Crater Density Research Articles

Experimental Investigation on the Effect of Masked Multiple Passes Abrasive Waterjet Machining Surface Texturing on Coefficient of Friction

The surface texturing method is popular because of its ability to improve surface properties, specifically surface functioning, and friction control. It is a common technique used on material surfaces to improve friction performance. Laser surface texturing is the popular choice; however, this method suffers drawbacks such as cracking, heat-affected zone, and generation of hazardous fumes. The Abrasive Water Jet Machining (AWJM) was chosen is that, because the eroded material is carried by the waterjet, the process is clean and does not produce dust, chips, or chemical contaminants. This experiment examines the influence of AWJM and investigates how crater density and a multiple-pass machining path affect the stainless-steel friction characteristics when sliding in dry conditions. The texture was applied on the surface of stainless steel by masked multi-passes AWJM technique. According to the findings, there is less friction in craters with greater densities because there are more craters in the contact zone, which improves the trapping of debris particles and reduces friction, when the crater density rises from 4% to 18%, there is a greater chance of worn debris becoming trapped, which reduces friction. The coefficient of friction and crater roughness of the stainless-steel surface are all proportionally affected by the multiple-passes approach. The coefficient of friction increases with higher machining passes. There is more erosion and greater roughness when there are more jet passes. It is concluded that the masked multiple passes AWJM Surface Texturing technique has a significant impact on the Coefficient of Friction (COF).

The Production Population of Impact Craters in the Chang’E-6 Landing Mare

The Chang’E-6 mission accomplished the first sample return from the lunar farside. Earlier crater population measurements estimated the model age of the landing mare to range from the Eratosthenian to Late Imbrian, both of which are underrepresented by earlier returned samples. Establishing a new calibration point for lunar impact flux based on isotopic ages of the samples is promising, but the representative crater density for the landing mare (i.e., spatial density of craters with D ≥ 1 km; N (1)) is equally important for this purpose, which lacks good constraints. After excluding the effects of background secondaries, crater equilibrium, and observational uncertainties on crater statistics, this work extracts production populations in different diameter ranges (∼200 m–2 km) from multiple subareas of the landing mare. Cross-validation of the production populations verifies that N (1) derived from direct measurements of craters with D ≥ 1 km in sketched areas are reliable, which is (2.01 ± 0.90) × 10−3 and (6.05 ± 2.71) × 10−3 km2 for the western and eastern mare, respectively.

Effect of Target Properties on Regolith Production

Based on the measurements of regolith thicknesses on the lunar maria (basalts), the lunar regolith was determined to have accumulated at a rate of about 1 m/Gyr since the era of the late heavy bombardment. However, regolith production on porous targets (e.g., crater ejecta deposits) is less studied, especially for Copernican units, and how target properties affect regolith production is not well understood. Here, we measured regolith thicknesses on the ejecta blanket of the Copernicus crater, showing that the regolith production rate sensitively depends on the initial target properties. The regolith production rate of the Copernicus ejecta blanket (3.0 ± 0.1 m/Gyr) is significantly larger than that of the Copernicus impact melt, which was previously estimated to be 1.2 ± 0.2 m/Gyr. Although crater production varies with different targets, our observed crater density of the Copernicus impact melt is indistinguishable from that of the Copernicus ejecta because impacts fracture the melt, causing it to resemble the ejecta. However, due to the fact that the formation of crater ejecta had already caused them to undergo fragmentation, ejecta require fewer fragmentation times to become regolith compared to impact melt; thus, the growth of regolith on the ejecta is faster than the melt. This indicates that similar observed size–frequency distributions do not indicate similar regolith production, especially for the targets with significant differences in initial physical properties.

