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The Charity Shoal structure is a circular, ∼1.2‐km‐diameter, bedrock‐rimmed shoal in eastern Lake Ontario with a ∼20‐m‐deep central basin. The structure has been proposed as a possible Middle Ordovician impact crater or volcanic intrusion. We conducted marine seismic and magnetic surveys (9‐km2) and 3‐D geophysical modeling to better resolve the Charity Shoal subsurface geology and possible origins. Three models were evaluated: (a) a buried (>450 m) impact structure in Mesoproterozoic basement, (b) a maar‐diatreme, (c) a cylindrical, zoned volcanic plug. Seismic profiles and multi‐beam bathymetry revealed >30 m of Quaternary sediments overlying Middle Ordovician (Trenton Group) carbonate bedrock and complex, 3‐dimensional folding and faulting of the structure rim. Magnetic surveys recorded an annular magnetic high (>600 nT) over the structure rim and a central magnetic low (∼500–600 nT) coincident with a ∼−1.7 mGal Bouguer gravity anomaly. The continuity of Trenton Group strata in seismic profiles rules out a previously proposed Mesozoic maar‐diatreme intruded into Paleozoic strata. The zoned volcanic plug model reproduced the annular magnetic anomaly but was incompatible with Bouguer gravity profiles. The magnetic anomaly was best reproduced by a simple impact structure seated in Mesoproterozoic basement at 450–500 m depth with a rim‐to‐rim diameter of ∼1.2 km and rim height of ∼10–20 m. A 100‐m wide and 50‐m‐deep channel in the Mesoproterozoic basement may record fluvial dissection of the southwestern rim. A buried (>450 m), simple impact crater is most compatible with all available geophysical data at Charity Shoal. Plain Language Summary: The Charity Shoal structure is 1.2‐km‐diameter, circular bedrock‐rimmed shoal on the lakebed of eastern Lake Ontario. The crater‐like structure has been investigated in three previous studies (Holcombe et al., 2001, https://doi.org/10.1016/s0380‐1330(01)70664‐8; Holcombe et al., 2013, https://doi.org/10.1007/s00367‐013‐0322‐6; Suttak, 2013, http://hdl.handle.net/11375/13532) and proposed as a possible karst sinkhole, glacial erosional feature, volcanic intrusion or meteorite impact crater. We conducted geophysical surveys and 3‐D modeling at Charity Shoal to evaluate several possible geological origins. An impact crater model was most compatible with the available geophysical data, which indicate a deeply buried "crater‐form" structure in the Precambrian basement at a depth of >450 m. Our geophysical results rule out a proposed impact crater within the Middle Ordovician sedimentary rocks, as that model cannot reproduce the large gravity and magnetic anomalies recorded at Charity Shoal. Key Points: Charity Shoal is a 1.2 km diameter, crater‐like bedrock shoal in northeastern Lake Ontario previously proposed as a Middle Ordovician impact structure or maar‐diatreme3‐D subsurface modeling of magnetic, seismic, and gravity data indicates a deep‐seated (>450 m) crater‐form structure in Mesoproterozoic basementGeophysical modeling supports a probable origin as a Mesoproterozoic‐early Paleozoic simple impact structure [ABSTRACT FROM AUTHOR]

The three largest impact craters, the remains of which have been found on Earth to date, had diameters of about 200 km immediately after formation. The search for traces of larger impact structures continues. This paper presents the results of numerical modeling of the formation of terrestrial impact craters larger than those already found. It is shown that the inferred geothermal gradient significantly influences the initial geometry of the impact melt region, which may facilitate the search for the remains of deeply eroded ancient impact structures. [ABSTRACT FROM AUTHOR]

When Peter Millman, an astronomer at the Dominion Observatory in Ottawa, read Ralph Baldwin's 1949 book The Face of the Moon, he excitedly brought it to the attention of the Observatory's recently-appointed Director, Carlyle Beals. Baldwin's book argued that the Moon's numerous circular features were not of volcanic origin, but were due to meteorite impacts, and that the Earth should similarly have an abundance of meteorite impact scars. Beals and Millman decided to test Baldwin's arguments, and Beals initiated an innovative program at the Observatory to search for meteorite craters on the Canadian Shield. By the mid-1960s, ten craters had been discovered in Canada. Today, 190 meteorite craters have been confirmed worldwide, with nearly one-sixth of them in Canada. Investigations of the Canadian craters, employing gravity, magnetic, seismic, and diamond drilling studies, became a model for all future crater studies, and brought international attention to Canadian scientists. [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]

