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Depleted shergottites record unique information about the primary composition and differentiation of the mantle of Mars. Their petrology, geochemistry, and cosmic ray exposure and crystallization ages suggest that most of them were excavated by a single young impact in the Amazonian‐aged lava flows of the Tharsis and Elysium volcanic provinces. However, the difficulties of deriving consistent model ages for individual craters and inadequate evaluation of 3‐7 km craters capable of ejecting martian meteorites have not been settled. Here we perform detailed geological investigations and crater statistics in patches of impact melt deposits for potential source craters of depleted shergottites with D > 3 km, especially those in the Tharsis and Elysium volcanic provinces. By excluding the effect of heterogeneous textures across ejecta deposits, which hinder straightforward extraction of superposed production populations, our systematically updated model ages reveal that Chakpar crater at the northern flank of Ascraeus Mons is the best‐fit candidate. The local context of this crater permits establishing a link between the meteorites and specific lava flows. The long‐lived volcanic center here may experience an eruption and/or local deposition hiatus for about 1.8 billion years, and abundant subsurface water existed when the impact occurred at about 1.1 million years. [ABSTRACT FROM AUTHOR]

Detection of extra-terrestrial geochemical components in melt generated during meteorite impact provides diagnostic evidence that can be used to confirm a hypervelocity impact event, and in some cases, classify the projectile. However, projectile contamination is often present at sub-percent levels, and can be difficult to detect. In contrast, meteoritic abundances in glass from small impact craters (<1 km diameter) formed by iron meteorites can be anomalously high, which has been attributed to glass originating from the projectile-target interface. Emulsion textures, immiscible liquids, metal spherules, and non-meteoritic siderophile element ratios have been cited as evidence that the projectile component is typically fractionated in impact glass. Here we present compositional data for impact glass from the Henbury crater field in Australia, where the largest crater is 145 m in diameter and the subgreywacke target rock and IIIAB iron projectile are geochemically distinct. Mixing models (Fe-Si, Ni-Co, Cr-Ir) and high platinum group element abundances indicate average projectile contributions ranging from 3 to 13 % in Henbury glass, comparable to ranges reported in glass from the Kamil (Egypt) and Wabar (Saudi Arabia) impact craters. However meteoritic siderophile element ratios (Fe:Ni, Fe:Co, Ni:Co) in Henbury glass appear nearly unfractionated, whereas Wabar and Kamil glasses have more fractionated ratios. Observed variations are attributed to fractionation of meteoritic Ni by formation of immiscible Ni-rich spherules during oxidation of meteoritic iron, and subsequent separation of Ni-rich spherules from glass during ejection. The Henbury glass sample analyzed is interpreted as an example of an interface melt that quenched prior to extensive oxidation and phase separation, and thus may represent one of the least fractionated samples of melt from the projectile-target interface described thus far, whereas Wabar and Kamil glasses record more evidence of fractionation processes. These results further highlight the influence of metal spherule formation on the composition of ejected glass from small impact structures formed by iron meteorites and provide new insights that explain textural features observed in natural impact glasses. [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]

On Venus, radar observations of the surface have highlighted two categories of craters: bright‐floored, interpreted as pristine, and dark‐floored, interpreted as being partially filled by lava. While volcanic resurfacing occurs within and outside craters in the plains, it seems mainly concentrated within the interior of dark‐floored craters in the crustal plateaus, suggesting that the magma is negatively buoyant there. Indeed, crater unloading may facilitate vertical ascent of a negatively buoyant magma by decompressing the underlying crust. However, the crater topography also generates a shear stress which would tend to horizontalize the vertical propagation of a dyke. We use numerical simulations of magma ascent in an axisymmetric crater stress field to demonstrate that, depending on the crust thickness and the magma‐crust density contrast, a negatively buoyant magma can indeed erupt only in the crater interior while remaining stored in the crust elsewhere. In particular, we identify four different behaviors depending on if and where a magma‐filled crack ascending below a crater reaches the surface. We draw a regime diagram as a function of two characteristic dimensionless numbers. For eruption to occur only in the crater interior requires a crust thinner than 45 km and a limited range of magma‐crust density contrasts, between 40 and 280 kg m−3 for crust thicknesses between 20 and 45 km, the permissible range decreasing for increasing crustal thicknesses. These results suggest that the crustal plateaus may not be particularly thick and could be slightly differentiated, but probably not very felsic. Plain Language Summary: The Magellan mission revealed two categories of impact craters at the surface of Venus: the pristine bright‐floored and the dark‐floored craters, which are interpreted as craters partially filled by smooth lava after their formation. In the crustal plateaus of Venus, the magma reaches the surface mainly within craters, suggesting that it is denser than the crust. Because of the crater negative topography, the underlying crust is decompressed relative to its surroundings, which, in turn, facilitates magma ascent below the crater despite its negative buoyancy. We first gather surface observations on a set of craters located in the crustal plateaus of Venus to construct a characteristic fresh crater topography. We then use a model of magma ascent below a crater in the crust of Venus to constrain the magma and crust densities as well as the initial magma storage depth that allow for magma eruption within the crater interior only. We show that magma reaches the surface only in the interior of the crater if the crust is slightly less dense than the magma and if it is not too thick (≤45 km in thickness). Key Points: We identify four different behaviors for magma‐filled crack propagation below cratersWe draw a behavior diagram as a function of two dimensionless numbers characterizing dyke propagation below a craterMagma infilling of dark‐floored craters in Venus' plateaus requires a crustal thickness ≤45 km and a small crust‐magma density contrast [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 study examines new bathymetric and geophysical evidence that questions the existence of the Mahuika Crater: a proposed impact depression 20.2 km wide lying on the continental shelf ∼250 km SW of New Zealand. Multibeam echo sounder and sub-bottom profiler data across the published location of the crater were collected and synthesised with existing bathymetric data for the wider region to assess the validity of such a claim. We conclude that there is no geophysical basis for the existence for the Mahuika impact crater in the region, the initial presumption of a crater was unsubstantiated, and is a myth propagated in the literature. [ABSTRACT FROM AUTHOR]

