Characteristics Of Craters Research Articles

Morphometric Characterization and Reconstruction Effect Among Lunar Impact Craters

Impact craters on the lunar surface have a variety of morphometric characteristics that are very useful in understanding the evolutionary history of lunar landscape morphologies. Based on digital elevation model data and photographs from China’s Chang’E-1 lunar orbiter, we develop morphologic parameters and quantitative methods for presenting the morphometric characteristics of impact craters, analyzing their relational distribution, and estimating the relative order of their formation. We also analyze features in profile where craters show signs of having formed on the edge of previously existing craters to show that superimposed impacts affect morphologic reconstructions. As a result, impact craters have significant effects on the reconstruction of ancient topography and the estimation of relative formation ages.

A Novel Saliency Detection Method for Lunar Remote Sensing Images

The saliency detection provides an alternative methodology to semantic image understanding in many applications, for example, content-based image retrieval. To detect saliency for lunar remote sensing images, this letter proposes a crater feature model by analyzing the relationship between local interest points and saliency of lunar images. Based on the model, we propose a novel saliency detection method for lunar images. Our method merges and combines the speed-up robust feature features of the highlight region and shadow region of an impact crater to get the candidate regions of interest (ROI). Then, a descriptive feature vector is generated for each ROI, and the resulting saliency regions are distinguished from false detected and inconspicuous ones through a support vector machine. The method has been put into test on Chang'e-1 and Chang'e-2 lunar image data, and confirmed to be able to detect the salient region of impact craters correctly, with results much better than those obtained by the classical saliency detection method.

The ages of pedestal craters on Mars: Evidence for a late-Amazonian extended period of episodic emplacement of decameters-thick mid-latitude ice deposits

There is significant geomorphologic evidence for the past presence of longitudinally widespread, latitudinally zoned deposits composed of ice-rich material at the northern and southern mid latitudes on Mars (lobate debris aprons, lineated valley fill, concentric crater fill, pedestal craters, etc.). Among these features, pedestal craters (Pd) are impact craters interpreted to have produced a protective layer on top of decameters-thick ice deposits now missing in intercrater regions. The time during which these various deposits were present is still highly debated. To address this question we have analyzed the distribution and characteristics of pedestal craters; here, we use a population of 2287 pedestal craters (Pd) to derive a crater retention age for the entire population, obtaining a minimum timescale of formation of ~90Myr. Given that the ice-rich deposit has not been continuously present for this duration, the timescale of formation is necessarily longer than ~100Myr. We then compiled impact crater size-frequency distribution dates for 50 individual pedestal craters in both hemispheres to further assess the frequency distribution of individual ages. We calculated pedestal crater ages that ranged from ~1Myr to ~3.6Gyr, with a median of ~140Myr. In addition, 70% of the pedestal ages are less than 250Myr. During the 150Myr period between 25Ma and 175Ma, we found at least one pedestal age every 15Myr. This suggests that the ice-rich paleodeposit accumulated frequently during that time period. We then applied these results to the relationship between obliquity and latitudinal ice stability to suggest some constraints on the obliquity history of Mars over the past 200Myr. Atmospheric general circulation models indicate that ice stability over long periods in the mid latitudes is favored by moderate mean obliquities in the ~35° range. Models of spin-axis/orbital parameter evolution predict that the average obliquity of Mars is ~38°. Our data represent specific observational evidence that ice-rich deposits accumulated frequently during the past 200Myr, supporting the prediction that Mars was characterized by this obliquity range during an extensive part of that time period. Using these results as a foundation, the dating of other non-polar ice deposits will permit the specific obliquity history to be derived and lead to an assessment of volatile transport paths in the climate history of Mars.

Microwave brightness temperature features of lunar craters: observation from Chang’E-1 mission

Topographic features of lunar craters have been found from the brightness temperature (TB) observed by the multichannel (3.0, 7.8, 19.35, and 37 GHz) microwave radiometer (MRM) aboard Chang’E-1 (CE-1) in a single track view. As the topographic effect is more obvious at 37 GHz, 37 GHz TB has been focused on in this work. The variation of 37 GHz daytime (nighttime) TB along the profile of a crater is found to show an oscillatory behavior. The amplitude of daytime TB is significantly affected by the observation time and the shape of the crater, whose diameter is bigger than the spatial resolution of MRM onboard CE-1. The large and typical diurnal TB difference (nighttime TB minus daytime TB) at 37 GHz over selected young craters due to the large rock abundance in craters, have been discussed and compared with the altitude profile.