The Ordovician-aged Lawn Hill Impact Structure is perhaps unique among documented craters, in that it is largely filled with slumped, allochthonous Cambrian carbonates partly fluidised by the impact shock. It is a complex geological feature, with a thin horizon of suevite beneath carbonate sheets. The bulk of the impact ejecta material was either deposited on top of the mobilised carbonates, and not preserved owing to erosion, or is present beneath the base of current drilling. The geometry of the crater in its final form has been modelled in three dimensions using gravity data and dipole–dipole-induced polarisation geophysics, with control from an extensive drill-hole library. Post-impact modification, including terrace formation and carbonate fill, has resulted in an asymmetric ring syncline, which extends to depths >600 m. In the data-rich area of the Century zinc–lead–silver deposit, on the southwest margin of the crater, both intact and remnants of the crater rim and impact ejecta blanket were preserved above the deposit. The Proterozoic ore deposit is located on a detached terrace, which slumped into the crater and was buried by allochthonous carbonates from the Georgina basin. The sequence of events can be shown to comprise: impact with crater formation and injection of carbonate dykes and inter-thrust wedges in the crater walls with concurrent suevite deposits inside and surge deposits outside the crater; this was rapidly followed by slumping of carbonate mega-blocks transported by a fluidised carbonate slurry into the crater, concomitant with collapse of Proterozoic terraces; finally, collapse of the central crater uplift generated imbricate slices of Cambrian carbonate among mainly Proterozoic rocks inside the ring syncline. After impact, the Ordovician-aged Lawn Hill Impact Structure crater was filled with slumped terraces of Proterozoic sediments and Pb–Zn ore, fluidised Cambrian carbonate, plus mega-clasts of both of those, on top of a thin but persistent hematitic suevite. Outside the crater, remnants of base surge and debris deposits represent the ejecta blanket. The Century Zn–Pb deposit was preserved on a disrupted terrace; the crater rim was partially preserved above the deposit and the mineralised sequence truncated by the crater wall. Geophysical and drilling data show a terraced, asymmetric ring syncline, up to at least 600 m thick in places. [ABSTRACT FROM AUTHOR]

Since the impact ∼50,000 yr ago, surface runoff has entrained and transported sediment from the walls to the floor of Meteor Crater (Arizona, USA). Previous work interpreted this erosion and deposition to be due to predominantly fluvial (i.e., dilute water transport) processes. However, light detection and ranging (LiDAR)-derived topographic data and field observations indicate that debris flows dominated, which were likely generated by runoff that entrained the talus that borders bedrock cliffs high on the crater walls. The low gradient of the crater floor caused debris flows to stop, leaving lobate deposits, while fluvial processes delivered sediment toward the center of the crater. Cosmogenic radionuclide dating of levee deposits suggests that debris-flow activity ceased in the late Pleistocene, synchronous with regional drying. Assuming a rock-to-water ratio of 0.3 at the time of transport by mass flows, it would have taken ∼2 × 106 m3 of water to transport the estimated ∼6.8 × 106 m3 of debris-flow deposits found at the surface of the crater floor. This extensive erosion would require ∼6 m of total runoff over the 0.35 km2 upslope source area of the crater, or ∼18 mm of runoff per debris-flow event. Much more runoff did occur, as evidenced by crater lake deposits, Holocene fluvial activity (which produced little erosion), and contemporary rainfall rates. Rarely on Earth is the total amount of water that creates and runs through a landscape estimated, yet such calculations are commonly done on Mars. Our analysis suggests that erosional and depositional landforms may record only a small fraction of the total runoff. [ABSTRACT FROM AUTHOR]

A model of the genesis of stishovite and other SiO2 phases in terrestrial matter is developed; it combines the physicochemical and geodynamic conditions of their formation. Based on the experimental data, a P–T diagram of SiO2 polymorphs in combination with the boundaries of geospheres and geotherm was plotted. Stishovite and other SiO2 phases of cosmic-impact synthesis were buried in the early Earth during the period of meteorite accretion (50 Ma). These SiO2 phases are completely assimilated by melts of the pyrolite global magma ocean that existed for 500 Ma. By 2.0 Ga, the magma ocean crystallized, and the Earth's crust, upper mantle, transition zone, and lower mantle with layer D" (with seismic boundaries between them) were formed. During this period, the main mass of the Earth's core was separated, which completed by 2.7 Ga. As a result, the gravitational field intensified, which contributed to the fractional ultramafic–mafic evolution of mantle magmas with peritectic reactions of ringwoodite–akimotoite in the transition zone and bridgmanite in the lower mantle with melts and the formation of stishovite (shown experimentally at 20 and 26 GPa). These reactions in diamond-forming carbonate–silicate–carbon melts provided the formation of stishovite, which was captured as a paragenetic inclusion by diamonds and transported to the Earth's surface by magmas. The genesis of stishovite under the terrestrial conditions is controlled by global mantle convection as well. The subduction of lithospheric plates to layer D'' near the liquid core was accompanied by the formation of stishovite, and then its transformation into poststishovite phases. When superplumes rise from layer D'' to the Earth's crust, the peritectic reactions of postperovskite and bridgmanite, and then ringwoodite–akimotoite, with melts are likely to form stishovite and cause its subsequent transformation into low-pressure SiO2 phases. With the emergence of the Earth's crust, the impact-meteorite genesis of stishovite resumes. Stishovite that formed under the terrestrial conditions appears as an inclusion in ultradeep diamonds on the Earth's surface. Stishovite of cosmic-impact synthesis is preserved in meteorite craters. In both cases, stishovite is a metastable phase. [ABSTRACT FROM AUTHOR]

