Meteorite Classes Research Articles

AFM and SNOM characterization of ordinary chondrites: A contribution to solving the problem of asteroid reddening

AbstractSpace weathering (SW) is an ensemble of processes that act on a body exposed to the space environment. Typically, the exposure to SW results in the accumulation, at the surface, of nanoparticles, that are thought to be produced through a vaporization and subsequent cooling of the metallo‐silicaceous components exposed to the space environment. The presence of such nanoparticles is responsible for the so‐called reddening of the asteroids' reflectance spectra (i.e., the increase in Vis–NIR reflectance with increase in wavelength) observed by remote‐sensing measurements. To investigate the mechanism of formation of these nanoparticles, we have employed atomic force microscopy (AFM) and scanning near‐field optical microscopy (SNOM) to morphologically and optically characterize ordinary chondrites (OC), the most abundant class of meteorites collected on Earth and whose parent bodies are the S‐type asteroids. The AFM study reveals the occurrence of a diffuse nanophase (martensite) in the meteorite's metal inclusions. Since the same areas show a reddening of the reflectivity spectra, this suggests that such spectral modification is based on a shock‐induced phase transformation of the metal components of the extraterrestrial body. To gain more insight into this nanophase and on its role in the SW of the asteroids, an optical characterization by SNOM has been performed on OCs. In this work we exploited the peculiarity of this technique to search for a correlation between the topography on the nanoscale and the spectral characteristics, at different wavelengths in the red‐NIR range, of the observed nanophase. Indeed, a high‐resolution mapping of the optical properties of the meteorite provides an interesting method to discriminate between martensite‐based and Fe‐silicaceous nanoparticles.

Fluid flow and chemical alteration in carbonaceous chondrite parent bodies

Carbonaceous chondrites are a class of primitive meteorites that likely represent early solar system materials, thus providing critical insights about planetary evolution. However, evidence shows that they have undergone considerable processing. Elucidating the complex formation history of aqueously altered chondrite groups has been a principal objective of cosmochemistry. Fulfilling this objective requires understanding the nature of the water–rock interactions involved. Many current alteration models are generally founded upon an assumption of uniform alteration in a closed system. In these models, different chondrite groups must originate on separate parent bodies. Contrary to this common view, we show that chondrite data are consistent with non-uniform alteration in a convecting system so that multiple chondrite groups can form within a single body.

Heterogeneous Accretion and the Moderately Volatile Element Budget of Earth

Several models exist to describe the growth and evolution of Earth; however, variables such as the type of precursor materials, extent of mixing, and material loss during accretion are poorly constrained. High-precision palladium-silver isotope data show that Earth's mantle is similar in 107Ag/109Ag to primitive, volatile-rich chondrites, suggesting that Earth accreted a considerable amount of material with high contents of moderately volatile elements. Contradictory evidence from terrestrial chromium and strontium isotope data are reconciled by heterogeneous accretion, which includes a transition from dominantly volatile-depleted to volatile-rich materials with possibly high water contents. The Moon-forming giant impact probably involved the collision with a Mars-like protoplanet that had an oxidized mantle, enriched in moderately volatile elements.

