Crater Formation Research Articles

Gas Emission and Formation of Craters in the Arctic Permafrost Synopsis

This Special Issue of Geosciences is a collection of twelve research and overview papers devoted to shallow Arctic permafrost as a natural reservoir that stores large amounts of bound gas, mainly methane [...]

Silicon ablation in air by mono- and bichromatic laser pulses with wavelength 355 and 532 nm

Ablation of silicon sample in air under irradiance of single anddouble laser pulses with wavelengths 355 and 532 nm was studied by means ofoptical and scanning electron microscopy, raman spectroscopy, profilometryof laser craters as well as video registration of plasma's plume radiationin time. Dependence of specific sample's material removal on laser fluenceand time interval between coupled pulses of bichromatic laser irradiance wasestablished. Spallation of silicon was found in broad range of irradianceparameters and parameters of craters formed by ablation and spallation underthe action of bichromatic laser radiation were determined. Keywords: nanosecond laser ablation, specific mass removal, surface modification, laser plasma dynamics, crater formation, spallation\

Groove formation on Phobos from reimpacting orbital ejecta of the Stickney crater

Numerous linear grooves have long been recognized as covering the surface of Phobos, but the mechanisms of their formation are still unclear. One possible mechanism is related to the largest crater on Phobos, the Stickney crater, whose impact ejecta may slide, roll, bounce, and engrave groove-like features on Phobos. When the launch velocity is higher than the escape velocity, the impact ejecta can escape Phobos. A portion of these high-velocity ejecta are dragged by the gravitational force of Mars, fall back, and reimpact Phobos. In this research, we numerically test the hypothesis that the orbital ejecta of the Stickney crater that reimpact Phobos could be responsible for a particular subset of the observed grooves on Phobos. We adopt impact hydrocode iSALE-2D (impact-Simplified Arbitrary Lagrangian Eulerian, two-dimensional) to simulate the formation of the Stickney crater and track its impact ejecta, with a focus on orbital ejecta with launch velocities greater than the escape velocity of Phobos. The launch velocity distribution of the ejecta particles is then used to calculate their trajectories in space and determine their fates. For orbital ejecta reimpacting Phobos, we then apply the sliding boulder model to calculate the ejecta paths, which are compared with the observed groove distribution and length to search for causal relationships. Our ejecta trajectory calculations suggest that only ~1% of the orbital ejecta from the Stickney crater can reimpact Phobos. Applying the sliding boulder model, we predict ejecta sliding paths of 9−20 km in a westward direction to the east of the zone of avoidance, closely matching the observed grooves in that region. The best-fit model assumes an ejecta radius of ~150 m and a speed restitution coefficient of 0.3, consistent with the expected ejecta and regolith properties. Our calculations thus suggest the groove class located to the east of the zone of avoidance may have been caused by reimpact orbital ejecta from the Stickney crater.

ЭМИССИЯ ПАРНИКОВЫХ ГАЗОВ, ГЛОБАЛЬНОЕ ПОТЕПЛЕНИЕ И НЕФТЕГАЗОВАЯ ОТРАСЛЬ РОССИИ

Due to global climate change, the degradation of permafrost rocks has intensified, threats of large-scale damage and destruction of various objects in cities and towns, as well as the infrastructure of oil and gas fields, have arisen and are expanding in the territorial plan. The necessity of expanding the study, forecasting and reducing the threats of exogenous and dangerous endogenous geological processes and phenomenon, among which powerful blowouts, self-ignition and explosions of gas with the formation of giant craters, stand out is substantiated. The importance of developing domestic technical means and technologies for complex monitoring of dangerous phenomenon was noted. It is shown that despite the adopted legislative acts, the share of associated petroleum gas utilization is decreasing. New threats to the national security of the country are analyzed.

Multiobjective Optimization of EDM Parameters for Rice Husk Ash/Cu/Mg‐Reinforced Hybrid Al‐0.7Fe‐0.6Si‐0.375Cr‐0.25Zn Metal Matrix Nanocomposites for Engineering Applications: Fabrication and Morphological Analysis