Abstract The Zhurong rover of the Tianwen-1 mission successfully landed in the southern part of the Utopian Planitia and the northern region of the dichotomy boundary. Craters within a ~ 134 km2 region surrounding the Zhurong rover were identified and divided into seven degradation classes based on their preservation states and morphological details. Assessing how craters have degraded over time provides insight into local surface processes and then speculates on the climate evolution of the study area. The small depth/diameter (d/D) of craters in the study area may be caused by the rapid filling of sediments or by impact processes occurring in poorly cohesive weathering layers, and may also be associated with the volatile material alteration. As time went by, the process of crater degradation is nonlinear, and the degradation rate of the fresh crater in the study area at the initial stage of degradation may be as high as 0.2 m/Myr. The calculated surface erosion rate for the study area is ~ 10–2–10–3 m/Myr, indicating that the erosion of the Martian surface since the Middle Amazonian occurred in the dry environment dominated by wind-sand erosion. Graphical Abstract

The Zhurong rover of the Tianwen-1 mission successfully landed in the southern part of the Utopian Planitia and the northern region of the dichotomy boundary. Craters within a ~ 134 km2 region surrounding the Zhurong rover were identified and divided into seven degradation classes based on their preservation states and morphological details. Assessing how craters have degraded over time provides insight into local surface processes and then speculates on the climate evolution of the study area. The small depth/diameter (d/D) of craters in the study area may be caused by the rapid filling of sediments or by impact processes occurring in poorly cohesive weathering layers, and may also be associated with the volatile material alteration. As time went by, the process of crater degradation is nonlinear, and the degradation rate of the fresh crater in the study area at the initial stage of degradation may be as high as 0.2 m/Myr. The calculated surface erosion rate for the study area is ~ 10–2–10–3 m/Myr, indicating that the erosion of the Martian surface since the Middle Amazonian occurred in the dry environment dominated by wind-sand erosion. [ABSTRACT FROM AUTHOR]

The Ries impact structure (Germany) contains well‐preserved ejecta deposits consisting of melt‐free lithic breccia (Bunte Breccia) overlain by suevite. To test their emplacement conditions, we investigated the magnetic properties and microstructures of 26 polymict breccia clasts and a stratigraphic profile from the clasts into the suevite at the Aumühle quarry. Remanent magnetization directions of the Bunte Breccia clasts fall into two groups: those whose directions mostly lie parallel to the reversed field during impact carried mostly by magnetite, and those whose directions vary widely among each clast carried by titanohematite. Basement clasts containing titanohematite acquired a chemical remanent magnetization (CRM) during the ejection process and then rotated during turbulent deposition. Clasts of sedimentary rocks grew magnetite after turbulent deposition, with CRM directions lying parallel to the paleofield. Suevite holds a thermal remanent magnetization carried by magnetite, except for ∼12 cm from the contact with the Bunte Breccia, where hematite concentrations increase due to hydrothermal alteration. These observations lead us to propose a three‐stage model of (a) turbulent deposition of the melt‐free breccia with clast rotation <580°C, (b) deposition of the overlying suevite, which acted as a semi‐permeable barrier that confined hot (<300°C) oxidizing fluids to the permeable breccia zone, and (c) prolonged hydrothermal activity producing further alteration which ended before the next geomagnetic reversal. Basement outcrops have significantly different magnetic properties than the Bunte Breccia basement clasts with similar lithology. Two basement blocks situated near the inner ring may have been thermally overprinted up to 550°C. Plain Language Summary: The 26‐km‐diameter, ∼15‐million‐year‐old Ries meteorite impact structure in southern Germany is characterized by well‐preserved ejecta deposits expelled from the crater within seconds after the impact. These deposits consist of two main layers: melt‐free, lithic breccia (Bunte Breccia), overlain by melt‐bearing breccia (suevite). To understand the formation conditions of the ejecta deposits, we performed paleomagnetic and rock magnetic measurements and microstructural experiments on clasts within Bunte Breccia and on the overlying suevite at the Aumühle quarry. We found that clasts derived from crystalline basement materials experienced high pressures during the impact. These clasts had randomly oriented magnetization directions carried by titanohematite. In contrast, clasts derived from sedimentary rocks experienced only low pressures and had coherent magnetization directions oriented parallel to the reversed field during the impact that are carried by magnetite. Our findings can be interpreted by a three‐stage model that explains the thermal and structural formation of impact ejecta at the Ries impact structure. Key Points: Randomly oriented paleomagnetic directions in basement clasts in ejecta deposits suggest turbulent emplacementBunte Breccia was chemically altered and locally heated by the overlying suevite, resulting in hydrothermal activity up to 300°CBasement rocks near the inner ring may have experienced temperatures up to 550°C from cratering [ABSTRACT FROM AUTHOR]

The ring structure of Siljan, located in the central part of Sweden, is considered by many researchers to be a meteorite (impact) crater. Impact craters are among the most complex geological objects on the Earth. The origin and formation of these structures still raises many questions. To find answers to these questions we need reliable geological information about the structure of the crater and the composition of the rocks. Information about the thickness and geological structure of the Siljan Ring area sedimentary cover will help to understand the process of the Siljan Ring structure's formation as well as other similar geological formations on the Earth. Here, we present the results of laboratory studies of sedimentary rock samples taken from four exploration wells drilled in the vicinity of the Siljan Ring crater, which made it possible to compile their detailed lithological description. The laboratory studies included a structural analysis of the samples, and a texture and mineralogical analysis in thin sections. A structure analysis was carried out visually, while structural and mineralogical analyses were carried out on thin sections using a polarizing microscope and a scanning electron microscope. The main components of the rocks (minerals and fragments), along with their ratio and secondary transformations, were determined. The results of the structural analysis of the samples, and the textural and mineralogical analysis of the rocks in thin sections, showed that the sediments' composition in the sedimentary cover near the Siljan Ring structure changes in different areas in accordance with their facies and stratigraphic characteristics. Furthermore, a change in the thickness of the sections and the succession sequences of rock units was established. A change of this nature is presumably caused by tectonic disturbances of an endogenous or impact source. [ABSTRACT FROM AUTHOR]

