Antarctic Meteorites Research Articles

Physicochemical Properties and Complexity of Amino Acids beyond Our Biosphere: Analysis of the Isoleucine Group from Meteorites

Understanding the physicochemical properties of biomolecules and how these properties drive the emergence of complexity in the assembly/condensation of such systems is important for understanding a variety of reactions taking place in astrophysical environments, in particular those where polymerization processes occur on mineral surfaces or solid organic matter form in cold-chemistry processes. Here, a computational study of the structural and electronic properties of the gas and condensed phases of the isoleucine group of amino acids, found with large enantiomeric excess in Antarctic meteorites, is presented. An analysis of a statistical complexity measure related to their electronic properties, of the degree of chirality, and of the H-bond patterns is also reported. The results, based on Density Functional Theory, Many Body Perturbation Theory, and Moller–Plesset perturbation theory, show that a) the condensed amino acids keep reminiscence of structural and electronic properties of the gas phase molecules, b) the proteinogenic l-isoleucine gains in complexity and chirality upon condensation, contrary to its diastereomer, which is absent in living systems, and c) the complexity based on electronic properties can contrast with the notion of structural/geometrical complexity. The findings suggest that future scoring strategies of organic molecules should rely on both structural/geometrical molecular complexity and on the electronic properties, which in different states of matter are determined by other degrees of freedom (configurational or chiral) to a different extent, as well as on information storage capability of self-assembly configurations constrained by an atomistic chemistry perspective.

Bulk chemical compositions of Antarctic meteorites in the NIPR collection

Bulk chemical compositions of meteorites were traditionally analyzed by wet chemical analysis, and NIPR has data for 1162 meteorites as of September 2017. We discuss the classification of meteorites on the basis of these data. Chondrite data are distributed in an anomalously wide range of compositions on the Urey-Craig diagram. One of the reasons for such wide distribution is terrestrial weathering producing Fe2O3–bearing phases from Fe-Ni metal and sulfides. Another important factor affecting the bulk compositional data is brecciation. Our observations indicate that many brecciated chondrites contain anomalously abundant opaque minerals, or are depleted in them, resulting in unusual compositions. In case of enstatite and some carbonaceous chondrites, the bulk compositions are distributed in wider ranges than reported before. The bulk compositions of HED meteorites are consistent with their mineralogy and classification. Our study suggests that wet chemical data are still significant for the meteorite classification. However, petrographic observation is indispensable for evaluating the bulk chemistry and classification of meteorites.

Oxygen isotopic ratios of primordial water in carbonaceous chondrites

In this work, I estimate the δ18O and δ17O values of primordial water in CM chondrites to be 55 ± 13 and 35 ± 9‰, respectively, based on whole-rock O and H data. Also, I found that the O and/or H data of Antarctic meteorites are biased, which is attributed to terrestrial weathering. This characteristic O isotopic ratio of water together with corresponding water abundances in CM chondrites are consistent with the origin of water as ice processed by photochemical reactions at the outer regions of the solar nebula, where mass-independent O isotopic fractionation and water destruction may have occurred. Another possible mechanism to produce the inferred O isotopic ratio of water would be O isotopic fractionation between water vapor and ice, which likely occurred near the condensation front of H2O (snow line) in the solar nebula. The inferred O isotopic ratio of water suggests that carbonate in CM chondrites formed at low temperatures of <150 °C. The O isotopic ratios of primordial water in chondrites other than CM chondrites are not well constrained.

