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1.
Abstract– Eight saponite‐rich micrometeorites with very similar mineralogy were found from the recent surface snow in Antarctica. They might have come to Earth as a larger meteoroid and broke up into pieces on Earth, because they were recovered from the same layer and the same location of the snow. Synchrotron X‐ray diffraction (XRD) analysis indicates that saponite, Mg‐Fe carbonate, and pyrrhotite are major phases and serpentine, magnetite, and pentlandite are minor phases. Anhydrous silicates are entirely absent from all micrometeorites, suggesting that their parental object has undergone heavy aqueous alteration. Saponite/serpentine ratios are higher than in the Orgueil CI chondrite and are similar to the Tagish Lake carbonaceous chondrite. Transmission electron microscope (TEM) observation indicates that serpentine occupies core regions of fine‐grained saponite, pyrrhotite has a low‐Ni concentration, and Mg‐Fe carbonate shows unique concentric ring structures and has a mean molar Mg/(Mg + Fe) ratio of 0.7. Comparison of the mineralogy to hydrated chondrites and interplanetary dust particles (IDPs) suggests that the micrometeorites are most similar to the carbonate‐poor lithology of the Tagish Lake carbonaceous chondrite and some hydrous IDPs, but they show a carbonate mineralogy dissimilar to any primitive chondritic materials. Therefore, they are a new variant of saponite‐rich micrometeorite extracted from a primitive hydrous asteroid and recently accreted to Antarctica.  相似文献   

2.
Abstract— The radicals in the insoluble organic matter (IOM) from the Tagish Lake meteorite were studied by electron paramagnetic resonance and compared to those existing in the Orgueil and Murchison meteorites. As in the Orgueil and Murchison meteorites, the radicals in the Tagish Lake meteorite are heterogeneously distributed and comprise a substantial amount (?42%) of species with a thermally accessible triplet state and with the same singlet‐triplet gap, ΔE ?0.1 eV, as in the Orgueil and Murchison meteorites. These species were identified as diradicaloid moieties. The existence of similar diradicaloid moieties in three different carbonaceous chondrites but not in terrestrial IOM strongly suggests that these moieties could be “fingerprints” of the extraterrestrial origin of meteoritic IOM and markers of its synthetic pathway before its inclusion into a parent body.  相似文献   

3.
Dicarboxylic acids were searched for in three Sutter's Mill (SM) fragments (SM2 collected prerain, SM12, and SM41) and found to occur almost exclusively as linear species of 3‐ to 14‐carbon long. Between these, concentrations were low, with measured quantities typically less than 10 nmole g?1 of meteorite and a maximum of 6.8 nmole g?1 of meteorite for suberic acid in SM12. The SM acids' molecular distribution is consistent with a nonbiological origin and differs from those of CMs, such as Murchison or Murray, and of some stones of the C2‐ungrouped Tagish Lake meteorite, where they are abundant and varied. Powder X‐ray diffraction of SM12 and SM41 show them to be dominated by clays/amorphous material, with lesser amounts of Fe‐sulfides, magnetite, and calcite. Thermal gravimetric (TG) analysis shows mass losses up to 1000 °C of 11.4% (SM12) and 9.4% (SM41). These losses are low compared with other clay‐rich carbonaceous chondrites, such as Murchison (14.5%) and Orgueil (21.1%). The TG data are indicative of partially dehydrated clays, in accordance with published work on SM2, for which mineralogical studies suggest asteroidal heating to around 500 °C. In view of these compositional traits and mineralogical features, it is suggested that the dicarboxylic acids observed in the SM fragments we analyzed likely represent a combination of molecular species original to the meteorite as well as secondary products formed during parent‐body alteration processes, such as asteroidal heating.  相似文献   