This article explores the importance of pattern recognition in geography and the challenges that can arise when identifying patterns on maps. It emphasizes the significance of patterns, symmetries, sequences, and hierarchies in understanding spatial arrangements and variations. The author suggests various activities for teachers to help students develop their spatial thinking skills, such as learning the sequence of rooms in their school or naming ecoregions in a sequence from the equator to the Sahara. The article also discusses the concept of hierarchical thinking in geography and provides additional activities for teachers to use. [Extracted from the article]

At present, there are still many meteorite craters and boulders on the surface of Mars and the Moon that cannot be accessed by existing planetary exploration robots. To provide a solution to this issue, this paper proposes a four-link rocker-suspension planetary exploration robot that combines both the reliability and low complexity of wheeled rovers with competent terrain adaptability and obstacle-crossing performance. Relying on its special differential pitch device, the robot can adapt to fluctuations in terrain by using both active and passive modes. Moreover, the four-link rocker suspensions on both sides of the robot can increase the instantaneous rotation radius of the rockers when the robot climbs over obstacles. In this paper, using modelling and simulations, we demonstrate that the four-link rocker suspension can improve the robot's obstacle-crossing capability. The geometric and static conditions required for the robot to cross obstacles are derived and discussed, and numerical simulations are conducted to identify the maximum obstacle-crossing heights that satisfy different conditions. Finally, a physical prototype of the robot is developed. [ABSTRACT FROM AUTHOR]

We provide new support for habitable microenvironments in the near-subsurface of Mars, hosted in Fe- and Mg-rich rock units, and present a list of minerals that can serve as indicators of specific water–rock reactions in recent geologic paleohabitats for follow-on study. We modeled, using a thermodynamic basis without selective phase suppression, the reactions of published Martian meteorites and Jezero Crater igneous rock compositions and reasonable planetary waters (saline, alkaline waters) using Geochemist's Workbench Ver. 12.0. Solid-phase inputs were meteorite compositions for ALH 77005, Nakhla, and Chassigny, and two rock units from the Mars 2020 Perseverance rover sites, Máaz and Séítah. Six plausible Martian groundwater types [NaClO4, Mg(ClO4)2, Ca(ClO4)2, Mg-Na2(ClO4)2, Ca-Na2(ClO4)2, Mg-Ca(ClO4)2] and a unique Mars soil-water analog solution (dilute saline solution) named "Rosy Red", related to the Phoenix Lander mission, were the aqueous-phase inputs. Geophysical conditions were tuned to near-subsurface Mars (100 °C or 373.15 K, associated with residual heat from a magmatic system, impact event, or a concentration of radionuclides, and 101.3 kPa, similar to <10 m depth). Mineral products were dominated by phyllosilicates such as serpentine-group minerals in most reaction paths, but differed in some important indicator minerals. Modeled products varied in physicochemical properties (pH, Eh, conductivity), major ion activities, and related gas fugacities, with different ecological implications. The microbial habitability of pore spaces in subsurface groundwater percolation systems was interrogated at equilibrium in a thermodynamic framework, based on Gibbs Free Energy Minimization. Models run with the Chassigny meteorite produced the overall highest H2 fugacity. Models reliant on the Rosy Red soil-water analog produced the highest sustained CH4 fugacity (maximum values observed for reactant ALH 77005). In general, Chassigny meteorite protoliths produced the best yield regarding Gibbs Free Energy, from an astrobiological perspective. Occurrences of serpentine and saponite across models are key: these minerals have been observed using CRISM spectral data, and their formation via serpentinization would be consistent with geologically recent-past H2 and CH4 production and sustained energy sources for microbial life. We list index minerals to be used as diagnostic for paleo water–rock models that could have supported geologically recent-past microbial activity, and suggest their application as criteria for future astrobiology study-site selections. [ABSTRACT FROM AUTHOR]