A mutli-technique search for the most primitive CO chondrites

As part of a study to identify the most primitive COs and to look for weakly altered CMs amongst the COs, we have conducted a multi-technique study of 16 Antarctic meteorites that had been classified as primitive COs. For this study, we have determined: (1) the bulk H, C and N abundances and isotopes, (2) bulk O isotopic compositions, (3) bulk modal mineralogies, and (4) for some selected samples the abundances and compositions of their insoluble organic matter (IOM). Two of the 16 meteorites do appear to be CMs – BUC 10943 seems to be a fairly typical CM, while MIL 090073 has probably been heated. Of the COs, DOM 08006 appears to be the most primitive CO identified to date and is quite distinct from the other members of its pairing group. The other COs fall into two groups that are less primitive than DOM 08006 and ALH 77307, the previously most primitive CO. The first group is composed of members of the DOM 08004 pairing group, except DOM 08006. The second group is composed of meteorites belonging to the MIL 03377 and MIL 07099 pairing groups. These two pairing groups should probably be combined. There is a dichotomy in the bulk O isotopes between the primitive (all Antarctic finds) and the more metamorphosed COs (mostly falls). This dichotomy can only partly be explained by the terrestrial weathering experienced by the primitive Antarctic samples. It seems that the more equilibrated samples interacted to a greater extent with 16O-poor material, probably water, than the more primitive meteorites.

Origin of EL3 chondrites: Evidence for variable C/O ratios during their course of formation—A state of the art scrutiny

AbstractMineral inventories of enstatite chondrites; (EH and EL) are strictly dictated by combined parameters mainly very low dual oxygen (fO2) and sulfur (fS2) fugacities. They are best preserved in the Almahata Sitta MS‐17, MS‐177 fragments, and the ALHA 77295 and MAC 88136 Antarctic meteorites. These conditions induce a stark change of the geochemical behavior of nominally lithophile elements to chalcophile or even siderophile and changes in the elemental partitioning thus leading to formation of unusual mineral assemblages with high abundance of exotic sulfide species and enrichment in the metallic alloys, for example, silicides and phosphides. Origin and mode of formation of these exotic chondrites, and their parental source regions could be best scrutinized by multitask research experiments of the most primitive members covering mineralogical, petrological, cosmochemical, and indispensably short‐lived isotopic chronology. The magnitude of temperature and pressure prevailed during their formation in their source regions could eventually be reasonably estimated: pre‐ and postaccretionary could eventually be deduced. The dual low fugacities are regulated by the carbon to oxygen ratios estimated to be &gt;0.83 and &lt;1.03. These parameters not only induce unusual geochemical behavior of the elements inverting many nominally lithophile elements to chalcophile or even siderophile or anthracophile. Structure and mineral inventories in EL3 and EH3 chondrites are fundamentally different. Yet EH3 and EL3 members store crucial information relevant to eventual source regions and importantly possible variation in C/O ratio in the course of their evolution. EL3 and EH3 chondrites contain trichotomous lithologies (1) chondrules and their fragments, (2) polygonal enstatite‐dominated objects, and (3) multiphase metal‐rich nodules. Mineralogical and cosmochemical inventories of lithologies in the same EL3 indicate not only similarities (REE inventory and anomalies in oldhamite) but also distinct differences (sinoite‐enstatite‐graphite relationship). Oldhamite in chondrules and polygonal fragments in EL3 depict negative Eu anomaly attesting a common cosmochemical source. Metal‐dominated nodules in both EL3 and EH3 are conglomerates of metal clasts and sulfide fragments in EH3 and concentrically zoned C‐bearing metal micropebbles (≥25 μm ≤50 μm) in EL3 thus manifesting a frozen in unique primordial accretionary metal texture and composition. Sinoite‐enstatite‐diopside‐graphite textures reveal a nucleation and growth strongly suggestive of fluctuating C/O ratio during their nucleation and growth in the source regions. Mineral inventories, sulfide phase relations, sinoite‐enstatite‐graphite intergrowth, carbon and nitrogen isotopic compositions of graphite, spatial nitrogen abundance in graphite in metal nodules, and last but not least 129I/129Xe and 53Mn/53Cr systematics negate any previously suggested melting episode, pre‐accretionary or dynamic, in parental asteroids.