The advanced class of Al/(RHA+Mg+Cu) hybrid metal matrix nanocomposites (MMNCs) has exhibited superior physical, and mechanical properties with superior wettability and chemical compatibility. This work has also been reported on the machining and multiobjective optimization of process variables for the machining of Al/(RHA+Mg+Cu) hybrid MMNCs on EDM using L27 Taguchi’s orthogonal array integrated with Grey rational analysis (GRA). The primarily target goal of this study is to produce nanocomposite having better properties with minimal production cost, with the use of reinforcement rice husk ash (RHA). RHA is utilized in the base matrix of Al 6061 at wt.% of 6, 8, and 10. On the other hand, the elements such as Cu and Mg are placed fixed, i.e., 3 wt.% and 1 wt.%, respectively. The hardness, tensile strength, and impact strength of the nanocomposites increased with the maximum increment of 35.11%, 15.76%, and 16.67%, respectively, as compared to neat composite. Further, the purpose of this investigation was to determine the effect of various factors such as the percentage of RHA in the workpiece electrode (W), the discharge current (I), the voltage (V), the duty factor (τ), the pulse‐on time (Ton), and the flushing pressure (P) on the material removal rate (MRR), the surface roughness (SR), and the tool wear rate (TWR) during the machining of hybrid nanocomposites using Taguchi’s approach. The results revealed that MRR decreased with increasing the RHA content in the workpiece which can be reasoned to isolating nature of the RHA. It clearly shows that SR has decreased with an addition of RHA content from 6 wt.% to 8 wt.% in workpiece, but it slightly increased by further addition of RHA from 8 wt.% to 10 wt.%. SR has decreased with an increase in duty factor while performing EDM trials with the copper electrode, but it slightly increases with a further increase in duty factor. By the increase in pulse‐on time, spark energy also increases also leading to the formation of craters. Therefore, SR has increased with an increase in pulse‐on time. The TWR has increased with an increase in RHA content in the workpiece, because of the existence of hard reinforcements on the matrix which causes larger wear in the tool. Analysis of SEM micrographs showed the presence of voids, shallow and deep craters, and black voids on the machined surface of the fabricated hybrid nanocomposites. As calculated using the response graph for GRG, confirmation tests for optimal parametric setting show improvement over initial parametric setting of machining parameters. The mean of optimal MRR, SR, and TWR is estimated at the significant level of machining factors at A1B3C3D2E3F1, A2B1C1D2E1F3, and A1B1C1D1E1F3, respectively.

Влияние мощного импульсного ионного пучка на топографию поверхности вольфрама

The tungsten surface was processed by high power pulsed ion beam at the TEMP accelerator (Cn+ ions, accelerating voltage 200 ± 10 kV, energy density of a single pulse 2.6 – 3.0 J/cm2). Changes in the relief and structure of the surface of tungsten samples were studied by scanning electron microscopy. After treatment with a powerful pulsed ion beam (MIIP), defects in the form of craters form on the surface of tungsten. The number of craters decreases with an increase in the number of impact pulses. After exposure to 3 pulses, microcraters are forms in the surface layer along the grain boundaries. After 10 pulses, there are practically no cracks on the irradiated surface. An increase in the number of pulses leads to the formation of a more equiaxed ultrafine-grained structure in the near-surface layer of tungsten.

Single crater dimensions and wire diameter influence on Wire-EDM

In Wire Electrical Discharge Machining (WEDM) the erosion process is based on the superposition of craters. The plasma channel and the craters’ shape have an impact on the process and on the characteristics of the machined surface. This impact goes from the cutting speed to the surface roughness passing through workpiece temperature gradient during the spark. Several models simulate the crater formation through thermal analysis, yielding symmetrical shapes. Commonly non-homogeneous and random aspects in the dielectric and the electrode geometry are neglected. Such features introduce an asymmetric aspect to the crater shape. To investigate the influence of the tool electrode geometry on the craters’ shape, single craters on steel are produced at different pulse energy levels and with three different wire diameters 0.20mm, 0.25mm and 0.30mm. An optical microscope is used to map the single craters’ topography and subsequently extract their dimensions. The single craters’ lengths and aspect ratio are analyzed. In the lower energy range the random aspects dominate the crater shape, the craters are smaller and rounder. Higher energy pulses create consistently bigger and elongated craters. The aspect ratio depends on the wire geometry, thinner wires produce more elongated craters. This behavior reinforces the idea that from a certain energy level on the tool geometry effects overcome the random aspect of the process, generating elongated craters.

Reinforcement of ultrahigh thermoresistant polybenzimidazole films by hard craters

Ultrahigh thermoresistant polybenzimidazole films with uniform pores and hard craters on the surface were prepared by a silica template method. The pore and crater formation enhanced elongation and Young's modulus.

Gamma-ray spectrometry of the Araguainha impact structure, Brazil: Additional insights into element mobilization due to hydrothermal alteration.

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.

