^1,2Lionel G. Vacher,¹Maxime Piralla,³Matthieu Gounelle,⁴⁵Martin Bizzarro,¹Yves Marrocchi
The Astrophysical Journal, Letters 882, L20 Link to Article [DOI
https://doi.org/10.3847/2041-8213/ab3bd0]
¹CRPG, CNRS, Université de Lorraine, UMR 7358, Vandoeuvre les Nancy, F-54501, France
²Department of Physics, Washington University, St. Louis, MO, USA
³IMPMC, MNHN, UPMC, UMR CNRS 7590, 61 rue Buffon, F-75005 Paris, France
⁴Centre for Star and Planet Formation and Natural History Museum of Denmark, University of Copenhagen, DK-1350 Copenhagen, Denmark

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^1,2K. J. Mathew,¹K. Marti
The Astrophysical Journal, Letters 882, L17 Link to Article [DOI
https://doi.org/10.3847/2041-8213/ab357b]
¹Department of Chemistry and Biochemistry, University of California San Diego, La Jolla, CA 92093, USA
²Actinide Analytical Chemistry, Los Alamos National Lab, MS G740, Los Alamos, NM 87545, USA

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^1,2Shiyong Liao,¹Weibiao Hsu,¹Ying Wang,¹Ye Li,²Chipui Tang,²Bao Mei
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13408]
¹CAS Center for Excellence in Comparative Planetology, Purple Mountain Observatory, Nanjing, 210034 China
²State Key Laboratory for Lunar and Planetary Sciences, Macau University of Science and Technology, Taipa, Macau
Published by arrangement with John Wiley & Sons

Eucrites represent one of the major lithologies of the Vestan upper crust, which had experienced pervasive and intense thermal metamorphism. To better constrain the timing and mechanism of thermal metamorphism, we carried out in situ Pb‐isotope analysis of an unbrecciated basaltic eucrite NWA 6594 on the basis of detailed mineralogical and petrographic investigations. Zircon Pb‐Pb dating reveals that NWA 6594 emplaced before or at 4547 ± 11 Ma (95% confidence, MSWD = 1.3). Studies of silica minerals indicate that NWA 6594 had experienced intense thermal metamorphism after emplacement, followed by a late impact reheating and rapid cooling. Apatite grains yield a weighted mean Pb‐Pb age of 4523 ± 2 Ma (95% confidence, MSWD = 0.76). This age could not be attributed to slow cooling after the initial crystallization, but most likely related to an independent thermal event that induced thermal metamorphism. The protracted time lag (~24 ± 13 Myr) between zircon and apatite closure ages indicates that this thermal event is most probably induced by an intense impact event that was synchronous with the metal–silicate mixing event recorded by mesosiderites. HEDs may have experienced multiple stages of thermal metamorphism after emplacement. The late impact reheating occurred after thermal metamorphism, which caused crystallization of tridymite.

¹Jan Leitner,²Knut Metzler,³Christian Vollmer,⁴Christine Floss,⁴Pierre Haenecour,¹János Kodolányi,⁵Dennis Harries,¹Peter Hoppe
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13412]
¹Max Planck Institute for Chemistry, Particle Chemistry Department, Hahn‐Meitner‐Weg 1, 55128 Mainz, Germany
²Institute for Planetology, University of Münster, 48149 Münster, Germany
³Institute for Mineralogy, University of Münster, 48149 Münster, Germany
⁴Laboratory for Space Sciences, Physics Department and McDonnell Center for Space Sciences, Washington University in St. Louis, One Brookings Drive, St. Louis, Missouri, 63130 USA
⁵Institute of Geoscience, Friedrich Schiller University Jena, Carl‐Zeiss‐Promenade 10, 07745 Jena, Germany
Published by arrangement with John Wiley & Sons