4.
Abstract— The Tagish Lake meteorite soluble organic suite has a general composition that differs from those of both CI and CM chondrites. These differences suggest that distinct processes may have been involved in the formation of different groups of organics in meteorites. Tagish Lake alkyl dicarboxylic acids have a varied, abundant distribution and are, with carboxylated pyridines, the only compounds to have an occurrence comparable to that of the Murchison meteorite. This study has undertaken their molecular and isotopic characterization, with the aim to understand their origin and to gain insights into the evolutionary history of the meteorite parent body. Tagish Lake alkyl dicarboxylic acids are present as a homologous series of saturated and unsaturated species with three‐ through ten‐carbon atom chain length. Linear saturated acids are predominant and show decreasing amounts with increasing chain length. A total of 44 of these compounds were detected with the most abundant, succinic acid, present at ?40 nmol/g meteorite. Overall the molecular distribution of Tagish Lake dicarboxylic acids shows a remarkable compound‐to‐compound correspondence with those observed in the Murchison and Murray meteorites. In both Tagish Lake and Murchison, the imides of the more abundant dicarboxylic acids were also observed. The hydrogen and carbon isotopic compositions of individual Tagish Lake dicarboxylic acids were determined and compared to those of the corresponding acids in the Murchison meteorite. All δD and δ13C values for Tagish Lake acids are positive and show a substantial isotopic enrichment. δD values vary from, approximately, +1120%o for succinic acid to +1530%o for methyl glutaric acid. δ13C values ranged from +12.6%o for methyl glutaric acid to +22.9%o for glutaric acid, with adipic acid having a significantly lower value (+5.5%o). Murchison dicarboxylic acid showed similar isotopic values: their δ513C values were generally higher by an average 17% and δD values were lower for succinic and glutaric acids, possibly due to contamination. The molecular and isotopic data collected for these compounds restrict their possible origin to processes, either interstellar or of very cold nebular regions, that produced significant isotopic enrichments. Saturated or partially unsaturated nitriles and dinitriles appear to be good precursor candidates as their hydrolysis, upon water exposure, would produce dicarboxylic acids and other carboxylated species found in Tagish Lake. This evolutionary course could possibly include pre‐accretionary processes.  相似文献   

5.
Abstract— Depending on their velocity, entry angle and mass, extraterrestrial dust particles suffer certain degrees of heating during entry into Earth's atmosphere, and the mineralogy and chemical composition of these dust particles are significantly changed. In the present study, pulse-heating experiments simulating the atmospheric entry heating of micrometeoroids were carried out in order to understand the mineralogical and chemical changes quantitatively as well as to estimate the peak temperature experienced by the particles during entry heating. Fragments of the CI chondrites Orgueil and Alais as well as pyrrhotites from Orgueil were used as analogue material. The experiments show that the volatile elements S, Zn, Ga, Ge, and Se can be lost from 50 to 100 μm sized CI meteorite fragments at temperatures and heating times applicable to the entry heating of similar sized cosmic dust particles. It is concluded that depletions of these elements relative to CI as observed in micrometeorites are mainly caused by atmospheric entry heating. Besides explaining the element abundances in micrometeorites, the experimentally obtained release patterns can also be used as indicators to estimate the peak heating of dust particles during entry. Using the abundances of Zn and Ge and assuming their original concentrations close to CI, a maximum heating of 1100–1200 °C is obtained for previously analyzed Antarctic micrometeroites. Thermal alteration also strongly influenced the mineralogy of the meteorite fragments. While the unheated samples mainly consisted of phyllosilicates, these phases almost completely transformed into olivine and pyroxene in the fragments heated to ≥800 °C. Therefore, dust particles that still contain hydrous minerals were probably never heated to temperatures ≥800 °C in the atmosphere. During continued heating, the grain size of the newly formed silicates increased and the composition of the olivines equilibrated. Applying these results quantitatively to Antarctic micrometeorites, typical peak temperatures in the range of 1100–1200 °C during atmospheric entry heating are deduced. This temperature range corresponds to the one obtained from the volatile element concentrations measured in these micrometeorites and points to an asteroidal origin of the particles.  相似文献   

