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NASA NTRS2014

Bulk Composition of Vesta as Constrained by the Dawn Mission and the HED Meteorites

Of the objects in the main asteroid belt, Vesta is of particular interest as it is large enough to have experienced internal differentiation (520 km diameter), and it is known to have a basaltic surface dominated by FeO-bearing pyroxenes. Furthermore, visible-IR spectra of Vesta and associated Vestoids are remarkably similar to laboratory spectra of Howardite-Eucrite-Diogenite (HED) meteorites, leading to the paradigm that the HEDs ultimately came from Vesta. Geochemical and petrological studies of the HEDs confirm the differentiated nature of the near-surface region of their parent body, and imply that crust extraction occurred well within the first 10 Ma of solar system history Vesta is therefore a prime target for studies that aim to constrain the earliest stages of planet building, and it is within this context that the NASA Dawn spacecraft orbited Vesta from July 2011 to September 2012. The results of the Dawn mission so far have significantly reinforced the HED-Vesta connection, confirming a significant degree of internal differentiation, a surface mineralogy compatible with that of the HEDs, and near-surface ratios of Fe/O and Fe/Si consistent with HED lithologies. The combination of data from the HED meteorites and the Dawn mission thus presents an unprecedented opportunity to use Vesta as a natural laboratory of early differentiation processes in the early solar system. However, the bulk composition of Vesta remains a significant unknown parameter, but one that plays a key role on the physical and chemical properties of the internal and surface reservoirs (core, mantle, crust). Several attempts have been made to constrain the bulk composition of the eucrite parent body, early endeavours relying on petrological or cosmochemical constraints. More recently, individual chondrite class compositions, or mixtures thereof, have been considered, constrained by considerations such as O-isotopes, trace-element ratios and siderophile element concentrations of the eucrites. The work presented here builds upon these latter studies, with the primary aims of: i) illustrating the potential diversity of the geochemical and geophysical properties of a fully differentiated Vesta-sized parent body, and ii) assessing which, if any, of the known chondritic bulk compositions are plausible analogues for proto-Vesta.

Toplis, M. J.↗
NASA NTRS2015

Melt Inclusion Analysis of RBT 04262 with Relationship to Shergottites and Mars Surface Compositions

Martian meteorite RBT 04262 is in the shergottite class. It displays the two lithologies typically found in "lherzolitic shergottites": one with a poikilitic texture of large pyroxene enclosing olivine and another with non-poikilitic texture. In the case of RBT 04262, the latter strongly ressembles an olivine- phyric shergottite which led the initial classification of this meteorite in that class. RBT 04262 has been studied with regards to its petrology, geochemistry and cosmic ray exposure and belongs to the enriched oxidized end-member of the shergottites. Studies on RBT 04262 have primarily focused on the bulk rock composition or each of the lithologies independently. To further elucidate RBT 04262's petrology and use it to better understand Martian geologic history, an in-depth study of its melt inclusions (MI) is being conducted. The MI chosen for this study are found within olivine grains. MI are thought to be trapped melts of the crystallizing magma preserved by the encapsulating olivine and offer snapshots of the composition of the magma as it evolves. Some MI, in the most Mg-rich part of the olivine of olivine-pyric shergottites, may even be representative of the meteorite parent melt.

Potter, S. A.↗
NASA NTRS2015

Impact History on Vesta: Petrographic, Compositional and Future Chronological Studies of Melt Clasts in Howardites