In impact crater lakes, the lacustrine sedimentary records may not solely reflect climatic changes but also potential erosional effects from lithologically distinct impactite formations. The hydrochemical and biogeochemical processes during the deposition of the Nördlinger Ries impact crater lake, which fall in the range of the mid-Miocene Climate Transition, were studied by analysing microcrystalline authigenic carbonates in a drill core succession, using stable oxygen and carbon isotopes in conjunction with biomarkers. These investigations revealed an early sulfidic interval characterized by thiophenes, iso- and anteiso-C 15:0 acids derived from sulfate reducing bacteria, and dolomites with low to intermediate δ13C carb values. The subsequent distinctive interval is characterized by extremely 13C-enriched dolomite (δ13C carb up to +20.93 ± 0.05‰ V-PDB), decline of iso- and anteiso-C 15:0 acids and is rich in an Archaea-derived archaeol that is 13C-enriched (−14.7‰), indicating extensive methanogenesis in sulfate-depleted lake porewater during early diagenesis. The sulfate decline results from successive sulfate reduction when replenishment by sulfate-bearing inflow water is limited. The carbonates exhibit enriched 18O due to pronounced evaporation in a long-resided water body and enriched 13C by methanogenesis. A change in provenance of water derived from the sulfur-rich suevite (impact melt-bearing breccia) and crystalline source rocks to the sulfur-poor Bunte Breccia (continuous ejecta blanket) is required. Intermittently high Si/Al and Zr/Al at the high δ13C interval suggests sporadic short-term runoff increase, leading to fluctuating physiochemical lake conditions. A subsequent decline in both δ13C carb and archaeol indicates a decreasing lake level with intermittent subaerial exposure events, supported by bioturbation and mud cracks. The concomitant lake oxygenation is well supported by increasing Pr/Ph ratios and lipids derived from aerobic methanotrophs (13C-depleted 3-methyl-hopanoids). In the youngest unit, allochthonous lignites and biomarkers from lacustrine/soil sources appear, high total sulphur contents and thiophenes recur, and stable C and O isotope values decrease again. These observations suggest another major provenance change of the inflowing solutes, with increasing influx from weathered pyrite-bearing Jurassic claystones. These findings demonstrate that the climatic record expected from the stable carbon and oxygen isotopes of the Ries carbonates is strongly overprinted by hydrochemical and biogeochemical processes due to changing ion influx from substrate rocks, along the course of the successive ejecta erosion and catchment changes. Such an intrinsic control of lacustrine biogeochemical processes is also expected for other hydrologically closed impact crater lake basins, where catchment rocks with distinctively different lithologies are present. [ABSTRACT FROM AUTHOR]

The present work reports on the first evidence of a possible hypervelocity impact crater in the Sultanate of Oman. The impact origin of the structure is determined based on field observations, microscopic observations of shatter cones, planar fractures (PFs) and feather features (FFs) in quartz, calcite, and feldspar, and melt-bearing polymict breccias with various types of melts. The structure consists of an elliptical bowl-shaped ridge 750 m long and 550 m wide, oriented roughly north-northeast to south-southwest. The elliptical shape and relief asymmetry indicate an oblique collision. The precursor target lithologies include local late Proterozoic Masirah Bay siliciclastic formations, carbonate and acidic volcanic rocks of the late Precambrian Halfayn Formation, and basement rocks. The crater rim, up to 15–20 m above ground, is composed of quartzite, jasper, agate, monomict siliceous and hematite breccia, and metamorphosed shale (hornfels). An ejecta blanket composed of target rocks covers the floor, outer rim, and the area extending to the immediate northeast and east of the structure. Quaternary aeolian sand covers most of the crater surface, including the 1 to 2 m thick melt-rich polymict breccia found in the crater center. The planar fractures (PFs) and feather features (FFS) in quartz and feldspar suggest a low shock pressure between 5 and 14 GPa. Our observations are consistent with set criterions for impact crater identification, confirming the possible impact origin of the Mahout structure. [ABSTRACT FROM AUTHOR]

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]

Abstract Large meteorite impacts release kinetic energy that induces rock deformation, high temperatures and fluid circulation during the cratering process. To understand the correlation between rock deformation and fluid circulation, it is relevant to investigate post-impact hydrothermal flux and its relation to the local geology. The Cerro do Jarau impact structure is a ~13.5 km diameter impact structure located in southern Brazil and formed on Cretaceous continental flood basalts of the Serra Geral Formation and underlying sedimentary strata. This study collected ground gamma-ray data over the structure and produced K, eTh and eU concentrations, eTh/K ratio and F-factor maps to characterize it in terms of its radiometric signatures and their respective spatial distribution. A general decrease in the concentration of the three elements was observed from the outer-rim towards the center of the crater. The central area is defined by very low radiometric values, with relatively high K values, thus indicating the occurrence of K-bearing rocks. Numerical simulations using the HYDROTHERM 3 code showed the fluid circulation pattern over the impact structure. Data interpretation resulted in a scenery consistent with potential fluid remobilization within the impact structure related to hydrothermal processes in the late stages of the crater formation process.

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.

Discrepancies have emerged concerning the application of sulfur stable isotope ratios as a biosignature in impact crater paleolakes. The first in situ δ34S data from Mars at Gale crater display a ∼75‰ range that has been attributed to an abiotic mechanism. Yet biogeochemical studies of ancient environments on Earth generally interpret δ34S fractionations >21‰ as indicative of a biological origin, and studies of δ34S at analog impact crater lakes on Earth have followed the same approach. We performed analyses (including δ34S, total organic carbon wt%, and scanning electron microscope imaging) on multiple lithologies from the Nördlinger Ries impact crater, focusing on hydrothermally altered impact breccias and associated sedimentary lake-fill sequences to determine whether the δ34S properties define a biosignature. The differences in δ34S between the host lithologies may have resulted from thermochemical sulfate reduction, microbial sulfate reduction, hydrothermal equilibrium fractionation, or any combination thereof. Despite abundant samples and instrumental precision currently exclusive to Earth-bound analyses, assertions of biogenicity from δ34S variations >21‰ at the Miocene Ries impact crater are tenuous. This discourages the use of δ34S as a biosignature in similar environments without independent checks that include the full geologic, biogeochemical, and textural context, as well as a comprehensive acknowledgment of alternative hypotheses. [ABSTRACT FROM AUTHOR]