6.
Abstract— We have studied the carbon and nitrogen stable isotope geochemistry of a small pristine sample of the Tagish Lake carbonaceous chondrite by high‐resolution stepped‐combustion mass spectrometry, and compared the results with data from the Orgueil (CI1), Elephant Moraine (EET) 83334 (CM1) and Murchison (CM2) chondrites. The small chip of Tagish Lake analysed herein had a higher carbon abundance (5.81 wt%) than any other chondrite, and a nitrogen content (?1220 ppm) between that of CI1 and CM2 chondrites. Owing to the heterogeneous nature of the meteorite, the measured carbon abundance might be artificially high: the carbon inventory and whole‐rock carbon isotopic composition (δ13C ? +24.4%o) of the chip was dominated by 13C‐enriched carbon from the decomposition of carbonates (between 1.29 and 2.69 wt%; δ13C ? +67%o and δ18O ? +35%o, in the proportions ?4:1 dolomite to calcite). In addition to carbonates, Tagish Lake contains organic carbon (?2.6 wt%, δ13C ? ?9%o; 1033 ppm N, δ15N ? +77%o), a level intermediate between CI and CM chondrites. Around 2% of the organic material is thermally labile and solvent soluble. A further ?18% of the organic species are liberated by acid hydrolysis. Tagish Lake also contains a complement of presolar grains. It has a higher nanodiamond abundance (approximately 3650–4330 ppm) than other carbonaceous chondrites, along with ?8 ppm silicon carbide. Whilst carbon and nitrogen isotope geochemistry is not diagnostic, the data are consistent with classification of Tagish Lake as a CI2 chondrite.  相似文献   

7.
Abstract— The saturation magnetization, saturation remanent magnetization, the coercive, and remanent coercive force were determined at room and liquid nitrogen temperatures for three pieces of the Tagish Lake meteorite. The results are compared to similar data for four other chondrites (Allende, Murray, Orgueil, and Murchison). The data suggests that the Tagish Lake meteorite is magnetically homogeneous, and is not as magnetically hard as the comparison chondrites. The magnetization measurements indicate that it contains about 10–11% multi‐domain magnetite. Magnetic susceptibility measurements on all the samples from 77 K to room temperature showed a Verwey transition for all the samples which contain a significant amount of multi‐domain magnetite. The coercive force data further indicate that the magnetite in Tagish Lake is multi‐domain and that the grain size is small and approximately 4–9 μm.  相似文献   

8.
Abstract— High‐performance liquid chromatography (HPLC) based amino acid analysis of a Tagish Lake meteorite sample recovered 3 months after the meteorite fell to Earth have revealed that the amino acid composition of Tagish Lake is strikingly different from that of the CM and CI carbonaceous chondrites. We found that the Tagish Lake meteorite contains only trace levels of amino acids (total abundance = 880 ppb), which is much lower than the total abundance of amino acids in the CI Orgueil (4100 ppb) and the CM Murchison (16 900 ppb). Because most of the same amino acids found in the Tagish Lake meteorite are also present in the Tagish Lake ice melt water, we conclude that the amino acids detected in the meteorite are terrestrial contamination. We found that the exposure of a sample of Murchison to cold water lead to a substantial reduction over a period of several weeks in the amount of amino acids that are not strongly bound to the meteorite matrix. However, strongly bound amino acids that are extracted by direct HCl hydrolysis are not affected by the leaching process. Thus even if there had been leaching of amino acids from our Tagish Lake meteorite sample during its 3 month residence in Tagish Lake ice and melt water, a Murchison type abundance of endogenous amino acids in the meteorite would have still been readily detectable. The low amino acid content of Tagish Lake indicates that this meteorite originated from a different type of parent body than the CM and CI chondrites. The parent body was apparently devoid of the reagents such as aldehyldes/ketones, HCN and ammonia needed for the effective abiotic synthesis of amino acids. Based on reflectance spectral measurements, Tagish Lake has been associated with P‐ or D‐type asteroids. If the Tagish Lake meteorite was indeed derived from these types of parent bodies, our understanding of these primitive asteroids needs to be reevaluated with respect to their potential inventory of biologically important organic compounds.  相似文献   