26Al– 26Mg dating of asteroidal magmatism in the young Solar System

We present high-precision Mg isotope data for most classes of basaltic meteorites including eucrites, mesosiderite silicate clasts, angrites and the ungrouped Northwest Africa (NWA) 2976 measured by pseudo-high-resolution multiple-collector inductively coupled plasma mass spectrometry and utilising improved techniques for chemical purification of Mg. With the exception of the angrites Angra dos Reis, Lewis Cliff (LEW) 86010, NWA 1296 and NWA 2999 and the diogenite Bilanga, which have either been shown to have young ages by other dating techniques or have low Al/Mg ratios, all bulk samples of basaltic meteorites have 26Mg excesses ( δ 26 Mg ∗ = + 0.0135 to +0.0392‰). The 26Mg excesses cannot be explained by analytical artefacts, cosmogenic effects or heterogeneity of initial 26Al/ 27Al, Al/Mg ratios or Mg isotopes in asteroidal parent bodies as compared to Earth or chondrites. The 26Mg excesses record asteroidal melting and formation of basaltic magmas with super-chondritic Al/Mg and confirm that radioactive decay of short-lived 26Al was the primary heat source that melted planetesimals. Model 26Al– 26Mg ages for magmatism on the eucrite/mesosiderite, angrite and NWA 2976 parent bodies are 2.6–3.2, 3.9–4.1 and 3.5 Myr, respectively, after formation of calcium–aluminium-rich inclusions (CAIs). However, the validity of these model ages depends on whether the elevated Al/Mg ratios of basaltic meteorites result from magma ocean evolution on asteroids through fractional crystallisation or directly during partial melting. Mineral isochrons for the angrites Sahara (Sah) 99555 and D’Orbigny, and NWA 2976, yield ages of 5.06 - 0.05 + 0.06 Myr and 4.86 - 0.09 + 0.10 Myr , respectively, after CAI formation. Both isochrons have elevated initial δ 26 Mg ∗ values. Given the brecciated and equilibrated texture of NWA 2976 it is probable that its isochron age and elevated initial δ 26 Mg ∗ ( + 0.0175 ± 0.0034 ‰ ) reflects thermal resetting during an impact event and slow cooling on its parent body. However, in the case of the angrites the marginally elevated initial δ 26 Mg ∗ ( + 0.0068 ± 0.0058 ‰ ) may reflect either δ 26 Mg ∗ ingrowth in a magma ocean prior to eruption and crystallisation or in an older igneous protolith with super-chondritic Al/Mg prior to impact melting and crystallisation of these angrites, or partial internal re-equilibration of Mg isotopes after crystallisation. 26Al– 26Mg model ages and an olivine + pyroxene + whole rock isochron for the angrites Sah 99555 and D’Orbigny are in good agreement with age constraints from 53Mn– 53Cr and 182Hf– 182W short-lived chronometers, suggesting that the 26Al– 26Mg feldspar-controlled isochron ages for these angrites may be compromised by the partial resetting of feldspar Mg isotope systematics. Even when age constraints from the 26Al– 26Mg angrite model ages or the mafic mineral + whole rock isochron are considered, the relative time difference between Sah 99555/D’Orbigny crystallisation and CAI formation cannot be reconciled with Pb–Pb ages for Sah 99555/D’Orbigny and CAIs, which are ca. 1.0 Myr too old (angrites) or too young (CAIs) for reasons that are not clear. This discrepancy might indicate that 26Al was markedly lower (ca. 40%) in the planetesimal- and planet-forming regions of the proto-planetary disc as compared to CAIs, or that CAI Pb–Pb ages may not accurately date CAI formation, which might be better dated by the 182Hf– 182W and 26Al– 26Mg chronometers as 4568.3 ± 0.7 (Burkhardt et al., 2008) and 4568.5 ± 0.3 Ma (herein), respectively, when mapped onto an absolute timescale using Pb–Pb ages for angrites.

Chondritic lithic clasts in the CB/CH-like meteorite Isheyevo: Fragments of previously unsampled parent bodies

The CB/CH-like chondrite Isheyevo is characterized by the absence of fine-grained interchondrule matrix material; the only present fine-grained material is found as chondritic lithic clasts. In contrast to the pristine high-temperature components of Isheyevo, these clasts experienced extensive aqueous alteration in an asteroidal setting. Hence, the clasts are foreign objects that either accreted together with the high-temperature components or were added later to the final Isheyevo parent body during regolith gardening. In order to constrain the origin and secondary alteration of the clasts in Isheyevo, we studied their mineralogy, petrography, structural order of the polyaromatic carbonaceous matter, and oxygen isotopic compositions of carbonates. Three main groups of clasts were defined based on mineralogy and petrology. Group I clasts consist of phyllosilicates, carbonates, magnetite, and lath-shaped Fe,Ni-sulfides. Group II clasts contain different abundances of anhydrous silicates embedded in a hydrated matrix; sulfides, magnetite, and carbonates are rare. With only a few exceptions, groups I and II clasts did not experienced significant thermal metamorphism. Group III clasts are characterized by the absence of magnetite and the presence of Fe,Ni-metal. In addition to aqueous alteration, they experienced thermal metamorphism as reflected by the structure of their polyaromatic carbonaceous matter. While there are some similarities between the Isheyevo clasts, CI chondrites, and the matrices of CM and CR chondrites, on the whole, the characteristics of the clasts do not match those of any of these aqueously altered meteorite classes. Nor do they match those of similar material in various types of chondritic clasts present in other meteorite groups. We conclude that the Isheyevo clasts represent fragments of previously unsampled parent bodies.

