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Author(s): H. J. Melosh (corresponding author) [1]; G. S. Collins [1, 2] [illus. 1] Meteor Crater in Arizona was the first terrestrial structure to be widely recognized as a meteorite [...]

Introduction: Allan Hills 84001 (ALH 84001) is an orthopyroxenite Martian meteorite containing coarse-grained inclusions of chromites, carbonates and plagioclase feldspar, in addition to fine-grained iron oxides and sulfides that host a heterogeneously oriented natural remanent magnetization (NRM) [1]-[4]. The meteorite contains several shockinduced textures and mineral thermometers indicative of one or more impact events. The NRM hosted in the iron oxides and chromite-sulfide assemblages within the meteorite is understood to be a thermoremanent magnetization (TRM) and has two strongly magnetized components that do not share common alignment, in addition to several incoherent, weakly magnetized grains, indicative of an underlying mechanism capable of localized (~200 nm) heating [5]. We have developed a methodology, using thermal constraints from paleomagnetism and petrologic observation, where we are able to place new constraints on the shock pressures associated with multiple impacts suffered by the meteorite up to and including its ejection from Mars. To reconcile the reported thermal histories of the meteorite, we have simulated planar shock wave propagation through computational analogs of two samples of ALH 84001. Modeling: Using the iSALE-2D shock physics code [6]-[8], we have performed a suite of 'mesoscale' simulations to quantify the effects of impact-induced shockwaves likely to have been experienced by the meteorite. The materials used in our simulations are each described by an equation of state and strength model. As the availability of accurate equations of state for meteoritic materials is limited, we have used the closest analog materials possible. Results: We found strong and complex material shear responsible for steep thermal gradients throughout the sample. Shearing occurs principally in the rock matrix, using the (weaker) inclusions as nucleation points (Fig. 1). We see both intraand inter-material variations in temperature on length scales of tens of microns. Subsequent modeling of post-impact thermal equilibration reveals that the constituent materials reach equilibrium ~3 seconds after the release wave has passed through the meteorite (Fig. 1). This has implications for paleomagnetism: small fractions of the meteorite may be remagnetized in low-pressure impacts, meaning the meteorite is capable of hosting NRMs recorded at different times. Implications for Paleomagnetism: Palaeomagnetic studies of this meteorite have found a heterogeneously oriented pattern of remanent magnetization, indicative of remagnetization in the meteorite on the sub-millimeter scale, but the mechanism for such heterogeneous heating was unclear. We observe that portions of chromite grains close to shear zones will experience temperatures significantly higher than those elsewhere in the meteorite which only warm up to the equilibrium temperature. Since the meteorite was magnetized in an initial extensive thermal event where the whole meteorite was heated above the curie point of the chromite-sulfide assemblages, our simulations suggest that a subsequent impact with a bulk shock pressure between 25-45 GPa would achieve partial remagnetization. [ABSTRACT FROM AUTHOR]

Introduction: Numerical simulations have made important contributions to our understanding of impact cratering and its products for more than fifty years. They provide our only means of replicating the impact process in regimes that cannot be accessed in a laboratory and complement and enhance experimental studies in more accessible cratering regimes. Simulations also provide a means of extrapolating between and beyond incomplete geological, geophysical and remote sensing observations. Here, I review advances in our understanding of the impact process driven by recent evolution and application of numerical impact simulations. Advances: The fundamental methods employed in most impact simulations to solve the differential equations that describe impact dynamics have not changed dramatically in thirty years. Instead, most scientific advances have come from three complementary directions: (1) improvements in material modelling; (2) increases in solution efficiency, resolution and dimensionality; (3) application of numerical modelling to new problems. Correctly describing the response of complex, heterogeneous geologic materials to the extreme forces of impact cratering continues to be the major challenge in impact modelling. Recent progress has focused on the interplay between deformation, fragmentation, strength and porosity. This has advanced our ability to predict geophysical anomalies [1], fracture patterns [2] and fragment size distributions [3] and the effects of layering [4]. Advances in our understanding of the thermodynamic response of rocks to planet-forming collisions have also been made [e.g., 5, 6], but their influence on the cratering process has yet to be explored. The inexorable increase in computer power, together with software optimized to exploit it, has allowed simulations with higher fidelity and longer time scales than ever before and allowed three-dimensional simulations of oblique impacts to become more routine. This has revealed new insight into previously inaccessible aspects of the impact process, such as jetting [7, 8] and high-speed ejection in oblique impacts [8], large-scale faulting in multi-ring basins [9] and asymmetric collapse of complex craters [10]. Many recent advances in our knowledge of the impact process, however, have come not from new models or increases in computer power, but simply from the novel application of existing tools to new problems or old problems with new insight. For example, simulations have revealed that shear heating rather than shock heating can be the dominant heating mechanism in low-velocity impacts [11] and that the thermal state of the target can have dramatic influence on the size and structure of large impact basins [12]. Simulations have provided new insight into the timing and orientation of structural deformation [13], the origin of large-scale faulting [9] and the influence of layering on crater morphology [14]. Simulations have also revealed the importance of ejecta-atmosphere interactions for the global transportation and deposition of dust following large impacts on Earth. Future perspective: Numerical modelling will remain a key pillar of impact research. In the coming years, ever increasing performance and availability of compute resources will make three-dimensional simulations of impact more common-place and allow different scales of deformation, currently studied independently [e.g., 15], to be connected and coupled. Accurate and realistic material models of a wider range of geological materials is desperately needed, especially fully coupled and consistent multi-phase equations of state [5]. I expect a growing focus on the environmental consequences of impact cratering, especially the interaction of ejecta with the atmosphere. Application of machine learning may also lead to a new breed of highly efficient surrogate impact models trained to emulate conventional but costly impact simulations. [ABSTRACT FROM AUTHOR]