9.
Abstract— Carbonaceous chondrites are among the most analyzed geological materials on Earth. However, despite this attention, and unlike most terrestrial rocks, little is known on the abundance of individual phases within them. Here, we show how a combination of several novel X‐ray diffraction (XRD) techniques (including a high‐brightness X‐ray MicroSource®), and Mössbauer spectroscopy, allows a complete modal mineralogy to be ascertained from even the most highly unequilibrated, fine‐grained chondrites for all minerals of abundance >1 wt%. Knowledge of the modal mineralogy of a sample also allows us to calculate grain density. We analyzed Allende, Murchison, Tagish Lake, and Orgueil. Based on our modal data, the grain density estimates for Allende, Murchison, and Orgueil are close to literature values. In the case of Tagish Lake, there is no published grain density, although a bulk density measurement does exist. Taking our estimate of grain density, and the measured bulk density, we calculate an exceptionally high porosity of 41% for this meteorite, similar to some chondritic IDPs and in line with a porosity calculated from an entry model for the Tagish Lake fireball. Although it is an oxidized CV, magnetite is present in Allende at a level of <0.5 wt% or <0.3 vol%, a result that is substantiated by several other instrumental studies. This may be an oxidized meteorite, but that oxidation is not manifested in abundant magnetite. In addition, we note appreciable fayalitic olivine in Orgueil, detected by both XRD and Mössbauer. We employed MicroSource® XRD to look at heterogeneity in mineral abundance in Orgueil and found substantial variation, with phyllosilicates varying inversely with olivine. The data suggest that Orgueil was initially composed primarily of anhydrous materials, which have been partially, but not completely, altered. Although the data are preliminary, comparison between our XRD modal assessment, bulk chemistry, grain density, and Mössbauer data, suggests that our estimates of mineral abundance are robust. The advent of MicroSource® XRD allows similar modal data to be acquired from samples as small as a few hundred micrograms.  相似文献   

10.
The CI1 Orgueil meteorite is a highly aqueously altered carbonaceous chondrite. It has been extensively studied, and despite its extensive degree of aqueous alteration and some documented instances of contamination, several indigenous organic compounds including amino acids, carboxylic acids, and nucleobases have been detected in its carbon‐rich matrix. We recently developed a novel gas chromatographic method for the enantiomeric and compound‐specific isotopic analyses of meteoritic aliphatic monoamines in extracts and have now applied this method to investigate the monoamine content in Orgueil. We detected 12 amines in Orgueil, with concentrations ranging from 1.1 to 332 nmol g?1 of meteorite and compared this amine content in Orgueil with that of the CM2 Murchison meteorite, which experienced less parent‐body aqueous alteration. Methylamine is four times more abundant in Orgueil than in Murchison. As with other species, the amine content in Orgueil extracts shows less structural diversity than that in Murchison extracts. We measured the compound‐specific stable carbon isotopic ratios (δ13C) for 5 of the 12 monoamines detected in Orgueil and found a range of δ13C values from –20 to +59‰. These δ13C values fall into the range of other meteoritic organic compounds, although they are 13C‐depleted relative to their counterparts extracted from the Murchison meteorite. In addition, we measured the enantiomeric composition for the chiral monoamines (R)‐ and (S)‐sec‐butylamine in Orgueil, and found it was racemic within experimental error, in contrast with the l ‐enantiomeric excess found for its amino acid structural analog isovaline. The racemic nature of sec‐butylamine in Orgueil was comparable to that previously observed in Murchison, and to other CM2 and CR2 carbonaceous chondrites measured in this work (ALH 83100 [CM1/2], LON 94101 [CM2], LEW 90500 [CM2], LAP 02342 [CR2], and GRA 95229 [CR2]). These results allow us to place some constraints on the effects of aqueous alteration observed over the monoamine concentrations in Orgueil and Murchison, and to evaluate the primordial synthetic relationships between meteoritic monoamines and amino acids.  相似文献   