Contributors to chromium isotope variation of meteorites

We report the results of a comprehensive, high precision survey of the Cr isotopic compositions of primitive chondrites, along with some differentiated meteorites. To ensure complete dissolution of our samples, they were first fused with lithium borate–tetraborate at 1050–1000 °C. Relative to the NIST Cr standard SRM 3112a, carbonaceous chondrites exhibit excesses in 54Cr/ 52Cr from 0.4 to 1.6 ε (1 ε = 1 part in 10,000), and ordinary chondrites display a common 54Cr/ 52Cr deficit of ∼0.4 ε. Analyses of acid-digestion residues of chondrites show that carbonaceous and ordinary chondrites share a common 54Cr-enriched carrier, which is characterized by a large excess in 54Cr/ 52Cr (up to 200 ε) associated with a very small deficit in 53Cr/ 52Cr (<2 ε). We did not find 54Cr anomalies in either bulk enstatite chondrites or in leachates of their acid-digestion residues. This either requires that the enstatite chondrite parent bodies did not incorporate the 54Cr anomaly carrier phase during their accretion, or the phase was destroyed by parent body metamorphism. Chromium in the terrestrial rocks and lunar samples analyzed here show no deviation from the NIST SRM 3112a Cr standard. The eucrite and Martian meteorites studied exhibit small deficits in 54Cr/ 52Cr. The 54Cr/ 52Cr variations among different meteorite classes suggest that there was a spatial and/or temporal heterogeneity in the distribution of a 54Cr-rich component in the inner Solar System. We confirm the correlated excesses in 54Cr/ 52Cr and 53Cr/ 52Cr for bulk carbonaceous chondrites, but the new data yield a steeper slope (∼6.6) than that reported in Shukolyukov and Lugmair (2006). The correlated excesses may affect the use of the Mn–Cr chronometer in carbonaceous chondrites. We could not confirm the bulk carbonaceous chondrite Mn–Cr isochron reported by Shukolyukov and Lugmair (2006) and Moynier et al. (2007), mostly because we find much smaller total variations in ε 53Cr (∼0.2). All bulk chondrites have small ε 53Cr excesses (up to 0.3) relative to the Earth, most likely reflecting the sub-chondritic Mn/Cr ratio of the Earth. The ε 53Cr variations in chondrites do seem to grossly correlate with Mn/Cr and yield an initial Solar System 53Mn/ 55Mn value of 5.4(±2.4) × 10 −6, corresponding to an absolute age of 4566.4 (±2.2) Ma. Nuclear interactions with cosmic rays result in coupled excesses in ε 54Cr and ε 53Cr with a ∼4:1 ratio in phases with high Fe/Cr. These are most dramatically demonstrated in the iron meteorite Carbo, showing excesses in ε 54Cr of up to 140 ε. These new results show that the Mn–Cr chronometer should be used with caution in samples/minerals with high Fe/Cr and long cosmic ray exposure ages.