Global Lunar Crater Density Using Buffered Nonsparseness Correction

The density of craters on a planetary surface directly relates to the age of the surface. As the surface ages, however, craters can be erased by subsequent large impacts via direct overprinting, known as geometric crater obliteration. Such counts become increasingly limited as surfaces become more heavily cratered. Techniques to infer the statistics of the regions obliterated by craters were developed in the past decade. Such techniques, however, have only been used for regional studies. Herein, we present a study of the global density of lunar impact craters ≥20 km in diameter using both traditional crater-counting and buffered nonsparseness correction (BNSC) crater-counting techniques. By comparing the measurements, we quantify the influence of geometric crater obliteration on the visible lunar crater record. Our results reveal that geometric crater obliteration erased up to three-fifths of craters ≥20 km in diameter that formed on the most ancient lunar terrains, whereas younger surfaces, like the Procellarum KREEP Terrane, show little to no evidence of such crater obliteration. The differences in derived crater densities highlight ancient surfaces in which the effects of geometric crater obliteration must be considered to characterize their cratering histories. Furthermore, our results identify the most heavily cratered area on the Moon, a region of the lunar highlands between Smythii basin and the South Pole–Aitken (SPA) basin (Smythii–SPA–Highlands); the number of impacts revealed by the BNSC technique for this region is consistent with estimates derived from the abundance of highly siderophile elements and from modeling crustal porosity.

An estimate of the impact rate on Mars from statistics of very-high-frequency marsquakes

The number density of impact craters on a planetary surface is used to determine its age, which requires a model for the production rate of craters of different sizes. On Mars, however, estimates of the production rate of small craters (<60 m) from orbital imagery and from extrapolation of lunar impact data do not match. Here we provide a new independent estimate of the impact rate by analysing the seismic events recorded by the seismometer onboard NASA’s InSight lander. Some previously confirmed seismically detected impacts are part of a larger class of marsquakes (very high frequency, VF). Although a non-impact origin cannot be definitively excluded for each VF event, we show that the VF class as a whole is plausibly caused by meteorite impacts. We use an empirical scaling relationship to convert between seismic moment and crater diameter. Applying area and time corrections to derive a global impact rate, we find that 280–360 craters >8 m diameter are formed globally per year, consistent with previously published chronology model rates and above the rates derived from freshly imaged craters. Our work shows that seismology is an effective tool for determining meteoroid impact rates and complements other methods such as orbital imaging.

Characterization of High-priority Landing Sites for Robotic Exploration Missions in the Apollo Basin, Moon

The South Pole–Aitken (SPA) basin is the oldest and largest visible impact structure on the Moon, making it a high priority science site for exploration missions. The 492 km diameter Apollo peak-ring basin is one of the youngest and largest basins within the SPA basin. We selected three regions of interest (ROIs) in the Apollo basin for which the landing and operational hazards are minimized and evaluated their science and in situ resource utilization (ISRU) potential. We examined topography, slope, crater density, rock abundance, geologic mapping, mineralogy, and inferred subsurface stratigraphy within each ROI. The results show that the terrain is safe for landing without precision landing (within a few hundred meters). The mare materials have high ISRU potential with relatively high FeO (∼16–20 wt%) and TiO2 (∼3–10 wt%) contents. Two robotic exploration mission architectures were examined for their scientific potential: (1) lander and rover with a dedicated payload suite and (2) the same architecture with sample return capability. In situ observations can address six of seven National Research Council concepts (1–3, 5–7) and Campaigns 1 and 5 of the European Space Agency’s Strategy for Science at the Moon.

The peculiar alterations of the optical and mechanical characteristics of the quartz glass plates with a reinforcing coating under the collision with a hyper-velocity flux of microparticles

This article experimentally investigates the collision of a high-velocity (5–8 km/s) flux of iron microparticles with quartz-glass plates and the effect of such collisions on the optical and mechanical properties of the plates protected by In–Sn–O-based coatings. Such coatings are used to protect the optical systems of spacecraft from the impacts of micrometeoroids and fragments of space debris. To ensure the safety of the optical systems of manned vehicles is crucial for the future of space exploration. This requires special protective materials that can resist external factors.In the present article, thin and thick protective coatings were formed by pulsed reactive magnetron sputtering of a tin-doped (7.5 wt%) indium target.The collision of the particles with the target's surface forms craters. The surface density of the craters ρ depends on the thickness of the coating and its physical and mechanical properties. The increased thickness up to ∼6 μm decreases the crater density 3.3 times, which is due to increased elastic modulus and crack resistance and decreased microhardness of the coated glass. For the quartz-glass specimens without the protective coating, the bombardment by the high-speed flux of iron microparticles decreases the visible-region light transmittance by ~ 6 %. The bombardment of quartz-glass specimens with thin protective In–Sn–O coating reduces the light transmittance to a lesser extent, while there is no reduction in the case of a thick coating. The transmittance linearly depends on the crater density and is inversely proportional to the total area occupied by the craters on the surface under study. This effect is due to the partial shading of the glass working area when rays of light pass through the zones occupied by the craters.