We investigated the inventory of presolar silicate, oxide, and silicon carbide (SiC) grains of fine‐grained chondrule rims in six Mighei‐type (CM) carbonaceous chondrites (Banten, Jbilet Winselwan, Maribo, Murchison, Murray and Yamato 791198), and the CM‐related carbonaceous chondrite Sutter’s Mill. Sixteen O‐anomalous grains (nine silicates, six oxides) were detected, corresponding to a combined matrix‐normalized abundance of ~18 ppm, together with 21 presolar SiC grains (~42 ppm). Twelve of the O‐rich grains are enriched in ¹⁷O, and could originate from low‐mass asymptotic giant branch stars. One grain is enriched in ¹⁷O and significantly depleted in ¹⁸O, indicative of additional cool bottom processing or hot bottom burning in its stellar parent, and three grains are of likely core‐collapse supernova origin showing enhanced ¹⁸O/¹⁶O ratios relative to the solar system ratio. We find a presolar silicate/oxide ratio of 1.5, significantly lower than the ratios typically observed for chondritic meteorites. This may indicate a higher degree of aqueous alteration in the studied meteorites, or hint at a heterogeneous distribution of presolar silicates and oxides in the solar nebula. Nevertheless, the low O‐anomalous grain abundance is consistent with aqueous alteration occurring in the protosolar nebula and/or on the respective parent bodies. Six O‐rich presolar grains were studied by Auger Electron Spectroscopy, revealing two Fe‐rich silicates, one forsterite‐like Mg‐rich silicate, two Al‐oxides with spinel‐like compositions, and one Fe‐(Mg‐)oxide. Scanning electron and transmission electron microscopic investigation of a relatively large silicate grain (490 nm × 735 nm) revealed that it was crystalline åkermanite (Ca₂Mg[Si₂O₇]) or a an åkermanite‐diopside (MgCaSi₂O₆) intergrowth.

¹Steven Goderis¹Bastien Soens,^1,2Matthew S.Huber,^1,3,4Seann McKibbin,⁵Matthias van Ginneken,¹Flore Van Maldeghem,⁶Vinciane Debaille,⁷Richard C.Greenwood,⁷Ian A.Franchi,⁸ Veerle Cnudde,¹⁰Stijn Van Malderen,¹⁰ Frank Vanhaecke,^11,12Christian Koeberl,¹²Dan Topal,¹Philippe Claeys
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2019.11.016]
¹Analytical-, Environmental-, and Geo-Chemistry, Vrije Universiteit Brussel, Pleinlaan 2, B-1050 Brussels, Belgium
²Department of Geology, University of the Free State, 205 Nelson Mandela Dr., Bloemfontein 9300, South Africa1
³Institut für Erd- und Umweltwissenschaften, Universität Potsdam, Haus 27, Karl-Liebknecht-Straße 24-25, Potsdam-Golm 14476, Germany1
⁴Geowissenschaftliches Zentrum, Abteilung Isotopengeologie, Georg-August-Universität Göttingen, Goldschmidtstraße 1, Göttingen 37073, Germany1
⁵Royal Belgian Institute of Natural Sciences, 29 Rue Vautier, B-1000 Brussels, Belgium
⁶Laboratoire G-Time, Université Libre de Bruxelles 50, Av. F.D. Roosevelt CP 160/02, B-1050 Brussels, Belgium
⁷Planetary and Space Sciences, School of Physical Sciences, The Open University, Walton Hall, Milton Keynes, MK7 6AA, United Kingdom
⁸Department of Geology, Ghent University, Campus Sterre, Krijgslaan 281 – S8, B-9000 Ghent, Belgium
⁹Department of Earth Sciences, Utrecht University, Princetonlaan 8a, 3584CB Utrecht, the Netherlands
¹⁰Department of Chemistry, Ghent University, Krijgslaan, 281 – S12, B-9000 Ghent, Belgium
¹¹Department of Lithospheric Research, University of Vienna, Althanstrasse 14, A-1090 Vienna, Austria
¹²Natural History Museum, Burgring 7, A-1010 Vienna, Austria