Howardite meteorites are polymict breccias composed mainly of eucritic and diogenitic material that likely originate from the surface of the Asteroid 4 Vesta. They can be separated into two subtypes: Regolithic, which represent the lithified remains of the active vestan regolith; Fragmental, which represent simpler polymict breccias. Amongst the regolithic features observed in the former, melt clasts are particularly striking for their appearance and compositional variability. They range from glassy spherules to finely crystalline (i.e., devitrified) clasts, and clasts containing only relict mineral grains to those containing only phenocrysts. Glasses can be separated into compositional sub-types including those with low FeO/MgO ratios (less than 5) -low alkali glasses, K-rich (K2O greater than 0.2 wt.%), Na-rich (Na2O greater than 0.6 wt.%) and CaO-rich, and those with high FeO/MgO ratios (greater than 10). There is also a distinction to be made between primary volcanic melt clasts and those produced by impacts. While suggested that a lack of chemical homogeneity among their studied melt clasts ruled out a primary volcanic origin, the low siderophile element contents observed in such clasts suggest less compositional influence from impactors than commonly assumed. Studying the chronology of the impact melt clasts in howardites can help us to better determine the timing of impact events on Vesta and the asteroid belt. In this research, we are launching an investigation into the petrology, composition (major/trace element and noble gas) and chronology of melt clasts in howardites. We have selected a set of howardites known to contain large quantities of melt clasts, and have begun the petrological and compositional studies of these materials. Once the melt clasts have been fully classified, we aim to perform chronological studies of individual clasts using both the Ar-40/Ar-39 and Pb-Pb chronometers, as well as determine the noble gas components present. Of particular note, the study will take advantage of the laser ablation techniques associated with the noble gas facilities at ASU, which will allow high-resolution, in-situ analysis of individual clasts. The broader aim of this work is to ascertain whether the impact flux in the region of the asteroid belt was similar to that on the Moon. Our understanding of impact events in the inner Solar System relies heavily on our analyses of lunar meteorites and returned samples, and there is currently some debate regarding whether there was a "Lunar Cataclysm" event around approx. 3.9 Ga, or the end of an epoch of "Late Heavy Bombardment" (LHB) at this time. New and more comprehensive constraints on howardite melt clast ages may help determine whether the asteroid belt experienced such a cataclysm or LHB.

Cartwright, J. A.↗
NASA NTRS2015

Are the Clast Lithologies Contained in Lunar Breccia 64435 Mixtures of Anorthositic Magmas

The anorthositic crust of the Moon is often used as the archtypical example of a primary planetary crust. The abundance and purity of anorthosite in the Apollo sample collection and remote sensing data are generally attributed to an early global magma ocean which produced widespread floating plagioclase cumulates (the ferroan anorthosites; FANs. Recent geochronology studies report evidence of young (less than 4.4 Ga) FAN ages, which suggest that either some may not be directly produced from the magma ocean or that the final solidification age of the magma ocean was younger than previous estimates. A greater diversity of anorthositic rocks have been identified among lunar meteorites as compared to returned lunar samples. Granted that these lithologies are often based on small clasts in lunar breccias and therefore may not represent their actual whole rock composition. Nevertheless, as suggested by the abundance of anorthositic clasts with Mg# [Mg/(Mg+Fe)] less than 0.80 and the difficulty of producing the extremely high plagioclase contents observed in Apollo samples and the remote sensing data, modification of the standard Lunar Magma Ocean (LMO) model may be in order. To ground truth mission science and to further test the LMO and other hypotheses for the formation of the lunar crust, additional coordinated petrology and geochronology studies of lunar anorthosites would be informative. Here we report new mineral chemistry and trace element geochemistry studies of thick sections of a composite of FAN-suite igneous clasts contained in the lunar breccia 64435 in order to assess the significance of this type of sample for petrogenetic studies of the Moon. This work follows recent isotopic studies of the lithologies in 64435 focusing on the same sample materials and expands on previous petrology studies who identified three lithologies in this sample and worked on thin sections.

Simon, J. I.↗
NASA NTRS2015

Na, K-Rich Rim Around a Chondrule in Unequilibrated Ordinary Chondrite Lew 86018 (L3.1)