The record of terrestrial impact events is incomplete with no Archean impact structures discovered, despite the expected abundance of collisions that must have occurred. Because no Archean impact structures have been identified, the necessary conditions to preserve an impact structure longer than 2 Byr are unknown. One significant effect of shock metamorphism is that the physical properties of the target rocks change, resulting in distinctive geophysical signatures of impact structures. To evaluate the preservation potential of impact structures, we evaluate the deeply eroded Proterozoic Vredefort impact structure to examine the changes in physical properties and the remnant of the geophysical signature and compare the results with the well‐preserved Chicxulub impact structure. The major structural features of Vredefort are similar to the expected profile of the Chicxulub structure at a depth of 8–10 km. The Vredefort target rocks, while shocked, do not preserve measurable changes in their physical properties. The gravity signature of the impact structure is minor and is controlled by the remnant of the collapsed transient crater rim and the uplifted Moho surface. We anticipate that erosion of the Vredefort structure by an additional 1 km would remove evidence of impact, and regardless of initial size, erosion by >10 km would result in the removal of most of the evidence for any impact structure from the geological record. This study demonstrates that the identification of geologically old (i.e., Archean) impact structures is limited by a lack of geophysical signatures associated with deeply eroded craters. Plain Language Summary: Meteorite collisions should have formed throughout the 4.5 billion‐year‐long history of Earth, but we have only found impact craters that are less than half of the age of the Earth (2 billion years) and younger. In order to understand how to find very old impact craters, we studied the largest of the oldest preserved impact craters. The 2 Byr old Vredefort structure in South Africa has been deeply eroded, and thus provides a good view of its deep roots. We collected a series of samples of the exposed rocks known to have evidence of shock effects and measured their physical properties. We found that the physical properties do not show evidence of the meteorite impact event. We also established that the gravity profile of the crater preserves a weak signal. When the Vredefort structure erodes a bit more, the geophysical characteristics that make it identifiable will be gone. We expect that signatures of ancient impact structures even larger than Vredefort would be completely removed by erosion by now. Therefore, to find very old impact craters, we need to look in areas that have experienced unusually little erosion. Key Points: The target rocks exposed on the surface of the central core of the Vredefort structure do not preserve changes in physical propertiesRegardless of initial size, changes in the physical properties of impact structures on Earth might be unidentifiable if they are eroded by more than 10 kmArchean impact structures on Earth can only be identified if extraordinary preservation takes place [ABSTRACT FROM AUTHOR]

The Ramgarh structure of south-east Rajasthan is currently established as an asteroid impact crater in India that was excavated in undeformed target sedimentary rocks of the Vindhyan Supergroup of Meso- to Neoproterozoic age. The size of this impact crater is debatable, and two opposing ideas of ~2.4 km and ~10 km diameter exist. The geomorphology of the crater has been re-evaluated using a Sentinel-2A false-coloured imagery of band combination 8, 4, 3 (spatial resolution 10 m) and Landsat-7 Satellite panchromatic imagery of Path/Row 146/042 and SRTM data (spatial resolution 30 m), along with satellite Bouguer gravity data downloaded from GGMplus besides our routine geological field work. Our observation on satellite imageries suggests that the geomorphologic high (~200 m) encircling the Ramgarh structure represents the actual crater’s rim which has a diameter of ~2.4 km. Our satellite gravity data show that the maximum negative Bouguer anomalies (–60 to –51 mGal) only coincide with this geomorphological high surrounding the Ramgarh structure, confirming this structural high of diameter ~2.4 km represents the rim of the crater. [ABSTRACT FROM AUTHOR]

Impact craters with layered ejecta deposits are widespread on Mars. Prevailing views suggest that such ejecta were formed due to the involvement of target water and/or water ice in the impact excavation and/or the post-deposition movement of the impact ejecta. The long-runout landslides and lobate debris aprons that are likely formed due to the involvement of water ice are used as analogs to compare roughness at multiple scales, considering that these three landforms share some similarities in their geomorphology. Analog studies of the morphological similarities and differences of layered ejecta deposits with different emplacement mechanisms are an important approach to untangling how layered ejecta deposits might form on Mars and beyond. Earlier morphological comparisons were usually based on qualitative descriptions or one-dimensional topographic roughness characteristics at given azimuths; however, the emplacement processes of layered deposits are recorded in two-dimensional topography and at multiple scales. In this study, we designed a multiwavelet algorithm to characterize the multi-scale topographic roughness of different forms of Martian layered deposits. Our comparisons show that the inner facies of the layered ejecta deposits and long-runout landslides exhibited similar roughness characteristics, and the outer facies of the layered ejecta deposits were more similar in roughness to lobate debris aprons. This study highlights the importance of the spatial resolution of digital terrain models in characterizing fine topographic fluctuations on layered ejecta deposits, providing additional insights into the possible emplacement mechanisms of different parts of layered ejecta deposits. [ABSTRACT FROM AUTHOR]

In the present study, high resolution stereo camera DEM and Martian crater catalog data have been used to analyze 154 craters with radii ranging from 900 m to 23 kms in the Gale crater and surrounding region. These craters are classified based on crater shape and crater degradation using morphometric parameters like crater rim, diameter, depth, slope, circularity index, and topographic roughness index (TRI). A positive linear correlation was observed between diameter and depth with R2 of 0.66 for small craters and 0.81 for large craters. A similar positive trend was observed between diameter and slope for small craters, whereas it was negative for large craters. TRI showed no correlation with diameter. As per crater degradation, 19.48% of the craters were found to be in class A (Fresh crater), 53.89% were in class B (Moderately degraded) and 26.62% were in class C (Degraded). For round floored craters, maximum craters were found to be in Class B and Class A and very few in Class C. In case of flat floored craters, maximum craters were falling under class B and Class C and very few in class A. Further, it was found that a maximum number of craters (102 out of 154) were found to be flat floored and degraded which may be due to the possible erosional or infilling activities. [ABSTRACT FROM AUTHOR]

The object of research is the products of the Zhamanshin crater: tektites — irgizites, subtectites, zhamanshinites. Features of morphology are revealed and compositions of products are defined. Eu and Ce anomalies are manifested in the REE distribution of irgizites. The crystalline components of jamanshinite consist of fayalite, ferrosilite, and magnetite. Large inclusions of jamanshinite are represented by a solid solution of copper and boron, small inclusions are represented by galena with admixtures of iron and tungsten. Contractional cracks and polymer threads were found in the subtectites. Xenotime, iocite, and coesite were found among their accessory minerals. The proximity of the mineral compositions of subtectites and some comets has been confirmed. [ABSTRACT FROM AUTHOR]

