¹Robert W.Nicklas,¹James M.D.Day,²Zoltan Vaci,³Arya Udry,⁴Yang Liu,⁵Kimberly T.Tait
Earth and Planetary Science Letters 564, 116876 Link to Article [https://doi.org/10.1016/j.epsl.2021.116876]
¹Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA, 92093, USA
²Institute of Meteoritics, Department of Earth and Planetary Science, University of New Mexico, Albuquerque, NM, 87131, USA
³Department of Geoscience, University of Nevada, Las Vegas, Las Vegas, NV 89154, USA
⁴Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA
⁵Department of Natural History, Royal Ontario Museum, Toronto, ON, M5S 2C6, Canada
Copyright Elsevier

Martian meteorites are the only available samples that can be directly measured to constrain the geological evolution of Mars. It has been suggested that the oxygen fugacity (fO2) of martian shergottite meteorites, which have low (∼7 wt.%) to high-MgO (∼30 wt.%) compositions, correlates with incompatible trace element enrichment (i.e., La/Yb), and 87Sr/86Sr, 143Nd/144Nd, 187Os/188Os and 176Hf/177Hf at the time of crystallization. These relationships have been interpreted to result from early magmatic processes segregating enriched and more oxidized from depleted and more reduced reservoirs in Mars. Here we use the V-in-olivine oxybarometer to constrain the fO2 of shergottites and the dunitic chassignites. These data, utilizing early crystallizing silicate phases, constrain the shergottite fO2 range to between −3.72 ± 0.07 and −0.21 ± 0.55 ΔFMQ (log units relative to the fayalite-magnetite-quartz buffer), with no correlation with trace element enrichment or Nd isotope systematics. Previously employed oxybarometers that use later-formed or multiple mineral phases, and that show such correlations, likely differ from the V-in-olivine oxybarometer in that they record effects from late-stage magmatic processes. In contrast to shergottites, chassignites are relatively oxidized, at +2.1 ± 0.4 to +2.2 ± 0.5 ΔFMQ. The chassignites, along with the nakhlites, have been proposed to be sourced from metasomatized lithospheric mantle, and their high fO2 strengthens this model. The new data implies that the martian mantle sources of shergottites have fO2 of −2.1 ± 1.8 ΔFMQ. This estimate indicates that the mantle and core of Mars are not in redox equilibrium and therefore that oxidation of the martian mantle following core formation is required.

¹Johan Vandenborre,³Laurent Truche,¹Amaury Costagliola,¹Emeline Craff,¹Guillaume Blain,¹Véronique Baty,²Ferid Haddad,²Massoud Fattahi
Earth and Planetary Science Letters 564, 116892 Link to Article [https://doi.org/10.1016/j.epsl.2021.116892]
¹Subatech, UMR 6457, Institut Mines-Télécom Atlantique, CNRS/IN2P3, Université de Nantes, 4, Rue Alfred Kastler, La chantrerie BP 20722, 44307 Nantes cedex 3, France
²GIP ARRONAX, 1 rue ARRONAX, CS 10112, 44817 Saint-Herblain Cedex, France
³University Grenoble Alpes, CNRS, ISTerre, CS 40700, 38058 Grenoble, France
Copyright Elsevier

Low molecular weight carboxylate anions such as formate (HCOO−), acetate (CH3COO−) and oxalate (C2O) have been shown to play an important role in supporting deep subsurface microbial ecosystems. Their origin whether biological or abiotic is currently highly debated, but surprisingly radiolytic production has rarely been considered, as it is the case for H2. Here, we address this question through dedicated irradiation experiments. Aqueous solutions containing carbonate, formate, acetate or oxalate have been irradiated using both the 60.7 MeV α-beam of the ARRONAX cyclotron (Nantes, France) and 661.7 keV γ-Ray in order to reveal the mechanism and chemical yield of radiation-induced dissolved carbonate degradation.

The yields (G-values) of carboxylate anions production/degradation in low-concentration carbonate solution (0.01 to 1 mmol L−1) are measured. Carbonate degradation occurs through three consecutive steps (Carbonate
Formate Acetate Oxalate) involving formate radical (CO2−•), dihydrogen (H2), and carbon dioxide (CO2) generation. Dissolved carbonate radiolysis provides a consistent pathway for both enhancing two-fold the radiolytic H2 production compared to pure water and generating carboxylic species, chiefly oxalate, readily available for microbes. Radiation-induced carbonate degradation may produce substantial amount (millimolar concentration) of carboxylate anions in ancient groundwaters from deep crystalline bedrocks. Subsurface lithoautotrophic microbial ecosystems may not only be supported by radiolytic H2 but also by carboxylate species from carbonate radiolysis. Carbonate radiolysis can be also an endogenous source of carboxylate species on Mars and other planetary bodies.