Thermal history of type 3 chondrites from the Antarctic meteorite collection determined by Raman spectroscopy of their polyaromatic carbonaceous matter

This paper is focused on the characterization of the thermal history of 151 CV, CO and unequilibrated ordinary chondrites (UOCs) from the NASA Antarctic meteorite collection, using an approach based on the structure of the included polyaromatic carbonaceous matter determined by Raman spectroscopy. 114 out of these 151 chondrites provided Raman spectra of carbonaceous matter and allowing to assign a petrologic type, which mostly reflects the peak temperature experienced by the rock on the parent body. A thorough review of literature shows however that it is not possible to deduce a peak temperature because accurate calibration is not available. Twenty-three new weakly metamorphosed chondrites have been identified: MIL 07671 (CV3.1); DOM 08006 (CO3.0); DOM 03238, MIL 05024, MIL 05104, MIL 07193 (CO3.1); TIL 82408, LAR 06279 (LL3.05-3.1); EET 90628 (L3.0); GRO 06054, QUE 97008 (L3.05), ALHA 77176, EET 90066, LAR 04380, MET 96515, MIL 05050 (L3.1); ALHA 78133, EET 87735, EET 90909, LEW 87208, PRE 95401 (L3.05-3.1); MCY 05218 (H3.05-3.1) and MET 00506 (H3.1). This study confirms that the width of the D band (FWHMD) and the ratio of the peak intensity of the D and G bands (ID/IG) are the most adapted tracers of the extent of thermal metamorphism in type 3 chondrites. It also unambiguously shows, thanks to the large number of samples, that the width of the G band (FWHMG) does not correlate with the maturity of polyaromatic carbonaceous matter. This parameter is nevertheless very valuable because it shows that Raman spectra of CV chondrites preserve memory of either the metamorphic conditions (possibly oxidation controlled by aqueous alteration) or the nature of the organic precursor. Oxidation memory is our preferred interpretation, however an extensive petrologic characterization of this CV series is required to get firm conclusions. Pre-graphitic carbonaceous matter is reported in seven chondrites and is even the only carbonaceous material detected in the chondrites ALHA 78119 and DAV 92302. This pre-graphitic carbonaceous matter cannot be formed through radiogenic thermal metamorphism without metal catalysis. Shock metamorphism is another possible process for accounting its formation, but it appears less plausible.

X‐ray computed tomography imaging: A not‐so‐nondestructive technique

AbstractX‐ray computed tomography has become a popular means for examining the interiors of meteorites and has been advocated for routine curation and for the examination of samples returned by missions. Here, we report the results of a blind test that indicate that CT imaging deposits a considerable radiation dose in a meteorite and seriously compromises its natural radiation record. Ten vials of the Bruderheim L6 chondrite were placed in CT imager and exposed to radiation levels typical for meteorite studies. Half were retained as controls. Their thermoluminescence (TL) properties were then measured in a blind test. Five of the samples had TL data unaltered from their original (~10 cps) while five had very strong signals (~20,000 cps). It was therefore very clear which samples had been in the CT scanner. For comparison, the natural TL signal from Antarctic meteorites is ~5000–50,000 cps. Using the methods developed for Antarctic meteorites, the apparent dose absorbed by the five test samples was calculated to be 83 ± 5 krad, comparable with the highest doses observed in Antarctic meteorites and freshly fallen meteorites. While these results do not preclude the use of CT scanners when scientifically justified, it should be remembered that the record of radiation exposure to ionizing radiations for the sample will be destroyed and that TL, or the related optically stimulated luminescence, are the primary modern techniques for radiation dosimetry. This is particularly important with irreplaceable samples, such as meteorite main masses, returned samples, and samples destined for archive.