Accelerated cluster ions formed during the outflow of inert gases are a unique tool for the precision surface treatment of various materials, including nonlinear optical single crystals. However, the interaction of gas cluster ions with the surface of nonlinear single crystals has been little studied. In this paper, we consider the features of the formation of anomalous craters during treatment of the surface of hygroscopic lithium-triborate single crystals with argon cluster ions at various bombardment doses. The treatment is carried out at a kinetic energy of clusters of 22 keV, an average cluster size of about 210 atoms per cluster at a normal angle of incidence. It is shown that the anomalous craters have a diameter of 150 to 820 nm, which are two orders of magnitude larger than the diameter of ordinary impact craters. The depth of the craters varies from 5 to 9 nm. Such craters are formed at a target etching depth of up to 320 nm. A statistical analysis of the geometrical parameters of anomalous craters is carried out at various treatment doses. It is established that with an increase in the irradiation dose and, accordingly, the etching depth, the density of anomalous craters per unit surface of the target decreases, while their depth and average diameter increase significantly. [ABSTRACT FROM AUTHOR]

The Hapcheon impact crater is the only meteorite impact crater identified on the Korean peninsula. However, the morphology of the impact crater and the nature of the meteorite collision are unknown. In this study, we analyzed the sedimentary facies using grain size data; computed tomography images, 14C, 10Be, and optically stimulated luminescence dating on a >66-m-long sediment core (20HCL04) recovered from the Hapcheon Basin. Four sedimentary units and 10 types of facies were documented in the Hapcheon Basin sediment core. The sedimentary units comprise 1) a lower part (unit 1) that is dominated by moderately to well-sorted coarse gravel, which contains some impact-related sediments; 2) a middle part (units 2 and 3) dominated by well-laminated mud; and 3) an upper part (Unit 4) that is dominated by poorly sorted coarse gravel supplied from the surrounding mountain slopes by alluvial and fluvial processes. After the meteorite impact, the Hapcheon impact crater was filled with deposits from the crater wall after ca. 1.3 Ma and the Hapcheon Basin became a deep lake environment. After ca. 0.5 Ma, sediments were supplied from the surrounding mountains until the lake was filled. Finally, sediments were deposited in an alluvial fan setting. In addition, the Hapcheon Basin sedimentary cores contain a tephra layer and deformed soft sediments that can be used to investigate volcanic and seismic events on the Korean Peninsula over the past 1.3 Ma.

The ring structure of Siljan, located in the central part of Sweden, is considered by many researchers to be a meteorite (impact) crater. Impact craters are among the most complex geological objects on the Earth. The origin and formation of these structures still raises many questions. To find answers to these questions we need reliable geological information about the structure of the crater and the composition of the rocks. Information about the thickness and geological structure of the Siljan Ring area sedimentary cover will help to understand the process of the Siljan Ring structure’s formation as well as other similar geological formations on the Earth. Here, we present the results of laboratory studies of sedimentary rock samples taken from four exploration wells drilled in the vicinity of the Siljan Ring crater, which made it possible to compile their detailed lithological description. The laboratory studies included a structural analysis of the samples, and a texture and mineralogical analysis in thin sections. A structure analysis was carried out visually, while structural and mineralogical analyses were carried out on thin sections using a polarizing microscope and a scanning electron microscope. The main components of the rocks (minerals and fragments), along with their ratio and secondary transformations, were determined. The results of the structural analysis of the samples, and the textural and mineralogical analysis of the rocks in thin sections, showed that the sediments’ composition in the sedimentary cover near the Siljan Ring structure changes in different areas in accordance with their facies and stratigraphic characteristics. Furthermore, a change in the thickness of the sections and the succession sequences of rock units was established. A change of this nature is presumably caused by tectonic disturbances of an endogenous or impact source.

The present work reports on the first evidence of a possible hypervelocity impact crater in the Sultanate of Oman. The impact origin of the structure is determined based on field observations, microscopic observations of shatter cones, planar fractures (PFs) and feather features (FFs) in quartz, calcite, and feldspar, and melt-bearing polymict breccias with various types of melts. The structure consists of an elliptical bowl-shaped ridge 750 m long and 550 m wide, oriented roughly north-northeast to south-southwest. The elliptical shape and relief asymmetry indicate an oblique collision. The precursor target lithologies include local late Proterozoic Masirah Bay siliciclastic formations, carbonate and acidic volcanic rocks of the late Precambrian Halfayn Formation, and basement rocks. The crater rim, up to 15–20 m above ground, is composed of quartzite, jasper, agate, monomict siliceous and hematite breccia, and metamorphosed shale (hornfels). An ejecta blanket composed of target rocks covers the floor, outer rim, and the area extending to the immediate northeast and east of the structure. Quaternary aeolian sand covers most of the crater surface, including the 1 to 2 m thick melt-rich polymict breccia found in the crater center. The planar fractures (PFs) and feather features (FFS) in quartz and feldspar suggest a low shock pressure between 5 and 14 GPa. Our observations are consistent with set criterions for impact crater identification, confirming the possible impact origin of the Mahout structure.

Lonar Impact Crater is a simple meteorite impact crater carved out on the ~ 65 Ma old Deccan tholeiitic flood basalts. The crater, though scoured in a basaltic terrain, is still preserved in its most pristine form, with a central crater lake. The geomorphology, geochemistry, geochronology, hydrology, geophysical parameters, and structural aspects of Lonar Crater have been explored in detail, but still continue to contribute valid scientific insights into the geology of terrestrial impact craters. Lonar serves as a potential analog site for studying impact cratering on planetary surfaces with basaltic terrains such as the Moon and Mars. Besides being a highly recognizable impact crater in India, the Lonar crater and its hinterland stand out with its archeological relevance and spiritual influence among the people. The numerous temples in and around the crater premises uphold the cultural significance of the region. The crater and adjacent areas are rich in flora and fauna representing a diverse ecosystem in the vastness of the arid Deccan Flood Basalts. Hence, the astrobleme and its surrounding is declared a Ramsar site and is also a protected wildlife sanctuary. The Indian Government has also declared the crater a National Geological Monument as well as an archaeological monument. Furthermore, the astrobleme is a unique site with socio-cultural and economic significance. With these plethoras of importance, combined with the geological and socio-cultural aspects in its hinterland, together with the most acclaimed UNESCO world heritage centers Ajantha and Ellora caves in the neighborhood, it stands as the right candidate for a UNESCO Global Geopark. However, the crater and its ecosystem are not preserved well enough, and the uniqueness of the crater is diminishing. But after selection as a Ramsar site, the area shows increased vegetation growth. The SWOT analysis conducted in this study accounts for Lonar Crater and its adjoining areas as a potential global geopark. Thus, through this study, we try to propagate the vivid and myriad importance of the Lonar crater and the necessity of protecting this geological monument from both anthropogenic and natural processes and to appraise the necessity for nominating this area as a UNESCO Global Geopark. [ABSTRACT FROM AUTHOR]