Introduction: More than ~1000 newly formed impact features have been detected in images taken by orbiting spacecraft around Mars [1]. In recent months, several of these impacts were also detected seismically by the InSight seismometer [2]. Detailed characterization of the observed impact features [3, 4] has been used to calibrate a model of atmospheric disruption of meteoroids on Mars [5]. This paves the way for relating observed impact features to the properties of the impacting meteoroids. Here we use a Markov-Chain Monte Carlo (MCMC) approach to determine the statistical distribution of impactor parameters that are most likely to have formed recent impact craters and crater clusters observed on Mars that were also detected seismically. Our results inform interpretation of seismic wave signals generated by these impacts [2]. Methods: We simulate the formation of specific craters and clusters on Mars using an implementation of the Separate Fragments Model [SFM; 6, 7], calibrated by comparison with observed craters and clusters on Mars [5]. Crater sizes are predicted from fragment properties at the ground using p-group crater scaling relationships [8]. A MCMC approach is used to generate a statistical distribution of impact scenarios consistent with the observed feature. Given an observed crater or cluster of craters, we determine its characteristics B (e.g., size and number of craters). Using the SFM, together with knowledge about the variability of cluster characteristics, we compute the likelihood p(B|A) that an impact with parameters A (mass, velocity, etc.), produces a crater or cluster with the same characteristics B as the observed one. p(A) expresses our prior knowledge of impactor parameter probability. Then, with Bayes' theorem p(A|B) ? p(A)p(B|A), we can infer the likelihood of impact parameters A given the observations B. We employed the Metropolis-Hastings MCMC algorithm with Metropolis sampling, which assumes that there is no correlation between impactor parameters. Prior distributions of impactor mass [9], angle [10], velocity [11] and strength [5] were based on previous work. Impactor density and ablation parameter were held constant at representative values for stoney meteorites. We defined the likelihood p(B|A) to be the product of likelihoods for four cluster characteristics: effective diameter, number of craters, median separation distance between craters and the aspect ratio of the best-fit ellipse encompassing the craters. We assumed that all characteristics are log-normally distributed with the standard deviations based on observed cluster characteristics [4]. Because MCMC algorithms reach the desired distribution asymptotically, the first n samples were discarded. The distribution of remaining accepted samples defines the impactor parameters of maximum likelihood. Results: Impactor parameter likelihood distributions were determined for four impacts (two single craters and two clusters). One cluster-forming impact provides a particularly useful test of the approach as its highly elongated distribution of craters implies a shallow trajectory angle. The inferred trajectory is consistent with the interpreted ray paths of acoustic phases in the seismogram of the associated seismic event that were generated by the meteoroid's flight through the atmosphere [2]. The most likely pre-entry impactor mass informs comparison of the impact flux rate at the top of the atmosphere on Earth and Mars [5, 9]. The most likely impactor momentum at the ground provides a test of empirical relationships between seismic moment and impactor momentum [e.g., 12]. Acknowledgments: GSC and NW were funded by UK Space Agency grants ST/T002026/1 and ST/S001514/1. IJD was funded by NASA award 80NSSC20K0789. TN, KM and EKS were funded by the Australian Research Council (DE180100584, DP180100661 and DP200102073). [ABSTRACT FROM AUTHOR]