Ordinary chondrites represent the most abundant early Solar system extra-terrestrial (approximately 85% abundance) material available for laboratory studies and expectedly record the most extensive range of alterations effects from unmetamorphosed chondritic material to the highest temperatures of thermal metamorphism. The least metamorphosed chondrites belonging to petrologic type 3, the so called unequili-brated ordinary chondrites (UOCs), provide insights into alteration that happened during the primeval, ear-liest stage of Solar system formation. The higher grade petrologic types 4-6 ordinary chondrites on the other hand document up to near textural equilibrium (in type 6) extensive thermal metamorphism consisting of minerals and phases providing evidence of equilibration of heterogeneous mineral composition, solid-state recrystallization. Despite being the most abundant, the effect of alteration is less explicitly understood in ordinary chondrites (even less in UOCs) compared to other groups (e.g. CV, CO, CR). Additionally, the relationship between metasomatism (also referred as aqueous alteration or fluid-assisted metamorphism) and metamorphism (primarily thermal driven) has not been studied and alterations in the ordinary chondrites have been considered to have occurred in absence of fluids in general. Despite this conventional view, UOCs of lowest grades (3.0-3.2) show some evidence of low temperature (approximately 200 C), fluid assisted metamorphism in the form of the presence of phyllosilicates, ferroan olivine, and magnetites in their matrices and occasionally in chondrules. Here, we present petrographic and mineralogical studies of UOC, Lewis Hills (LEW) 86018 to further our understanding of the extent and relative importance of metasomatism and/or metamorphism in UOCs.

Mishra, R. K.↗
NASA NTRS2015

Striking Graphite Bearing Clasts Found in Two Ordinary Chondrite Samples; NWA6169 and NWA8330

Meteorites play an integral role in understanding the history of the solar system. Not only can they contain some of the oldest material found in the solar system they also can contain material that is unique. Many lithologies are only found as foreign clasts within distinctly different host meteorites. In this investigation two foreign clasts within the meteorites, NWA6169 and NWA8330 were studied. The purpose of this investigation was to examine the mineralogy and petrography of the clasts within the samples. From there an identification and possible origin were to be inferred. NWA6169 is an unclassified ordinary chondrite that has a presumed petrologic type of L3. NWA8330 is a classified ordinary chondrite that has a petrologic type of LL3. Both meteorites were found to contain clasts that were similar; both modally were comprised of about 5% acicular graphite. Through SEM and Raman Spectroscopy it was found that they contained olivine, pyroxene, plagioclase, Fe-Ni sulfides, graphite, and metals. They were found to portray an igneous texture with relationships that suggest concurrent growth. Analytical microprobe results for NWA6169 revealed mineral compositions of Fa31-34, Fs23-83, and Ab7-85. For NWA8330 these were Fa28-32, Fs10-24, and Ab4-83. Only one similar material has been reported, in the L3 chondrite Krymka (Semenenko & Girich, 1995). The clast they described exhibited similar mineralogies including the unusual graphite. Krymka data displayed compositional values of Fa28.5-35.0 and Fs9-25.9. These ranges are fairly similar to that of NWA6169 and NWA8330. These samples may all be melt clasts, probably of impact origin. Two possibilities are (1) impact of a C-type asteroid onto the L chondrite parent asteroid, and (2) a piece of proto-earth ejected from the moon-forming collision event. These possibilities present abundant questions, and can be tested. The measurement of oxygen isotope compositions from the clasts should reveal the original source of the melt clasts. It may also be possible to perform Ar dating of the plagioclase present. Former analyses are now being performed.

Johnson, Jessica M.↗
NASA NTRS2016

Mineralogy of the Mercurian Surface

The MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft orbited Mercury for four years until April 2015, revealing its structure, chemical makeup, and compositional diversity. Data from the mission have confirmed that Mercury is a compositional end-member among the terrestrial planets. The X-Ray Spectrometer (XRS) and Gamma-Ray Spectrometer (GRS) on board MESSENGER provided the first detailed geochemical analyses of Mercury's surface. These instruments have been used in conjunction with the Neutron Spectrometer and the Mercury Dual Imaging System to classify numerous geological and geochemical features on the surface of Mercury that were previously unknown. Furthermore, the data have revealed several surprising characteristics about Mercury's surface, including elevated S abundances (up to 4 wt%) and low Fe abundances (less than 2.5 wt%). The S and Fe abundances were used to quantify Mercury's highly reduced state, i.e., between 2.6 and 7.3 log10 units below the Iron-Wustite (IW) buffer. This fO2 is lower than any of the other terrestrial planets in the inner Solar System and has important consequences for the thermal and magmatic evolution of Mercury, its surface mineralogy and geochemistry, and the petrogenesis of the planet's magmas. Although MESSENGER has revealed substantial geochemical diversity across the surface of Mercury, until now, there have been only limited efforts to understand the mineralogical and petrological diversity of the planet. Here we present a systematic and comprehensive study of the potential mineralogical and petrological diversity of Mercury.