Taking the 260t BOF steelmaking process as the research object, it is of great significance to study the Gas-metal-slag interaction with oxygen lance. In this paper, a 3D mathematical model is established by using fluent. Through changing some physical parameters of lance height and slag, the impact depth, impact cavity area and energy transfer and flow are analyzed. The numerical results show that with the increase of lance height, the diameter of impact cavity in molten steel becomes larger, but the impact depth decreases. When the lance height is 32de, the area of high speed zone in the molten steel pool is the largest, the energy in oxygen jet is mostly dissipated in the process of reaching the slag level, and the kinetic energy obtained by the slag is only about 14% of the kinetic energy of molten steel. With the increase of slag thickness, the depth and area of the cavity decrease, and the flow of molten steel is restrained. The change of slag viscosity and slag density has little effect on the flow velocity. This study can provide reference and guidance for the regulation and control of the process parameters of converter refining. [ABSTRACT FROM AUTHOR]

Secondary craters (i.e., secondaries) formed by the landing of impact ejecta are an important crater population in planetary geology. Typical secondaries on planetary surfaces occur in chains and clusters, and they have irregular-shaped crater rims and/or floors. Background secondaries are a special type of secondaries that were formed by more-dispersed impact ejecta, and they have similarly circular morphology and dispersed spatial distribution with same-sized primary craters (i.e., primaries) that are formed by asteroids and comets. While individual background secondaries have been recognized at different planetary bodies, there is no reliable method to differentiate populations of background secondaries from those of primaries. In this work, we design a novel method to extract background secondaries based on multiscale and multifacies topography characteristics of impact craters. To characterize the complex topography fluctuations across continuous ejecta deposits of secondaries, we design a multiwavelet method to present their full-wavelength topography variations. Selecting three populations of secondaries formed by the Orientale basin and a population of primaries, we investigate and compare their crater interior slopes and roughness of continuous ejecta deposits, determining the threshold ranges that can differentiate background secondaries from same-sized and coeval primaries. The two sets of threshold values are then fused together to create a standard T-score terrain indicator, which are combined with our modeled theoretical spatial distribution of secondaries, and abundant previously unrecognized Orientale background secondaries were discovered. Our results demonstrate that the production of background secondaries is much more efficient than manifested by the observed spatial density of obvious secondaries in chains and clusters. This study establishes a promising method to detect populations of background secondaries, which can be extended further to smaller primary craters on various airless planetary bodies. [ABSTRACT FROM AUTHOR]

Models of near order of tektites-irgizites were built. The simulation relies on data of X-ray experiment. When constructing models, the maximum entropy and Warren–Finbuck methods were used. The near order parameters of the models are indicative of the highly disordered microstructure of tektite samples, as compared to that of crystalline counterparts and industrial glasses. [ABSTRACT FROM AUTHOR]

Abstract Hypervelocity impacts are among the fundamental phenomena occurring during the evolution of the solar system and are characterized by instantaneous ultrahigh pressure and temperature. Varied physicochemical changes have occurred in the building blocks of celestial bodies under such extreme conditions. The constituent material has transformed into a denser form, a high-pressure polymorph. The high-pressure polymorph is also thought to be the constituent of the deep Earth’s interior. Hence, experiments using a high-pressure and temperature generating apparatus have been conducted to clarify its crystal structure, pressure–temperature stability range, and transformation mechanisms. A natural high-pressure polymorph (mineral) is found from terrestrial and extraterrestrial rocks that experienced a hypervelocity impact. Mineralogists and planetary scientists have investigated high-pressure minerals in meteorites and rocks near terrestrial craters over a half-century. Here, we report brief reviews about the experiments producing high-pressure polymorphs and then summarize the research histories of high-pressure minerals occurring in shocked meteorites and rocks near terrestrial craters. Finally, some implications of high-pressure minerals found in impact-induced shocked rocks are also mentioned. Graphic abstract

The Nördlinger Ries (NR) impact crater in southern Germany contains Miocene lacustrine fine-grained post-impact sediments, which were deposited under saline, alkaline, and hydrologically closed aquatic conditions. To obtain information on the organic matter quantity, quality and environmental evolution, samples from one central (NR 1973) and one more marginal (Enkingen SUBO-18) well were analyzed by pyrolytic, organic geochemical and micro-petrographic techniques. Deposits of the marginal drilling can be linked to the thicker stratigraphic units of the well from the lake center based on total organic carbon (TOC), hydrogen index (HI) and lithology. Central deposits contain mainly hydrogen-rich type I kerogen with a mean HI of 447 mg HC/g TOC, whereas the marginal sequence contains type II-III kerogen with an average HI of 206 mg HC/g TOC. In the center, high total sulfur (TS) over TOC ratios of 1.5 on average, and δ13C values of biomarkers in combination with low α-/total MTTC (α-/total methyl-trimethyltridecyl chromans ∼

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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]

A new set of physical property measurements was undertaken on 29 peak‐ring samples from the IODP‐ICDP Expedition 364. Among the studied lithologies, the dominant one recovered in the peak ring consists of shocked granitoid rocks (19 samples). Porosity measurements with two independent methods (triple weight and 14C‐PMMA porosity mapping) concur and bring new observations on the intensity and distribution of fracturing and porosity in these shocked target rocks. Characterization of the porous network is taken a step further with two other independent methods (electrical and permeability measurements). Electrical properties such as the cementation exponent (1.59 < m < 1.87) and the formation factor (21 < F < 103) do not compare with other granites from the published literature; they point at a type of porosity closer to clastic sedimentary rocks than to crystalline rocks. Permeabilities of the granitoid rocks range from 0.1 to 7.1 mD under an effective pressure of ∼10 MPa. Unlike other fresh to deformed and altered granitoid rocks from the literature compared in this study, this permeability appears to be relatively insensitive to increasing stress (up to ∼40 MPa), with implications for the nature of the porous network, again, behaving more like cemented clastic rocks than fractured crystalline rocks. Other analyzed lithologies include suevite and impact melt rocks. Relatively low permeability (10−3 mD) measured in melt‐rich facies suggest that, at the matrix scale, these lithologies cutting through more permeable peak‐ring granitoid rocks may have been a barrier to fluid flow, with implications for hydrothermal systems. Plain Language Summary: Sixty‐six million years ago, a 10–15 km sized meteorite ended its trajectory on Earth. The resulting crater, Chicxulub, is still preserved to this day in Mexico. The impact had dramatic consequences on Earth's organisms. Drilled core samples from its peak ring help to better understand what are the physical mechanisms involved in such large impact events, on Earth and other planets. This study looks at how the rocks shocked during the impact have been affected, they consist principally of granites. Intact granites are crystalline rocks known to have low porosity (<2%), typically resulting from microscopic cracks. Granites recovered from the crater have higher porosities (∼10%) and are so densely cracked that they behave more like a sandstone than cracked crystalline rocks. This observation results from physical measurements, presented in this paper, that also suggested that fluid can flow relatively easily in these granites, with implications for hydrothermal systems and life in the aftermath of the impact. Key Points: Independant petrophysical measurements are used to caracterize the nature of the porosity in Chicxulub impact crater's peak ringShocked granites behave more like a cemented clastic rock than a fractured crystalline rockMatrix permeabilities of peak‐ring lithologies bring new insight on fluid flow in postimpact hydrothermal systems [ABSTRACT FROM AUTHOR]