Comprehensive ablation study of near-IR femtosecond laser action on the titanium-based alloy Ti6Al4V: morphological effects and surface structures at low and high fluences

The surface of a titanium-based alloy Ti6Al4V was subjected to modifications by a near-IR femtosecond Ti:Sapphire laser, emitting at 775 nm pulses of 200 fs duration, in single-pulse and multi-pulse regimes, with up to 400 accumulated pulses, and pulse energies ranging from 2.5 to 250 upmu J. The whole range of induced effects is presented, from gentle ablation and pattern occurrence to substantial crater formation. Very observable laser-induced parallel periodic surface structures are reported, appearing both within the damage spot area, with low fluences, and at the peripheries of the craters, with higher fluences—but also on crater walls, and inside the crater structures. Damage threshold fluences ({F}_{mathrm{th}}) and the incubation factor (zeta ) were also determined.Graphic abstract

Numerical modeling of crater formation during electrical discharge machining of closed cell titanium foam

In this paper, the electrical discharge machining (EDM) is utilized to machine closed cell titanium foam using pure brass tool electrode. Discharge time, current and discharge voltage were taken as input factors. By varying these input factors discharge energy (E) alters. Hence, the effect of E on crater diameter is studied. A numerical simulation model using finite element analysis is developed to forecast the diameter of crater. Scanning electron microscope images were used to measure the experimentally formed crater. The crater diameter grows with the rise in E. The proposed numerical model is in good agreement with experimental results at low discharge energy and over predicts at higher discharge energy. The proposed model forecasts crater diameter with overall error of 5.57%.

Meteorite impact craters as hotspots for mineral resources and energy fuels: A global review

The ever-increasing recovery rate of natural resources from terrestrial impact craters over the last few decades across the globe offers new avenues for further exploration of mineral and hydrocarbon resources in such settings. As of today, 60 of the 208 terrestrial craters have been identified to host diverse resources such as hydrocarbons, metals and construction materials. The potential of craters as plausible resource contributors to the energy sector is therefore, worthy of consideration, as 42 (70%) of the 60 craters host energy resources such as oil, gas, coal, uranium, mercury, critical and major minerals as well as hydropower resources. Among others, 19 craters are of well-developed hydrocarbon reserves. Mineral deposits associated with craters are also classified similar to other mineral resources such as progenetic, syngenetic and epigenetic sources. Of these, the progenetic and syngenetic mineralization are confined to the early and late excavation stage of impact crater evolution, respectively, whereas epigenetic deposits are formed during and after the modification stage of crater formation. Thus, progenetic and syngenetic mineral deposits (like Fe, Ni, Pb, Zn and Cu) associated with craters are formed as a direct result of the impact event, whereas epigenetic deposits (e.g. hydrocarbon) are hosted by the impact structure and result from post-impact processes. In the progenetic and syngenetic deposits, the shock-wave induced fracturing and melting aid the formation of deposits, whereas in the epigenetic deposits, the highly fractured lithostratigraphic units of higher porosity and permeability, like the central elevated area (CEA) or the rim, act as traps. In this review, we provide a holistic view of the mineral and energy resources associated with impact craters, and use some of the remote sensing techniques to identify the mineral deposits as supplemented by a schematic model of the types of deposits formed during cratering process.

The role of target strength on the ejection of martian meteorites

Our collection of meteorites recovered here on Earth contain over 200 samples believed to have originated on Mars. It is commonly accepted that these rocks were launched as ejecta during the formation of impact craters. The majority of the meteorites are young and basaltic representing only a small fraction of the martian surface. Previous studies have only examined impacts into basalt or other competent material, but the material bias remains unexplained. In this study we define fragmentation parameters for dry tuff, a proxy for the weakly cemented regolith and sedimentary material covering much of Mars. We simulate hypervelocity impacts into the martian surface using a joint Eulerian-Lagrangian shock physics code. A wide parameter search is conducted over impactor sizes ranging from 10 meter to 10 kilometers in radius. We find that dry tuff produces significantly smaller fragments than basalt for all impactor sizes. Maximum fragment size and amount of material ejected scale with impactor size. We also examine impacts into mixed targets, mainly simple layers and embedded boulders. We find that a layer of basalt overtop dry tuff inhibits ejection, while a layer of tuff overtop basalt enhances ejection and increases dry tuff fragment sizes. Boulders create a complex pressure field in the near-surface region, but fragment sizes are relatively unchanged.