Vander Kaaden, Kathleen E.↗
NASA NTRS2016

The Mineralogy, Geochemistry, and Redox State of Multivalent Cations During the Crystallization of Primitive Shergottitic Liquids at Various (f)O2. Insights into the (f)O2 Fugacity of the Martian Mantle and Crustal Influences on Redox Conditions of Martian Magmas.

The (f)O2 [oxygen fugacity] of crystallization for martian basalts has been estimated in various studies to range from IW-1 to QFM+4 [1-3]. A striking geochemical feature of the shergottites is the large range in initial Sr isotopic ratios and initial epsilon(sup Nd) values. Studies by observed that within the shergottite group the (f)O2 [oxygen fugacity] of crystallization is highly correlated with these chemical and isotopic characteristics with depleted shergottites generally crystallizing at reduced conditions and enriched shergottites crystallizing under more oxidizing conditions. More recent work has shown that (f)O2 [oxygen fugacity] changed during the crystallization of these magmas from one order of magnitude in Y980459 (Y98) to several orders of magnitude in Larkman Nunatak 06319. These real or apparent variations within single shergottitic magmas have been attributed to mixing of a xenocrystic olivine component, volatile loss-water disassociation, auto-oxidation during crystallization of mafic phases, and assimilation of an oxidizing crustal component (e.g. sulfate). In contrast to the shergottites, augite basalts such as NWA 8159 are highly depleted yet appear to be highly oxidized (e.g. QFM+4). As a first step in attempting to unravel petrologic complexities that influence (f)O2 [oxygen fugacity] in martian magmas, this study explores the effect of (f)O2 [oxygen fugacity] on the liquid line of descent (LLD) for a primitive shergottite liquid composition (Y98). The results of this study will provide a fundamental basis for reconstructing the record of (f)O2 [oxygen fugacity] in shergottites and other martian basalts, its effect on both mineral chemistries and valence state partitioning, and a means for examining the role of crystallization (and other more complex processes) on the petrologic linkages between olivine-phyric and pyroxene-plagioclase shergottites.

Shearer, C. K.↗
NASA NTRS2016

Constraints on Mantle Plume Melting Conditions in the Martian Mantle Based on Improved Melting Phase Relationships of Olivine-Phyric Shergottite Yamato 980459

Martian meteorite Yamato 980459 (hereafter Y98) is an olivine-phyric shergottite that has been interpreted as closely approximating a martian mantle melt [1-4], making it an important constraint on adiabatic decompression melting models. It has long been recognized that low pressure melting of the Y98 composition occurs at extremely high temperatures relative to martian basalts (1430 degC at 1 bar), which caused great difficulties in a previous attempt to explain Y98 magma generation via a mantle plume model [2]. However, previous studies of the phase diagram were limited to pressures of 2 GPa and less [2, 5], whereas decompression melting in the present-day martian mantle occurs at pressures of 3-7 GPa, with the shallow boundary of the melt production zone occurring just below the base of the thermal lithosphere [6]. Recent experimental work has now extended our knowledge of the Y98 melting phase relationships to 8 GPa. In light of this improved petrological knowledge, we are therefore reassessing the constraints that Y98 imposes on melting conditions in martian mantle plumes. Two recently discovered olivine- phyric shergottites, Northwest Africa (NWA) 5789 and NWA 6234, may also be primary melts from the martian mantle [7, 8]. However, these latter meteorites have not been the subject of detailed experimental petrology studies, so we focus here on Y98.

