids accounting for collisions. Future research employing our CYORP model may explore the implications of space-varying roughness distribution, roughness in binary systems, and the development of a comprehensive rotational evolution model for asteroid groups. [ABSTRACT FROM AUTHOR]

Evidence from Arrokoth and comets strongly suggests a very low density for this and similar small Kuiper belt objects. Plausible compositions imply high porosities, in excess of 70%, and low compaction crush strengths. If so, impact craters on Arrokoth (especially Sky, its largest) formed largely by compaction of pore space and material displacement. This is consistent with geological evidence from New Horizons imaging. High porosity reduces cratering efficiency in the gravity regime whereas compaction moves it toward crush strength scaling and increased efficiency. Compaction also guarantees that most impactor kinetic energy is taken up as waste heat near the impact point, with momentum transferred to the rest of the body by elastic waves only. Monte Carlo simulations of Sky‐forming conditions indicate that the momentum imparted likely separated Arrokoth's two lobes, but displacement was limited by dissipation at the neck between them. Unusual strength properties are not required to preserve Arrokoth's bilobate configuration. Plain Language Summary: It has become apparent over the last few years that small asteroids and comets are very underdense compared with the materials they are made of. This means that their total porosities are likely quite high, in excess of 70%, both as tiny voids within particles (so‐called microscopic porosity) and spaces between particles (macroscopic porosity). But none are likely as porous as the distant denizens of the Kuiper belt such as Arrokoth (visited by the New Horizons spacecraft in 2019). This paper concerns impact craters on Arrokoth and similar small bodies, and the rather unusual effects expected. Imagine a fluffy (fine powder) snowball striking a much larger fluffy snowball, only that the snow is not pure ice but a mixture of porous icy, rocky, and carbon‐rich particles. Even at high velocities (>100 s of m/s) craters should mostly form by compacting pore space and pushing material away from the impact point, not the traditional blasting of ejecta back into space. Similar to crush‐up of an automobile bumper, compaction helps to protect from the potentially catastrophic effects of large impacts, such as complete disruption of the target or breakup of bilobate bodies like Arrokoth, and should be incorporated in future collisional evolution studies. Key Points: Arrokoth is likely a low density, highly porous, contact binary planetesimalImpact craters on Arrokoth, and particularly its largest, likely formed as compaction craters, with modest or little ejectaHigh porosity acted to protect Arrokoth from catastrophic disruption, ejecta recoil, and lobe dislocation and rearrangement [ABSTRACT FROM AUTHOR]

The current rate of small impacts on Mars is informed by more than one thousand impact sites formed in the last 20 years, detected in images of the martian surface. More than half of these impacts produced a cluster of small craters formed by fragmentation of the meteoroid in the martian atmosphere. The spatial distributions, number and sizes of craters in these clusters provide valuable constraints on the properties of the impacting meteoroid population as well as the meteoroid fragmentation process. In this paper, we use a recently compiled database of crater cluster observations to calibrate a model of meteoroid fragmentation in Mars' atmosphere and constrain key model parameters, including the lift coefficient and fragment separation velocity, as well as meteoroid property distributions. The model distribution of dynamic meteoroid strength that produces the best match to observations has a minimum strength of 10–90 kPa, a maximum strength of 3–6 MPa and a median strength of 0.2–0.5 MPa. An important feature of the model is that individual fragmentation events are able to produce fragments with a wide range of dynamic strengths as much as 10 times stronger or weaker than the parent fragment. The calibrated model suggests that the rate of small impacts on Mars is 1.5–4 times higher than recent observation‐based estimates. It also shows how impactor properties relevant to seismic wave generation, such as the total impact momentum, can be inferred from cluster characteristics. Plain Language Summary: Over a thousand meteorite impacts have been detected in spacecraft images of the surface of Mars in the last two decades. In more than half of these, the meteoroid broke up under aerodynamic forces as it entered Mars' thin atmosphere. Fragments separated during flight to form a cluster of craters on the ground rather than a single crater. Observations of these crater clusters provide clues to the frequency and properties of meteoroids striking Mars, as well as the nature of their break‐up. Here we use cluster observations to calibrate a numerical model of meteoroid fragmentation in Mars' atmosphere. The model reproduces well the observed properties of clusters, demonstrating that small meteoroids colliding with Mars possess a wide range of strengths and appear to be very similar to those that form fireballs on Earth. The model suggests that about 90–240 craters or clusters larger than 10 m are produced somewhere on Mars each year, which is higher than estimates based on the number of craters detected in images. Our work will improve dating of surfaces on Mars, aid efforts to detect small impacts by the sound waves that they generate and help to determine past variations in atmospheric conditions from ancient craters. Key Points: Crater cluster observations used to calibrate model of meteoroid fragmentation in Mars' atmosphereFragments exhibit a wide range of dynamic strengths both weaker and stronger than parentThe rate of small impacts on Mars is 1.5–4 times higher than recent observation‐based estimates [ABSTRACT FROM AUTHOR]