Stardust Interstellar Preliminary Examination XI: Identification and elemental analysis of impact craters on Al foils from the Stardust Interstellar Dust Collector

AbstractThe Stardust Interstellar Preliminary Examination team analyzed thirteen Al foils from the NASA Stardust interstellar collector tray in order to locate candidate interstellar dust (ISD) grain impacts. Scanning electron microscope (SEM) images reveal that the foils possess abundant impact crater and crater‐like features. Elemental analyses of the crater features, with Auger electron spectroscopy, SEM‐based energy dispersive X‐ray (EDX) spectroscopy, and scanning transmission electron microscope‐based EDX spectroscopy, demonstrate that the majority are either the result of impacting debris fragments from the spacecraft solar panels, or intrinsic defects in the foil. The elemental analyses also reveal that four craters contain residues of a definite extraterrestrial origin, either as interplanetary dust particles or ISD particles. These four craters are designated level 2 interstellar candidates, based on the crater shapes indicative of hypervelocity impacts and the residue compositions inconsistent with spacecraft debris.

Formation of double‐layered ejecta craters on Mars: A glacial substrate model

AbstractA class of Martian impact craters with particularly unusual ejecta characteristics (double‐layered ejecta (DLE) craters) are preferentially located in the midlatitudes in both hemispheres of Mars. Unlike today, decameters thick deposits of snow and ice occupied these same latitudes for significant periods during the Amazonian period. We assess the hypothesis that the unusual double‐layer morphology could be related to impact into a snow and ice glacial substrate followed by landsliding of ejecta off of the structurally uplifted rim. We find that many characteristics of DLE craters (e.g., latitudinal distribution, lack of secondaries, landslide‐like textures, evidence for overthrusting, relation to other crater types, etc.) are consistent with such an origin.

Circular polarization ratio characteristics of impact craters from Mini‐RF observations and implications for ice detection at the polar regions of the Moon

In an attempt to reduce the ambiguity on radar detection of water ice at the permanently shadowed regions near the lunar poles, radar echo strength and circular polarization ratio (CPR) of impact craters are analyzed using the Miniature Radio Frequency (Mini‐RF) radar data from the Lunar Reconnaissance Orbiter mission. Eight typical craters, among over 70 craters, are selected and classified into four categories based on their locations and CPR characteristics: polar anomalous, polar fresh, nonpolar anomalous, and nonpolar fresh. The influences on CPR caused by surface slope, rocks, and dielectric constant are analyzed quantitatively using high‐resolution topography data and optical images. A two‐component mixed model for CPR that consists of a normal surface and a rocky surface is developed to study the effect of rocks that are perched on lunar surface and buried in regolith. Our analyses show that inner wall of a typical bowl‐shaped crater can give rise to a change of about 30° in local incidence angle of radar wave, which can further result in a CPR difference of about 0.2. There is a strong correlation between Mini‐RF CPR and rock abundance that is obtained from high‐resolution optical images, and predictions from the two‐component mixed model match well with the observed CPRs and the estimated rock abundances. Statistical results show that there is almost no apparent difference in CPR characteristics between the polar and nonpolar anomalous craters, or between the polar and nonpolar fresh craters. The enhanced CPR in the interior of anomalous craters is most probably caused by rocks that are perched on lunar surface or buried in regolith, instead of ice deposits as suggested in previous studies.

Underwater-laser drilling of aluminum

Pulsed-laser ablation of an aluminum bulk sample was performed both in water and air with a Q-switched Nd:YAG 1,064-nm laser over a range of high-output energies from 100 to 500 mJ. The effect of laser drilling in terms of produced crater volumes as a function of water-layer thickness was studied. The water-layer thickness was varied from 1 to 20 mm. In a special case, water droplets were added to the ablation region of the dry target in order to support ablation. Water-layer thickness in that case was estimated to be 0.5 mm. A comparison of the results obtained in air and underwater was performed. It is found that the aluminum target may be drilled more efficiently under the confinement of water compared to drilling in air environment. Further drilling efficiency can be achieved by varying the thickness of water. The optimized water thickness under the conditions of our experiment was found to be 3 mm. In that case, a 28-fold increase in crater volume and 18-fold increase in crater depth was achieved as compared to ablation in air. In underwater ablation, the formation of irregular surface structures of re-deposited material around the crater (rim) is avoided and the crater surface is smoother. In an air environment, the drilling is suppressed due to an immediate re-solidification and re-deposition of ablated material. This leads to a better characteristics of craters obtained underwater in terms of roughness, shape, volumes, and reproducibility.