The concentric impact rings of the Vredefort Crater contain rocks with elevated uranium concentrations resulting from the geological signature of a meteoric impact. The decay of this uranium was estimated to lead to elevated indoor radon concentrations in the Crater, but such a study has never been carried out. This study explores the relationship between the natural radionuclides i-0found in the geology of the Vredefort Crater and indoor radon concentrations. This was achieved through soil sampling and radionuclide surveys conducted on three impact rings, supplemented by indoor radon measurements in dwellings found in the area. In situ measurements revealed that one impact ring had higher-than-average uranium concentrations at 50 Bq/kg. Surprisingly, the measured indoor radon levels were lower than expected (113 Bq/m3). These measurements were taken during the COVID-19 pandemic and colder months, conditions that would typically result in elevated indoor radon levels. Soil samples indicated uranium activity of 30 Bq/kg, comparable to the world average of 35 Bq/kg. However, defunct mine tunnels in the area exhibited elevated radon concentrations, averaging 364 Bq/m3. The disparity between expected and measured indoor radon levels was attributed to the composition of surficial deposits, bedrock, and architectural features of the dwellings preventing radon accumulation. [ABSTRACT FROM AUTHOR]

Jeptha Knob is a deformed structure, 4.5 km in diameter, composed entirely of carbonate rocks in the stable craton of North America. At Jeptha Knob, conventional evidence of meteorite impact, shock metamorphism, has not been found. I used calcite twin analysis to test the hypothesis that Jeptha Knob is a meteorite impact crater. Calcite twinning gives differential stresses of >170 MPa in rocks that were 600 to ≈800 m below the surface when the rocks were deformed. Under these conditions, high differential stresses cannot be explained by tectonic processes. In addition, twin intensities are >150 twins/mm which are >50% higher than the highest twin intensities observed in limestone from a wide variety of tectonic settings. Twin intensities and differential stresses are the same magnitudes as those found at Serpent Mound, a proven impact structure. Consistent with meteorite impact, differential stresses increase toward the center of the structure. If one accepts that Jeptha Knob is a marine impact crater, then (1) the presence of high temperature (>250°C) thick twins in calcite from a resurge deposit; (2) the extensive dolomitization of the central uplift with water/rock ratios >1.0; and (3) two episodes of calcite twin recorded incremental strains, are explained. [ABSTRACT FROM AUTHOR]

Landing on small-bodies is a very challenging problem that requires high degrees of robustness and autonomy. Being able to perform simulations with great flexibility and accuracy is paramount for the development and design of landing systems. To this end, contact dynamics plays a fundamental role and is often handled by complex tools that require large amount of development and validation efforts and very specific expertise. In the last decade, the Visual Effects (VFX) industry has developed numerous suites that deal with contact dynamics frameworks. In this work, the possibility of leveraging on the work of the VFX industry by using Blender, one of these tools, as the source for the contact dynamics modelling is investigated. This research focuses on the description of the methodology used for the landing simulations and the validation of the tool developed. A step-by-step guide through the simulation setup is given, discussing how the wrapping GNC simulator and Blender interact. Validation tests for the different parameters and dynamic models involved in the simulations are also presented. The results refer to the landing of a CubeSat in the crater region of an asteroid. In particular, the artificial crater that will be generated on Dimorphos by NASA's DART impact in late September 2022, is considered in the simulations presented in this work. Safety maps are generated by post-processing these results, and are used to assess different landing strategies or site-selection criteria on the Dimorphos crater study case. Finally, the role of the developed tool in optimising the use of space resources and its contribution to landing design strategies is discussed. [ABSTRACT FROM AUTHOR]

Ultrahigh-pressure high-temperature glasses are characterized by unusual structural and phase aspects that require closer investigation in order to elucidate their physical properties and the possibility of using innovative materials as prototypes. Experimental modeling of an impact process in laboratory conditions makes it possible to shed light on the nature of phase transformations on impacto-genesis. Impact glasses were obtained experimentally by melting the aluminosilicate and quartz components of the rocks of the target of the Kara astro-problem at pressure about 90 GPa and temperature about 7000°C. Investigations have shown that as a result of extreme external conditions, glasses of a specific composition are formed containing a high proportion of Ca and carbon. Thus, the results obtained indicate the possibility of obtaining glass of wide compositions, including carbon-containing glass, which can be used for further research in order to develop new materials and technologies for their production. [ABSTRACT FROM AUTHOR]