2015 Service Award for Ralph Harvey

It is a great pleasure to present Ralph P. Harvey, Principal Investigator (PI) for the Antarctic Search for Meteorites (ANSMET) program from 1992 till present, as the recipient of the Meteoritical Society's Service Award for 2015. Ralph became the PI for the ANSMET program in 1992 when ANSMET founder Bill Cassidy passed the torch. Ralph has subsequently organized and led 24 ANSMET seasons resulting in the collection of ~16,000 meteorites that are now part of the U.S. Antarctic meteorite collection (Table 1). These seasons included ~150 volunteer field team members including many years with two teams—a main team and a reconnaissance (recon) team. During this period, Ralph experienced the 1996 announcement of possible evidence for life recorded in Martian meteorite Allan Hills (ALH) 84001; recovery of beautiful specimens from the Queen Alexandra (QUE), Meteorite Hills (MET), Miller Range (MIL), Dominion Range (DOM), LaPaz Icefield (LAP); and finished recovery efforts at Elephant Moraine (EET). Samples recovered in these areas include some key lunar and Martian meteorites, primitive and rare chondrites, and many unique achondrites from differentiated asteroids. Ralph also helped to establish two field teams for multiple collection years (main team and recon team) that required support of a second science leader—Nancy Chabot, Mike Rampey, and Jim Karner have filled those roles, working with Ralph and longtime ANSMET mountaineer John Schutt to take as many as 12 people per season into the field to recover meteorites. Ralph's distinction in his role of PI for ANSMET is truly due to his wealth of special talents and qualities that, when combined with his training from Bill, have led to an amazing collection of meteorite samples available to the worldwide research community. First under his direction, the goals of ANSMET have been well aligned with those of the Meteoritical Society: the substantial participation of international scientists (from at least 16 countries including the United States, UK, France, Japan, Germany, Russia, Denmark, Italy, Spain, Austria, Switzerland, China, Portugal, New Zealand, Canada, and South Africa), >40 female scientists, and nonscientists including several teachers and writers. Some ANSMET participants have stated that Ralph's invitation to participate in ANSMET teams has been influential and led them to carry out their own research in the field. Second, leading expeditions of this nature for over two decades has led to great personal sacrifice both with regard to family and research. Ralph has missed many holiday seasons with his wife and three children because the field expeditions typically start before Thanksgiving and end in mid to late January. Moreover, Ralph's stimulating research efforts—including statistics of Antarctic and non-Antarctic falls, water on Mars, cosmic spherules and dust, micrometeorites, Stardust particles, Martian soil weathering, and terrestrial analogs (Ferrar dolerite)—have no doubt been stunted by his dedication to managing and coordinating the annual ANSMET expeditions. These sacrifices would be insurmountable by many in our field yet Ralph has managed them well. Third, Ralph has a knack for managing people and good morale amongst those people. His energy, enthusiasm, sense of humor, patience, leadership, and even-tempered personality—all despite the long, difficult, and cold field seasons—as well as his ability to select team members to fit into this challenging environment, have all contributed to many successful seasons without incident. Finally, Ralph has made this an open adventure embracing the community with an informational webpage, field team blogs in the last decade or so, and the annual ANSMET night in mid-March during LPSC week. The numerous nomination letters for Ralph were full of personal stories of how ANSMET and Ralph had heavily influenced individuals in our field. Such is certainly true of this writer as well, having had the pleasure of spending time in the field with Ralph over 15 years ago! Please join me in congratulating Ralph for his outstanding efforts in collecting thousands of scienti-fically precious meteorites, influencing a great diversity of people who are now meteorite enthusiasts, and for his unique contributions to a hugely successful program that continues to grow and flourish. It is hard to imagine what the ANSMET program would be like without Ralph's influence! Mr. President, members of the society, distinguished guests, I am pleased to present our friend and colleague, Dr. Ralph P. Harvey for the 2015 Meteoritical Society Service Award.