Abstract We present the analysis of airborne and ground gamma-ray spectrometry signatures of the Araguainha impact structure, located in central Brazil, the largest impact structure in South America with ~ 40 km diameter. The airborne data are total gamma-ray counts per second collected along flight lines spaced 1 km apart. The ground gamma-ray data are concentrations of potassium, uranium, and thorium isotopes calculated from radiations measured in three individual channels. The objectives are to distinguish lithologies within the structure, which have naturally distinctive radiogenic signatures, and identify potential post-impact hydrothermal alteration zones, as indicated by high K concentrations. Based on results obtained by numerical modeling of the crater formation, we infer the locations of potential occurrences of target rocks that may have undergone hydrothermal alteration as a result of the impact. The deviations from the background potassium concentration show significant anomalous K values at the center and in the northwestern crater rim, where high concentrations of U are also observed. The numerical model shows that ideal temperature conditions for hydrothermal fluid circulation were attained right after pos-impact gravitational stabilization.

Abstract In the radargram obtained by the high-frequency lunar penetrating radar onboard the Chang’E-3 mission, we notice a potential subsurface cavity that has a smaller permittivity compared to the surrounding materials. The two-way travel time between the top and bottom boundaries of the potential cavity is ~ 21 ns, and the entire zone is located within the continuous ejecta deposits of the Ziwei crater, which generally have similar physical properties to typical lunar regolith. We carried out numerical simulations for electromagnetic wave propagation to investigate the nature of this low-permittivity zone. Assuming different shapes for this zone, a comprehensive comparison between our model results and the observed radargram suggests that the roof of this zone is convex and slightly inclined to the south. Modeling subsurface materials with different relative permittivities suggests that the low-permittivity zone is most likely formed due to a subsurface cavity. The maximum vertical dimension of this potential cavity is ~ 3.1 m. While the continuous ejecta deposits of Ziwei crater are largely composed of pre-impact regolith, competent mare basalts were also excavated, which is evident by the abundant meter-scale boulders on the wall and rim of Ziwei crater. We infer that the subsurface cavity is supported by excavated large boulders, which were stacked during the energetic emplacement of the continuous ejecta deposits. However, the exact geometry of this cavity (e.g., the width) cannot be constrained using the single two-dimensional radar profile. This discovery indicates that large voids formed during the emplacement of impact ejecta should be abundant on the Moon, which contributes to the high bulk porosity of the lunar shallow crust, as discovered by the GRAIL mission. Our results further suggest that ground penetrating radar is capable of detecting and deciphering subsurface cavities such as lava tubes, which can be applied in future lunar and deep space explorations. Subsurface cavities of the Moon are the ideal natural shelter for future lunar explorations since they provide ideal insulation from cosmic radiation, meteoroid impacts, temperature fluctuations, etc. In this paper, we first report that a potential subsurface cavity with a height of ~3.1 m is revealed by the lunar penetrating radar onboard Chang’E-3 Yutu Rover

Archaean granitoid gneisses and younger metadolerite and dolerite intrusions in a drill core from the late-Jurassic Morokweng impact structure, host mm- to m-wide aphanitic dykes that are spatially and geometrically associated with cataclasite-bearing reverse-slip faults. The dykes contain lithic and mineral clasts derived from their wallrocks. Petrographic and BSEM analysis indicates that the original dyke matrices are completely altered to a smectite-zeolite-magnetite paragenesis. However, a melt precursor is argued based on evidence for low-viscosity flow, high dyke aspect ratios and intrusive relationships into both the wallrocks and cataclasite, and the sharply contrasting matrix hydrothermal mineral grain size and textures relative to those found in the cataclasites. A subset of cm-wide pink-orange monomictic dykes have a felsic composition closely resembling their granitic wallrocks. More voluminous, polymictic, red dykes show compositions intermediate between the mafic and felsic wallrock endmembers in the drill core, which both occur in close proximity to the dykes. These hybrid compositions are interpreted to have developed either through mixing of mafic and felsic melts along faulted contacts between the doleritic and gneissic rocks, or by mechanical mixing, with or without assimilation, of a dolerite-derived melt with incohesive granitoid-derived cataclasite within the fault zones. The structural, petrographic and geochemical evidence support the dykes originating by friction melting (pseudotachylite, s.s.) caused by high-strain-rate faulting of the crater basement during the excavation and/or modification stages of the Morokweng impact, rather than by contamination of impact melt intrusions. Based on their spatial context relative to the impact melt sheet and the moderately high shock levels of their host rocks, these pseudotachylite dykes are interpreted as part of the parautochthonous peak ring of the Morokweng impact structure. • Aphanitic breccia dykes are linked to cataclastic reverse-slip faults. • Dykes are interpreted as pseudotachylite formed during the Morokweng impact. • Dykes are geochemically distinct from the Morokweng impact melt. • Melts were derived locally from granitoid and dolerite wallrocks. • Mingling of melt with incohesive cataclasite can explain variable dyke compositions. [ABSTRACT FROM AUTHOR]