Identification of Lunar Craters in the Chang’e-5 Landing Region Based on Kaguya TC Morning Map

Impact craters are extensively researched geological features that contribute to various aspects of lunar science, such as evaluating the model age, regolith thickness, etc. The method for identifying impact craters has gradually transitioned from manual counting to automated identification. Automatic crater detection based on the digital elevation model (DEM) is commonly used to detect larger craters. However, using only DEM has limitations in discerning smaller craters (diameter &lt; ~1 km). This study utilizes an improved Faster R-CNN algorithm and the Kaguya Terrain Camera (TC) morning map to detect small impact craters in the Chang’e-5 (CE-5) landing site. It uses model fusion to improve the precision of small crater identification. The results show a recall rate of 96.33% and a precision value of 90.19% for craters with diameters exceeding 200 m. The model found a total of 187,101 impact craters in the CE-5 region. The spatial distribution density of impact craters with diameters ranging from 100 m to 200 m is approximately 2.5706/km2. For craters with diameters ranging from 200 m to 1 km, the average spatial distribution density is about 0.9016/km2. By the unbiased impact crater density of chronological analysis, the model age of the Im2 and Em4 geological units in the CE-5 region is 3.78 Ga and 2.07 Ga, respectively.

Recalibration of the lunar chronology due to spatial cratering-rate variability

Cratering chronologies are used to derive the history of planetary bodies and assume an isotropic flux of impactors over the entire surface of the Moon. The impactor population is largely dominated by near-Earth-objects (NEOs) since ∼3.5 billion years ago. However, lunar impact probabilities from the currently known NEO population show an excess of impacts close to the poles compared to the equator as well as a latitudinal dependency of the approach angle of impactors. This is accompanied by a variation of the impact flux and speed with the distance from the apex due to the synchronicity of the lunar orbit around the Earth. Here, we compute the spatial dependency of the cratering rate produced by such variabilities and recalibrate the lunar chronology. We show that it allows to reconcile the crater density measured at mid-latitudes around the Chang'e-5 landing site with the age of the samples collected by this mission. Our updated chronology leads to differences in model ages of up to 30% compared to other chronology systems. The modeled cratering rate variability is then compared with the distribution of lunar craters younger than ∼1 Ma, 1 Ga and 4 Ga. The general trend of the cratering distribution is consistent with the one obtained from dynamical models of NEOs, thus potentially reflecting a nonuniform distribution of orbital parameters of ancient impactor populations, beyond 3.5 Ga ago, i.e., planetary leftovers and cometary bodies. If the nonuniformity of the cratering rate could be tested elsewhere in the Solar System, the recalibrated lunar chronology, corrected from spatial variations of the impact flux and approach conditions of impactors, could be extrapolated on other terrestrial bodies such as Mercury and Mars, at least over the last 3.5 billion years. The modeled cratering rate presented here has strong implications for interpreting results of the Artemis program, aiming to explore the South Pole of our satellite, in particular when it will come to link the radiometric age of the samples collected in this region and the crater density of the sampled units.

Study on subsurface damage behavior in ductile ultra-precision grinding of sapphire based on acoustic emission signal processing

Chemical corrosion, photothermal absorption and acoustic emission were used to multidimensionally evaluate and monitor subsurface damage behavior in ductile ultra-precision grinding of sapphire. The optimum ductile grinding surface can be obtained at different grinding depths when grinding with constant-depth. The density of corrosion dislocation craters and the value of photothermal absorption increased with grinding depth, and the subsurface damage scales under the ductile grinding surface were distinct. Subsurface damage was dominated by cracks and spalling. Severe brittle fractures occurred at greater grinding depths in varied-depth grinding. The corroded grinding surface consisted of the original polishing surface, the ductile grinding surface, and the brittle fracture characteristic. The amplitude and fluctuation of grinding force increased with grinding depth. The original signal and Fourier transform cannot monitor the damage behavior. A signal processing model based on wavelet transform, signal reconstruction and fast Fourier transform was developed. The processed signal characteristics can correspond to the damage behavior under the ductile grinding surface.