Hydrogen and carbon isotopic ratios of polycyclic aromatic compounds in two CM2 carbonaceous chondrites and implications for prebiotic organic synthesis

Study of meteoritic organic compounds offers a unique opportunity to understand the origins of the organic matter in the early Solar System. Meteoritic polycyclic aromatic hydrocarbons (PAHs) and heteropolycyclic aromatic compounds (HACs) have been studied for over fifty years, however; their hydrogen stable isotopic ratios (δD) have never been reported. Compound-specific δD measurements of PAHs and HACs are important, in part because the carbon isotopic ratios (δC13) of various meteoritic PAHs cannot be readily distinguished from their terrestrial counterparts and it is difficult to rule out terrestrial contamination based on carbon isotopic ratios alone. In this study, we have extracted and identified more than sixty PAHs and HACs present in two CM2 carbonaceous chondrites Murchison and LON 94101. Their carbon and hydrogen stable isotopic ratios (δC13 and δD) were measured and used to discuss about their synthetic environments and formation mechanisms. The concentration of aromatic compounds is ∼30% higher in Murchison than in the Antarctic meteorite LON 94101, but both samples contained similar suites of PAHs and HACs. All PAHs and HACs found exhibited positive δD values (up to 1100‰) consistent with an extraterrestrial origin, indicating the relatively low δC13 values are indeed an inherent feature of the meteoritic aromatic compounds. The hydrogen isotopic data suggest aromatic compounds in carbonaceous chondrites were mainly formed in the cold interstellar environments. Molecular level variations in hydrogen and carbon isotopic values offer new insights to the formation pathways for the aromatic compounds in carbonaceous chondrites.

Final reports of the Stardust Interstellar Preliminary Examination

AbstractWith the discovery of bona fide extraterrestrial materials in the Stardust Interstellar Dust Collector, NASA now has a fundamentally new returned sample collection, after the Apollo, Antarctic meteorite, Cosmic Dust, Genesis, Stardust Cometary, Hayabusa, and Exposed Space Hardware samples. Here, and in companion papers in this volume, we present the results from the Preliminary Examination of this collection, the Stardust Interstellar Preliminary Examination (ISPE). We found extraterrestrial materials in two tracks in aerogel whose trajectories and morphology are consistent with an origin in the interstellar dust stream, and in residues in four impacts in the aluminum foil collectors. While the preponderance of evidence, described in detail in companion papers in this volume, points toward an interstellar origin for some of these particles, alternative origins have not yet been eliminated, and definitive tests through isotopic analyses were not allowed under the terms of the ISPE. In this summary, we answer the central questions of the ISPE: How many tracks in the collector are consistent in their morphology and trajectory with interstellar particles? How many of these potential tracks are consistent with real interstellar particles, based on chemical analysis? Conversely, what fraction of candidates are consistent with either a secondary or interplanetary origin? What is the mass distribution of these particles, and what is their state? Are they particulate or diffuse? Is there any crystalline material? How many detectable impact craters (&gt;100 nm) are there in the foils, and what is their size distribution? How many of these craters have analyzable residue that is consistent with extraterrestrial material? And finally, can craters from secondaries be recognized through crater morphology (e.g., ellipticity)?

Antarctic meteorites and the origin of planetesimals and protoplanets

AbstractAlmost all meteorites (about 99% by number) are samples from a few hundreds of asteroids that are leftover from planetesimals and protoplanets formed within several million years after the birth of the Solar System. These meteorites record detailed evolutionary history of dust to planets, including condensation, accretion, aqueous alteration, thermal metamorphism, partial and total melting.