Kiefer, Walter S.↗
NASA NTRS2017

Effects of Short-Term Thermal Alteration on Organic Matter in Experimentally-Heated Tagish Lake Observed by Raman Spectroscopy

Carbonaceous chondrites exhibit a wide range of aqueous and thermal alteration characteristics, while some are known to demonstrate mineralogical and petrologic evidence of having been thermally metamorphosed after aqueous alteration. This group of meteorites are commonly referred as thermally met-amorphosed carbonaceous chondrites (TMCCs), and their reflectance spectra show resemblances to that of C-type asteroids which typically have low albedos. This suggests that the surfaces of the C-type asteroids are also composed of both hydrous and dehydrated minerals, and thus TMCCs are among the best samples that can be studied in laboratory to reveal the true nature of the C-type asteroids. Although TMCCs are usually meteorites that were previously categorized as CI and CM chondrites, they are not strictly CI/CM because they exhibit isotopic and petrographic characteristics that significantly deviate from typical CI/CM. More appropriately, they are called CI-like and/or CM-like chondrites. Typical examples of TMCCs include the C2-ung/CM2TIV Belgica (B)-7904 and Yamato (Y) 86720. Thermal alteration is virtually complete in these meteorites and thus they are considered typical end-members of TMCCs exhibiting complete dehydration of matrix phyllosilicates. The estimated heating conditions are 10 to 103 days at 700 C to 1 to 100 hours at 890 C, i.e. short-term heating induced by impact and/or solar radiation. While the petrology and chemistry of TMCCs have only recently been extensively characterized, we have just begun to study in detail their organic contents. In order to understand how short-term heating affects the maturity of insoluble organic matter (IOM) in hydrous chondrites, we investigated experimentally-heated Tagish Lake meteorite using Raman spectroscopy, as the chemical and bulk oxygen isotopic compositions of the matrix of the carbonate (CO3)-poor lithology of the Tagish Lake (hereafter Tag) meteorite bears similarities to the TMCCs.

Chan, Q. H. S.↗
NASA NTRS2017

Amino Acid Contents of Meteorite Mineral Separates

Indigenous amino acids have been found indigenous all 8 carbonaceous chondrite groups. However, the abundances, structural, enantiomeric and isotopic compositions of amino acids differ significantly among meteorites of different groups and petrologic types. This suggests that parent-body conditions (thermal or aqueous alteration), mineralogy, and the preservation of amino acids are linked. Previously, elucidating specific relationships between amino acids and mineralogy was not possible because the samples analyzed for amino acids were much larger than the scale at which petrologic heterogeneity is observed (sub mm-scale differences corresponding to sub-mg samples). Recent advances in amino acid measurements and application of techniques such as high resolution X-ray diffraction (HR-XRD) and scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS) for mineralogical characterizations allow us to perform coordinated analyses on the scale at which mineral heterogeneity is observed.

Berger, E. L.↗
NASA NTRS2018

Aqueous Alteration and Shock Metamorphism of Antarctic CR Chondrites

CR chondrites are the group of carbonaceous chondrites that best preserve records of formation of their components in the solar nebula. Although they are affected by aqueous alteration, many chondrules and CAIs are well-preserved, suggesting they have experienced little thermal metamorphism. We have been investigating the petrologic variations among the CR chondrites in the NIPR Antarctic meteorite collection. We focused particular attention on the petrology of amoeboid olivine aggregates (AOAs) in order to understand secondary alteration on the CR chondrite parent body. AOAs are composed of fine-grained forsteritic olivine and refractory minerals formed by condensation in the solar nebula, and can be used as sensitive indicators of secondary alteration processes.