A young age of formation of Rheasilvia basin on Vesta from floor deformation patterns and crater counts

AbstractDelivery of significant volumes of howardite–eucrite–diogenite (HED) meteorites from Vesta to Earth is linked to the largest impact events on that protoplanet, especially the giant Rheasilvia basin. Dawn mapping of Rheasilvia reveals a well‐preserved impact structure with extensive deformation patterns and moderate superposed cratering. Spiral and radial deformation features across the floor of Rheasilvia are also common to complex craters on Ceres and icy satellites, as well as larger bodies like the Moon, Mars, and Mercury, when floor units are not buried by impact melt and debris. These deformation features predate the solidification of such melt/debris mixtures and are important structural elements in complex craters related to failure in converging floor material during late stages of crater formation. The similarity and commonality of such features and lack of preserved ancient units within Rheasilvia indicate that these patterns formed during the latter stages of the impact event and that the original basin floor and subsequent cratering record are preserved. Updated counts and interpretation of this observed superposed cratering indicate an ~0.8–0.9 Ga age of basin formation, supporting a young impact and ejection age. This young age is consistent with recent Ar‐Ar ages of feldspar grains in HED (Lindsay et al., 2015), and it may also be consistent with ancient bulk Ar‐Ar ages (>~3.2 Ga) for some HEDs because resetting such ages requires prolonged heating from the residual impact heating of rocks left on Vesta during earlier impacts. The complex morphology and recent formation of Rheasilvia basin are also consistent with dynamical estimates for delivery of these meteorites to the Earth–Moon system.

The significance of the 1971 flank eruption of Etna from volcanological and historic viewpoints

The 1971 eruption represents a benchmark in the recent history of Etna volcano. From a volcanological point of view, this eruption was characterised by complex intrusive dynamics associated with significant ground deformation that induced the activation of the Moscarello seismogenic fault and the formation of a new summit crater: the Southeast Crater. At the same time, the 1971 event marks an important change in the eruptive style and composition of the magma towards products richer in K. It is no coincidence that, over the next fifty years, there would be an increase in the frequency of summit and flank eruptions and associated output rate. From an historical viewpoint, the eruptive event of 1971 was the first important flank eruption studied by the International Institute of Volcanology: the analysis of the scientific articles on this activity reveals a greater multidisciplinary content in the descriptions and explanations of volcanic activity. Particularly important were the collaborations of British and French research groups that, together with their Italian colleagues, succeeded in giving a complete picture of the eruption and describing the state of knowledge on the Sicilian volcano. The multidisciplinary methodology used to study this eruption is still valid today.

Surface characterisation of brass alloy in the correlation of hardness and electrical resistivity by carbon ion implantation

Material modification, as per demand of era, has been explored by several groups in different areas focusing its engineering prospect for better performance. Carbon ion implantation, using four different doses, has been done on α-brass (64% Cu; 36% Zn) to see its effects on hardness, microstructure and electrical resistivity. Carbon ions distorted the crystalline surface, increased defect density and hardened the surface by 13.2%. The crystallite size was found decreased by 41.15%, which in turn caused a significant increase in electrical resistivity, i.e. 234.8%. Overall, the lattice parameter found increased from 3.680 to 3.688 Å. SEM morphology exhibited nonuniform agglomerations in the form of pits, cracks, voids, cavities, craters, particulates, droplets and petals like structures at the surface by carbon ion implantation.

Three-Dimensional Measurement of the Crater Formation During Plume–Surface Interactions Using Stereo-Photogrammetry

The present investigation focused on adapting and validating stereo-photogrammetry for obtaining three-dimensional, time-resolved, nonintrusive, full-domain measurements of crater evolution during the plume–surface interaction (PSI) process. An atmospheric experimental facility was designed and constructed to facilitate the development of the stereo-photogrammetry technique for PSI applications. Stereo-photogrammetry was then used to measure the dynamic crater evolution process at nozzle heights of 25, 40, 55, and 70 nozzle diameters above the sand simulant bed. From the stereo-photogrammetry data, time-resolved three-dimensional reconstructions of the crater geometry were generated, and crater depth, radius, and volume time histories were extracted. Crater depth was observed to grow logarithmically for the two highest nozzle heights, and the depth growth rate for the lower two nozzle heights was more rapid. Crater volume growth was well characterized by a power law fit. The post-nozzle-flow slope of the collapsed crater was found to increase with nozzle height, along with the final crater volume. The results show that stereo-photogrammetry can be used to successfully measure the crater geometry in cases where optical access to the crater is not completely degraded by ejected particles.