Identifying meteorite source regions through near-Earth object spectroscopy

By virtue of their landing on Earth, meteorites reside in near-Earth object (NEO) orbits prior to their arrival. Thus the population of observable NEOs, in principle, gives important representation of meteorite source bodies. By linking meteorites to NEOs, and linking NEOs to their most likely main-belt source locations, we seek to gain insight into the original Solar System formation locations for different meteorite classes. To forge possible links between meteorites and NEOs, we have developed a three dimensional method for quantitative comparisons between laboratory measurements of meteorites and telescopic measurements of near-Earth objects. We utilize meteorite spectra from the Reflectance Experiment Laboratory (RELAB) database and NEO data from the SpeX instrument on the NASA Infrared Telescope Facility (IRTF). Using the Modified Gaussian Model (MGM) as a mathematical tool, we treat asteroid and meteorite spectra identically in the calculation of 1-μm and 2-μm Geometric Band Centers and their Band Area Ratios (BARs). Using these identical numerical parameters we quantitatively compare the spectral properties of S-, Sq-, Q- and V-type NEOs with the spectral properties of the meteorites in four classes: H, L, LL and HED. For each NEO spectrum, we assign a set of probabilities for it being related to each of these four meteorite classes. Our NEO-meteorite correlation probabilities are then convolved with NEO-source region probabilities to yield a final set of meteorite-source region correlations. While the ν6 resonance dominates the delivery for all four meteorite classes, an excess (significant at the 2.1-sigma level) source region signature is found for the H chondrites through the 3:1 mean motion resonance. This results suggest an H chondrite source with a higher than average delivery preference through the 3:1 resonance. A 3:1 resonance H chondrite source region is consistent with the short cosmic ray exposure ages known for H chondrites.

Characterization of Antarctic micrometeorites by thermoluminescence

Abstract— In order to explore the nature and history of micrometeorites, we have measured the thermoluminescence (TL) properties of four micrometeorites, three cosmic spherules, and one irregular scoriaceous particle, that we found in a survey of 17 micrometeorites. These micrometeorites have TL sensitivities ranging from 0.017 ± 0.002 to 0.087 ± 0.009 (on a scale normalized to 4 mg of the H3.9 chondrite Dhajala). The four micrometeorites have very similar TL peak temperatures and TL peak widths, and these distinguish them from CI, most CM, CV, CO, and ordinary chondrites. However, the TL properties of these micrometeorites closely resemble those of the unusual CM chondrite MacAlpine Hills (MAC) 87300 and terrestrial forsterites. Heating experiments on submillimeter chips of a CM chondrite and a H5 chondrite suggest that these TL properties are have not been significantly affected by atmospheric passage. Thus we suggest that there is no simple linkage between these micrometeorites and the established meteorite classes, and that forsterite is an important component of these micrometeorites, as it is in many primitive solar system materials.

The Earth’s missing lead may not be in the core

Relative to the CI chondrite class of meteorites (widely thought to be the 'building blocks' of the terrestrial planets), the Earth is depleted in volatile elements. For most elements this depletion is thought to be a solar nebular signature, as chondrites show depletions qualitatively similar to that of the Earth. On the other hand, as lead is a volatile element, some Pb may also have been lost after accretion. The unique (206)Pb/(204)Pb and (207)Pb/(204)Pb ratios of the Earth's mantle suggest that some lead was lost about 50 to 130 Myr after Solar System formation. This has commonly been explained by lead lost via the segregation of a sulphide melt to the Earth's core, which assumes that lead has an affinity towards sulphide. Some models, however, have reconciled the Earth's lead deficit with volatilization. Whichever model is preferred, the broad coincidence of U-Pb model ages with the age of the Moon suggests that lead loss may be related to the Moon-forming impact. Here we report partitioning experiments in metal-sulphide-silicate systems. We show that lead is neither siderophile nor chalcophile enough to explain the high U/Pb ratio of the Earth's mantle as being a result of lead pumping to the core. The Earth may have accreted from initially volatile-depleted material, some lead may have been lost to degassing following the Moon-forming giant impact, or a hidden reservoir exists in the deep mantle with lead isotope compositions complementary to upper-mantle values; it is unlikely though that the missing lead resides in the core.

Compositional differences between meteorites and near-Earth asteroids

Understanding the nature and origin of the asteroid population in Earth's vicinity (near-Earth asteroids, and its subset of potentially hazardous asteroids) is a matter of both scientific interest and practical importance. It is generally expected that the compositions of the asteroids that are most likely to hit Earth should reflect those of the most common meteorites. Here we report that most near-Earth asteroids (including the potentially hazardous subset) have spectral properties quantitatively similar to the class of meteorites known as LL chondrites. The prominent Flora family in the inner part of the asteroid belt shares the same spectral properties, suggesting that it is a dominant source of near-Earth asteroids. The observed similarity of near-Earth asteroids to LL chondrites is, however, surprising, as this meteorite class is relatively rare ( approximately 8 per cent of all meteorite falls). One possible explanation is the role of a size-dependent process, such as the Yarkovsky effect, in transporting material from the main belt.