A newly discovered sedimentary accumulation of micrometeorites in the Sør Rondane Mountains of East Antarctica, close to the Widerøefjellet summit at ∼2750 meter above sea level, is characterized in this work. The focus here lies on 2099 melted cosmic spherules larger than 200 μm, extracted from 3.2 kg of sampled sediment. Although the Widerøefjellet deposit shares similarities to the micrometeorite traps encountered in the Transantarctic Mountains, both subtle and more distinct differences in the physicochemical properties of the retrieved extraterrestrial particles and sedimentary host deposits are discernable (e.g., types of bedrock, degree of wind exposure, abundance of metal-rich particles). Unlike the Frontier Mountain and Miller Butte sedimentary traps, the size fraction below 240 μm indicates some degree of sorting at Widerøefjellet, potentially through the redistribution by wind, preferential alteration of smaller particles, or processing biases. However, the cosmic spherules larger than 300 μm appear largely unbiased following their size distribution, frequency by textural type, and bulk chemical compositions. Based on the available bedrock exposure ages for the Sør Rondane Mountains, extraterrestrial dust is estimated to have accumulated over a time span of ∼1 to 3 Ma at Widerøefjellet. Consequently, the Widerøefjellet collection reflects a substantial reservoir to sample the micrometeorite influx over this time interval. Petrographic observations and 3D microscopic CT imaging are combined with chemical and triple-oxygen isotopic analyses of silicate-rich cosmic spherules larger than 325 μm. The major element composition of 49 cosmic spherules confirms their principally chondritic parentage. For 18 glassy, 15 barred olivine, and 11 cryptocrystalline cosmic spherules, trace element concentrations are also reported on. Based on comparison with evaporation experiments reported in literature and accounting for siderophile and chalcophile element losses during high-density phase segregation and ejection, the observed compositional sequence largely reflects progressive heating and evaporation during atmospheric passage accompanied by significant redox shifts, although the influence of (refractory) chondrite mineral constituents and terrestrial alteration cannot be excluded in all cases. Twenty-eight cosmic spherules larger than 325 μm analyzed for triple-oxygen isotope ratios confirm inheritance from mostly carbonaceous chondritic precursor materials (∼55% of the particles). Yet, ∼30% of the measured cosmic spherules and ∼50% of all glassy cosmic spherules are characterized by oxygen isotope ratios above the terrestrial fractionation line, implying genetic links to ordinary chondrites and parent bodies currently unsampled by meteorites. The structural, textural, chemical, and isotopic characteristics of the cosmic spherules from the Sør Rondane Mountains, and particularly the high proportion of Mg-rich glass particles contained therein, imply a well-preserved and representative new sedimentary micrometeorite collection from a previously unstudied region in East Antarctica characterized by distinct geological and exposure histories.

¹Thomas Smith,²David L. Cook,³Silke Merchel,³Stefan Pavetich,³Georg Rugel,³Andreas Scharf,¹Ingo Leya
Meteoritics & Planetary Sciences (in Press) Link to Article [https://doi.org/10.1111/maps.13417]
¹Physics Institute, University of Bern, Sidlerstrasse 5, CH‐3012 Bern, Switzerland
²Institute for Geochemistry and Petrology, ETH Zürich, Clausiusstrasse 25, 8092 Zürich, Switzerland
³Heimholt‐Zentrum Dresden‐Rossendorf, Bautzner Landstrasse 400, 01328 Dresden, Germany
Published by arrangement with John Wiley & Sons

We measured the He, Ne, and Ar isotopic concentrations and the ¹⁰Be, ²⁶Al, ³⁶Cl, and ⁴¹Ca concentrations in 56 iron meteorites of groups IIIAB, IIAB, IVA, IC, IIA, IIB, and one ungrouped. From ⁴¹Ca and ³⁶Cl data, we calculated terrestrial ages indistinguishable from zero for six samples, indicating recent falls, up to 562 ± 86 ka. Three of the studied meteorites are falls. The data for the other 47 irons confirm that terrestrial ages for iron meteorites can be as long as a few hundred thousand years even in relatively humid conditions. The ³⁶Cl‐³⁶Ar cosmic ray exposure (CRE) ages range from 4.3 ± 0.4 Ma to 652 ± 99 Ma. By including literature data, we established a consistent and reliable CRE age database for 67 iron meteorites. The high quality of the CRE ages enables us to study structures in the CRE age histogram more reliably. At first sight, the CRE age histogram shows peaks at about 400 and 630 Ma. After correction for pairing, the updated CRE age histogram comprises 41 individual samples and shows no indications of temporal periodicity, especially not if one considers each iron meteorite group separately. Our study contradicts the hypothesis of periodic GCR intensity variations (Shaviv 2002, 2003), confirming other studies indicating that there are no periodic structures in the CRE age histogram (e.g., Rahmstorf et al. 2004; Jahnke 2005). The data contradict the hypothesis that periodic GCR intensity variations might have triggered periodic Earth climate changes. The ³⁶Cl‐³⁶Ar CRE ages are on average 40% lower than the ⁴¹K‐K CRE ages (e.g., Voshage 1967). This offset can either be due to an offset in the ⁴¹K‐K dating system or due to a significantly lower GCR intensity in the time interval 195–656 Ma compared to the recent past. A 40% lower GCR intensity, however, would have increased the Earth temperature by up to 2 °C, which seems unrealistic and leaves an ill‐defined ⁴¹K‐K CRE age system the most likely explanation. Finally, we present new ²⁶Al/²¹Ne and ¹⁰Be/²¹Ne production rate ratios of 0.32 ± 0.01 and 0.44 ± 0.03, respectively.