Small lunar crater identification and age estimation in Chang'e-5 landing area based on improved Faster R-CNN

The Chang'e-5 (CE-5) mission marks China's first lunar sample return endeavor, with its landing site (43.06°N, 51.92°W) situated in the Mons Rümker region of the northern Oceanus Procellarum on the Moon. This region hosts some of the youngest mare basalts of the Moon and contains a relatively youthful geologic unit characterized by crater's equilibrium diameters slightly over 100 m. By refining the Faster Region-based Convolutional Neural Network (Faster R-CNN) algorithm and leveraging high-resolution imagery to create training samples, accurate identification of lunar craters can be achieved. In this study, we enhance the algorithm in aspects such as anchor boxes and Region of Interest alignment. Additionally, we have utilized high-resolution images for training, and identify and statistics craters within the CE-5 landing area. Ultimately, our model attains a validation set Recall of 90%, Precision of 69%, and an Average Precision score of 0.83. Notably, in certain scales, such as for the crater larger than 400 m, recognition results reach Precision of 88% and Recall of 89%. The findings of this study are mapped into a crater catalog. Furthermore, we predict crater density and integrate it with geochronological functions to estimate the absolute model age of nine major geologic units within the CE-5 landing area. The results are generally in agreement with those of other studies who have used manual methods for crater counting, and verify the correctness of our automatic crater identification results.

A Crater Chronology for the Jupiter’s Trojan Asteroids

We present a new crater chronology for Jupiter’s Trojan asteroids. This tool can be used to interpret the collisional history of the bodies observed by NASA’s Lucy mission. The Lucy mission will visit a total of six Trojan asteroids: Eurybates, Polymele, Orus, Leucus, and the near-equal-mass binary Patroclus–Menoetius. In addition, Eurybates and Polymele each have a small satellite. Here we present a prediction of Trojan cratering based on current models of how the solar system and the objects themselves evolved. We give particular emphasis to the time lapsed since their implantation into stable regions near Jupiter’s Lagrangian L4 and L5 points. We find that cratering on Trojans is generally dominated by mutual collisions, with the exception of a short period of time (∼10 Myr) after implantation, in which cometary impacts may have been significant. For adopted crater scaling laws, we find that the overall spatial density of craters on Trojans is significantly lower than that of Main Belt asteroids on surfaces with similar formation ages. We also discuss specific predictions for similar-sized Eurybates and Orus, and the binary system Patroclus–Menoetius.

Saturn’s ancient regular satellites

Are Saturn’s regular satellites young or old? And how old are Enceladus’ cratered plains? To answer these questions we computed model surface ages of the most heavily cratered terrains on Saturn’s regular icy satellites using new high-resolution outer Solar System evolution simulations, and coupled with improved estimates of the trans-Neptunian objects populations. The output of the simulations allowed us to construct a model impact chronology onto Saturn which automatically applies to its regular satellites. We used crater densities and our impact chronology onto Saturn to construct model impact-crater isochrons, i.e., the scaling of the satellite crater production function with time. The surface ages derived for the cratered plains on Mimas, Enceladus, Tethys, Dione and Rhea range from 4.1 Ga to 4.4 Ga, with the surfaces of Mimas and Enceladus roughly 200 Myr younger than those of the outer three satellites. Uncertainties in these ages are less than 300 Myr. The calculated model surface ages of these satellites are consistent over as much as two orders of magnitude in the observed crater diameter. The similarity of the crater production function amongst all satellites suggests that they were bombarded by a single impactor source. This work supports the idea that Saturn’s regular satellites are ancient, and has implications for their formation and their tidal evolution.