ベルギー-日本共同南極隕石探査による「あすか10隕石」の発見と採集

ベルギー-日本共同南極隕石探査による「あすか10隕石」の発見と採集

A propensity for n‐ω‐amino acids in thermally altered Antarctic meteorites

Abstract– Asteroids and their fragments have impacted the Earth for the last 4.5 Gyr. Carbonaceous meteorites are known to contain a wealth of indigenous organic molecules, including amino acids, which suggests that these meteorites could have been an important source of prebiotic organic material during the origins of life on Earth and possibly elsewhere. We report the detection of extraterrestrial amino acids in thermally altered type 3 CV and CO carbonaceous chondrites and ureilites recovered from Antarctica. The amino acid concentrations of the thirteen Antarctic meteorites ranged from 300 to 3200 parts‐per‐billion (ppb), generally much less abundant than in amino acid‐rich CI, CM, and CR carbonaceous chondrites that experienced much lower temperature aqueous alteration on their parent bodies. In contrast to low‐temperature aqueously altered meteorites that show complete structural diversity in amino acids formed predominantly by Strecker–cyanohydrin synthesis, the thermally altered meteorites studied here are dominated by small, straight‐chain, amine terminal (n‐ω‐amino) amino acids that are not consistent with Strecker formation. The carbon isotopic ratios of two extraterrestrial n‐ω‐amino acids measured in one of the CV chondrites (δ13C approximately −25‰) are consistent with 13C‐depletions observed previously in hydrocarbons produced by Fischer‐Tropsch type reactions. The predominance of n‐ω‐amino acid isomers in thermally altered meteorites hints at cosmochemical mechanisms for the preferential formation and preservation of a small subset of the possible amino acids.

Oral histories in meteoritics and planetary science—XVI: Donald D. Bogard

Abstract– Donald D. Bogard (Don, Fig. 1) became interested in meteorites after seeing the Fayetteville meteorite in an undergraduate astronomy class at the University of Arkansas. During his graduate studies with Paul Kuroda at Arkansas, Don helped discover the Xe decay products of 244Pu. After a postdoctoral period at Caltech, where he learned much from Jerry Wasserburg, Peter Eberhardt, Don Burnett, and Sam Epstein, Don became one of a number of young Ph.D. scientists hired by NASA’s Manned Spacecraft Center to set up the Lunar Receiving Laboratory (LRL) and to perform a preliminary examination of Apollo samples. In collaboration with Oliver Schaeffer (SUNY), Joseph Zähringer (Max Planck, Heidelberg), and Raymond Davis (Brookhaven National Laboratory), he built a gas analysis laboratory at JSC, and the noble gas portion of this laboratory remained operational until he retired in 2010. At NASA, Don worked on the lunar regolith, performed pioneering work on cosmic ray produced noble gas isotopes and Ar‐Ar dating, the latter for important insights into the thermal and shock history of meteorites and lunar samples. During this work, he discovered that the trapped gases in SNC meteorites were very similar to those of the Martian atmosphere and thus established their Martian origin. Among Don’s many administrative accomplishments are helping to establish the Antarctic meteorite and cosmic dust processing programs at JSC and serving as a NASA‐HQ discipline scientist, where he advanced peer review and helped create new programs. Don is a recipient of NASA’s Scientific Achievement and Exceptional Service Medals and the Meteoritical Society’s Leonard Medal. Donald Bogard.image

H/L chondrite LaPaz Icefield 031047 – A feather of Icarus?

Antarctic meteorite LAP 031047 is an ordinary chondrite composed of loosely consolidated chondritic fragments. Its petrography, oxygen isotopic composition and geochemical inventory are ambiguous and indicate an intermediate character between H and L chondrites. Petrographic indicators suggest LAP 031047 suffered a shock metamorphic overprint below ∼10 GPa, which did not destroy its unusually high porosity of ∼27 vol%. Metallographic textures in LAP 031047 indicate heating above ∼700 °C and subsequent cooling, which caused massive transformation of taenite to kamacite. The depletion of thermally labile trace elements, the crystallization of chondritic glass to microcrystalline plagioclase of unusual composition, and the occurrence of coarsely crystallized chondrule fragments is further evidence for post-metamorphic heating to ∼700–750 °C. However, this heating event had a transient character because olivine and low-Ca pyroxene did not equilibrate. Nearly complete degassing up to very high temperatures is indicated by the thorough resetting of LAP 031047’s Ar–Ar reservoir ∼100 ± 55 Ma ago. A noble gas cosmic-ray exposure age indicates it was reduced to a meter-size fragment at <0.5 Ma. In light of the fact that shock heating cannot account for the thermal history of LAP 031047 in its entirety, we test the hypothesis that this meteorite belonged to the near-surface of an Aten or Apollo asteroid that underwent heating during orbital passages close to the Sun.