Komatsu, M.↗
NASA NTRS2018

Correlated Amino Acid and Mineralogical Analyses of Milligram and Submilligram Samples of Carbonaceous Chondrite Lonewolf Nunataks 94101

Amino acids, the building blocks of proteins, have been found to be indigenous in the eight carbonaceous chondrite groups. The abundances, structural, enantiomeric and isotopic compositions of amino acids differ significantly among meteorites of different groups and petrologic types. These results suggest parent-body conditions (thermal or aqueous alteration), mineralogy, and the preservation of amino acids are linked. Previously, elucidating specific relationships between amino acids and mineralogy was not possible because the samples analyzed for amino acids were much larger than the scale at which petrologic heterogeneity is observed (sub mm-scale differences corresponding to sub-mg samples); for example, Pizzarello and coworkers measured amino acid abundances and performed X-ray diffraction (XRD) on several samples of the Murchison meteorite, but these analyses were performed on bulk samples that were 500 mg or larger. Advances in the sensitivity of amino acid measurements by liquid chromatography with fluorescence detection/time-of-flight mass spectrometry (LC-FD/TOF-MS), and application of techniques such as high resolution X-ray diffraction (HR-XRD) and scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS) for mineralogical characterizations have now enabled coordinated analyses on the scale at which mineral heterogeneity is observed. In this work, we have analyzed samples of the Lonewolf Nunataks (LON) 94101 CM2 carbonaceous chondrite. We are investigating the link(s) between parent body processes, mineralogical context, and amino acid compositions in meteorites on bulk samples (approx. 20mg) and mineral separates (< or = 3mg) from several of spatial locations within our allocated samples. Preliminary results of these analyses are presented here.

LONEWOLF NUNATAKS 94101↗
NASA NTRS2019

Elemental Variation and Petrogenesis of Pyroxenes in HED Meteorites by Multivariable Discriminant Analysis Method

HED (Howardite, Eucrite and Diogenite) are meteorites with mafic and ultramafic igneous composition. Previous studies suggested HED came from asteroid (4) Vesta and they were generated by magmatic melting followed by differentiation crystallization, metamorphic, and impact. Uniform oxygen isotopic composition of HED samples favors global magma ocean for (4) Vesta. However, the petrological diversity of HED may indicate more complex magma processes in the meteorites. In general, most of the geochemical studies are using traditional methods (e.g. element to element or ratio to ratio plots) to classify the different rock type and groups. With the traditional methods, only limited elements can be shown in a figure. As such, some meteorites may have been identified as HED by a traditional method but found different either in isotopic composition or other elemental characteristic. These anomalous HED meteorites may or may not come from asteroid (4) Vesta. In fact, magma is a unit system where any elemental change should affect to all other elements as a whole, it would be reasonable to consider all elements together to look for the systematical changes. Using multivariable discriminant analysis (MDA) method is one of such testing for their geochemical variation. The method may be able to help us to better understand the petrologic processes and the relationship among elements. This study is to test the MDA method by focus mainly on pyroxene composition of eucrite and diogenite.

Peng, Z. X.↗
NASA NTRS2019

Investigating the History of Aubrites Using X-Ray Computed Tomography and Bulk Partition Coefficients

The aubrites are a unique group of differentiated meteorites that formed on parent bodies with oxygen fugacities (ƒO2) from ~2 to ~6 log units below the iron-wustite buffer. At these highly reduced condi- tions, elements deviate from the geochemical behavior exhibited at terrestrial ƒO2, and may form FeO-poor silicates, Si-bearing metals, and exotic sulfides. Geochemical examinations of aubrites, such as mineral major-element compositions, bulk-rock compositions, O isotopes, and crystallization ages, are crucial to understand their formation and evolution at extreme ƒO2 conditions. In this study, we determine partitioning relationships of elements between bulk silicate, sulfide, and metal phases within aubrites, and compare the results to partition coefficients determined from petrologic experiments run under mercurian conditions. While previous studies have described the petrology and 2D modal abundances of aubrites, this work provides the first 3D view of aubritic mineralogies, which are com- pared to the available 2D data. Constraints of 3D modal abundances will increase the accuracy of computed bulk distribution coefficients; therefore, 3D scans of aubrite samples are imperative. We utilize X-ray computed tomogra- phy (XCT) to non-destructively analyze the distribution and abundances of mineral phases in aubrites and locate composite clasts of sulfide grains for future analysis.