¹Caroline AVRIL,¹Valérie MALAVERGNE,²Eric D. VAN HULLEBUSCH,³Fabrice BRUNET,²Stephan BORENSZTAJN,⁴Jérôme LABANOWSKI,⁵Louis HENNET,⁶François GUYOT
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13641]
¹Laboratoire Géomatériaux et Environnement, Université Gustave Eiffel, EA 4508, UPEM, 5 boulevard Descartes, 77454 Marne‐la‐Vallée, Cedex 2, France
²Institut de physique du globe de Paris, CNRS, Université de Paris, F‐75005 Paris, France
³ISTerre, CNRS—Univ. Grenoble Alpes, Maison des Géosciences, BP 53, 38041 Grenoble Cedex 9, France
⁴Laboratoire de Chimie et Microbiologie de l’Eau, UMR CNRS 6008, Université de Poitiers, 40 avenue du recteur Pineau, 86022 Poitiers, France
⁵Conditions Extrêmes et Matériaux: Haute Température et Irradiation, UPR 3079 CNRS et université d’Orléans, 1d avenue de la recherche scientifique, 45071 Orléans Cedex 2, France
⁶Muséum National d’Histoire Naturelle, Sorbonne Universités, IMPMC UMR 7590 CNRS, 61 rue Buffon, 75005 Paris, France
Published by arrangement with John Wiley & Sons

Understanding the transformations of highly reduced enstatite chondrites (EC) in terrestrial environments, even on very short timescales, is important to make the best use of the cosmochemical and mineralogical information carried by these extraterrestrial rocks. Analogs of EC meteorites were synthesized at high pressure and high temperature. Then, their aqueous alterations, either abiotic or in the presence of the bacteria Acidithiobacillus ferrooxidans or Acidithiobacillus thiooxidans, were studied under air, at pH ~2, 20 °C, and atmospheric pressure. They stayed in shaken batch reactors for 15 days. Reference experiments were carried out separately by altering only one mineral phase among those composing the synthetic EC (i.e., sulfides: troilite or Mg‐Ca‐rich sulfides, enstatite, and Fe70Si30). Composition of the alteration aqueous media and microstructures of the weathered solids were monitored by inductively coupled plasma atomic emission spectroscopy and by scanning electron microscopy, respectively. Alteration sequence of the different mineral components of the synthetic EC was found to occur in the following order: magnesium‐calcium sulfides > troilite > iron‐silicon metallic phase > enstatite regardless of the presence or absence of the microorganisms. Such small biological effects might be due to the fact that the alteration conditions are far from biologically optimal, which is likely the case in most natural environments. The exposed surfaces of an EC meteorite falling on Earth in a wet and acidic environment could lose within a few hours their Ca‐ and Mg‐rich sulfides (oldhamite and niningerite). Then, in <1 week, troilite and kamacite could be altered. In a wet and acidic environment, only the enstatite would remain intact and would weather on a much slower geological timescale.

¹R. P. Lozano,²J. A. Sánchez,¹R. González‐Laguna,³T. Martín‐Crespo
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13645]
¹Museo Geominero, Instituto Geológico y Minero de España, C/Ríos Rosas 23, Madrid, 28003 Spain
²C/Rio Añamaza 4, 29620 Torremolinos, Málaga, Spain
³Departamento de Biología y Geología, Física y Química Inorgánica, ESCET, Universidad Rey Juan Carlos, C/Tulipán s/n, Móstoles, 28933 Madrid, Spain
Published by arrangement with John Wiley & Sons

Colomera is the Spanish meteorite (IIE) that has aroused the greatest interest among the international scientific community. Until now, the story of the find was only partially known and certain data are incorrect. The amazing journey of this meteorite has been recounted in this work. It reveals unpublished information derived from local archives, and testimonies from the descendants of the family that found the meteorite in 1913, and from the inhabitants of Colomera (Granada, Spain). We also document the story after its discovery, which culminated in a 2015 court ruling demanding the return of the largest part the mass (120.34 kg) to the heirs of the Spanish family that discovered the meteorite. Some of the material initially extracted in Spain (305 g) is currently housed in the Natural History Museum (121.3 g; London, UK). Nine kilograms of fragments remains in the United States after returning the meteorite to Spain in 1969. Of these, we have only located slightly more than 4 kg in several American institutions. Recently, 235 g has been returned to Spain: two fragments in private collections and two fragments in the Museo Geominero, Spanish Geological and Mining Institute (Spanish acronym: IGME).