Review and Revision of the Lunar Cratering Chronology—Lunar Timescale Part 2

Times and rates of planetary surface-modifying processes are crucial for the sequence and correlation of events on planetary bodies. For most planetary surfaces, superposition principles and crater densities are commonly used methods to collect relative age information. Lunar-based cratering-chronology models, which pair crater densities and sample ages from several lunar landing and sampling sites, calibrate the relative age information in absolute time. Here, we propose calibration pairs based on new crater statistics and spectrally supported sample-age assignments for the lunar cratering-chronology model. The resulting model reflects modern high-precision, radiometric ages, compositional and spectral information, and an up-to-date crater-production function. This revision supports a crater-forming projectile flux with monotonic decay, similar to previous standard models, but of distinctively lower flux. This originates from lower crater densities identified in spectrally and morphologically defined reference units, and from assigning more precise sample ages accounting for spectral resemblance between reference unit and sample. The observed maximal values for crater densities and ages provide the oldest and most densely cratered calibration pair. Because of the nature of highland samples, age constraints for the Luna 20 and Apollo 16 sampling sites remain challenging, which restricts the confidence in times for individual basin-formation events older than Orientale Basin. The new cratering-chronology model, when transferred to other planetary bodies, would cause aging of the surfaces, because of the lower overall flux.

Lunar Surface Model Age Derivation: Comparisons Between Automatic and Human Crater Counting Using LRO‐NAC and Kaguya TC Images

AbstractDating young lunar surfaces, such as impact ejecta blankets and terrains associated with recent volcanic activities, provides critical information on the recent events that shaped the surface of the Moon. Model age derivation of young or small areas using a crater chronology is typically achieved through manual counting, which requires a lot of small impact craters to be tediously mapped. In this study, we present the use of a Crater Detection Algorithm (CDA) to extract crater populations on Lunar Reconnaissance Orbiter—Narrow Angle Camera (LRO‐NAC) and Kaguya Terrain Camera images. We applied our algorithm to images covering the ejecta blankets of four Copernican impact craters and across four young mare terrains, where manually derived model ages were already published. Across the eight areas, 10 model ages were derived. We assessed the reproducibility of our model using two populations for each site: (a) an unprocessed population and (b) a population adjusted to remove contaminations of secondary and buried craters. The results showed that unprocessed detections led to overestimating crater densities by 12%–48%, but “adjusted” populations produced consistent results within &lt;20% of published values in 80% of cases. Regarding the discrepancies observed, we found no significant error in our detections that could explain the differences with crater densities manually measured. With careful processing, we conclude that a CDA can be used to determine model ages and crater densities for the Moon. We also emphasize that automated crater datasets need to be processed, interpreted and used carefully, in unity with geologic reasoning. The presented approach can offer a consistent and reproducible way to derive model ages.

The Complex Exhumation History of Jezero Crater Floor Unit and Its Implication for Mars Sample Return

AbstractDuring the first year of NASA's Mars 2020 mission, Perseverance rover has investigated the dark crater floor unit of Jezero crater and four samples of this unit have been collected. The focus of this paper is to assess the potential of these samples to calibrate the crater‐based Martian chronology. We first review the previous estimation of crater‐based model age of this unit. Then, we investigate the impact crater density distribution across the floor unit. It reveals that the crater density is heterogeneous from areas which have been exposed to the bombardment during the last 3 Ga to areas very recently exposed to bombardment. It suggests a complex history of exposure to impact cratering. We also display evidence of several remnants of deposits on the top of the dark floor unit across Jezero below which the dark floor unit may have been buried. We propose the following scenario of burying/exhumation: the dark floor unit would have been initially buried below a unit that was a few tens of meters thick. This unit then gradually eroded away due to Aeolian processes from the northeast to the west, resulting in uneven exposure to impact bombardment over 3 Ga. A cratering model reproducing this scenario confirms the feasibility of this hypothesis. Due to the complexity of its exposure history, the Jezero dark crater floor unit will require additional detailed analysis to understand how the Mars 2020 mission samples of the crater floor can be used to inform the Martian cratering chronology.