Eugene (also spelled Yevgeniy or Evgeny) Gurov (Figure 1) was born in Kharkov, Ukrainian SSR, on March 24, 1934. 10th Lunar and Planetary Science Conference, pp. 479 - 81. 22 Gurov, E. P., Valter, A. A., Gurova, E. P., and Serebrennikov, A. I. 1978. The geological structure of the crater rim was described by Gurov and Gurova ([4]) and Gurov and Yamnichenko ([23]); see also Gurov et al. ([16]). 21 Gurov, E. P., Valter, A. A., Gurova, E. P., and Kotlovskaya, F. I. 1979. [Extracted from the article]

The article discusses the integration of technology and art in landscape design.The author argues that laser surveying technology can be used to measure the variability of sand and to create accurate 3D models of sand formations.The author concludes by arguing that the integration of art and technology is essential for the expansion of artistic landscape design. The author proposes that laser surveying technology may soon become an essential tool for this purpose.

The basal contact of the Sudbury Igneous Complex (SIC) on the North Range is interpreted as the outer edge of a meteorite impact crater. Yet, the base of the SIC, and contacts within the SIC, and the overlying Onaping are not circular. Their outline is elliptical. This and other details of the geology of the North Range which have not been fully explained include variations in the width of the metamorphic contact aureole, lateral discontinuous variations in the thickness of the norite and granophyre units, paleomagnetic evidence that the North Range contact of the SIC originally had a dip of around 20°, and differing magnetic fabrics in the norite/gabbro versus the granophyre. Several metrics are used to determine how much of the current outline of the North Range is the result of post-impact deformation and how much is a primary feature related to a meteorite impact. Uplift, rotation, and translation experienced by different segments of the North Range of the SIC are established using dyke azimuth and petrographic analysis of Matachewan diabase dykes, and paleomagnetic and magnetic fabric data analysis. These analyses show (a) the elliptical form of the North Range is a primary feature associated with a near-circular impact crater, (b) some of the original crater wall must have been preserved, and (c) deformation of the North Range is limited to regional scale block rotation producing a southwest dip modified by minor block rotation tilting and vertical displacement associated with north–northwest-trending faults. [ABSTRACT FROM AUTHOR]

Microplastic pollution is a worldwide concern affecting all environmental matrices, including pristine lakes. Lentic lakes operate as a sink for microplastics (MPs), which interfere with a biogeochemical cycle and, therefore, deserve immediate attention. We present a comprehensive assessment of MPs contamination in the sediment and surface water of a geo-heritage site, Lonar lake (India). It is the third largest natural saltwater lake and only basaltic crater in the world formed by meteoric impact around 52,000 years ago. Mean MPs abundance in lakeshore sediment and surface water was 14.44 particles/kg and 2.66 particles/L, respectively. Small-sized MPs dominate the hypersaline region of the lake. Transparent and green fragments and filaments morphotypes were abundant. Most of the MPs in Lonar lake were secondary in origin. FTIR-ATR analysis revealed 16 types of polymers in the lake, of which polypropylene, polyvinyl chloride, polyethylene, high-density polyethylene, low-density polyethylene, polystyrene, and polyester were the most common. The overall pollution load index (PLI) for Lonar lake sediment and water was 1.39 and 2.58, respectively. Although all sampling stations had significant MPs pollution (PLI > 1), there was noticeable station-specific variability, which could be linked to anthropogenic activities. Irresponsible tourist behavior and religious activities, coupled with poor waste management are the leading causes of MPs contamination in the lake. The current work fills a gap in the investigation of MP pollution in a crater lake formed by a meteorite impact by being the first to provide a precise estimate of the MPs contamination in the Lonar lake. [ABSTRACT FROM AUTHOR]

Wispy Terrain, with its chasmata, is one of the enigmatic regions of Dione. It consists of quasi-parallel graben, and troughs, in parts with horsts, indicating extensional and shear stresses. This study introduces some observations of compression-related features and proposes a new regional formation model. The study of the relationship between impact craters and tectonic features revealed certain "lost" parts of some crosscut craters, indicating additional cryotectonic features, the appearance of accretionary prism-like phenomena, and, theoretically, subsumption-like processes. This study provides new information about the surface renewal processes at one of the youngest and probably still active regions of Dione. [ABSTRACT FROM AUTHOR]