¹Devin L.Schrader,¹Jemma Davidson,²Timothy J.McCoy,³Thomas J.Zega,⁴Sara S.Russell,³Kenneth J.Domanik,⁴Ashley J.King
Geochimica et Cosmochimica Acta (in Press) Link to Articel [https://doi.org/10.1016/j.gca.2021.03.019]
¹Center for Meteorite Studies, School of Earth and Space Exploration, Arizona State University, 781 East Terrace Road, Tempe, AZ 85287, USA
²Department of Mineral Sciences, National Museum of Natural History, Smithsonian Institution, 10th & Constitution Avenue NW, Washington, DC 20560-0119, USA
³Lunar and Planetary Laboratory, University of Arizona, Tucson, Arizona 85721, USA
⁴Planetary Materials Group, Department of Earth Sciences, Natural History Museum, Cromwell Road, London SW7 5BD, UK
Copyright Elsevier

Determining compositional trends among individual minerals is key to understanding the thermodynamic conditions under which they formed and altered, and is also essential to maximizing the scientific value of small extraterrestrial samples, including returned samples and meteorites. Here we report the chemical compositions of Fe-sulfides, focusing on the pyrrhotite-group sulfides, which are ubiquitous in chondrites and are sensitive indicators of formation and alteration conditions in the protoplanetary disk and in small Solar System bodies. Our data show that while there are trends with the at.% Fe/S ratio of pyrrhotite with thermal and aqueous alteration in some meteorite groups, there is a universal trend between the Fe/S ratio and degree of oxidation. Relatively reducing conditions led to the formation of troilite during: (1) chondrule formation in the protoplanetary disk (i.e., pristine chondrites) and (2) parent body thermal alteration (i.e., LL4 to LL6, CR1, CM, and CY chondrites). Oxidizing and sulfidizing conditions led to the formation of Fe-depleted pyrrhotite with low Fe/S ratios during: (1) aqueous alteration (i.e., CM and CI chondrites), and (2) thermal alteration (i.e., CK and R chondrites). The presence of troilite in highly aqueously altered carbonaceous chondrites (e.g., CY, CR1, and some CM chondrites) indicates they were heated after aqueous alteration. The presence of troilite, Fe-depleted pyrrhotite, or pyrite in a chondrite can provide an estimate of the oxygen and sulfur fugacities at which it was formed or altered. The data reported here can be used to estimate the oxygen fugacity of formation and potentially the aqueous and/or thermal histories of sulfides in extraterrestrial samples, including those returned by the Hayabusa2 mission and due to be returned by the OSIRIS-REx mission in the near future.

¹T.J.Barrett,¹A.Černok,¹G.Degli-Alessandrini,¹X.Zhao,^1,2M.Anand,¹I.A.Franchi,³J.R.Darling
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2021.03.018]
¹The Open University, School of Physical Sciences, Walton Hall, Milton Keynes, MK7 6AA, UK
²Department of Earth Sciences, Natural History Museum, London, SW7 5BD, UK
¹University of Portsmouth, School of the Environment, Geography and Geosciences, Burnaby Road Portsmouth, PO1 3QL, UK
Copyright Elsevier

The abundance and isotopic composition of volatile elements in meteorites is critical for understanding planetary evolution, given their importance in a variety of geochemical processes. There has been significant interest in the mineral apatite, which occurs as a minor phase in most meteorites and is known to contain appreciable amounts of volatiles (up to wt. % F, Cl, and OH). Impact-driven shock metamorphism, pervasive within many meteorites, can potentially modify the original signatures of volatiles through processes such as devolatilization and diffusion.

In this study, we investigate the microstructures of apatite grains from six eucrites across a broad range of shock stages (S1–S5) using electron backscatter diffraction (EBSD) to explore shock-induced crystallographic features in apatite. New Cl and H abundance and isotopic composition data were collected on moderate to highly shocked samples (S3-S5) by Nano Secondary Ion Mass Spectrometry (NanoSIMS). Previously reported volatile data for S1 and S2 eucrites were integrated with EBSD findings in this study.

Our findings indicate that apatite microstructures become increasingly more complex at higher shock stages. At low shock stages (S1–S2) samples display brecciation and fracturing of apatite. Samples in S3 and S4 display increasing crystal plastic deformation indicated by increasing spread in pole figures. At the higher shock stages (S4/S5) there is potential recrystallisation demonstrated by an increased density of subgrain boundaries.