11.
Abstract– We have carried out a sample‐correlated spectroscopic and mineralogical investigation of samples from seven different collection sites of the Tagish Lake C2 chondrite. Rietveld refinement of high‐resolution powder X‐ray diffraction (XRD) data was used to determine quantitative major mineral abundances. Thermal infrared (400–4500 cm−1, 2.2–25.0 μm) spectra of the same samples were obtained using diffuse (biconical) reflectance infrared Fourier transform spectroscopy (DRIFTS). Our results are in good agreement with previous studies of the mineralogy of the Tagish Lake meteorite; we find however that Tagish Lake is more varied in major mineralogy than has previously been reported. In particular, we observed two new distinct lithologies, an inclusion‐poor magnetite‐ and sulfide‐rich lithology, and a carbonate‐rich, siderite‐dominated lithology in addition to the previously documented carbonate‐rich and carbonate‐poor lithologies. Grain density for each Tagish Lake sample was calculated from the measured mineral modal abundances and known mineral densities. For powders from three originally intact inclusion‐rich samples, the calculated grain density is 2.77 ± 0.05 g cm−3, in excellent agreement with those reported in the literature for other intact inclusion‐rich Tagish Lake samples. Tagish Lake disaggregated samples have a significantly higher calculated grain density due to their lower saponite‐serpentine content, likely a result of mineral separation in the meltwater holes from which they were collected; the disaggregated samples may not therefore adequately represent bulk samples of the Tagish Lake meteorite. The predominance of very fine‐grained material in the Tagish Lake samples investigated in this study is expected to produce infrared spectra representative of asteroidal regolith. Gypsum and talc have been found by XRD in powders from the inclusion‐rich, intact Tagish Lake samples in this study, and may have been present in the parent body; if present, these hydrous sulfates would complicate the interpretation of possible hydrated mineral features in asteroid infrared spectra.  相似文献   

12.
Seven trace elements (Ag, Co, Cs, Ga, In, Te, Tl) are either completely retained or are lost to the same extent in Abee samples heated at 700 °C for one week at 10?5-10?3 atm Ne or in 10?5 atm H2. Bi and Se are lost significantly more easily and Zn is better retained in samples heated in Ne than in H2. Zn retention varies inversely with ambient Ne pressure. Mobile element transport seems unaffected by physical interactions in the gas phase but may reflect solid-state surface effects. During week-long heating at low pressures (initially ～ 10?5 atm H2) S is mobilized only at 1000 °C while C contents decrease progressively from 600–1000 °C. Apparent activation energies for C are 60 kcal/mole below 700 °C and 16 kcal/mole above this temperature suggesting diffusive loss from different hosts and/or processes over different temperature intervals. In E4–6 chondrites C and S contents largely reflect nebular fractionation and condensation processes.  相似文献   

13.
Abstract— During preliminary examination of 81P/Wild 2 particles collected by the NASA Stardust spacecraft, we analyzed seven, sulfur embedded and ultramicrotomed particles extracted from five different tracks. Sections were analyzed using a scanning transmission X‐ray microscope (SXTM) and carbon X‐ray absorption near edge structure (XANES) spectra were collected. We compared the carbon XANES spectra of these Wild 2 samples with a database of spectra on thirty‐four interplanetary dust particles (IDPs) and with several meteorites. Two of the particles analyzed are iron sulfides and there is evidence that an aliphatic compound associated with these particles can survive high temperatures. An iron sulfide from an IDP demonstrates the same phenomenon. Another, mostly carbon free containing particle radiation damaged, something we have not observed in any IDPs we have analyzed or any indigenous organic matter from the carbonaceous meteorites, Tagish Lake, Orgueil, Bells and Murchison. The carbonaceous material associated with this particle showed no mass loss during the initial analysis but chemically changed over a period of two months. The carbon XANES spectra of the other four particles varied more than spectra from IDPs and indigenous organic matter from meteorites. Comparison of the carbon XANES spectra from these particles with 1. the carbon XANES spectra from thirty‐four IDPs (<15 micron in size) and 2. the carbon XANES spectra from carbonaceous material from the Tagish Lake, Orgueil, Bells, and Murchison meteorites show that 81P/Wild 2 carbon XANES spectra are more similar to IDP carbon XANES spectra then to the carbon XANES spectra of meteorites.  相似文献   