• Earth may have had a ring during the middle Ordovician, from ca. 466 Ma. • Breakup of an asteroid passing within Earth's Roche limit likely formed the ring. • Among several features preserved is a near-equatorial band of impact craters. • Shading of Earth by the ring may have triggered a global icehouse period. All large planets in our Solar System have rings, and it has been suggested that Mars may have had a ring in the past. This raises the question of whether Earth also had a ring in the past. Here, we examine the paleolatitudes of 21 asteroid impact craters from an anomalous ∼40 m.y. period of enhanced meteor impact cratering known as the Ordovician impact spike, and find that all craters fall in an equatorial band at ≤30°, despite ∼70 % of exposed, potentially crater-preserving crust lying outside this band. The beginning of this period is marked by a large increase in L chondrite material accumulated in sedimentary rocks at 465.76 ± 0.30 Ma, which, together with the impact spike, has long been suggested to result from break-up of the L chondrite parent body in the asteroid belt. Our binomial probability calculation indicates that it is highly unlikely that the observed crater distribution was produced by bolides on orbits directly from the asteroid belt (P = 4 × 10–8). We therefore propose that instead, a large fragment of the L chondrite parent body broke up due to tidal forces during a near-miss encounter with the Earth at ∼466 Ma. Given the longevity of the impact spike and sediment-hosted L chondrite debris accumulation, we suggest that a debris ring formed after this break up event, from which material deorbited to produce the observed crater distribution. We further speculate that shading of Earth by this ring may have triggered cooling into the Hirnantian global icehouse period. [ABSTRACT FROM AUTHOR]

The release and transformation mechanism of residual stress contributes to the improvement of metal materials' processing and performance, enhancing their structural stability, surface integrity, and fracture resistance. This paper focuses on the Ultrasonic Impact Treatment-Solid Particle Entrainment by Waterjet (UIT-SPEWJ) composite surface modification of 7075-T6 aluminum alloy, investigating the effects of UIT-SPEWJ process parameters (jet pressure and target distance) on the alloy's surface quality, roughness, microhardness, residual stress, and the evolution mechanism of microstructure. The results indicate that the 7075-T6 aluminum alloy modified by UIT-SPEWJ mainly exhibits a "meteorite crater" effect, accompanied by significant smearing and ploughing phenomena. Surface roughness shows a trend of first decreasing and then increasing with the rise of jet pressure and target distance. The minimum surface roughness, 0.852 μm, is achieved at a jet pressure of 25 MPa and a target distance of 7.5 mm. The microhardness of the samples modified by UIT-SPEWJ gradually decreases from the surface to the substrate with increasing depth. The hardened layer depths of the samples UIT-SPEWJ-1–6 after modification are approximately 174 μm, 226 μm, 200 μm, 196 μm, 176 μm, and 172 μm, respectively. After UIT, SPEWJ, and UIT-SPEWJ surface modifications, the surface of 7075-T6 aluminum alloy mainly exhibits compressive residual stress (CRS). The surface residual stress σ_srs of samples modified by UIT and SPEWJ are approximately 195.161 and 215.752 MPa, respectively. The surface residual stresses of UIT-SPEWJ-1–6 samples are significantly improved to 277.089, 529.499, 393.615, 459.261, 368.084, and 220.635 MPa, respectively, with UIT-SPEWJ-2 sample having the highest surface residual stress, which is 2.7 and 2.4 times that of UIT and SPEWJ modified surfaces. Samples modified by UIT-SPEWJ present significant dislocation phenomena, and the precipitated phases mainly include the needle-like metastable phase η', as well as the equilibrium phase η (MgZn 2) with a rod-like structure. At lower jet pressures and larger target distances, the 7075-T6 aluminum alloy exhibits a continuous PFZ with a size of approximately 12–23 nm. As jet pressure increases and target distance decreases, discontinuous grain boundary precipitate bands appear, sized around 8–17 nm. Moreover, when the jet pressure is 25 MPa and the target distance is 7.5 mm, the grain boundary precipitated phases are more dispersed. • The synergistic strengthening mechanism of ultrasonic impact and water jet is studied. • The release and transformation mechanism of residual stress induced by ultrasonic impact during jet strengthening process are analyzed. • The microstructure evolution mechanism under the composite strengthening process was studied. [ABSTRACT FROM AUTHOR]