The thermoluminescence of meteorites: A brief 2010 perspective

Abstract Early work on meteorite thermoluminescence, influenced by pottery dating and dosimetry applications, demonstrated a relationship between natural thermoluminescence and (1) the orbital perihelion of a meteorite and (2) the terrestrial age (time since fall) of a meteorite. For 14 years natural TL measurements were routinely made on newly recovered Antarctic meteorites to help identify unusual thermal and radiation histories, and to sort them by terrestrial age and perihelion. Two examples of the value of such data are presented, an Antarctic meteorite that underwent a major orbit change prior to fall and the collection mechanics of meteorites at the Lewis Cliff collection site. A second major area of focus for meteorite TL, that has no non-meteorite heritage, is the use of their induced TL to provide an extraordinarily sensitive and quantitative means of exploring metamorphic intensity and palaeothermometry. While especially valuable for unequilibrated ordinary chondrites, these types of measurement have proved useful with virtually every major class of meteorite, asteroidal and planetary. The challenge now is to extend the technique to small particles, micrometeorites, interplanetary dust particles, and cometary particles.

Evaporite formation during weathering of Antarctic meteorites––A weathering census analysis based on the ANSMET database

Abstract– Weathering of meteorites at the scale of the entire Antarctic Search for Meteorites program population is studied by analyzing the recent version of the online Antarctic meteorite classification database that includes information about 15,263 meteorites. This paper updates, supplements, and expands on the last Antarctic meteorite weathering census by Velbel (1988, Meteoritics 23:151–159). On average 5% of all Antarctic meteorites are indicated as evaporite bearing in the Antarctic Meteorite Database. Evaporite formation depends on compositional group. Evaporites are much more common on C chondrites than on ordinary chondrites, supporting previous findings. Ordinary chondrites of petrologic type 3 more often have evaporites on their surface than meteorites of other petrologic types. Contrary to previous findings, there is no apparent relation between evaporite formation and meteorite rustiness. Some meteorite‐bearing fields influence the frequency of evaporite‐mineral formation on meteorites. The influence of location is apparently related to differences in environmental conditions, most probably microclimate or/and hydrologic conditions. There is no relation between abundance of evaporite‐bearing meteorites and distance from the sea. Evaporite formation varies with year of collection; however, it was not possible to distinguish whether this is related to annual changes in environment or an artifact of sample categorization or curation.

The natural thermoluminescence of Antarctic meteorites and their terrestrial ages and orbits: A 2010 update

Abstract– We have examined the relationship between natural thermoluminescence (TL) and 26Al in 120 Antarctic meteorites in order to explore the orbital history and terrestrial ages of these meteorites. Our results confirm the observations of Hasan et al. (1987) which were based on 23 meteorites. For most meteorites there was a positive correlation between natural TL and 26Al, reflecting their similarity in decay rate under Antarctic conditions and thus in terrestrial age. For a small group with low TL and high 26Al a small perihelion was proposed. Within this group, natural TL decreases with terrestrial age as determined by 36Cl measurements, although the rate of TL decay is faster (half‐life approximately 10 ka) and the ages that can be determined are smaller (&lt;200 ka) than for most meteorites. The faster decay rate and lower natural TL levels are a reflection of recent exposure to higher radiation doses and higher temperatures, since this history would populate less stable TL traps with smaller electron densities. We sort the 120 meteorites by perihelion and terrestrial age. The normal perihelion group range up to approximately 1000 ka and the small perihelion group range up to approximately 200 ka. An intermediate perihelion group tends to have short terrestrial ages (20–60 ka). There is acceptable agreement between most (34 out of 43) of our present terrestrial age estimates and those determined by isotopic means, the exceptions reflecting complex irradiation histories, long burial times in the Antarctic, or other issues.