Subcontinental lithospheric mantle origin of high niobium/tantalum ratios in eclogites

Eclogites have been suggested as high niobium/tantalum reservoirs that complement the low niobium/tantalum ratios of the silicate Earth. However, the hafnium isotopic composition of eclogite fragments suggest that the high niobium/tantalum signature of eclogites is unlikely to be primary. Instead, it probably reflects chemical modification during residence in the subcontinental lithospheric mantle. Ratios of non-volatile elements such as zirconium, niobium (Nb) and tantalum (Ta) in the unfractionated Earth are commonly assumed to be similar to those in the class of meteorites known as chondrites1. However, the Nb/Ta ratio of the Earth’s major silicate reservoirs—the crust and mantle—is subchondritic, hinting at the existence of a complementary reservoir with high Nb/Ta (refs 2, 3). Eclogites, which are high-pressure metamorphic rocks that often form in subduction zones, can contain the mineral rutile (titanium dioxide) with high Nb/Ta. They have therefore been inferred to constitute this complementary reservoir2. More recent evidence from natural samples, however, suggests that residual eclogites have low Nb/Ta, which is confirmed by experiments3,4,5,6. Here, we present the Nb and Ta concentrations and hafnium (Hf) isotope compositions of rutiles from eclogite fragments that were entrained from the subcontinental lithospheric mantle in kimberlite melts. Rutiles with high 176Hf/177Hf ratios generally have subchondritic Nb/Ta (<19.9 (refs 3, 7)), similar to undisturbed melt residues of broadly basaltic precursors. On the other hand, rutiles with suprachondritic Nb/Ta ratios have low 176Hf/177Hf, suggesting Hf addition from a fluid or melt ultimately derived from ancient (≥2.9 Gyr), chemically modified (metasomatized) subcontinental lithospheric mantle, which has similarly low 176Hf/177Hf (ref. 8). Our results suggest that eclogites are unlikely to represent the high Nb/Ta reservoir; instead, the high Nb/Ta signatures of some eclogites are probably generated by metasomatism during long-term residence in the subcontinental lithospheric mantle.

Ancient Asteroids Enriched in Refractory Inclusions

Calcium- and aluminum-rich inclusions (CAIs) occur in all classes of chondritic meteorites and contain refractory minerals predicted to be the first condensates from the solar nebula. Near-infrared spectra of CAIs have strong 2-micrometer absorptions, attributed to iron oxide-bearing aluminous spinel. Similar absorptions are present in the telescopic spectra of several asteroids; modeling indicates that these contain approximately 30 +/- 10% CAIs (two to three times that of any meteorite). Survival of these undifferentiated, large (50- to 100-kilometer diameter) CAI-rich bodies suggests that they may have formed before the injection of radiogenic 26Al into the solar system. They have also experienced only modest post-accretionary alteration. Thus, these asteroids have higher concentrations of CAI material, appear less altered, and are more ancient than any known sample in our meteorite collection, making them prime candidates for sample return.

Organic matter in the Solar System: From colors to spectral bands

AbstractThe reflected spectral energy distribution of low-albedo, red-colored, airless bodies in the outer Solar System (planetary satellites, Centaur objects, Kuiper Belt objects, bare comet nuclei) can be modeled with spectral models that incorporate the optical properties of refractory complex organic materials synthesized in the laboratory and called tholins. These materials are strongly colored and impart their color properties to the models. The colors of the bodies cannot be matched with plausible minerals, ices, or metals. Iapetus, a satellite of Saturn, is one such red-colored body that is well matched with tholin-rich models. Detection of aromatic and aliphatic hydrocarbons on Iapetus by the Cassini spacecraft, and the presence of these hydrocarbons in the tholins, is taken as evidence for the widespread presence of solid organic complexes aromatic and aliphatic units on many bodies in the outer Solar System. These organic complexes may be compositionally similar to the insoluble organic matter in some classes of the carbonaceous meteorites, and thus may ultimately derive from the organic matter in the interstellar medium.