14.
Abstract— We present instrumental observations of the Tagish Lake fireball and interpret the observed characteristics in the context of two different models of ablation. From these models we estimate the pre‐atmospheric mass of the Tagish Lake meteoroid to be ?56 tonnes and its porosity to be between 37 and 58%, with the lowest part of this range most probable. These models further suggest that some 1300 kg of gram‐sized or larger Tagish Lake material survived ablation to reach the Earth's surface, representing an ablation loss of 97% for the fireball. Satellite recordings of the Tagish Lake fireball indicate that 1.1 times 1012 J of optical energy were emitted by the fireball during the last 4 s of its flight. The fraction of the total kinetic energy converted to light in the satellite pass band is found to be 16%. Infrasonic observations of the airwave associated with the fireball establish a total energy for the event of 1.66 ± 0.70 kT TNT equivalent energy. The fraction of this total energy converted to acoustic signal energy is found to be between 0.10 and 0.23%. Examination of the seismic recordings of the airwave from Tagish Lake have established that the acoustic energy near the sub‐terminal point is converted to seismic body waves in the upper‐most portion of the Earth's crust. The acoustic energy to seismic energy coupling efficiency is found to be near 10?6 for the Tagish Lake fireball. The resulting energy estimate is near 1.7 kT, corresponding to a meteoroid 4 m in diameter. The seismic record indicates extensive, nearly continuous fragmentation of the body over the height intervals from 50 to 32 km. Seismic and infrasound energy estimates are in close agreement with the pre‐atmospheric mass of 56 tonnes established from the modeling. The observed flight characteristics of the Tagish Lake fireball indicate that the bulk compressive strength of the pre‐atmospheric Tagish Lake meteoroid was near 0.25 MPa, while the material compressive strength (most appropriate to the recovered meteorites) was closer to 0.7 MPa. These are much lower than values found for fireballs of ordinary chondritic composition. The behavior of the Tagish Lake fireball suggests that it represents the lowest end of the strength spectrum of carbonaceous chondrites or the high end of cometary meteoroids. The bulk density and porosity results for the Tagish Lake meteoroid suggest that the low bulk densities measured for some small primitive bodies in the solar system may reflect physical structure dominated by microporosity rather than macroporosity and rubble‐pile assemblages.  相似文献   

15.
Abstract– Insight into the chemical history of an ungrouped type 2 carbonaceous chondrite meteorite, Wisconsin Range (WIS) 91600, is gained through molecular analyses of insoluble organic matter (IOM) using solid‐state 13C nuclear magnetic resonance (NMR) spectroscopy, X‐ray absorption near edge structure spectroscopy (XANES), and pyrolysis‐gas chromatography coupled with mass spectrometry (pyr‐GC/MS), and our previous bulk elemental and isotopic data. The IOM from WIS 91600 exhibits similarities in its abundance and bulk δ15N value with IOM from another ungrouped carbonaceous chondrite Tagish Lake, while it exhibits H/C, δ13C, and δD values that are more similar to IOM from the heated CM, Pecora Escarpment (PCA) 91008. The 13C NMR spectra of IOM of WIS 91600 and Tagish Lake are similar, except for a greater abundance of CHxO species in the latter and sharper carbonyl absorption in the former. Unusual cross‐polarization (CP) dynamics is observed for WIS 91600 that indicate the presence of two physically distinct organic domains, in which the degrees of aromatic condensation are distinctly different. The presence of two different organic domains in WIS 91600 is consistent with its brecciated nature. The formation of more condensed aromatics is the likely result of short duration thermal excursions during impacts. The fact that both WIS 91600 and PCA 91008 were subjected to short duration heating that is distinct from the thermal history of type 3 chondrites is confirmed by Carbon‐XANES. Finally, after being briefly heated (400 °C for 10 s), the pyrolysis behavior of Tagish Lake IOM is similar to that of WIS 91600 and PCA 91008. We conclude that WIS 91600 experienced very moderate, short duration heating at low temperatures (<500 °C) after an episode of aqueous alteration under conditions that were similar to those experienced by Tagish Lake.  相似文献   