Introduction: The 2500-km diameter South Pole-Aitken (SPA) basin is the largest known impact structure in the Solar System, which dominates the topography, crustal structure, surface composition and subsurface density of the lunar farside and South Pole [1-3]. Numerical modeling of the formation of SPA could help constrain the thermal state of the Moon at the time of impact [4] and thereby illuminate the Moon's earliest bombardment history [5]. Numerical modeling can also predict the spatial distribution of ejecta, the depth from which mantle was exposed, and the fate of the impactor, which have implications for interpreting lunar compositional and geophysical anomalies [3, 6, 7]. Vertical-incidence simulations have previously investigated the influence of the near-surface thermal gradient on crater size [4]. SPA's elliptical planform and asymmetric surrounding topography, however, imply that the impact was oblique [1]. 3D models of SPA have included an oblique incidence angle [6, 7] but did not simulate until the final crater was formed, did not distinguish between different target layers, and did not consider different thermal profiles. Here we present results from new high-resolution 3D simulations of the formation of the SPA basin as an oblique impact. We investigate the effect of different thermal profiles, and of including compositionally distinct layers in the Moon and the impactor, on final crater structure, ejecta production and impactor fate. Modeling: The SPA impact was simulated using the iSALE3D shock physics code [8]. Two lunar thermal profiles were considered (a hot 50 K/km profile, and a colder 10 K/km profile). To produce similar sized transient craters, we used a velocity of 10 km/s with the hot profile and 15 km/s with the cold profile. For both scenarios, impacts were simulated with angles of 30‰ and 45‰. The 200-km diameter differentiated impactor consisted of an iron core (33% by mass) and a dunite mantle. The Moon consisted of a 350 km radius iron core, a dunite mantle and a 50 km granitic crust. All materials used ANEOS-derived equation of state tables [9-12] and strength models used by [4]. The mesh resolution was 5 km per cell (20 cells per impactor radius), equivalent to the resolution used in previous 2D SPA simulations [4] and 2-4 times higher than previous 3D SPA simulations [6, 7]. Lagrangian tracer particles tracked cratering motions. The landing positions of ejected tracers were determined using ballistic projection. Results: For the cold profile, transient crater diameters of 1050 and 920 km were formed for the 45‰ and 30‰, respectively, within the range considered by previous works [4, 6, 7]. For the hot profile, the transient diameters were 960 km and 860 km. The ellipticity (ratio of semimajor axis to semiminor axis) of the transient craters was ‰1.15 for both 45‰ simulations, similar to the ellipticity of the outer topography of the SPA basin (1.17), but not as elliptical as the inner ellipse (1.35) [1]. The transient craters from the 30‰ simulations have ellipticities in the range 1.2-1.3. The radius of the zone of excavated crust in the basin center was 470-540 km in the two cold-profile simulations, and 460 km in the 30‰, hot-profile simulation. These are consistent with the observed paucity of upper crustal material inside a radius of 630 km from the crater centre [13] and the size of the hole in lower crustal material predicted by [4] (500 km). However, the 45‰, hot profile simulation produced a region of excavated crust of 690 km, which was too large to match these observations. Ejected material was widely distributed across the lunar farside in all simulations, with some material reaching the nearside. In the 45‰ simulations mantle material was ejected from depths of 130-150 km. In the 30‰ simulations, much less mantle was excavated; the deepest material came from 80-90 km depth. Conclusions: High resolution, multi-material simulations of the SPA basin formation have shown that the spatial distribution and thickness of ejecta, the depth of excavated mantle and the amount of ejected projectile are all strongly dependent on the impact angle, impact velocity and target thermal profile. Comparisons with observational constraints on the spatial distribution and thickness of SPA ejecta [e.g. 14] will allow discrimination between impact scenarios. Acknowledgements: We thank the iSALE developers (isale-code.de), in particular Oskar Thoren, Lorenzo Paganelli and Athena Elafrou. TMD and GSC were funded by STFC grant ST/S000615/1. This work used the DiRAC Data Intensive service at Leicester, operated by University of Leicester IT Services, part of the STFC DiRAC HPC Facility (www.dirac.ac.uk). The equipment was funded by BEIS capital funding via STFC capital grants ST/K000373/1 and ST/R002363/1 and STFC DiRAC Operations grant ST/R001014/1. DiRAC is part of the National e-Infrastructure. [ABSTRACT FROM AUTHOR]