The Aouelloul circular structure (Mauritania), 0.4 km in diameter, is a simple impact crater, which formed approximately 3 Myr ago. The Aouelloul crater was confirmed to be an impact crater based on the presence of an extraterrestrial component in glass fragments found around the crater, but so far, no convincing evidence of shock metamorphism in minerals, such as shocked quartz grains, is reported. The crater has been visited by a small number of geologists and limited information is available on deformations and impact-related effects at the macroscopic and microscopic scales. Detailed petrographic investigations of eight sandstone samples, all collected at the rim of Aouelloul during a 2019's field campaign, show that tectonic deformation lamellae occur in a number of quartz grains, but did not reveal any evidence of shock metamorphism. New observations on the distribution of the impact glass at the Aouelloul crater, exclusively located in the southern and eastern outer parts of the crater, suggest an oblique impact, from possible directions ranging from south-west to north (clockwise). Geological and lithostructural data are also presented and show that the rim of the crater is characterized by more or less disturbed metric to pluri-metric blocks of rocks showing fracturing and dipping toward either the interior or the exterior of the crater. This study confirms previous works conducted at the Aouelloul crater and illustrates the difficulty in demonstrating the impact origin of relatively small craters. • New petrological and structural data on Aouelloul a small impact crater of Mauritania. Distribution of impact glass suggests an oblique impact. [ABSTRACT FROM AUTHOR]

Impact craters with layered ejecta deposits are widespread on Mars. Prevailing views suggest that such ejecta were formed due to the involvement of target water and/or water ice in the impact excavation and/or the post-deposition movement of the impact ejecta. The long-runout landslides and lobate debris aprons that are likely formed due to the involvement of water ice are used as analogs to compare roughness at multiple scales, considering that these three landforms share some similarities in their geomorphology. Analog studies of the morphological similarities and differences of layered ejecta deposits with different emplacement mechanisms are an important approach to untangling how layered ejecta deposits might form on Mars and beyond. Earlier morphological comparisons were usually based on qualitative descriptions or one-dimensional topographic roughness characteristics at given azimuths; however, the emplacement processes of layered deposits are recorded in two-dimensional topography and at multiple scales. In this study, we designed a multiwavelet algorithm to characterize the multi-scale topographic roughness of different forms of Martian layered deposits. Our comparisons show that the inner facies of the layered ejecta deposits and long-runout landslides exhibited similar roughness characteristics, and the outer facies of the layered ejecta deposits were more similar in roughness to lobate debris aprons. This study highlights the importance of the spatial resolution of digital terrain models in characterizing fine topographic fluctuations on layered ejecta deposits, providing additional insights into the possible emplacement mechanisms of different parts of layered ejecta deposits.

Here we present a detailed accounting of organic microfossils from late Ediacaran sediments of Finland, from the island of Hailuoto (northwest Finnish coast), and the Saarijärvi meteorite impact structure (~170 km northeast of Hailuoto, mainland Finland). Fossils were recovered from fine-grained thermally immature mudstones and siltstones and are preserved in exquisite detail. The majority of recovered forms are sourced from filamentous prokaryotic and protistan-grade organisms forming interwoven microbial mats. Flattened Nostoc-ball-like masses of bundled Siphonophycus filaments are abundant, alongside Rugosoopsis and Palaeolyngbya of probable cyanobacterial origin. Acritarchs include Chuaria, Leiosphaeridia, Symplassosphaeridium and Synsphaeridium. Significantly, rare spine-shaped sclerites of bilaterian origin were recovered, providing new evidence for a nascent bilaterian fauna in the terminal Ediacaran. These findings offer a direct body-fossil insight into Ediacaran mat-forming microbial communities, and demonstrate that alongside trace fossils, detection of a bilaterian fauna prior to the Cambrian might also be sought among the emerging record of small carbonaceous fossils (SCFs). [ABSTRACT FROM AUTHOR]

The Chinese Chang'e-3 mission landed close to the eastern rim of the ~450 m diameter Ziwei crater. Regional stratigraphy of the landing site and impact excavation model suggest that the bulk continuous ejecta deposits of the Ziwei crater are composed by Erathothenian-aged mare basalts. Along the traverse of the Yutu rover, the western segment features a gentle topographic uplift (~0.5 m high over ~4 m), which is spatially connected with the structurally-uplifted crater rim. Assuming that this broad topographic uplift has physical properties discontinuous with materials below, we use data returned by the high-frequency lunar penetrating radar onboard the Yutu rover to estimate the possible range of relative permittivity for this topographic uplift. Only when the relative permittivity is ~9 is the observed radar reflection consistent with the observed topography, suggesting that the topographic uplift is composed of basaltic blocks that were excavated by the Ziwei crater. This result is consistent both with the impact excavation model that predicts deeper basaltic materials being deposited closer to the crater rim, and with observation of numerous half-buried boulders on the surface of this hill. We note that this study is the first to use topography and radargram data to estimate the relative permittivity of lunar surface uplifts, an approach that has had many successful applications on Mars. Similar approaches can apply other ground penetrating radar data for the Moon, such as will be available from the ongoing Chang'e-4 mission.

Hypervelocity impacts are among the fundamental phenomena occurring during the evolution of the solar system and are characterized by instantaneous ultrahigh pressure and temperature. Varied physicochemical changes have occurred in the building blocks of celestial bodies under such extreme conditions. The constituent material has transformed into a denser form, a high-pressure polymorph. The high-pressure polymorph is also thought to be the constituent of the deep Earth's interior. Hence, experiments using a high-pressure and temperature generating apparatus have been conducted to clarify its crystal structure, pressure–temperature stability range, and transformation mechanisms. A natural high-pressure polymorph (mineral) is found from terrestrial and extraterrestrial rocks that experienced a hypervelocity impact. Mineralogists and planetary scientists have investigated high-pressure minerals in meteorites and rocks near terrestrial craters over a half-century. Here, we report brief reviews about the experiments producing high-pressure polymorphs and then summarize the research histories of high-pressure minerals occurring in shocked meteorites and rocks near terrestrial craters. Finally, some implications of high-pressure minerals found in impact-induced shocked rocks are also mentioned. [ABSTRACT FROM AUTHOR]

Abstract—Modeling the relative motion of large crustal blocks vitally depends on an adequate description of the forces acting between the blocks. To describe motion at high strain rates, it proved necessary to assume a dry friction to depend on the shear strain rate and, in some cases, on the amplitude of fault side displacement. The best known examples of large-scale motions with dynamically decreasing friction are long-runout rock avalanches and gravity-driven collapsing of the transitional cavities of large impact craters. In this work, the experience is discussed of using the model of acoustic fluidization as a factor of a temporary decrease in friction to quantitatively simulate impact crater shape on the Earth and other planetary bodies. Immediate promising ways to find more adequate models are outlined. [ABSTRACT FROM AUTHOR]