16.
Abstract— Depending on their velocity, entry angle and mass, micrometeorites suffer different degrees of heating during their deceleration in the Earth's atmosphere, leading, in most cases, to significant textural, mineralogical and chemical modifications. One of these modifications is the formation of a magnetite shell around most micrometeorites, which until now could not be reproduced, neither theoretically nor experimentally. The present study was designed to better understand the entry heating effects on micrometeorites and especially the formation of the magnetite shell. Fragments of the Murchison and Orgueil meteorites were used as analogue material in flash‐heating experiments performed in a high‐temperature furnace; effects of temperature, heating duration, and oxygen fugacity were investigated. These experiments were able to reproduce most of the micrometeorites textures, from the vesicular fine‐grained micrometeorites to the totally melted cosmic spherules. For the first time, the formation of a magnetite shell could be observed on micrometeorite analogues. We suggest that the most plausible mechanism for the formation of this shell is a peripheral partial melting with subsequent magnetite crystallization at the surface of the micrometeorite. Furthermore, with this study, it is possible to estimate the atmospheric entry conditions of micrometeorites, such as the peak temperature and the duration of flash‐heating.  相似文献   

17.
Abstract— Using a nuclear microprobe, we measured the carbon and nitrogen concentrations and distributions in several interplanetary dust particles (IDPs) and Antarctic micrometeorites (MMs), and compared them to 2 carbonaceous chondrites: Tagish Lake and Murchison. We observed that IDPs are richest in both elements. All the MMs studied contain carbon, and all but the coarse‐grained and 1 melted MM contained nitrogen. We also observed a correlation in the distribution of carbon and nitrogen, suggesting that they may be held in an organic material. The implications for astrobiology of these results are discussed, as small extraterrestrial particles could have contributed to the origin of life on Earth by delivering important quantities of these 2 bio‐elements to the Earth's surface and their gas counterparts, CO2 and N2, to the early atmosphere.  相似文献   

18.
Most phyllosilicates on Mars appear to be associated with ancient terrains. As such, they may have experienced shock heating produced by impacts and could have been significantly altered or melted. We characterized the effects of high temperatures on the mid-to-far-infrared (mid-to-far-IR) emission (100–1400 cm?1; 7.1–100 μm) and near-infrared (NIR) reflectance (1.2–2.5 μm) spectra of phyllosilicates by measuring experimentally calcined (100–900 °C) phyllosilicates and also two zeolites. Correlated differential scanning calorimetry (DSC) measurements were also performed on each sample to provide insight into the thermal activities of the phyllosilicates and natural zeolites. Our results indicate that all phyllosilicates exhibit characteristic degradations in both NIR and mid-to-far-IR spectral properties between 400 and 800 °C, mainly attributable to the dehydroxylation and recrystallization processes as temperature increases. Spectral features of natural zeolites persist to higher temperatures compared to features of phyllosilicates during heating treatments. The thermal behaviors of phyllosilicate infrared (IR) properties are greatly influenced by the compositions of the octahedral cations: (1) changes in both the NIR and mid-to-far-IR spectra of phyllosilicates tend to occur at lower temperatures (300–400 °C) in the Fe3+-rich samples as compared to the Al3+-rich types (400–600 °C); (2) Mg2+-trioctahedral phyllosilicates hectorite, saponite, and sepiolite all display major mid-to-far-IR spectral changes at 700 °C, corresponding to the formation of enstatite; (3) phyllosilicates that have minor replacement of Mg2+ for Al3+ in octahedral positions (e.g. cheto-type montmorillonite and palygorskite) show an absorption band at ～920 cm?1 that becomes strong at 900 °C. Inconsistency between spectral behaviors in the mid-to-far-IR and NIR regions is also discussed for phyllosilicates. Results from this study have provided suggestive evidence for the scenario that some phyllosilicates could lose all original spectral features in mid-to-far-IR region while maintaining their characteristic hydration bands in NIR region in the same temperature range.  相似文献   