Rapid fabrication and piezoelectric tuning of micro- and nanopores in single crystal quartz

We outline the fabrication of piezoelectric through-pores in crystalline quartz using a rapid micromachining process, and demonstrate piezoelectric deformation of the pore. The single-step fabrication technique combines ultraviolet (UV) laser irradiation with a thin layer of absorbing liquid in contact with the UV-transparent quartz chip. The effects of different liquid media are shown. We demonstrate that small exit pores, with diameters nearing the 193 nm laser wavelength and with a smooth periphery, can be achieved in 350 μm thick quartz wafers. Special crater features centring on the exit pores are also fabricated, and the depth of these craters are tuned. Moreover, by applying a voltage bias across the thickness of this piezoelectric wafer, we controllably contract and expand the pore diameter. We also provide a sample application of this device by piezoelectrically actuating alamethicin ion channels suspended over the deformable pore.

Resuspension onset and crater erosion by a vortex ring interacting with a particle layer

This paper presents results from an experimental investigation of the interaction of a vortex ring with a particle layer. The flow dynamics during the onset of particle resuspension are analysed using particle image velocimetry, while a light attenuation method provides accurate measurements of the final eroded crater shape. This work is a continuation of the research described in R. J. Munro, N. Bethke, and S. B. Dalziel, “Sediment resuspension and erosion by vortex rings,” Phys. Fluids 21, 046601 (2009)10.1063/1.3083318, which focussed on the general resuspension onset dynamics and initial crater formation. Here, we analyse the velocity induced by the vortex ring on the particle layer surface during the resuspension of particles for different particle sizes, and the shape and size of the final craters that are formed by the impact of the vortex ring. We find that the boundary condition is characterised by a quasi-slip velocity at the particle layer surface, independent of the particle size. The particle diameter, and thus bed permeability, is found to have a significant effect on the final crater characteristics.

Investigation of single pulse discharge on silicon: crater and plasma characteristics

Micro electric discharge machining (μ-EDM) process is being used to machine complex shapes on silicon. In specific, dry-μ-EDM can be used to process assembled or semi assembled silicon products. However, there is lack of investigation on the effect of single pulse discharge machining and its plasma characteristics on silicon. Hence, in this paper we investigate the crater and plasma characteristics of single discharge for various conditions such as different electrode diameters and different energy conditions (fixed voltage with varying capacitance and vice-versa). The plasma temperature and electron density have been calculated by line pair method and modified Saha equation respectively. The values are mapped into the plasma classification plot based on log scale of plasma temperature and electron density and realised that at µ-scale EDM plasma was found to be ideal up to 50 mJ energy and tends to become weakly non-ideal plasma for 98 mJ energy. Also from the influence of energy on plasma characteristics it is understood that electron density also plays a major role along with the plasma temperature.

Effect of pulse repetition rate and number of pulses in the analysis of polypropylene and high density polyethylene by nanosecond infrared laser induced breakdown spectroscopy

Pulse repetition rates and the number of laser pulses are among the most important parameters that do affect the analysis of solid materials by laser induced breakdown spectroscopy, and the knowledge of their effects is of fundamental importance for suggesting analytical strategies when dealing with laser ablation processes of polymers. In this contribution, the influence of these parameters in the ablated mass and in the features of craters was evaluated in polypropylene and high density polyethylene plates containing pigment-based PbCrO4. Surface characterization and craters profile were carried out by perfilometry and scanning electron microscopy. Area, volume and profile of craters were obtained using Taylor Map software. A laser induced breakdown spectroscopy system consisted of a Q-Switched Nd:YAG laser (1064nm, 5ns) and an Echelle spectrometer equipped with ICCD detector were used. The evaluated operating conditions consisted of 10, 25 and 50 laser pulses at 1, 5 and 10Hz, 250mJ/pulse (85Jcm−2), 2μs delay time and 6μs integration time gate. Differences in the topographical features among craters of both polymers were observed. The decrease in the repetition rate resulted in irregular craters and formation of edges, especially in polypropylene sample. The differences in the topographical features and ablated masses were attributed to the influence of the degree of crystallinity, crystalline melting temperature and glass transition temperature in the ablation process of the high density polyethylene and polypropylene. It was also observed that the intensities of chromium and lead emission signals obtained at 10Hz were two times higher than at 5Hz by keeping the number of laser pulses constant.