Astrobiology is an intensively developing field of science aiming to explain the origin of life on Earth. Detailed studies of organic matter in impactites of the Earth's meteorite craters can provide important information for understanding the possible conditions for the preservation of biological material under the extreme conditions of large meteorite impacts. During the study of impact diamonds in impactites from the giant Kara astrobleme, 65 km in diameter, (Kara Sea coast, European Arctic Zone, Russia) in 2015, diamond fossils—diamond paramorphs after slightly modified plant organics (wood), preserving the fine micromorphology of cell structure and relict fragments of lignin and cellulose—were discovered and described in detail (Shumilova et al., 2020). These structures were classified as a new variety of natural diamond—karite. This discovery of impact diamond fossils can be used to solve an astrobiological problem, indicating the possible preservation of relict organics during the impact process even under diamond-forming ultrahigh-pressure conditions. The present paper briefly describes diamond fossils that retained relict fragments of lignin and cellulose during meteorite impact, as well as information on the variety of fossilized organics in solidified impact melts. The discovery of the diamond fossils shows the possibility of the arrival of organics on Earth with meteorites and asteroids, as well as the possibility of preservation of relict organics in the products of impact metamorphism. [ABSTRACT FROM AUTHOR]

The paper presents the characteristics of impact diamonds from the Popigai meteorite crater, formed by martensite transformation of graphite-bearing gneisses due to meteorite impacts. These diamonds have a nanopolycrystalline structure and consist of two phases, i.e., cubic (diamond) and hexagonal (lonsdaleite). They are distinguished by phenomenal abrasion resistance, on average twice as high as the abrasion resistance of single-crystalline diamonds. The work considers the possibility of producing similar diamonds by explosion. It is noted that diamonds, which are most similar in structure, are produced through exploding a composition of graphite and hexogen; lonsdaleite is present in the material obtained in this way. However, in any case, diamonds produced by explosion are very small in size, incomparable with natural ones. [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]

Compared to intensive research on km‐sized meteorite impact craters, fewer studies focus on smaller craters. The small craters are often hard or impossible to recognize using "classical" criteria like the presence of shatter cones, shocked quartz, and geochemical indicators. Therefore, a long list of candidate structures awaiting approval/disapproval of their origin has been formed over the last decades. One of them is the Tor structure in central Sweden. To test a hypothesis of an impact origin of this structure, we have performed topographical analysis, geophysical studies, 10Be exposure dating of boulders, and 14C dating of Tor‐associated charcoal. None of the methods gave us a reason to claim the Tor structure is of impact origin. Thus, we support a recently suggested idea of Tor being formed by a grounded iceberg within a glacial lake. [ABSTRACT FROM AUTHOR]

The frequency of crater-producing asteroid impacts on Earth is not known. Of the predicted Holocene asteroid impact craters of <200 m diameter, only -30% have been located. Until now there has been no way to distinguish them from "normal" terrestrial structures unless pieces of iron meteorites were found nearby. We show that the reflective properties of charcoal found in the proximal ejecta of small impact craters are distinct from those produced by wildfires. Impact-produced charcoals and wildfire charcoals must derive from different heating regimes. We suggest that charcoal with specific reflective properties may help to recognize the meteoritic origin of small craters. [ABSTRACT FROM AUTHOR]

The data on the concentrations of major and trace elements, including platinum group elements (PGE) and Re, in suevite samples collected in different parts of the Popigai meteorite crater are reported. The suevite studied shows the identity of the bulk composition; gneiss of the Anabar Shield is identified as the protolith. It was found that the total concentrations of PGEs in suevite are not uniform: they decrease successively in the samples from the western to the southern, and further to the eastern part of the crater. The results of this study showed that the enrichment of suevite on PGEs is a characteristic of meteoritic contamination and is not associated with either crustal or mantle rocks of mafic or ultramafic composition. [ABSTRACT FROM AUTHOR]

The paradigm of plate tectonics has aided in the identification of the journey of continents on the globe, their assembly into supercontinents, disruption, and re‐assembly. Here, we use meteorite impact craters as proxies for tracking the voyage of lithospheric plates. Employing the provisions in GPlates, an interactive geographic information system‐based plate tectonic reconstruction model, we were able to identify the palaeo‐position, and velocity of the 174 terrestrial impact craters, formed after 1,100 Ma, across the globe. These parameters of craters were evaluated for independent tectonic plates and were correlated with global tectonic events. For example, the similarity in the velocity of Beaverhead (900 Ma) and Holleford (550 Ma) craters since 550 Ma is traced to the connection between the Eastern Basin and North America Craton commencing 1,100 Ma, and through the South Basin and Range. Likewise, the drastic reduction in the velocity of Spider Crater (700 Ma) in Australia after 600 Ma can be attributed to the subduction between east and west Gondwana. The accelerated motion of the Indian Plate at 63 Ma, when the lithosphere was hovering over the Réunion hotspot, is also explained. With the advent of more improved plate tectonic models and the discovery of more impact craters, improvised interpretations will be possible. [ABSTRACT FROM AUTHOR]