^1,2H. C. Bates,^1,3A. J. King,^2,4K. L. Donaldson Hanna,²N. E. Bowles,¹S. S. Russell
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13411]
¹Planetary Materials Group, Department of Earth Sciences, Natural History Museum, Cromwell Road, London, SW7 5BD UK
²Atmospheric, Oceanic and Planetary Physics, University of Oxford, Oxford, OX1 3PU UK
³School of Physical Sciences, The Open University, Milton Keynes, MK7 6AA UK
⁴Department of Physics, University of Central Florida, 4111 Libra Drive, Orlando, Florida, 32816 USA
Published by arrangement with John Wiley & Sons

The highly hydrated, petrologic type 1 CM and CI carbonaceous chondrites likely derived from primitive, water‐rich asteroids, two of which are the targets for JAXA’s Hayabusa2 and NASA’s OSIRIS‐REx missions. We have collected visible and near‐infrared (VNIR) and mid infrared (MIR) reflectance spectra from well‐characterized CM1/2, CM1, and CI1 chondrites and identified trends related to their mineralogy and degree of secondary processing. The spectral slope between 0.65 and 1.05 μm decreases with increasing total phyllosilicate abundance and increasing magnetite abundance, both of which are associated with more extensive aqueous alteration. Furthermore, features at ~3 μm shift from centers near 2.80 μm in the intermediately altered CM1/2 chondrites to near 2.73 μm in the highly altered CM1 chondrites. The Christiansen features (CF) and the transparency features shift to shorter wavelengths as the phyllosilicate composition of the meteorites becomes more Mg‐rich, which occurs as aqueous alteration proceeds. Spectra also show a feature near 6 μm, which is related to the presence of phyllosilicates, but is not a reliable parameter for estimating the degree of aqueous alteration. The observed trends can be used to estimate the surface mineralogy and the degree of aqueous alteration in remote observations of asteroids. For example, (1) Ceres has a sharp feature near 2.72 μm, which is similar in both position and shape to the same feature in the spectra of the highly altered CM1 MIL 05137, suggesting abundant Mg‐rich phyllosilicates on the surface. Notably, both OSIRIS‐REx and Hayabusa2 have onboard instruments which cover the VNIR and MIR wavelength ranges, so the results presented here will help in corroborating initial results from Bennu and Ryugu.

¹Yoshihiro Furukawa,^2,3Yoshito Chikaraishi,³Naohiko Ohkouchi,³Nanako O. Ogawa,⁴Daniel P. Glavin,⁴Jason P. Dworkin,¹Chiaki Abe,¹Tomoki Nakamura
Proceedings of the Nationall Academy of Sciences of the Unites States of America (in Press) Link to Article [https://doi.org/10.1073/pnas.1907169116]
¹Department of Earth Science, Tohoku University, 980-8578 Sendai, Japan;
²Institute of Low Temperature Science, Hokkaido University, 060-0819 Sapporo, Japan;
³Biogeochemistry Program, Japan Agency for Marine-Earth Science and Technology, 237-0061 Yokosuka, Japan;
⁴Solar System Exploration Division, NASA Goddard Space Flight Center, Greenbelt, MD 20771

Sugars are essential molecules for all terrestrial biota working in many biological processes. Ribose is particularly essential as a building block of RNA, which could have both stored information and catalyzed reactions in primitive life on Earth. Meteorites contain a number of organic compounds including key building blocks of life, i.e., amino acids, nucleobases, and phosphate. An amino acid has also been identified in a cometary sample. However, the presence of extraterrestrial bioimportant sugars remains unclear. We analyzed sugars in 3 carbonaceous chondrites and show evidence of extraterrestrial ribose and other bioessential sugars in primitive meteorites. The ¹³C-enriched stable carbon isotope compositions (δ¹³C _{vs. VPDB}) of the detected sugars show that the sugars are of extraterrestrial origin. We also conducted a laboratory simulation experiment of a potential sugar formation reaction in space. The compositions of pentoses in meteorites and the composition of the products of the laboratory simulation suggest that meteoritic sugars were formed by formose-like processes. The mineral compositions of these meteorites further suggest the formation of these sugars both before and after the accretion of their parent asteroids. Meteorites were carriers of prebiotic organic molecules to the early Earth; thus, the detection of extraterrestrial sugars in meteorites establishes the existence of natural geological routes to make and preserve them as well as raising the possibility that extraterrestrial sugars contributed to forming functional biopolymers like RNA on the early Earth or other primitive worlds.