Variations in lunar elastic thickness from admittance spectral analysis

We infer the elastic thickness of regions of the Moon by performing an admittance analysis on GRAIL gravity and LOLA topography data. Reliable results are generally confined to the lunar farside, away from large mare deposits. We find that elastic thickness varies between 13 km and 72 km, with a mean elastic thickness (Te) of 29 km. The highest reliable elastic thicknesses are found to the northwest of South Pole-Aitken (SPA) basin while the lowest elastic thicknesses are found in the equatorial farside and within SPA. Our findings suggest that much of the loading on the Moon must have taken place within the first 200 Myr after lunar magma ocean solidification, though some areas (Te > 40 km) may be recording events as late at 3.5 Ga. We find no correlation between elastic thickness and crater density, crustal thickness, or mean elevation in areas where reliable estimates of elastic thickness can be made, though we do note that regions with the highest crustal thickness and mean elevation are associated with lower elastic thickness values. We also demonstrate that smaller localization windows can lead to systematically lower elastic thickness estimates.

MORPHOLOGICAL CHARACTERISTICS OF CRATERS ON THE SURFACE OF AA1933 ALUMINUM ALLOY IRRADIATED BY PULSED ELECTRON BEAM

Irradiation of an industrial aluminum alloy AA1933 with an intense pulsed electron beam with particle energy of 0.35 MeV, a beam current of 2.0 kA, a pulse duration of 5 μs, and a beam diameter of 3 cm results in the formation of a surface layer with a modified structural-phase state. A characteristic feature of the irradiated surface is the presence of cracks and craters on it. This study features the types and morphology of craters on the surface of aluminum alloy AA1933 formed as a result of irradiation by a pulsed electron beam. The study includes figures of a variety of crater types. The distribution of craters according to size and crater density on the irradiated surface was examined. The study also provides for the discussion of the significance of these observations for the sake of a better understanding of the mechanisms of crater formation during irradiation by pulsed electron beams.

Unravelling the geological and geomorphological evolution of the Terra Cimmeria-Nepenthes Mensae transitional zone, Mars

The Terra Cimmeria-Nepenthes Mensae Transitional Zone comprises two highly contrasting geologic-geomorphic domains bounded by the dichotomy escarpment in the equatorial region of Mars. This research provides insight into the geological and geomorphological evolution of the poorly explored NW Terra Cimmeria and SE Nepenthes Mensae. A detailed study largely based on cartographic work and complemented by multiple analyses focused on crater densities, spectral data and radar profiles reveals that (1) the exposed geological record of this transitional zone formed over a long time-span from the Early Noachian to recent times, (2) the inferred compressional and extensional tectonic stresses shaped the landscape at least from the Late Noachian to Late Hesperian, and (3) extensional tectonics, which post-dated the compressional deformation, has controlled the development and evolution of the 2-km-high dichotomy escarpment, the system of NW-SE-oriented basins that used to host paleolakes from the Late Noachian to Late Hesperian, and the fissure volcanism in their deepest areas. These findings shed light into the fundamental morphogenetic role played by compressional and extensional tectonics, and fluvio-lacustrine activity on the configuration of the landscape in these regions. This work provides a reference geologic-geomorphologic framework for future studies in this area and other sectors along the highland-lowland transitional zone of Mars.

Untrackable distal ejecta on planetary surfaces

Impact ejecta are important references to establish regional and global stratigraphy of planetary bodies. Canonical views advocate radial distributions of distal ejecta with respect to the source crater, and their trajectories are significantly deflected on fast-rotating bodies. The Hokusai crater on Mercury formed a peculiar ray that features a hyperbola shape, and the sharp swerve of orientation was interpreted as a sign of a faster planetary rotation in the near past. Here, we show that this ray was not caused by a hypothesized larger Coriolis force, but due to abruptly-steepened ejection angles. Heterogeneous shock impedances of pre-impact impactor and/or target, such as topographic undulations, affect local propagation paths of shock and rarefaction waves, causing sudden changes of ejection angles. Distal ejecta with non-radial distributions are an inherent product of planetary impacts, and their unobvious provenances could mislead stratigraphic interpretations and hamper age estimations based on spatial densities of impact craters.