The JAXA Hayabusa2 mission accomplished the formation of an artificial crater on the asteroid Ryugu. The aim of this work is to analyse the area surrounding the artificial crater and reveal spectral variability compared to the same region before the crater formation, to mineralogically and physically characterize the subsurface exposed material. The crater's investigation focused on the analysis of two regions corresponding to the inner part of crater (the pit and the crater wall/floor), two areas related to ejecta deposited close to the crater, two areas of ejecta moved far from the crater, and two external areas. Each area was investigated both before and after the crater formation, by the study of the photometrically corrected spectral parameters: the 1.9  |$\mu$| m reflectance, the near-infrared spectral slope, and the depth of the bands at 2.7 and 2.8  |$\mu$| m. The subsurface material of the post-crater areas shows deeper absorption bands, a decrease in reflectance, and a reddening in spectral slope with respect to the surface material of pre-crater areas. The subsurface regolith could have experienced a lower OH devolatilization due to space weathering and/or could be composed of finer dark grains than the surface layer. The ejecta reached distances of |$\sim $| 20 m from the impact point, mainly moving in the northern direction; nevertheless, a few ejecta also reached the south-eastern part of crater. [ABSTRACT FROM AUTHOR]

The article discusses research on the use of two-dimensional (2D) seismic reflection dataset to examine the evidence of a complex impact crater referred to as the Nadir Crater in West Africa. Topics explored include the construction of a seismic stratigraphic framework for the Guinea Plateau region to estimate the age and paleoenvironment of the said crater, the seismic characteristics particularly morphology and damage zone of the crater, and the observed deformation in the crater subsurface.

We performed cratering experiments on targets composed of glass beads with a power‐law size distribution that simulated the surface of rubble‐pile asteroids, and we improved the previously studied reduction factor on the crater size scaling relationship including the armoring effect using the momentum transfer efficiency. Cratering experiments were conducted using light gas guns at Kobe University and ISAS/JAXA to control the impact velocity, vi ${v}_{\mathrm{i}}$, from 50 to 4,400 m s−1. Two kinds of mixed targets were prepared by mixing glass beads with diameters of 0.1, 1, 3, and 10 mm—one with the smallest diameter beads, and one without. The size ratio of the target bead to the projectile (diameter of 1–3 mm), ϕ $\phi $, changed from 0.03 to 10. The crater size scaling relationships for the mixed targets were found to depend on the first contacted bead size. Notably, first contact with a 10 mm‐sized bead reduced the crater radius by 35% in maximum. The reduction factor due to this armoring effect on the crater size scaling relationship is written as follows: f(ϕ)=1+8.99×10−3vi0.630.34ϕ−0.19 $f(\phi)={\left[1+\left(8.99\times {10}^{-3}\right){v}_{\mathrm{i}}^{0.63}\right]}^{0.34}{\phi }^{-0.19}$; it decreased with the increase of the size ratio of the target bead to the projectile, while it increased with the increase of the impact velocity and approached unity. Our improved crater size scaling relationship that includes the reduction factor could be used to reconstruct the crater size frequency distribution on rubble‐pile asteroids such as Ryugu, and it may lead to a revision of the crater chronology of asteroids. Plain Language Summary: A rubble‐pile asteroid, 162173 Ryugu, was explored by Hayabusa2, and the crater size frequency distribution on the surface was examined. Ryugu's surface age can be estimated from this size distribution using the impact crater chronology, but the size of the asteroids forming the craters is necessary for this estimate. The crater size scaling law is used to estimate the impactor size, but this law was established using homogeneous grains such as granular sand, so it might not be applicable for rubble‐pile asteroids covered with boulders of various sizes. Moreover, because it is well known that cratering efficiency is significantly reduced by an armoring effect when a smaller asteroid collides with a larger boulder, a scaling law that includes the armoring effect is required. In this study, we performed cratering experiments on the surface of simulated rubble‐pile asteroids and examined the armoring effect on the crater size. Based on the results, we improved the previously studied armoring effect and introduced the momentum transfer efficiency, β $\beta $, into the effect, instead of a restitution coefficient, which was assumed to be zero. Using this improved scaling relationship, a more accurate chronology can be established for the asteroid craters. Key Points: We performed cratering experiments on glass bead targets with a power‐law bead size distribution at 50–4,400 m s−1The size of craters formed in the mixed bead target was speculated to be changed with the size of the first contacted beadThe armoring effect is less efficient for granular targets with a size distribution, compared with equal‐sized granular targets [ABSTRACT FROM AUTHOR]