This study analyzes the mechanical and elemental properties of lunar meteorites DHOFAR 1084, JAH 838, NWA 11444, and HED meteorite NWA 6013. Utilizing microscale rock mechanics experiments, that is, ...nanoindentation testing, this research reveals significant heterogeneity in both mechanical and elemental attributes across the mineral samples. Olivines, pyroxene, feldspar, and spinel demonstrate similar compositional and mechanical characteristics. Conversely, other silicate and oxide minerals display variations in their mechanical properties. Terrestrial olivines subjected to nanoindentation tests exhibit increased hardness and a higher Young's modulus than their lunar counterparts. A linear correlation is observed between the H/Er ratio and both plastic and elastic energies. Additionally, the alignment of mineral phases along a constant H/Er ratio suggests variations in local porosity. This study also highlights the need for further research focusing on porosity, phase insertions within the matrix, and structural orientations to refine our understanding of these mechanical characteristics. The findings have direct implications for in situ resource utilization strategies and future state‐of‐the‐art impact models. This comprehensive characterization serves as a foundational resource for future research efforts in space science and mining.
Meteoroid behaviour during atmospheric interaction provides clues about the strength and density of cometary disintegration products, establishing a bridge between different research fields. We have ...estimated the strength of cometary meteoroids by studying meteor ablation light curves measured accurately from multiple-station meteor observation programmes. Our approach assumes that the typical height for meteoroid fragmentation is associated with the peak of meteor luminosity. The strength of cometary meteoroids is independent of the entry velocity and very similar for cometary streams with similar ages. Meteoroids from periodic comets have typical strength of ∼104 dyn cm−2. The only exception among the studied comets is the extremely fluffy particles from 21P/Giacobini–Zinner that exhibit ∼4×102 dyn cm−2. Finally, evolved bodies, e.g. 2P/Encke and 3200 Phaeton, release the toughest meteoroids. We suggest that the main physical difference between cometary particles reaching the Earth from several sources could be a different degree of compaction arising from different physical processing of cometary nuclei by collisional processes, thermal and, perhaps, aqueous alteration. Meteor data suggest that highly processed cometary nuclei produce the meteoroids with the largest tensile strength values while ‘pristine comets’ are producing meteoroids with the lowest strength values characteristic of bodies with a low degree of compaction.
ABSTRACT
Meteoroids impacting the Earth atmosphere are commonly classified using the PE criterion. This criterion was introduced to support the identification of the fireball type by empirically ...linking its orbital origin and composition characteristics. Additionally, it is used as an indicator of the meteoroid tensile strength and its ability to penetrate the atmosphere. However, the level of classification accuracy of the PE criterion depends on the ability to constrain the value of the input data, retrieved from the fireball observation, required to derive the PE value. To overcome these uncertainties and achieve a greater classification detail, we propose a new formulation using scaling laws and dimensionless variables that groups all the input variables into two parameters that are directly obtained from the fireball observations. These two parameters, α and β, represent the drag and the mass-loss rates along the luminous part of the trajectory, respectively, and are linked to the shape, strength, ablation efficiency, mineralogical nature of the projectile, and duration of the fireball. Thus, the new formulation relies on a physical basis. This work shows the mathematical equivalence between the PE criterion and the logarithm of 2αβ under the same PE criterion assumptions. We demonstrate that log(2αβ) offers a more general formulation that does not require any preliminary constraint on the meteor flight scenario and discuss the suitability of the new formulation for expanding the classification beyond fully disintegrating fireballs to larger impactors including meteorite-dropping fireballs. The reliability of the new formulation is validated using the Prairie Network meteor observations.
CM chondrites are aqueously altered rocks that contain ∼9
wt% H
2O
+ (i.e., indigenous water) bound in phyllosilicates; also present are clumps of serpentine-tochilinite intergrowths (previously ...called “poorly characterized phases” or PCP), pentlandite and Ni-bearing pyrrhotite. We studied 11 CM chondrites that span the known range from least altered to most altered. We used various petrologic properties (many previously identified) that provide information regarding the degree of aqueous alteration. There are no known unaltered or slightly altered CM chondrites (e.g., rocks containing numerous chondrules with primary igneous glass). Some CM properties result from processes associated with early and intermediate stages of the alteration sequence (i.e., hydration of matrix, alteration of chondrule glass, and production of large PCP clumps). Other petrologic properties reflect processes active throughout the alteration sequence; these include oxidation of metallic Fe–Ni, alteration of chondrule phenocrysts, changes in PCP composition (reflecting an increase in the phyllosilicate/sulfide ratio), and changes in carbonate mineralogy (reflecting the development of dolomite and complex carbonates at the expense of Ca carbonate).