Introduction: Metal-rich asteroids are widely believed to be the exposed cores of differentiated planetesimals, although the process that leads to their formation is still not well understood. One of the leading hypotheses that explains an asteroid's rich metal composition supposes that most of the primitive crust and mantle of the differentiated progenitor body was stripped off by hit-and-run collisions, leaving behind a bare core [1]. However, these collisions are not able to strip off the entirety of the mantle, without disrupting the metallic core. Here we use numerical simulations to explore different formation scenarios for metal-rich asteroids. We also investigate the crater sizes and morphologies that may be found on such bodies today. Our results have important implications for the NASA's 'Psyche' mission at asteroid (16) Psyche [2]. Numerical Model: We use the iSALE-2D shock physics code [3, 4] to simulate high-velocity impacts into differentiated small bodies. iSALE-2D includes strength models suitable for impacts into geologic targets [5] and has been extensively validated against laboratory impact experiments [3], as well as benchmarked against other hydrocodes [6, 7]. We assume that the structure of a differentiated body has a layered configuration in which an olivine-rich mantle covers an iron core (e.g., [8]). Here we varied the mantle layer thickness between 10 and 50 km. Formation mechanism for metal-rich asteroids: We investigated impacts in the sub-catastrophic collision regime [9, 10] as a potential formation mechanism for metal-rich small bodies. Based on our results we propose a new mechanism of efficient mantle removal on small bodies, through such impacts (after the body already experienced hit-and-run collisions). Mantle material is removed by a process of back-side spallation with minimal loss of core material. According to our numerical simulations, we find that head-on sub-catastrophic collisions can remove up to 95% of the residual mantle material from mantle-poor differentiated asteroids. The specific impact energy required to remove a given fraction of the mantle is well fit by: Qcrit = agR3μg, where ag is a constant and μg is a coupling parameter to the target, in the gravity regime. Our proposed mechanism is applicable over a large range of scales, up to ≈ 1000 km. Previous studies of mantle-removing collisions have focused on much larger scales (e.g., [11, 12]). Crater sizes and morphologies on metal-rich asteroids today: Our numerical simulations of impacts less than a few km in diameter into Psyche-analogues show that craters on metal-rich asteroids can exhibit a variety of morphologies, depending on the surface material and asteroid structure [13]. For example, if Psyche's structure is homogeneous, then craters are expected to be simple, circular depressions. For iron targets, the craters exhibit tall curled rims, characteristic of impacts into ductile materials, and large depth-to-diameter ratios compared with craters in rocky targets. On the other hand, if Psyche has a layered structure, the craters could be concentric or have flat floors. Small craters, which are more susceptible to small scale variations in the target structure, can exhibit even more exotic morphologies. The morphologies of craters on Psyche today can be used to discriminate between different formation scenarios. Conclusions Our results suggest that metal-rich small bodies had a complicated evolutionary history and experienced more than one collision regime. We propose that sub-catastrophic, mantle-spalling impacts represent the missing link between the typical products of hit-and-run collisions and the observed metal-rich asteroids. Based on the crater morphologies on Psyche and together with our numerical simulations, we will be able to provide an insight into possible formation mechanisms for metal-rich asteroids. Acknowledgements: We gratefully acknowledge the developers of iSALE. This work has received funding from the UK's Science and Technology Facilities Council (STFC) (Grant ST/S000615/1) and from the European Union's Horizon 2020 research and innovation programme, under grant agreement No. 870377 (project NEO-MAPP). [ABSTRACT FROM AUTHOR]