The identification of impact craters on the Moon and other planetary bodies is of great significance to studying and constraining the dynamical process and evolution of the Solar System. Traditionally, this has been performed through the visual examination of images. Due to the effect of overburden, some structural features cannot be effectively identified from optical images, resulting in limitations in the scope, efficiency and accuracy of identification. In this paper, we investigate the viability of convolutional neural networks (CNNs) to perform the detection of impact craters from GRAIL-acquired gravity data. The ideal values of each hyperparameter in U-net architecture are determined after dozens of iterations of model training, testing and evaluation. The final model was evaluated by the Loss function with the low value of 0.04, indicating that the predicted output of the model reached a relatively high fitting degree with the prior labelled output. The comparative results with different methods show that the proposed method has a clear detection of the target features, with an accuracy of more than 80%. In addition, the detection results of the whole image account for 83% of the number of manually delineated gravity anomalies. The proposed method can still achieve the same quality for the identification of the gravity anomalies caused by impact craters under the condition that the resolution of GRAIL gravity data are not superior. Our results demonstrate that the U-net architecture can be a very effective tool for the rapid and automatic identification of impact craters from gravity map on the Moon, as well as other Solar System bodies. [ABSTRACT FROM AUTHOR]

The paper estimates the minimum, mean and maximum thickness of regolith and degree of its impact-caused reworking as a function of depth based on spatial density of small impact craters for the floors of polar craters Shoemaker, Sverdrup and Shackleton and for the landing sites of Luna-16, -17, and -24. Key parameter for these calculations is Dcr, the boundary diameter between the equilibrium and non-equilibrium parts of crater population. It was found to be 80 m for the Luna-24 site and crater Shackleton, 100 m for the Luna-16 and -17 sites, 350 m for crater Sverdrup and 1000 m for crater Shoemaker. The median thicknesses of regolith for these areas were found to be 3,2, 4, 14, and 40 m, respectively. For these areas, the number of the reworking events was found to be 1, 6, 2, 7, and 20 for the 2 m depth, 3, 4, 14 and 40 times for the 1 m depth, 6, 8, 28 and 80 times for the 0,5 m depth, 16, 20, 70, and 200 times for the 0.2 m depth, and 64, 80, 280, and 800 times for the 0.05 m depth. These reworking impacts should mechanically mix the polar regolith and cause multiple local vaporization / condensation of the frozen volatiles leading to their physico-chemical differentiation. [ABSTRACT FROM AUTHOR]

Impact-generated hydrothermal systems are a potential habitat for life on Earth and other planetary bodies. The ubiquity of impact craters on Mars makes them of particular interest for the search for life on this planet although their viability as a habitat is not well understood. To better understand such systems, two analogue impact structures on Earth were investigated, as their dominantly basaltic target rock makes them similar to impact structures in the Martian crust: the Vista Alegre and Vargeão Dome impact structures in Brazil. The goals of this paper are to 1) better understand the Vista Alegre and Vargeão Dome impact structures, and 2) understand how impact-generated hydrothermal systems on Earth can be compared with similar systems on Mars. To enable comparison, the software HYDROTHERM is used to reconstruct the hydrothermal evolution of both impact systems on Earth. Permeability, porosity, thermal conductivity, and initial temperature distributions are varied to simulate slow--, medium-, and fast-cooling models. The medium cooling rate models are then adapted to Martian conditions and scaled to 1×, 2×, 4×, and 8× the size on Earth, also adapting the impact energy and initial heat distribution, to check the comparability using similar target rocks. Finally, target rocks are changed to a basaltic composition only, to check how a lower-permeability Martian surface composition would affect the hydrothermal system. The models indicate between 150 and 650 thousand years (ka) of hydrothermal activity for both the Vista Alegre and Vargeão Dome impact structures. Due to the limited availability of water in the initial, high-temperature situation in the crater centre, water flux first increases and then decreases, although after 650 kyr the water flux towards the crater centre remains active in Vargeão Dome only. This sustained water flux is likely related to the low relative pressure in the crater centre due to the lack of overlying rock in comparison to outside the crater, as well as the direct connection of an underlying sandstone aquifer with high-permeability, fractured basalt in the centre of the structure. The Martian models with the same lithologies as on Earth show overall lower water flux and contain permafrost, which prevents the water flux within the aquifer from outside the crater towards the crater centre as seen in Vargeão Dome. The cooling times increase with scaling from 1× to 8× the size to ∼0.2 and 5 Myr, respectively. With only basalts in the target, cooling times reach ∼0.2 to 9 Myr. However, in that case, the water flow only remains active for up to the first Myr, and a minimum crater diameter of approximately 40 km is needed to achieve surface water fluxes close to those in Vargeão Dome and Vista Alegre. Below the Martian surface, hydrothermal system activity can persist for millions of years, providing potential for supporting life. Unfortunately, these parts of the system are currently unreachable for both sampling and spectroscopic techniques, and the short lifetime and low water fluxes at the surface related to the permafrost layers do not favour impact-generated hydrothermal systems on present-day Mars as targets for the search for life. However, these systems are highly dependent on the rock types and related permeabilities and could have provided habitats before 3.5 Ga, when the planet was warmer and liquid water was present at the surface. • This is the first fluid-flow model of terrestrial impact craters in basaltic targets. • This is the first direct comparison of fluid-flow models for impact-generated hydrothermal systems on Earth and Mars. • This is the first time a (semi)quantitative limit is set for impact-generated hydrothermal systems on Mars. • The paper provides new insights into impact-generated hydrothermal systems on Mars and their potential as a habitat. [ABSTRACT FROM AUTHOR]