Tactile Earth and Space Science Materials for Students with Visual Impairments: Contours, Craters, Asteroids, and Features of Mars

New tactile curriculum materials for teaching Earth and planetary science lessons on rotation/revolution, silhouettes of objects from different views, contour maps, impact craters, asteroids, and topographic features of Mars to 11 elementary and middle school students with sight impairments at a week-long residential summer camp are presented along with tips for constructing/obtaining the materials. Many of the lessons focused on spatial skills, an important skill area for persons with visual impairments. The pretest-intervention-post-test design study measured both attitude changes and gains in content knowledge. Students reported significant improvements (with large effect sizes) in the frequency of science lessons, the concrete nature of science lessons, the enjoyment these lessons produced, and the amount of participation in the lessons at the summer camp for students with visual disabilities compared to students' regular schools. Students generally showed a lack of knowledge of lesson topics on the pretest; on the post-test, most students were able to articulate basic facts about contour maps, impact crater formation, volcanic rocks, and features of Mars. The materials are recommended for use with sighted students as well as those with visual impairments because of their concrete, tactile nature.

Pattern analysis on dielectric breakdown characteristics of biodegradable polyethylene film under nonuniform electric field

SUMMARY This article presents pattern analysis to identify the dielectric breakdown characteristics of biodegradable polyethylene film under nonuniform electric field affected by the contaminated conditions, with low-density polyethylene (LDPE) film as the reference. When the specimens were immersed in the electrolyte for different periods, their degradation was observed and the breakdown experiments were carried out by the needle-plane electrode pattern with the air gap of 10 mm. The breakdown voltage was measured to determine the discharge and breakdown mechanism in the air/film gap under the nonuniform electric field. Meanwhile, the breakdown phenomena were captured by a monocular-video-zoom microscope, and the related breakdown characteristics were quantitatively analyzed through the methods of image processing and fractal dimension to establish the relationship between the pattern characteristics of breakdown craters and the dielectric properties. It is found that the morphology of breakdown region and the distribution of discharge profile in relationship with the contaminated levels can provide an optical evaluation method for the insulating materials. Compared with LDPE, biodegradable polyethylene shows the better breakdown endurance. By increasing the electrolyte conductivity and the immersion time, the breakdown voltage, the breakdown area, and the box dimension of the breakdown crater decrease. The breakdown voltage is higher than that of LDPE, whereas the breakdown area and the box dimension are lower. The results obtained indicate that the image–pattern identification technique is fairly well to quantify the breakdown phenomena of polymer films. Both breakdown area and box dimension reasonably give a scale to identify the dielectric properties for further investigation on feasibility of using biodegradable polymers. Copyright © 2011 John Wiley & Sons, Ltd.

Origin of craters on Phoebe: comparison withCassini’s data

Phoebe is one of the irregular satellites of Saturn; the images taken by Cassini-Huygens spacecraft allowed us to analyze its surface and the craters on it. We study the craters on Phoebe produced by Centaur objects from the Scattered Disk (SD) and plutinos escaped from the 3:2 mean motion resonance with Neptune and compare our results with the observations by Cassini. We use previous simulations on trans-Neptunian Objects and a method that allows us to obtain the number of craters and the cratering rate on Phoebe. We obtain the number of craters and the greatest crater on Phoebe produced by Centaurs in the present configuration of the Solar System. Moreover, we obtain a present normalized rate of encounters of Centaurs with Saturn of $\dot F = 7.1 \times 10^{-11}$ per year, from which we can infer the current cratering rate on Phoebe for each crater diameter. Our study and the comparison with the observations suggest that the main crater features on Phoebe are unlikely to have been produced in the present configuration of the Solar System and that they must have been acquired when the SD were depleted in the early Solar System. If this is what happened and the craters were produced when Phoebe was a satellite of Saturn, then it had to be captured, very early in the evolution of the Solar System.