The Cl content and δ37Cl values of highly-shocked apatite grains range from ∼ 940–1410 ppm and – 3.38 to + 7.70 ‰, respectively, within the range observed in less-shocked eucrites. In contrast, H2O abundances are more variable (from 186 to ∼ 4010 ppm), however, the measured water content still falls within the range previously reported for low-shock eucrites. The measured δD values range from – 157 to + 163 ‰, also within the range of values from known low-shock basaltic eucrites. Weighted averages for both isotopic systems (δD − 122 ± 20 ‰, δ37Cl + 1.76 ± 0.66 ‰) are consistent with the range displayed in other inner Solar System bodies.

NanoSIMS isotope images of apatite grains display heterogeneity in their Cl abundance at the nanoscale which increases in complexity with shock stage. This increasing complexity, however, does not correlate with deformation microstructures observed in EBSD or with the Cl isotopic composition at either an inter-grain or intra-grain scale. These findings are similar to analyses of variably shocked lunar apatite and, therefore, apatite appears to be a robust recorder of Cl and H (at least at spatial resolution and precision currently achievable by NanoSIMS) on airless bodies, despite intensive shock.

^1,2,5Derek Sears,^1,2,5Daniel Ostrowski,³Heather Smith,^1,6Adonay Sissay,⁴Mihir Trivedi
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2021.114442]
¹Arkansas Center for Space and Planetary Sciences, University of Arkansas, Fayetteville, AR 72701, USA
²BAER Institute/NASA Ames Research Center, Moffett Field, CA 94035, USA
³USRA/NASA Ames Research Center, Moffett Field, CA 94035, USA
⁴NASA Ames Research Center, Moffett Field, CA 94035, USA
⁵Department of Chemistry and Biochemistry, University of Arkansas, Fayetteville, AR 72701, USA
Copyright Elsevier

In order to find an additional quantitative way to estimate the petrographic type of unequilibrated ordinary chondrites (UOC), and one that can be used remotely in the study of asteroids, we have analyzed the near-infrared spectra of a suite of UOC observed falls. We obtained spectra from the RELAB database at Brown University and applied several methods for determining the amount of clinopyroxene (CPX) as a percentage of the total pyroxene in the meteorites. The presence of low-Ca CPX has long been known to be characteristic of little-metamorphosed ordinary chondrites. The methods we used were (1) naked-eye determination of the wavelength of the absorption features at ~1 μm and ~2 μm, (2) determination of the wavelengths of these features by fitting polynomial equations, and (3) determining the relative intensities of the CPX and OPX features after isolation by a curve fitting procedure. The measurements were then “calibrated” using data from the literature to obtain values for the amount of CPX in the total pyroxene. We find that there is an empirical relationship between the amount of CPX detected by these methods of spectrum analysis and the petrologic type.

Petrologic type = +4.402–0.019 × CPX%

We explain this empirical relationship (1) as evidence that in pyroxene bearing rocks the spectrum of pyroxene dominates (this has been known in the 1970s), (2) that low-Ca CPX is so abundant in these meteorites (up to 40 vol%) that it is easily detected by reflectance spectroscopy, and (3) compositional effects caused by Ca and Fe in the pyroxenes partially cancel out or are small. We thus have a new method of quantitatively measuring the level of metamorphic alteration experienced by these important meteorites and of assigning them a petrologic type of 3.0 to 3.9. More importantly, unlike existing methods, this can be applied remotely so that chondritic asteroid surfaces (i.e. those of Q and S asteroids) can also be characterized in terms of their metamorphic history. As an example, (433) Eros and (25143) Itokawa were found to be types ~3.5 and ~3.4, respectively. We briefly discuss the implications of this for understanding the history of meteorites and asteroids.

¹Maxime Piralla,²Romain Tartèse,¹Yves Marrocchi,²Katherine H. Joy
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13639]
¹CRPG, CNRS, UMR 7358, Université de Lorraine, Vandœuvre‐lès‐Nancy, F‐54500 France
²Department of Earth and Environmental Sciences, School of Natural Sciences, The University of Manchester, Oxford Road, Manchester, M13 9PL UK
Published by arrangement with John Wiley & Sons