Lunar craters and rilles are significant topographic features on the lunar surface that will play an essential role in future research on space energy resources and geological evolution. However, previous studies have shown low efficiency in detecting lunar impact craters and poor accuracy in detecting lunar rilles. There is no complete automated identification method for lunar features to explore space energy resources further. In this paper, we propose a new specific deep-learning method called high-resolution global–local networks (HR-GLNet) to explore craters and rilles and to discover space energy simultaneously. Based on the GLNet network, the ResNet structure in the global branch is replaced by HRNet, and the residual network and FPN are the local branches. Principal loss function and auxiliary loss function are used to aggregate global and local branches. In experiments, the model, combined with transfer learning methods, can accurately detect lunar craters, Mars craters, and lunar rilles. Compared with other networks, such as UNet, ERU-Net, HRNet, and GLNet, GL-HRNet has a higher accuracy (88.7 ± 8.9) and recall rate (80.1 ± 2.7) in lunar impact crater detection. In addition, the mean absolute error (MAE) of the GL-HRNet on global and local branches is 0.0612 and 0.0429, which are better than the GLNet in terms of segmentation accuracy and MAE. Finally, by analyzing the density distribution of lunar impact craters with a diameter of less than 5 km, it was found that: (i) small impact craters in a local area of the lunar north pole and highland (5°–85°E, 25°–50°S) show apparent high density, and (ii) the density of impact craters in the Orientale Basin is not significantly different from that in the surrounding areas, which is the direction for future geological research. [ABSTRACT FROM AUTHOR]

Asteroid impacts are destructive and low-probability threats to the Earth. The numerical simulation is considered an applicable analysis tool in asteroid deflection programs. As a novel shock-capturing strategy, the space–time conservation element and solution element (CESE) method can reliably predict shock waves and mechanical behaviors under high pressure and large strain conditions. In this paper, based on an elastoplastic flow model and an updated CESE scheme, the laboratory-scale iron asteroid impacts are modeled numerically, and the multi-material boundary treatment and the interface tracing strategy are introduced. Under hypervelocity impacts of the projectile to the iron asteroid target, the construction and realization of morphologies of impact craters and the implantation of projectile material into the target are numerically calculated. Numerical results show that the crater diameter and depth increase with increasing impact velocity and with increasing temperature, which softens the target. Computational results are compared with experimental observations available in the open literature, and good agreement is found. Therefore, the CESE method is successfully extended for capturing the key features of laboratory-scale hypervelocity asteroid impacts. [ABSTRACT FROM AUTHOR]

Impact craters are formed by collisions of cosmic bodies moving with hypervelocity. The formation of these features is not restricted to the distant geological past; new structures are constantly being created and at least 13 confirmed impact craters and crater fields have formed during the Holocene alone. This short review paper: (1) introduces the basics of the impact cratering process to physical geographers and Quaternary geologists; (2) provides a short description of representative examples of such features (Morasko, Kaali, Kamil, Ilumetsa); and (3) discusses the similarities and differences among very small craters, and contrasts these with larger impact structures. This manuscript may be useful to researchers planning to test whether a small Quaternary depression in the ground may be of impact origin. [ABSTRACT FROM AUTHOR]

NASA's Stardust mission utilized a sample collector composed of aerogel and aluminum foil to return cometary and interstellar particles to Earth. Analysis of the aluminum foil begins with locating craters produced by hypervelocity impacts of cometary and interstellar dust. Interstellar dust craters are typically less than one micrometer in size and are sparsely distributed, making them difficult to find. In this paper, we describe a convolutional neural network based on the VGG16 architecture that achieves high specificity and sensitivity in locating impact craters in the Stardust interstellar collector foils. We evaluate its implications for current and future analyses of Stardust samples. [ABSTRACT FROM AUTHOR]