Introduction: Carbonaceous chondrites (CCs) are among the most primitive Solar System objects on Earth. These meteorites are understood to have originated from undifferentiated planetesimals, meaning their unmelted and relatively unaltered nature since accretion has allowed them to retain a record of the earliest processes in the formation of the Solar System. Some CCs have been found to host an ancient natural remanent magnetization (NRM) that forms a planar magnetic fabric, suggesting the remanence was recorded during an impact-induced event [1]. Numerical modelling of impact compaction of chondritic meteorites has shown that low-intensity (<2 GPa) impacts into highly porous chondritic precursor material [2] can generate final states with crystallographic matrix fabric and porosities consistent with recovered chondrites [3]. Moreover, in such impacts, there is a strong thermal dichotomy, where the temperatures in the compacted porous matrix are far greater than the temperatures experienced by chondrules. This means that magnetic carriers present in the matrix could reach high enough temperatures and record a 'snapshot' of an ambient magnetic background field, such as the one that existed throughout the planet-forming regions of the Solar Nebula [1, 4]. Experiments: To determine whether the remanence hosted in chondrite matrix material can be recorded during an impact event, we developed shock recovery experiments with synthetic chondrites under controlled magnetic conditions. The light-gas gun experiments imparted a planar shockwave with a peak pressure around 1 GPa through synthetic analog chondritic precursor material in the presence of a magnetic field which we varied the strength of between 0-150 μT, in line with estimates of the strength of the Solar Nebula field [4]. The analog samples were a silica-magnetite-hematite powder mixture with a bulk porosity ~70%, consistent with chondrite precursor material [3]. Modeling: We used the iSALE-2D shock physics code [5, 6] to better understand the PT conditions experienced by the sample and capsule during our impact experiments. Compaction of matrix porosity was calculated using the ε-α porous-compaction model [6, 7]. Our iSALE simulations were also used to optimize the experimental parameters, predicting average peak temperatures of 390°C and an average peak pressure around 1.35 GPa, consistent with inferred impact compaction of carbonaceous chondrite Allende. Results: Our magnetic results were measured using an ORION sample magnetometer [8]. We have identified a strong NRM in our recovered samples. The thermal demagnetization profile (Fig. 1), reveals the remanence is a TRM with a broad peak, centered just below 400°C, consistent with the peak temperature predicted by the iSALE simulation of the experiment. We have also found a strong planar fabric, confirming the shock-induced origin of the NRM imparted onto the sample. [ABSTRACT FROM AUTHOR]

Introduction: Fusion crusts form during the atmospheric entry heating of meteorites and preserve a record of the conditions that occurred in the last few seconds of their deceleration in the atmosphere [1]. Although fusion crusts are ubiquitous they are rarely characterised and studied because they obscure the primary features of meteorites. Here we report the results of a study of the fusion crust of the Winchcombe CM2 chondrite. The Winchcombe meteorite fell at 21:54 hours on 28 February 2021 in Gloucestershire in the UK and was recovered over the next week. The fall was observed on UKFAll network cameras and recorded by CCTV. The meteoroid had a low entry velocity compared to other observed falls of 13.5 km/s. Study of the fusion crust reveals unique textural features that testify to previously unknown processes related to vigorous degassing of this intensely altered CM2 chondrite. Methods: Six polished blocks of Winchcombe were studied using backscattered electron imaging, elemental mapping, energy dispersive spectroscopy (EDS), electron backscatter diffraction (EBSD) and micro-X-ray fluorescence (XRF). Apparent size distributions and abundances were obtained by threshold analysis using ImageJ. Results: The fusion crust consists of an inner thermally altered substrate and outer melted crust. The altered substrate exhibits unusually abundant dehydration cracks extending up to 5 mm into the meteorite. The crack network encompasses fragments up to 70 μm in diameter (dense rock equivalent) with increasing abundance with decreasing size. Loss of sheet-like habits for phyllosilicates and tochilinite testifies to progressive dehydration towards the exterior. The outer melted crust has a vesicular porphyritic texture with olivine phenocrysts and magnetite in a glassy mesostasis. Grain-size and magnetite abundance increase outwards similar to other CI/CM2 fusion crusts [2]. High Ni (<80 wt%) sulphide-metal droplets occur - often as menisci on vesicles. A magnetite rim occurs on the exterior surface and some vesicles, and include some tabular, rim-parallel magnetite crystals. Unique features in the fusion crust are oscillatory zoned olivine crystals, monolayers of magnetite and silicate warts. Monolayers form chains of magnetite crystals within the mesostasis that have tabular crystals similar to magnetite rims. EBSD data reveals [111] is parallel to the length of tabular crystals and is layer parallel in rims and monolayers. Oscillatory zoned crystals are equant with up to 4 Mg-rich zones. Silicate warts form lenticular features on the surface of the fusion crust and contain dendritic olivine - their compositions are, however, similar to the rest of the crust. Magnetite monolayers lie between warts and the underlying crust. Discussion: The unusualy high abundance of dehydration cracks suggests the tochlinite-rich matrix of the Winchcombe meteorite is particularly sensitive to dehydration, owing to the low decomposition temperature of this mineral (250oC [3]). Mechanical failure of the substrate, in part driven by gas pressure, is likely to inject large abundances of particulates into the meteoroid gas stream. Observations of episodic pulsed plasma in the trail of the fireball may be a phenomena associated with calving of the dehydrated substrate and generate thermal pulses explaining the presence of oscillatory zoning. Other features also are consistent with vigorous degassing. Magnetite monolayers appear to have formed as surface magnetite rims - owing to their similar alignment of tabular crystals. Trapping of surface magneite rims through collapse of melt protrusions is likely to explain how these layers become buried within the crust and is probably driven by perturbation of surface melt by rapid vesicle loss. Finally, silicate warts are likely to be droplets attached to the crust surface. Their dendritic textures suggest higher peak temperatures and strongly suggest they represent droplets removed from other stones in the shower. Warts represent the first discovery of intershower transport of ablation materials, possibly owing to enhanced ablation as a result of vigorous degassing. Implications: The fusion crust of the Winchcombe meteorite illustrates the complexity of processes affecting meteorites during atmospheric flight. Features such as magnetite monolayers and silicate warts have not previously been described, and may be unique to tochlinite-rich CM2 chondrites, which experience vigorous degassing. They may also allow ablation debris to be related to particular types of meteorite, thus providing a distributed record of the meteorite flux. Winchcombe underlines the utility of fusion crust, which should be routinely characterised in addition to meteorite interiors. [ABSTRACT FROM AUTHOR]