Wilbur, Z. E.↗
NASA NTRS2020

Plagioclase Compositions of Eucrites and Eucrite-Type Achondrites

Eucrites are basalts, diabases and gabbros composed of ferroan pigeonite and augite, calcic plagioclase, and a silica phase, with accessory amounts of ilmenite, chromite, Ca-phosphate, troilite, metal and olivine. Many of the gabbroic-textured eucrites are cumulates from a mafic magma, while most other eucrites are close to melt compositions. These are referred to as cumulate and basaltic eucrites. Petrologic, compositional and isotopic studies have identified several mafic achondrites with eucritic mineralogy that have anomalous properties, and some of these are considered to have been derived from different parent asteroids than normal eucrites. These are referred to as eucrite-type achondrites, and they include cumulate and basaltic types. Petrologic studies of eucrites often concentrate on pyroxene compositions to reveal the petrogenetic history of the rocks and plagioclase compositions are less utilized. Here I examine Na and K variations of a suite of basaltic and cumulate eucrites and eucrite-type achondrites.

Mittlefehldt, David W.↗
NASA NTRS2020

Abundant Extraterrestrial Amino Acids in the Primitive CM Carbonaceous Chondrite Asuka 12236

The Asuka (A)-12236 meteorite has recently been classified as a CM carbonaceous chondrite of petrologic type 3.0/2.9 and is among the most primitive CM meteorites studied to date. Here, we report the concentrations, relative distributions, and enantiomeric ratios of amino acids in water extracts of the A-12236 meteorite and another primitive CM chondrite Elephant Moraine(EET) 96029 (CM2.7) determined by ultra-high-performance liquid chromatography time-of-flight mass spectrometry. EET 96029 was highly depleted in amino acids and dominated by glycine, while a wide diversity of two- to six-carbon aliphatic primary amino acids were identified in A-12236, which had a total amino acid abundance of 360 ± 18 nmol g-1, with most amino acids present without hydrolysis (free). The amino acid concentrations of A-12236 were double those previously measured in the CM2.7 Paris meteorite, consistent with A-12236 being a highly primitive and unheated CM chondrite. The high relative abundance of α-amino acids in A-12236 are consistent with formation by a Strecker-cyanohydrin dominated synthesis during a limited early aqueous alteration phase on the CM meteorite parent body. The presence of predominantly free glycine, a near racemic mixture of alanine (D/L ~0.93 to 0.96), and elevated abundances of several terrestrially rare non-protein amino acids including α-amino isobutyric acid (α-AIB) and racemic isovaline, indicate that these amino acids in A-12236 are extraterrestrial in origin. Given a lack of evidence for biological amino acid contamination in A-12236, it is possible that some of the L-enantiomeric excesses (Lee ~34 to 64%) of the protein amino acids aspartic and glutamic acids and serine are indigenous to the meteorite; however, isotopic measurements are needed for confirmation. In contrast to more aqueously altered CMs of petrologic types ≤ 2.5, no L-isovaline excesses were detected in A-12236. This observation strengthens the hypothesis that extensive parent body aqueous activity is required to produce or amplify the large L-isovaline excesses that cannot be explained solely by exposure to circularly polarized radiation or other chiral symmetry breaking mechanisms prior to incorporation into the asteroid parent body.

Daniel P Glavin↗
NASA NTRSDate not supplied

New Directions in the Quest for Unaltered Ci-Like Material From the Early Solar System

CI meteorites have bulk chemical compositions closely matching the solar photosphere (except volatiles) and thus are considered to represent the starting composition of the Solar System. The return of CI-like samples from asteroid (162173) Ryugu by Hayabusa2 has greatly bolstered studies of CI. However, both CI and the Ryugu samples are CI1, i.e., they were extensively altered by aqueous fluids on their parent bodies so the mineralogy, textures, and oxygen isotope compositions of their CI3 precursors have been obscured. Fortunately, they contain rare remnants of primordial minerals in the form of small anhydrous silicate and Ca-Al-rich grains, and detailed petrologic and isotopic studies of these grains have helped elucidate the nature of their precursors. Here, we continue our work on petrologic and isotopic studies of such phases in Ryugu particle C0137.

C A Goodrich↗