Redox Conditions on Small Bodies, the Moon and Mars

Research Article| January 01, 2008 Redox Conditions on Small Bodies, the Moon and Mars Meenakshi Wadhwa Meenakshi Wadhwa School of Earth and Space Exploration, Arizona State University, Tempe, Arizona 85287, U.S.A., wadhwa@asu.edu Search for other works by this author on: GSW Google Scholar Reviews in Mineralogy and Geochemistry (2008) 68 (1): 493–510. https://doi.org/10.2138/rmg.2008.68.17 Article history first online: 03 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Meenakshi Wadhwa; Redox Conditions on Small Bodies, the Moon and Mars. Reviews in Mineralogy and Geochemistry 2008;; 68 (1): 493–510. doi: https://doi.org/10.2138/rmg.2008.68.17 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyReviews in Mineralogy and Geochemistry Search Advanced Search Abstract The current state of knowledge regarding redox conditions of rocks from asteroidal bodies (as represented by various classes of meteorites), the Moon and Mars is discussed here. In the case of the differentiated meteorite parent bodies, the redox conditions range over at least six orders of magnitude (from ~5 log units below the Iron-Wüstite buffer to slightly above it) and are determined in large part by the compositions of the undifferentiated precursor materials that accreted to form these parent bodies. Lunar basalts record oxygen fugacities ranging from close to the Iron-Wüstite (IW) buffer to ~2 log units below it. The current best estimate of the oxygen fugacity of the lunar mantle is ~1 log unit below IW. Martian crustal rocks represented by the Shergottite-Nakhlite-Chassignite group of meteorites record a wide range of oxygen fugacities. The basaltic shergottites range from slightly below the IW buffer to ~2 log units above it, whereas the cumulate nakhlites (and chassignites) are relatively oxidized (~3–4 log units above the IW buffer). Following early metal-silicate and crust-mantle differentiation on Mars, the depleted martian mantle is likely to have been reduced (close to the IW buffer or slightly lower). Metasomatism and secondary (hydrous) alteration are likely to have produced silicate reservoirs on Mars that are relatively more oxidized (most likely ≥3 log units above the IW buffer). The redox conditions on the other terrestrial planets (Mercury and Venus) are not well constrained. Based on the limited information from remote spacecraft and telescopic observations of surface rocks on these planets, it is inferred that silicate reservoirs on Mercury are highly reduced; those on Venus are likely to be somewhat more oxidized than on Mercury, possibly similar to the lower mantle of Earth. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Appendix: Meteorites - A Brief Tutorial

There are four broad categories of meteorites—chondrites, achondrites, irons and stony irons. These are subdivided into meteorite groups, the basic unit of meteorite classification. Although no formal guideline is in place for the minimum number of meteorites needed to define a group, common practice is that there should be five or more members in a group. A defined meteorite group is thought to be derived from a single asteroid. However, some groups are genetically related and are derived from a common parent asteroid. Chondrites are primitive stony meteorites; rocks whose compositions are little changed since their formation in the solar nebula. There are fourteen defined groups of chondrites, and they make up the vast majority of meteorites falling to Earth in the current epoch. Achondrites are stony meteorites of two broad types. Some are primitive materials like chondrites, but most are the products of igneous differentiation. There are ten defined groups of achondrites, of which seven are differentiated types. Irons are also the products of asteroidal differentiation, having crystallized from metallic melts separated from chondritic precursors. There are thirteen defined groups of iron meteorites. Stony-irons are also differentiated materials, and both the rocky and metallic phases were formed by igneous processes on asteroids. There are two defined groups of stony-iron meteorites. In addition to those that fit into groups, there are many meteorites that are unique, or for which there are less than five examples. These ungrouped meteorites make up a substantial fraction of meteorites recovered to date.

What was the Volatile Composition of the Planetesimals that Formed the Earth?