On the basis of these parameters, we propose a numerical alteration sequence for CM chondrites. Because there are no known CM samples that display only incipient alteration, the least altered sample was arbitrarily assigned to subtype 2.6. The most altered CM chondrites, currently classified CM1, are assigned to subtype 2.0. These highly altered rocks have essentially no mafic silicates; they contain chondrule pseudomorphs composed mainly of phyllosilicate. However, their bulk compositions are CM-like, and they are closer in texture to other C2 chondrites than to CI1 chondrites (which lack chondrule pseudomorphs). Using several diagnostic criteria, we assigned petrologic subtypes (±0.1) to every CM chondrite in our study: QUE 97990, CM2.6; Murchison, CM2.5; Kivesvaara, CM2.5; Murray, CM2.4/2.5; Y 791198, CM2.4; QUE 99355, CM2.3; Nogoya, CM2.2; Cold Bokkeveld, CM2.2; QUE 93005, CM2.1; LAP 02277, CM2.0; MET 01070, CM2.0.
The proposed CM numerical alteration sequence improves upon the existing scheme of
Browning et al. (1996) in that it does not require a complicated algorithm applied to electron-microprobe data to determine the average matrix phyllosilicate composition. The new sequence is more comprehensive and employs petrologic subtypes that are easier to use and remember than mineralogic alteration index values.
New neutron-activation analyses of QUE 97990, QUE 93005, MET 01070, Murchison and Crescent, together with literature data, confirm the compositional uniformity of the CM group; different degrees of alteration among CM chondrites do not lead to resolvable bulk compositional differences. This suggests that the textural differences among individual CM chondrites reflect progressive alteration of similar hypothetical CM3.0 starting materials in different regions of the same parent body, with minimal aqueous transport of materials over appreciable (e.g., meters) distances.
We have carried out a continuous multiband photometric monitoring of the nuclear activity of comet 29P/Schwassmann–Wachmann 1 from 2008 to 2010. Our main aim has been to study the outburst mechanism ...on the basis of a follow-up of the photometric variations associated with the release of dust. We have used a standardized method to obtain the 10-arcsec nucleus photometry in the V, R and I filters of the Johnson–Kron–Cousins system, which are accurately calibrated with standard Landolt stars. The production of dust in the R and I bands during the 2010 February 3 outburst has been also computed. We conclude that the massive ejection of large (optically thin) particles from the surface at the time of the outburst is the triggering mechanism to produce the outburst. The ulterior sublimation of these ice-rich dust particles during the following days induces fragmentation, generating micrometre-sized grains, which increase the dust spatial density to produce the outburst in the optical range as a result of the scattering of sunlight. The material leaving the nucleus adopts a fan-like dust feature, formed by micrometre-sized particles that decay in brightness as it evolves outwards. By analysing the photometric signal measured in a standardized 10-arcsec aperture using the phase dispersion minimization technique, we have found a clear periodicity of 50 d. Remarkably, this value is also consistent with an outburst frequency of 7.4 outbursts per yr deduced from the number of outbursts noticed during the effective observing time.
The petrology and mineralogy of shock melt veins in the L6 ordinary chondrite host of Villalbeto de la Peña, a highly shocked, L chondrite polymict breccia, have been investigated in detail using ...scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, and electron probe microanalysis. Entrained olivine, enstatite, diopside, and plagioclase are transformed into ringwoodite, low‐Ca majorite, high‐Ca majorite, and an assemblage of jadeite‐lingunite, respectively, in several shock melt veins and pockets. We have focused on the shock behavior of diopside in a particularly large shock melt vein (10 mm long and up to 4 mm wide) in order to provide additional insights into its high‐pressure polymorphic phase transformation mechanisms. We report the first evidence of diopside undergoing shock‐induced melting, and the occurrence of natural Ca‐majorite formed by solid‐state transformation from diopside. Magnesiowüstite has also been found as veins injected into diopside in the form of nanocrystalline grains that crystallized from a melt and also occurs interstitially between majorite‐pyrope grains in the melt‐vein matrix. In addition, we have observed compositional zoning in majorite‐pyrope grains in the matrix of the shock‐melt vein, which has not been described previously in any shocked meteorite. Collectively, all these different lines of evidence are suggestive of a major shock event with high cooling rates. The minimum peak shock conditions are difficult to constrain, because of the uncertainties in applying experimentally determined high‐pressure phase equilibria to complex natural systems. However, our results suggest that conditions between 16 and 28 GPa and 2000–2200 °C were reached.