Elemental and isotope behavior of macromolecular organic matter from CM chondrites during hydrous pyrolysis

Abstract— A new insight into carbon and hydrogen isotope variations of insoluble organic matter (IOM) is provided from seven CM chondrites, including Murchison and six Antarctic meteorites (Y‐791198, Y‐793321, A‐881280, A‐881334, A‐881458 and B‐7904) as well as Murchison IOM residues after hydrous pyrolysis at 270–330 °C for 72 h. Isotopic compositions of bulk carbon (δ13Cbulk) and hydrogen (δD) of the seven IOMs vary widely, ranging from −15.1 to −7.6%0 and +133 to +986%0, respectively. Intramolecular carboxyl carbon (δ13CCOOH) is more enriched in 13C by 7.5. 11%0 than bulk carbon. After hydrous pyrolysis of Murchison IOM at 330 °C, H/C ratio, δ13Cbulk, δ13CCOOH, and δD values decrease by up to 0.31, 3.5%0, 5.5%0, and 961%0, respectively. The O/C ratio increases from 0.22 to 0.46 at 270 °C and to 0.25 at 300 °C, and decreases to 0.10 at 330 °C. δ13Cbulk‐δD cross plot of Murchison IOM and its pyrolysis residues shows an isotopic sequence. Of the six Antarctic IOMs, A‐881280, A‐881458, Y‐791198 and B‐7904 lie on or near the isotopic sequence depending on the degree of hydrous and/or thermal alteration, while A‐881334 and Y‐793321 consist of another distinct isotope group. A δ13Cbulk‐δ13CCOOH cross‐plot of IOMs, including Murchison pyrolysis residues, has a positive correlation between them, implying that the oxidation process to produce carboxyls is similar among all IOMs. These isotope distributions reflect various degree of alteration on the meteorite parent bodies and/or difference in original isotopic compositions before the parent body processes.

Polycyclic aromatic hydrocarbons and amino acids in meteorites and ice samples from LaPaz Icefield, Antarctica

Abstract— –We have analyzed ice samples and meteorites from the LaPaz region of Antarctica to investigate the composition of polycyclic aromatic hydrocarbons (PAHs) and amino acids with the goal to understand whether or not there is a compositional relationship between the two reservoirs. Four LL5 ordinary chondrites (OCs) and one CK carbonaceous chondrite were collected as part of the 2003/2004 ANSMET season. Ice samples collected from directly underneath the meteorites were extracted. In addition, exhaust particles from the snowmobiles used during the expedition were collected to investigate possible contributions from this source. The meteorite samples, the particulate matter and solid‐state extracts of the ice samples and the exhaust filters were subjected to two‐step laser mass spectrometry (L2MS) to investigate the PAH composition. For amino acids analysis, the meteorites were extracted with water and acid hydrolyzed, and the extracts were analyzed with offline OPA/NAC derivatization combined with liquid chromatography with UV fluorescence detection and time of flight mass spectrometry (LC‐FD/ToF‐MS). PAHs in the particulate matter of the ice were found to be qualitatively similar to the meteorite samples, indicating that micron‐sized grains of the meteorite may be embedded in the ice samples. The concentration levels of dissolved PAHs in all the ice samples were found to be below the detection limit of the L2MS. The PAH composition of the snowmobile exhaust is significantly different to the one in particulate matter, making it an unlikely source of contamination for Antarctic meteorites. The amino acids glycine, β‐alanine and γ‐amino‐n‐butyric acid that were detected at concentrations of 3 to 19 parts per billion (ppb) are probably indigenous to the Antarctic meteorites. Some of the LaPaz ice samples were also found to contain amino acids at concentration levels of 1 to 33 parts per trillion (ppt), in particular α‐aminoisobutyric acid (AIB), an abundant non‐protein amino acid of extraterrestrial origin found in some carbonaceous chondrites. We hypothesize that this amino acid could have been extracted from Antarctic micrometeorites and the particulate matter of the meteorites during the concentration procedure of the ice samples.