Is there an asteroid type or meteorite class that best exemplifies the materials that went into the Earth? Carbonaceous chondrites were once the objects of choice, and in the minds of many this choice is still valid. However, the origin of primitive chondritic meteorites is unclear. At the extremes they could either be fragments of very small parent bodies that never became hot enough to undergo geochemical modification other than mild lithification, or remnants of the uppermost layers of a body that had undergone a significant degree of internal differentiation, while the top layers remained cool due to radiative heat loss or loss of volatiles to space. This latter case is problematic if one considers these objects as precursors to the Earth since the timescale for the evolution of such a small body could be longer than the timescale for the accretion of the Earth. Large-scale circulation of materials in the primitive solar nebula could greatly increase the diversity of materials near 1 AU while also making the entire inner solar system both more homogeneous and much wetter than previously expected. The total mass of the nebula is an important, but poorly constrained factor controlling the growth of planetesimals. There is also a selection effect that dominates our sampling of the planetesimals that may have existed 4.5 billion years ago; namely, small fragile bodies are more likely to be lost from the system or ground down by collisions between small bodies, yet these are precisely those that may have dominated the population from which the Earth accreted. The composition of these aggregates could have played a very important role in the early chemical evolution of the Earth. In particular, the Earth may have been much wetter and richer in hydrocarbons and other reducing materials than previously suspected.

Determination of oxygen triple isotope ratios of silicates without cryogenic separation of NF3 – technique with application to analyses of technical O2 gas and meteorite classification

A novel technique is described to determine Delta'(17)O(TFL) with high accuracy and precision by using infrared (IR) laser fluorination with F(2) as the reaction gas. The technique includes precise monitoring of the intensity ratio of the (14)NF(2)+ (m/z 52) to O(2) signals. The correlation between the intensity of (14)NF(2) + and positive error in delta(17)O(VSMOW) allows correction of measured data to obtain reliable Delta'(17)O(TFL) values. The resultant error in Delta'(17)O(TFL) of a single measurement after correction is in the range of +/-0.06 per thousand, i.e. sufficiently small to permit the technique to be useful for meteorite classification. Our data for technical O(2), in combination with literature data, suggest a negative anomaly of tropospheric air O(2) with Delta'(17)O(TFL) = -0.344 +/- 0.015 per thousand (1sigma).

Laser induced breakdown spectroscopy on meteorites

The classification of meteorites when geological analysis is unfeasible is generally made by the spectral line emission ratio of some characteristic elements. Indeed when a meteorite impacts Earth's atmosphere, hot plasma is generated, as a consequence of the braking effect of air, with the consequent ablation of the falling body. Usually, by the plasma emission spectrum, the meteorite composition is determined, assuming the Boltzmann equilibrium. The plasma generated during Laser Induced Breakdown Spectroscopy (LIBS) experiment shows similar characteristics and allows one to verify the mentioned method with higher accuracy. On the other hand the study of Laser Induced Breakdown Spectroscopy on meteorite can be useful for both improving meteorite classification methods and developing on-flight techniques for asteroid investigation. In this paper certified meteorites belonging to different typologies have been investigated by LIBS: Dofhar 461 (lunar meteorite), Chondrite L6 (stony meteorite), Dofhar 019 (Mars meteorite) and Sikhote Alin (irony meteorite).