The interaction of 14 different probe organic molecules with the crystalline (010) forsterite Mg
SiO
surface has been studied at quantum chemical level by means of B3LYP-D2* periodic simulations. The ...probe molecules are representatives of the class of soluble organic compounds found in carbonaceous meteorites, namely: aliphatic and aromatic hydrocarbons, alcohols, carbonyl compounds, amines, amides, nitrogen heterocycles, carboxylic and hydroxycarboxylic acids, sulfonic and phosphonic acids, amino acids, and carbohydrates. With the exception of the aliphatic and aromatic hydrocarbons, the interaction takes place mainly between the O and N electron donor atoms of the molecules and the outermost Mg surface cations, and/or by hydrogen bonds of H atoms of the molecules with O surface atoms. Dispersion also contributes to the final interaction energies. Each surface/molecule complex has also been characterized by computing its harmonic vibrational spectrum, in which the most significant frequency perturbations caused by the surface interaction are described. With the calculated interaction energies, a trend of the intrinsic affinity of the probe molecules with the silicate surface has been obtained. However, this affinity scale does not correlate with the experimental abundances of the class of compounds found in the Murchison meteorite. A brief discussion of this lack of correlation and the factors that can help us to understand the abundances is provided.
Although no known asteroid poses a threat to Earth for at least the next century, the catalogue of near-Earth asteroids is incomplete for objects whose impacts would produce regional devastation
. ...Several approaches have been proposed to potentially prevent an asteroid impact with Earth by deflecting or disrupting an asteroid
. A test of kinetic impact technology was identified as the highest-priority space mission related to asteroid mitigation
. NASA's Double Asteroid Redirection Test (DART) mission is a full-scale test of kinetic impact technology. The mission's target asteroid was Dimorphos, the secondary member of the S-type binary near-Earth asteroid (65803) Didymos. This binary asteroid system was chosen to enable ground-based telescopes to quantify the asteroid deflection caused by the impact of the DART spacecraft
. Although past missions have utilized impactors to investigate the properties of small bodies
, those earlier missions were not intended to deflect their targets and did not achieve measurable deflections. Here we report the DART spacecraft's autonomous kinetic impact into Dimorphos and reconstruct the impact event, including the timeline leading to impact, the location and nature of the DART impact site, and the size and shape of Dimorphos. The successful impact of the DART spacecraft with Dimorphos and the resulting change in the orbit of Dimorphos
demonstrates that kinetic impactor technology is a viable technique to potentially defend Earth if necessary.
Advances in Astronomy is pleased to announce the appointment of Prof Josep Trigo Rodríguez as its new Chief Editor. In this Editorial, Prof Trigo introduces himself, describes some of the journal’s ...journey and current status, and shares his vision and aspirations for its future.
Aims.
The existence of asteroid complexes produced by the disruption of these comets suggests that evolved comets could also produce high-strength materials able to survive as meteorites. We chose as ...an example comet 2P/Encke, one of the largest object of the so-called Taurid complex. We compare the reflectance spectrum of this comet with the laboratory spectra of some Antarctic ungrouped carbonaceous chondrites to investigate whether some of these meteorites could be associated with evolved comets.
Methods.
We compared the spectral behaviour of 2P/Encke with laboratory spectra of carbonaceous chondrites. Different specimens of the common carbonaceous chondrite groups do not match the overall features and slope of the comet 2P/Encke. By testing anomalous carbonaceous chondrites, we found two meteorites: Meteorite Hills 01017 and Grosvenor Mountains 95551, which could be good proxies for the dark materials that formed this short-period comet. We hypothesise that these two meteorites could be rare surviving samples, either from the Taurid complex or another compositionally similar body. In any case, it is difficult to get rid of the effects of terrestrial weathering in these Antarctic finds, and further studies are needed. A future sample return from the so-called dormant comets could also be useful to establish a ground truth on the materials forming evolved short-period comets.
Results.
As a natural outcome, we think that identifying good proxies of 2P/Encke-forming materials might have interesting implications for future sample-return missions to evolved, potentially dormant, or extinct comets. Understanding the compositional nature of evolved comets is particularly relevant in the context of the future mitigation of impact hazard from these dark and dangerous projectiles.
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