^1,2Queenie H. S. Chan,¹Ian A. Franchi,¹Xuchao Zhao,¹Alice Stephant,¹Ian P. Wright,²Conel M. O’D. Alexander
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13414]
¹Planetary and Space Sciences, School of Physical Sciences, The Open University, Walton Hall, Milton Keynes, MK7 6AA UK
²Department of Terrestrial Magnetism, Carnegie Institution of Washington, 5241 Broad Branch Road, NW, Washington, District of Columbia, 20015 USA
Published by arrangement with John Wiley & Sons

The chondritic‐porous subset of interplanetary dust particles (CP‐IDPs) are thought to have a cometary origin. Since the CP‐IDPs are anhydrous and unaltered by aqueous processes that are common to chondritic organic matter (OM), they represent the most pristine material of the solar system. However, the study of IDP OM might be hindered by their further alteration by flash heating during atmospheric entry, and we have limited understanding on how short‐term heating influences their organic content. In order to investigate this problem, five CP‐IDPs were studied for their OM contents, distributions, and isotopic compositions at the submicro‐ to nanoscale levels. The OM contained in the IDPs in this study spans the spectrum from primitive OM to that which has been significantly processed by heat. Similarities in the Raman D bands of the meteoritic and IDP OMs indicate that the overall gain in the sizes of crystalline domains in response to heating is similar. However, the Raman Γ_G values of the OM in all of the five IDPs clearly deviate from those of chondritic OM that had been processed during a prolonged episode of parent body heating. Such disparity suggests that the nonaromatic contents of the OM are different. Short duration heating further increases the H/C ratio and reduces the δ¹³C and δD values of the IDP OM. Our findings suggest that IDP OM contains a significant proportion of disordered C with low H content, such as sp² olefinic C=C, sp³ C–C, and/or carbonyl contents as bridging material.

¹Heather B. Franz,²Nanping Wu,³James Farquhar,⁴Anthony J. Irving
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13404]
¹NASA Goddard Space Flight Center, Greenbelt, Maryland, 20771 USA
²Department of Geology, University of Maryland, College Park, Maryland, 20742 USA
³Department of Geology and ESSIC, University of Maryland, College Park, Maryland, 20742 USA
⁴Department of Earth and Space Sciences, University of Washington, Seattle, Washington, 98195 USA
Published by arrangement with John Wiley & Sons

The isotopic composition and abundance of sulfur in extraterrestrial materials are of interest for constraining models of both planetary and solar system evolution. A previous study that included phase‐specific extraction of sulfur from 27 shergottites found the sulfur isotopic composition of the Martian mantle to be similar to that of terrestrial mid‐ocean ridge basalts, the Moon, and nonmagmatic iron meteorites. However, the presence of positive Δ33S anomalies in igneous sulfides from several shergottites, indicating incorporation of atmospherically processed sulfur into the subsurface, complicated this interpretation. The current study expands upon the previous work through analyses of 20 additional shergottites, enabling tighter constraints on the isotopic composition of juvenile Martian sulfur. The updated composition (δ34S = −0.24 ± 0.05‰, Δ33S = 0.0015 ± 0.0016‰, and Δ36S = 0.039 ± 0.054‰, 2 s.e.m.), representing the weighted mean for all shergottites within the combined population of 47 without significant Δ33S anomalies, strengthens our earlier result. The presence of sulfur isotopic anomalies in igneous sulfides of some meteorites suggests that their parent magmas may have assimilated crustal material. We observed small negative Δ33S anomalies in sulfides from two meteorites, NWA 7635 and NWA 11300. Although negative Δ33S anomalies have been observed in nakhlites and ALH 84001, previous anomalies in shergottites have all shown positive values of Δ33S. Because NWA 7635 has formation age of 2.4 Ga and is much more ancient than shergottites analyzed previously, this finding expands our perspective on the continuity of Martian atmospheric sulfur photochemistry over geologic time.