Astrochemistry: from astronomy to astrobiology

Preface. 1. The molecular universe. 1.1 The Standard Model Big Bang Theory. 1.2 Galaxies, stars and planets. 1.3 Origins of life. 1.4 Other intelligent life. 1.5 Theories of the origin of life. Concepts and calculations. 2. Starlight, galaxies and clusters. 2.1 Simple stellar models-black body radiation. 2.2 2.726 K-cosmic microwave background radiation. 2.3 Stellar classification. 2.4 Constellations. 2.5 Galaxies. 2.6 Cosmology. Concepts and calculations. Problems. 3. Atomic and molecular astronomy. 3.1 Spectroscopy and the structure of matter. 3.2 Line shape. 3.3 Telescopes. 3.4 Atomic spectroscopy. 3.5 Molecular astronomy. 3.6 Molecular masers. 3.7 Detection of hydrogen. 3.8 Diffuse interstellar bands. 3.9 Spectral mapping. Concepts and calculations. Problems. 4. Stellar chemistry. 4.1 Classes of stars. 4.2 Herzprung-Russell diagram. 4.3 Stellar evolution. 4.4 Stellar spectra. 4.5 Exotic stars. 4.6 Cycle of star formation. Concepts and calculations Problems. 5. The interstellar medium. 5.1 Mapping clouds of molecules. 5.2 Molecules in the interstellar and circumstellar medium. 5.3 Physical conditions in the interstellar medium. 5.4 Rates of chemical reactions. 5.5 Chemical reactions in the interstellar medium. 5.6 Photochemistry. 5.7 Charged particle chemistry. 5.8 Polycyclic aromatic hydrocarbons. 5.9 Dust grains. 5.10 Kinetic models of molecular clouds. 5.11 Prebiotic molecules in the interstellar medium. Concepts and calculations. Problems. 6. Meteorite and comet chemistry. 6.1 Formation of the solar system. 6.2 Classification of meteorites. 6.3 Meteorite mineralogy. 6.4 Geological time. 6.5 Chemical analysis of meteorites by L2MS. 6.6 The Murchison meteorite-kerogen. 6.7 Meteorite ALH84001. 6.8 Comet chemistry. 6.9 Structure of a comet. 6.10 Physicochemical conditions in a cometary coma. 6.11 Chemical composition of comets. 6.12 Cometary collisions. 6.13 The Rosetta mission-origin of the solar system. Concepts and calculations. Problems. 7. Planetary chemistry. 7.1 Structure of a star-planet system. 7.2 Surface gravity. 7.3 Formation of the Earth. 7.4 Earth-Moon system. 7.5 Geological time. 7.6 Radiative heating. 7.7 The habitable zone. 7.8 Extrasolar planets. 7.9 Planetary atmospheres. 7.10 Atmospheric photochemistry. 7.11 Biomarkers in the atmosphere. Concepts and calculations. Problems. 8. Prebiotic chemistry. 8.1 Carbon- and water-based life forms. 8.2 Spontaneous chemical reactions. 8.3 Rates of chemical reactions. 8.4 Endogenous production of organic molecules. 8.5 Exogenous delivery of organic molecules. 8.6 Homochirality. 8.7 Surface metabolism-'clay organisms'. 8.8 Geothermal vents-'black smokers'. 8.9 RNA World hypothesis. Concepts and calculations. Problems. 9. Primitive life forms. 9.1 Self-assembly and encapsulation. 9.2 Protocells. 9.3 Universal tree of life. 9.4 Astrobiology. 9.5 Microbial Mars. Concepts and calculations. Problems. 10. Titan. 10.1 Physical properties. 10.2 The atmosphere. 10.3 Temperature-dependent chemistry. 10.4 Energy balance and the greenhouse effect. 10.5 Atmospheric chemistry. 10.6 Astrobiology on Titan. Concepts and calculations. Problems. Glossary of terms and abbreviations. Appendix A: constants and units. Appendix B: astronomical data. Appendix C: thermodynamic properties of selected compounds. Answers to problems. Bibliography. Index.

Chromium isotopic studies of terrestrial impact craters: Identification of meteoritic components at Bosumtwi, Clearwater East, Lappajärvi, and Rochechouart

Chromium isotopic compositions and elemental abundances in impact melt rock and impact glass samples from four terrestrial impact craters were measured to verify the presence of an extraterrestrial component and to identify the meteorite type of the impactor. All meteorite classes have Cr isotopic signatures that are different from those of terrestrial rocks; thus, precise measurements of Cr isotopic abundances can unequivocally distinguish terrestrial from extraterrestrial materials. For all four studied craters — Bosumtwi (Ghana), Clearwater East (Canada), Lappajärvi (Finland), and Rochechouart (France) we found positive 53Cr excesses that eliminate carbonaceous chondrite projectiles (because those would show apparent negative excesses) and enstatite chondrites (because of the magnitude of the excess). In all four cases, ordinary chondrites have been identified as the best fit for the data; in the case of Lappajärvi interelement correlations together with the Cr isotope data make an H-chondrite the most likely projectile, whereas in the case of Clearwater East both L or H chondrites are possible. For Bosumtwi and Rochechouart the high indigenous contents of the siderophile elements, and disturbances of the elemental abundances by weathering and hydrothermal alteration, respectively, do not allow further constraints to be placed on the type of ordinary chondrite involved in the impact.