Insight Into Formation Processes of Layered Ejecta Craters on Mars From Thermophysical Observations

AbstractUnderstanding the morphological characteristics of craters that are indicative of their formation environment can provide insight into surface geology. Layered ejecta (LE) craters, found on Mars and some other planetary bodies, have been hypothesized to have formed as a result of either interaction with subsurface volatiles (volatile fluidization model) and/or with the atmosphere (atmospheric entrainment model). Formation of LE craters by either model should result in different grain size distributions throughout the ejecta deposit. Using thermal inertia to infer surface properties, we investigated LE craters and their ejecta deposits in an effort to distinguish between possible LE formation processes on Mars. We used thermophysical properties of crater ejecta to determine grain size distribution, to model horizontal mixtures and vertical layering, and to identify materials present within the ejecta. We assessed the thermal properties of 50 uniformly sampled LE craters using Mars Odyssey Thermal Emission Imaging System (THEMIS) and Mars Global Surveyor Thermal Emission Spectrometer (TES) data. Our THEMIS analysis identifies 12 craters with grain size distributions consistent with the volatile fluidization model, 3 craters that have characteristics potentially associated with either model, and 22 craters that do not exhibit characteristics matching either model. Our TES analysis identifies 11 craters with characteristics consistent with the volatile fluidization model and 8 craters that are consistent with the atmospheric entrainment model. While some observations of grain size distributions provide evidence for either or both models, there is not overwhelming support for either model, potentially due to uncertainties of derived thermal inertia data.

Collisions of Small Kuiper Belt Objects With (486958) Arrokoth: Implications for Its Spin Evolution and Bulk Density

AbstractThe orientation and morphology of the bilobate, cold classical Kuiper belt object (486958) Arrokoth (formerly 2014 MU69) is consistent with a slow, tidal merger of a close binary. However, the discrepancy between Arrokoth's present‐day rotation (15.9 hr) and synchronous rotation for nominal cometary densities near ∼500 kg/m3 implies reduction (up to 30%) in post‐merger spin angular momentum. We investigate how collisions with dynamically cold and hot classical Kuiper belt objects might have affected Arrokoth's post‐merger spin. Using a dynamically equivalent triaxial ellipsoid, 5000 Monte Carlo simulations of 100 impacts each, consistent with Arrokoth's cratering record, were carried out. Starting from the assumption of critical, synchronous rotation for a given density, these simulations rarely reproduce Arrokoth's present spin period, unless its true density is near 250 kg/m3. We explore in greater depth the effects of formation of Arrokoth's largest crater (now officially named Sky, previously informally named Maryland). We adopt point‐source scaling and randomly select impact parameters that lead to the crater, using Arrokoth's full bilobate shape. Results from Sky's formation alone are similar to those considering a full range of impactor sizes, unless we adopt low cratering efficiency due to high porosity, which implies substantially larger Sky‐forming impactors. Overall, results imply that the probability of substantial angular momentum change due to impacts alone over Solar System history is unlikely, and spindown from a synchronous, tidal rotation rate to a 15.9‐hr period unlikely unless Arrokoth itself was and is a very low density object (∼250 kg/m3), though we cannot statistically rule out densities up to 400 kg/m3.

Modeling Early Clustering of Impact-induced Ejecta Particles Based on Laboratory and Numerical Experiments

Abstract A projectile impact onto a granular target produces an ejecta curtain with heterogeneous material distribution. Understanding how the heterogeneous pattern forms is potentially important for understanding how crater rays form. Previous studies predicted that the pattern formation is induced by inelastic collisions of ejecta particles in early stages of crater formation and terminated by the ejecta’s expanding motion. In this study, we test this prediction based on a hypervelocity impact experiment together with N-body simulations where the trajectories of inelastically colliding granular particles are calculated. Our laboratory experiment suggests that pattern formation is already completed on a timescale comparable to the geometrical expansion of the ejecta curtain, which is ∼10 μs in our experiment. Our simulations confirm the previous prediction that the heterogeneous pattern grows through initial inelastic collisions of particle clusters and subsequent geometric expansion with no further cluster collisions. Furthermore, to better understand the two-stage evolution of the mesh pattern, we construct a simple analytical model that assumes perfect coalescence of particle clusters upon collision. The model shows that the pattern formation is completed on the timescale of the system’s expansion independently of the initial conditions. The model also reproduces the final size of the clusters observed in our simulations as a function of the initial conditions. It is known that particles in the target are ejected at lower speeds with increased distance to the impact point. The difference in the ejection speed of the particles may result in the evolution of the mesh pattern into rays.