Small-scale experiments of volcanic ash particle settling in water have demonstrated that ash particles can either settle slowly and individually, or rapidly and collectively as a gravitationally unstable ash-laden plume. This has important implications for the emplacement of tephra deposits on the seabed. Numerical modelling has the potential to extend the results of laboratory experiments to larger scales and explore the conditions under which plumes may form and persist, but many existing models are computationally restricted by the fixed mesh approaches that they employ. In contrast, this paper presents a new multiphase flow model that uses an adaptive unstructured mesh approach. As a simulation progresses, the mesh is optimized to focus numerical resolution in areas important to the dynamics and decrease it where it is not needed, thereby potentially reducing computational requirements. Model verification is performed using the method of manufactured solutions, which shows the correct solution convergence rates. Model validation and application considers 2-D simulations of plume formation in a water tank which replicate published laboratory experiments. The numerically predicted settling velocities for both individual particles and plumes, as well as instability behaviour, agree well with experimental data and observations. Plume settling is clearly hindered by the presence of a salinity gradient, and its influence must therefore be taken into account when considering particles in bodies of saline water. Furthermore, individual particles settle in the laminar flow regime while plume settling is shown (by plume Reynolds numbers greater than unity) to be in the turbulent flow regime, which has a significant impact on entrainment and settling rates. Mesh adaptivity maintains solution accuracy while providing a substantial reduction in computational requirements when compared to the same simulation performed using a fixed mesh, highlighting the benefits of an adaptive unstructured mesh approach. [ABSTRACT FROM AUTHOR]

This spatial bias is presumably a consequence of the detection method, which relies on 6 m/px CTX images to find extended "blast zones" around new craters, where the surface has been disturbed out to 10s of crater radii [13]. [Extracted from the article]

In this study we use micromagnetic modeling to show that the magnetizations of magnetically single‐vortex particles rotate toward the stress axis on the application of a differential compression stress. This is the exact opposite response to magnetically single‐domain particles, which previously provided the theoretical underpinning of the effect of stress on the magnetic signals of rocks. We show that the magnetization directions of single‐vortex and equant single‐domain particles are altered by much lower stresses than previously predicted, c.f., 100 versus 1,000 MPa; where a change in magnetization is defined as a rotation of >3° after the removal of stress. The magnetization intensity of assemblages also drops by ∼20%–30% on the application and removal of stress of ∼100 MPa. Given that single‐vortex particles are now thought to dominate the magnetization of most rocks, future studies should account for paleomagnetic directional uncertainties and potential underestimation of the ancient magnetic field intensity. Plain Language Summary: Magnetic minerals in rocks can record and retain magnetic information for millions of years. This magnetic information helps us to understand processes like plate tectonics and geomagnetic field behavior in the past. When rocks experience compressional forces, these affect the magnetization of the magnetic minerals within them, potentially altering this magnetic information. Previous theoretical studies of the affect of stress on magnetization used analytical theory, and predicted that stresses of >1,000 MPa are required to alter a rock's otherwise stable magnetization. We show that much lower stresses of only ∼100 MPa are required to compromise magnetic recordings in rocks. The reason for this is a change in our understanding of rock magnetic systems. Previous analytical models were for elongated particles <100 nm in size, as these were thought to be the primary carriers of stable magnetization in minerals. We now know that larger particles can retain stable magnetic recordings to high temperatures over geological time. This study shows that the magnetization of these particles are less stable than smaller particles when stresses are applied. This suggests that common geological processes such earthquakes might provide sufficient near‐surface stress to remagnetize rocks close to the fault zone, leading to a paleo‐stress recording. Key Points: Single‐vortex particles' net magnetization rotates toward the compression axis when subjected to differential stressSingle‐vortex particles display the opposite response to compressional stress compared to single‐domain particlesStress fields of only ∼100 MPa are required to alter paleomagnetic signals, lower than previously predicted [ABSTRACT FROM AUTHOR]