19.
Abstract— I have determined the composition via instrumental neutron activation analysis of a bulk pristine sample of the Tagish Lake carbonaceous chondrite fall, along with bulk samples of the CI chondrite Orgueil and of several CM chondrites. Tagish Lake has a mean of refractory lithophile element/Cr ratios like those of CM chondrites, and distinctly higher than the CI chondrite mean. Tagish Lake exhibits abundances of the moderately volatile lithophile elements Na and K that are slightly higher than those of mean CM chondrites. Refractory through moderately volatile siderophile element abundances in Tagish Lake are like those of CM chondrites. Tagish Lake is distinct from CM chondrites in abundances of the most volatile elements. Mean CI‐normalized Se/Co, Zn/Co and Cs/Co for Tagish Lake are 0.68 ± 0.01, 0.71 ± 0.07 and 0.76 ± 0.02, while for all available CM chondrite determinations, these ratios lie between 0.31 and 0.61, between 0.32 and 0.58, and between 0.39 and 0.74, respectively. Considering petrography, and oxygen isotopic and elemental compositions, Tagish Lake is an ungrouped member of the carbonaceous chondrite clan. The overall abundance pattern is similar to those of CM chondrites, indicating that Tagish Lake and CMs experienced very similar nebular fractionations. Bells is a CM chondrite with unusual petrologic characteristics. Bells has a mean CI‐normalized refractory lithophile element/Cr ratio of 0.96, lower than for any other CM chondrite, but shows CI‐normalized moderately volatile lithophile element/Cr ratios within the ranges of other CM chondrites, except for Na which is low. Iridium, Co, Ni and Fe abundances are like those of CM chondrites, but the moderately volatile siderophile elements, Au, As and Sb, have abundances below the ranges for CM chondrites. Abundances of the moderately volatile elements Se and Zn of Bells are within the CM ranges. Bells is best classified as an anomalous CM chondrite.  相似文献   

20.
Abstract— The C contents and δ13C values of eleven individual micrometeorites have been determined using a combination of stepped combustion and static mass spectrometry. A new low-blank procedure, involving pretreatment of the samples with a solvent to remove surficial contaminants, has enabled samples of 6–84 μg to be analysed successfully. The eleven samples (seven separated from Greenland cryoconite and four from Antarctic ice) were each split prior to C determination and a fragment taken for study using analytical electron microscopy. In this way, the chemical compositions were obtained thereby allowing comparison with other investigations. As with previous studies of micrometeorites collected at the Earth's surface, the major difficulty with interpreting the results involves distinguishing indigenous components from terrestrial contaminants. Overall C contents were typically <0.2 wt%, although one of the Greenland samples contained 1.5 wt% C, considered to arise mainly from algal contamination. For the other samples, around 0.05–0.15 wt% of the total C in each micrometeorite was considered to be organic in nature with at least some of this (if not all) being terrestrial in origin; the remainder was probably indigenous, being analogous to the macromolecular organic material found in primitive carbonaceous chondrites. The generally low content of this indigenous organic material, compared to conventional meteorites, is presumably a reflection of C loss from the micrometeorites either during atmospheric heating, or subsequent weathering. For that C combusting between 500 and 600 °C, ten of the samples appeared to show a simple two-component system (i.e., a mixture of blank and an isotopically light component; δ13C > ?32%). It is possible that the light component is Cδ, a fine-grained form of presolar diamond which is known to be prevalent in primitive chondritic meteorites. If so, then it is present in the micrometeorites at concentrations of ～30–600 ppm (typically 200 ppm), which is a similar level to that in meteorites. An analysis of algae separated from Greenland cryoconite shows tentative evidence for the presence of extraterrestrial silicon carbide; however, further work will be needed to substantiate this  相似文献   

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