Apatite has been widely used for assessing the volatile inventory and hydrothermal fluid compositions of asteroidal and planetary bodies. We report the OH, F, and Cl abundances, as well as the hydrogen isotope composition, of apatite in the CM1‐2 chondrite Boriskino and in the C1‐ungrouped Bench Crater meteorite. Apatite in both meteorites is halogen‐poor, close to the hydroxylapatite endmember composition, and characterized by average δDSMOW values of −226 ± 59% and 233 ± 92%, respectively. Compared to apatite, the matrix in Bench Crater is depleted in D with a δDSMOW value of −16 ± 119‰. Comparing apatite and water H isotope compositions yields similar apatite‐water D/H fractionation ΔDApatite‐Water of approximately 120–150‰ for both chondrites, suggesting that apatite formed at similar temperatures. Combining a lattice strain partitioning model with apatite F and Cl abundances in Boriskino and Bench Crater yields low F and Cl abundances <300 μg g−1 in apatite‐forming fluids, and fluid F/Cl ratios that are roughly consistent with the bulk F/Cl ratios of other CI and CM chondrites. This suggests that hydrothermal alteration on these meteorite parent bodies took place under closed‐system conditions. Based on the OH abundance estimates for the apatite‐forming fluids, we estimated the pH values of alteration fluids to be of approximately 10–13. Such alkaline fluid compositions are consistent with previous modeling and suggest that apatite formed late, toward the end of completion of hydrothermal alteration processes on the Boriskino and Bench Crater parent bodies.

¹Marc M. Hirschmann,²Edwin A. Bergin,³Geoff A. Blake,^4,5Fred J. Ciesla,⁶Jie Li
Proceedings of the National Academy of Sciences of the United States of America [PNAS] (in Press) Link to Article [https://doi.org/10.1073/pnas.2026779118]
¹Department of Earth and Environmental Sciences, University of Minnesota, Minneapolis, MN 55455;
²Department of Astronomy, University of Michigan, Ann Arbor, MI 48109;
³Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125;
⁴Department of Geophysical Sciences, University of Chicago, Chicago, IL 60637;
⁵Chicago Center for Cosmochemistry, University of Chicago, Chicago, IL 60637;
⁶Department of Earth and Environmental Sciences, University of Michigan, Ann Arbor, MI 48109

During the formation of terrestrial planets, volatile loss may occur through nebular processing, planetesimal differentiation, and planetary accretion. We investigate iron meteorites as an archive of volatile loss during planetesimal processing. The carbon contents of the parent bodies of magmatic iron meteorites are reconstructed by thermodynamic modeling. Calculated solid/molten alloy partitioning of C increases greatly with liquid S concentration, and inferred parent body C concentrations range from 0.0004 to 0.11 wt%. Parent bodies fall into two compositional clusters characterized by cores with medium and low C/S. Both of these require significant planetesimal degassing, as metamorphic devolatilization on chondrite-like precursors is insufficient to account for their C depletions. Planetesimal core formation models, ranging from closed-system extraction to degassing of a wholly molten body, show that significant open-system silicate melting and volatile loss are required to match medium and low C/S parent body core compositions. Greater depletion in C relative to S is the hallmark of silicate degassing, indicating that parent body core compositions record processes that affect composite silicate/iron planetesimals. Degassing of bare cores stripped of their silicate mantles would deplete S with negligible C loss and could not account for inferred parent body core compositions. Devolatilization during small-body differentiation is thus a key process in shaping the volatile inventory of terrestrial planets derived from planetesimals and planetary embryos.

¹Netra S.Pillai et al. (>10)
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2021.114436]
¹Space Astronomy Group, U R Rao Satellite Centre, ISRO, Bengaluru, India
Copyright Elsevier

The Chandrayaan-2 Large Area Soft X-ray Spectrometer (CLASS) onboard the Chandraayaan-2 spacecraft around the Moon, has been remotely measuring the lunar X-ray fluorescence spectra since September, 2019. The primary objective of the experiment is to provide global maps of O, Mg, Al, Si at a resolution of 12.5 km/pix and of Ca, Ti and Fe at localized regions during enhanced solar activity, using the lunar X-ray fluorescence measurements in the 0.5 to 10 KeV range. CLASS is an array of swept charge devices (SCDs), a variant of X ray Charge Coupled Devices (CCDs) that provide good spectral resolution and large area. The quality of X-ray measurements strongly depends on accuracy of its calibration techniques. In this work, the results from the pre-launch calibration of the instrument that combines experimental measurements and simulations are described. The spectral redistribution function of the swept charge device is simulated using an augmented version of a previously developed charge transport model (Athiray et al., 2015). Response matrices built from these models are verified with in-flight data. We study the background in SCDs arising from particles in the lunar orbit over many months and identify the sources. We demonstrate the in-flight performance of the instrument that enables generation of direct elemental maps. Elemental abundances for a region in the farside highland and in the nearside western mare are derived demonstrating the method and the instrument capability of deriving the elemental abundances at different spatial scales and at different solar activity levels.