Two ’130-meter-diameter impact craters formed on Mars during the later half of 2021. These are the two largest fresh impact craters discovered by the Mars Reconnaissance Orbiter since operations started 16 years ago. The impacts created two of the largest seismic events (magnitudes greater than 4) recorded by InSight during its 3-year mission. The combination of orbital imagery and seismic ground motion enables the investigation of subsurface and atmospheric energy partitioning of the impact process on a planet with a thin atmosphere and the first direct test of martian deep-interior seismic models with known event distances. The impact at 35°N excavated blocks of water ice, which is the lowest latitude at which ice has been directly observed on Mars. [ABSTRACT FROM AUTHOR]

The Allende meteorite, a relatively unaltered member of the CV carbonaceous chondrite group, contains primitive crystallographic textures that can inform our understanding of early Solar System planetary compaction. To test between models of porosity reduction on the CV parent body, complex microstructures within ~0.5-mm-diameter chondrules and ~10-µm-long matrix olivine grains were analyzed by electron backscatter diffraction (EBSD) techniques. The large area map presented is one of the most extensive EBSD maps to have been collected in application to extraterrestrial materials. Chondrule margins preferentially exhibit limited intragrain crystallographic misorientation due to localized crystal-plastic deformation. Crystallographic preferred orientations (CPOs) preserved by matrix olivine grains are strongly coupled to grain shape, most pronounced in shortest dimension , yet are locally variable in orientation and strength. Lithostatic pressure within plausible chondritic model asteroids is not sufficient to drive compaction or create the observed microstructures if the aggregate was cold. Significant local variability in the orientation and intensity of compaction is also inconsistent with a global process. Detailed microstructures indicative of crystal-plastic deformation are consistent with brief heating events that were small in magnitude. When combined with a lack of sintered grains and the spatially heterogeneous CPO, ubiquitous hot isostatic pressing is unlikely to be responsible. Furthermore, Allende is the most metamorphosed CV chondrite, so if sintering occurred at all on the CV parent body it would be evident here. We conclude that the crystallographic textures observed reflect impact compaction and indicate shock-wave directionality. We therefore present some of the first significant evidence for shock compaction of the CV parent body. [ABSTRACT FROM AUTHOR]

In recent years, one of the most important factors for success among baseball pitchers is fastball velocity. The purpose of this study was to (1) to develop statistical and machine learning models of fastball velocity, (2) to identify the strongest predictors of fastball velocity, and (3) to compare the models' prediction performances. Three dimensional biomechanical analyses were performed on high school (n = 165) and college (n = 62) baseball pitchers. A total of 16 kinetic and kinematic predictors from the entire pitching sequence were included in regression and machine learning models. All models were internally validated through ten-fold cross-validation. Model performance was evaluated through root mean square error (RMSE) and calibration with 95% confidence intervals. Gradient boosting machines demonstrated the best prediction performance [RMSE: 0.34; Calibration: 1.00 (95% CI: 0.999, 1.001)], while regression demonstrated the greatest prediction error [RMSE: 2.49; Calibration: 1.00 (95% CI: 0.85, 1.15)]. Maximum elbow extension velocity (relative influence: 19.3%), maximum humeral rotation velocity (9.6%), maximum lead leg ground reaction force resultant (9.1%), trunk forward flexion at release (7.9%), time difference of maximum pelvis rotation velocity and maximum trunk rotation velocity (7.8%) demonstrated the greatest influence on pitch velocity. Gradient boosting machines demonstrated better calibration and reduced RMSE compared to regression. The influence of lead leg ground reaction force resultant and trunk and arm kinematics on pitch velocity demonstrates the interdependent relationship of the entire kinetic chain during the pitching motion. Coaches, players, and performance professionals should focus on the identified metrics when designing pitch velocity improvement programs., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

The environmental severity of large impacts on Earth is influenced by their impact trajectory. Impact direction and angle to the target plane affect the volume and depth of origin of vaporized target, as well as the trajectories of ejected material. The asteroid impact that formed the 66 Ma Chicxulub crater had a profound and catastrophic effect on Earth's environment, but the impact trajectory is debated. Here we show that impact angle and direction can be diagnosed by asymmetries in the subsurface structure of the Chicxulub crater. Comparison of 3D numerical simulations of Chicxulub-scale impacts with geophysical observations suggests that the Chicxulub crater was formed by a steeply-inclined (45-60° to horizontal) impact from the northeast; several lines of evidence rule out a low angle (<30°) impact. A steeply-inclined impact produces a nearly symmetric distribution of ejected rock and releases more climate-changing gases per impactor mass than either a very shallow or near-vertical impact.