The widespread occurrence of high-calcium pyroxene in bright-ray craters on the Moon and implications for lunar-crust composition

[1] We investigated the continuous spectral features of fresh craters on the Moon accompanied by distinctive bright rays, with cavity diameters between 8 and 24 km. We used the data from the Spectral Profiler onboard SELENE (Kaguya) to gain a better understanding of the composition of the lunar highland crust. We found that the observed spectra exhibited strong symmetric absorption around 1 μm and recognizable absorption around 1.3 μm. The spectra around a few craters showed a drastic change in the relative strengths of these two absorption bands s1.3/1.0 at different locations in and around the craters, indicating differences in the abundance of plagioclase and mafic minerals. In contrast, the spectra around most of the craters showed no significant variation in spectral shape, with an essentially constant s1.3/1.0. We analyzed the absorption features of the craters with an essentially constant s1.3/1.0 using the Modified Gaussian Model. We found that the strongest symmetric absorption bands were centered at 0.97–1.01 μm with s1.3/1.0 ≈ 0.2–0.6. Comparing these values with data from known samples, we concluded that high-calcium pyroxene (HCP) is the most plausible dominant mafic mineral identified from the observed spectra. The fact that we detected such HCP-dominant spectra among rayed craters widely spaced across the lunar highland implies that the major mafic component of some portions of the lunar crust is HCP rather than low-calcium pyroxene (LCP).

Plasma Temperature and Electron Density of Dry µ-EDM on Stainless Steel and Silicon: A Comparison

Fabricating micro/nano-features in devices and largescale production with short lead times is challenging, and many individual and hybrid processes have been developed to meet this challenge. Among nonconventional processes, micro-electric discharge machining (µ-EDM) has many advantages due to the possibility of precise and accurate 2D and 3D machining of complex shapes. Dry µ-EDM is used to process assembled or semi-assembled products. Attempts are being made to improve the µ-EDM process, and further improvement is possible through better understanding the role of discharge plasma in the machining process. We studied plasma and crater characteristics during dry µ-EDM, calculating plasma parameters for different discharge energies using optical emission spectroscopy. Line pair method and modified Saha equations are used to calculate plasma temperature and electron density respectively. Craters were morphologically analyzed using scanning electron microscopy (SEM), and plasma and crater characteristics on stainless steel and silicon were compared.

Kamil Crater (Egypt): Ground truth for small-scale meteorite impacts on Earth

Kamil Crater (Egypt): Ground truth for small-scale meteorite impacts on Earth

Crater Characteristics of Tungsten Spheres Impacting Steel Target

The armed steel target impacted vertically by tungsten spheres with different initial velocities and masses was studied by experiments. The macroscopic properties of crater were analyzed by the shape features of crater, the size dimension of crater, cracks along the penetration tunnel and the characteristics of recovered tungsten spheres. The results show that the everted rimmed and irregular shape of crater is heavier with velocity and mass of tungsten sphere. The shape of the top surface of impactor changes from the original sphere to the flat profile and the mass shows an obvious drop at a higher impact velocity The ratio of the crater diameter to the diameter of tungsten sphere, and the ratio of the crater depth to the crater diameter both descend with the mass at the same initial velocity of tungsten sphere. The specific expression of nondimensional penetration depth versus dynamic pressure is given by experiment data.

Study on the nano-powder-mixed sinking and milling micro-EDM of WC-Co

Present study investigates the feasibility of improving surface characteristics in the micro-electric discharge machining (EDM) of cemented tungsten carbide (WC–Co), a widely used die and mould material, using graphite nano-powder-mixed dielectric. In this context, a comparative analysis has been carried out on the performance of powder-mixed sinking and milling micro-EDM with view of obtaining smooth and defect-free surfaces. The surface characteristics of the machined carbide were studied in terms of surface topography, crater characteristics, average surface roughness (Ra) and peak-to-valley roughness (Rmax). The effect of graphite powder concentration on the spark gap, material removal rate (MRR) and electrode wear ratio (EWR) were also discussed for both die-sinking and milling micro-EDM of WC–Co. It has been observed that the presence of semi-conductive graphite nano-powders in the dielectric can significantly improve the surface finish, enhance the MRR and reduce the EWR. Both the surface topography and crater distribution were improved due to the increased spark gap and uniform discharging in powder-mixed micro-EDM. The added nano-powder can lower the breakdown strength and facilitate the ignition process thus improving the MRR. However, for a fixed powder material and particle size, all the performance parameters were found to vary significantly with powder concentration. Among the two processes, powder-mixed milling micro-EDM was found to provide smoother and defect-free surface compared to sinking micro-EDM. The lowest value of Ra (38 nm) and Rmax (0.17 μm) was achieved in powder-mixed milling micro-EDM at optimum concentration of 0.2 g/L and electrical setting of 60 V and stray capacitance.