Type 2 diabetes mellitus (T2DM) is associated with an excess risk of fractures and overall mortality. This study compared hip fracture and post-hip fracture mortality in T2DM and non-diabetic subjects. The salient findings are that subjects in T2DM are at higher risk of dying after suffering a hip fracture., Introduction: Previous research suggests that individuals with T2DM are at an excess risk of both fractures and overall mortality, but their combined effect is unknown. Using multi-state cohort analyses, we estimate the association between T2DM and the transition to hip fracture, post-hip fracture mortality, and hip fracture-free all-cause death., Methods: Population-based cohort from Catalonia, Spain, including all individuals aged 65 to 80 years with a recorded diagnosis of T2DM on 1 January 2006; and non-T2DM matched (up to 2:1) by year of birth, gender, and primary care practice., Results: A total of 44,802 T2DM and 81,233 matched controls (53% women, mean age 72 years old) were followed for a median of 8 years: 23,818 died without fracturing and 3317 broke a hip, of whom 838 subsequently died. Adjusted HRs for hip fracture-free mortality were 1.32 (95% CI 1.28 to 1.37) for men and 1.72 (95% CI 1.65 to 1.79) for women. HRs for hip fracture were 1.24 (95% CI 1.08 to 1.43) and 1.48 (95% CI 1.36 to 1.60), whilst HRs for post-hip fracture mortality were 1.28 (95% CI 1.02 to 1.60) and 1.57 (95% CI 1.31 to 1.88) in men and women, respectively., Conclusion: T2DM individuals are at increased risk of hip fracture, post-hip fracture mortality, and hip fracture-free death. After adjustment, T2DM men were at a 28% higher risk of dying after suffering a hip fracture and women had 57% excess risk of post-hip fracture mortality.

Background: Comparisons between disease activity indices for ulcerative colitis (UC) are few. This study evaluates three indices, to determine the potential impact of inter-observer variation on clinical trial recruitment or outcome as well as their clinical relevance., Methods: One hundred patients with UC were prospectively evaluated, each by four specialists, followed by videosigmoidoscopy, which was later scored by each specialist. The Simple Clinical Colitis Activity (SCCAI), Mayo Clinic and Seo indices were compared by assigning a disease activity category from published thresholds for remission, mild, moderate and severe activity. Inter-observer variation was evaluated using Kappa statistics and its effect for each patient on recruitment and outcome measures for representative clinical trials calculated. Clinical relevance was assessed by comparing an independently assigned clinical category, taking all information into account as if in clinic, with the disease activity assigned by the indices., Results: Inter-observer agreement for SCCAI (κ=0.75, 95% CI 0.70-0.81), Mayo Clinic (κ=0.72, 95% CI 0.67-0.78) and Seo (κ=0.89, 95% CI 0.83-0.95) indices was good or very good as was the agreement for rectal bleeding (κ=0.77) and stool frequency (κ=0.90). Endoscopy in the Mayo Clinic index had the greatest variation (κ=0.38). Inter-observer variation alone would have excluded up to 1 in 5 patients from recruitment or remission criteria in representative trials. Categorisation by the SCCAI, Mayo Clinic and Seo indices agreed with the independently assigned clinical category in 61%, 67% and 47% of cases respectively., Conclusions: Trial recruitment and outcome measures are affected by inter-observer variation in UC activity indices, and endoscopic scoring was the component most susceptible to variation., (© 2013.)

Graphical methods are becoming increasingly used to monitor adverse outcomes from surgical interventions. However, uptake of such methods has largely been in the area of cardiothoracic surgery or in transplants with relatively little impact made in surgical oncology. A number of the more commonly used graphical methods including the Cumulative Mortality plot, Variable Life-Adjusted Display, Cumulative Sum (CUSUM) and funnel plots will be described. Accounting for heterogeneity in case-mix will be discussed and how ignoring case-mix can have considerable consequences. All methods will be illustrated using data from the Scottish Audit of Gastro-Oesophageal Cancer services (SAGOCS) data set., (Copyright © 2010 Elsevier Ltd. All rights reserved.)