^1,2Feng Yin,³Thomas G. Sharp,²Ming Chen
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13702]
¹Department of Geology, Hunan University of Science and Technology, Xiangtan, 411201 China
²Guangdong Provincial Key Laboratory of Mineral Physics and Materials, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou, 510640 China
³School of Earth and Space Exploration, Arizona State University, Tempe, Arizona, 85287 USA
Published by arrangement with John Wiley & Sons

Coesite embedded in silica glass in suevite from the Xiuyan crater has been studied by scanning and transmission electron microscopy to better understand the mechanisms at formation of coesite. Coesite grains in this study mainly occur as vein-like aggregates (10–40 μm in width) and irregular aggregates (IAs; <40 μm in size). Both aggregate types are composed of subhedral to anhedral coesite crystals with random orientations. Most of the crystals are 100–1000 nm in size, and some display twinning. The shape, twinning, and random orientation of coesite crystals suggest rapid crystallization in amorphous silica that became supercooled. The center of vein-like aggregates crystallized from localized silica melt within diaplectic silica glass, whereas the rim of vein-like aggregates and IAs crystallized from diaplectic silica glass. The size and amount of coesite crystals in the vein-like aggregate vary greatly from the rim to the center of such veins. Microstructures suggest that the crystals nucleated heterogeneously at the outer rim of the vein and nucleated homogeneously within the vein. IAs do not show any changes in size and amount of coesite crystals from the rim to core of such aggregates. Coesite crystals in IAs primarily nucleate heterogeneously in diaplectic silica glass. It can be concluded that vein-like coesite aggregates are mainly formed by crystallization from silica melt, and irregular coesite aggregates should be formed by solid-state transformation of diaplectic silica glass.

¹Bradley T. De Gregorio,²Jessica Opsahl-Ong,³Lysa Chizmadia,¹Todd H. Brintlinger,⁴Andrew J. Westphal,¹Rhonda M. Stroud
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13655]
¹Materials Science and Technology Division, U.S. Naval Research Laboratory, Washington, D.C., 20375 USA
²American Society for Engineering Education, Science & Engineering Apprenticeship Program, Washington, D.C., 20036 USA
³Department of Geology and Physics, Georgia Southwestern State University, Americus, Georgia, 31709 USA
⁴Space Sciences Laboratory, University of California Berkeley, Berkeley, California, 94720 USA
Published by arrangement with John Wiley & Sons

The NASA Stardust Interstellar Dust collection provides our current best sample set for direct laboratory analysis of dust grains from the contemporary interstellar dust stream. While a handful of likely interstellar dust grains were identified within the silica aerogel collection media, interstellar dust also impacted Al foils covering the collector frame. Locating these rare impacts requires labor-intensive collection and examination of tens of thousands of high-resolution SEM images. Here, we implement a Python-based algorithm to dramatically reduce the human time investment needed to locate impact craters. The algorithm employs a circular Hough transform to identify circular features in the foil images, followed by several tests to detect characteristic morphological features of impact craters—a dark center and a bright rim, with inclusion of multi-core processing capabilities to significantly increase processing speed. For most data sets, the code produced a pool of potential crater candidates in 1–5% of the input images, producing a more manageable subset of images for a human expert to review. We used this code to locate 31 impact craters across 12 Stardust interstellar foils, 25 of which were located on three adjacent foils, I1008W,1, I1009N,1, and I1020W,1. Many impacts on these foils formed shallow, oblique craters, with residue compositions consistent with solar cell glass and orientations consistent with debris ejected from the spacecraft solar cells. The code can be integrated into future searches for Stardust interstellar grain impacts and can be implemented as a general utility for dust impact studies on spacecraft materials.

¹Toshiki Koga,²Eric T. Parker,^2,3Hannah L. McLain,^2,3José C. Aponte,²Jamie E. Elsila,²Jason P. Dworkin,²Daniel P. Glavin,¹Hiroshi Naraoka
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13661]
¹Department of Earth and Planetary Sciences, Kyushu University, 744 Motooka, Nishi-ku, Fukuoka, 819-0395 Japan
²NASA Goddard Space Flight Center, Greenbelt, Maryland, 20771 USA
³Catholic University of America, Washington, District of Columbia, 20064 USA
Published by arrangement with John Wiley & Sons

The abundances, distributions, and enantiomeric ratios of a family of three- and four-carbon hydroxy amino acids (HAAs) were investigated in extracts of five CM and four CR carbonaceous chondrites by gas chromatography-mass spectrometry analyses. HAAs were detected in both the acid hydrolysates of the hot water extracts and the 6 M HCl extracts of all the CM and CR chondrites analyzed here with total hot water and HCl extractable HAA concentrations ranging from 6.94 to 315 nmol g−1. The HAA analyses performed in this study revealed: (1) the combined (hot water + HCl) extracts of CR2 chondrites contained greater abundances of α-HAAs than that of CM2 chondrites and (2) the combined extracts of CM and CR chondrites contained roughly similar abundances of β- and γ-HAAs. Application of the new GC-MS method developed here resulted in the first successful chromatographic resolution of the enantiomers of an α-dialkyl HAA, d,l-α-methylserine, in carbonaceous chondrite extracts. Meteoritic α-methylserine was found to be mostly racemic within error and did not show l-enantiomeric excesses correlating with the degree of aqueous alteration, a phenomenon observed in meteoritic isovaline, another α-dialkyl amino acid. The HAAs identified in CM and CR chondrite extracts could have been produced during parent body alteration from the Strecker cyanohydrin reaction (for α-HAAs) and an ammonia-involved formose-like reaction (for β-, and γ-HAAs).

¹M.Weyrauch,²J.Zipfel,¹S.Weyer
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2021.06.009]
¹Institut für Mineralogie, Leibniz Universität Hannover, Callinstr. 3, 30167 Hannover, Germany
²Senckenberg Forschungsinstitut und Naturmuseum Frankfurt, 60325 Frankfurt, Germany
Copyright Elsevier

Due to similarities in chemical composition and common Cr, Ti, N and O isotope trends, the metal-rich CR, CH and CB chondrites, often referred to as CR clan chondrites, are thought to be related to each other. This study aims to shed light on this relationship by the investigation of Fe and Ni isotope and trace element compositions of metal grains from CR and CH chondrites, in order to compare the results with previously reported data from CB chondrite metal. In situ trace element and Fe and Ni isotope analyses were conducted by femtosecond-laser ablation-(multicollector-)inductively coupled plasma-mass spectrometry (fs-LA-(MC-)ICP-MS). Furthermore, bulk CB metal and silicate separates were analyzed by solution MC-ICP-MS.

Chemical compositions of metal grains in metal-rich chondrites are depleted in moderately volatile siderophile elements relative to the solar values with the exception of Pd. Such element abundance patterns are consistent with models of incomplete condensation from a gas with solar composition. Both, zoned and unzoned metal grains from CH and CB chondrites display very similar Fe and Ni isotopes compositions, indicating they likely formed within the same event, during non-equilibrium fractional condensation from an impact-induced vapor plume. This scenario is also supported by non-equilibrium Fe isotope signatures between bulk CB metal and silicate. Zoned metal grains likely formed in the fast-cooling outer shell region of the plume and are dominated by kinetic fractionation, resulting in isotopically light cores, while unzoned metal grains condensed under nearly equilibrium conditions, likely in the slow-cooling interior of the plume. Variability in Fe and Ni isotope compositions among different unzoned grains may be explained by 1) a kinetic component during their condensation and/or 2) evaporation and condensation-driven reservoir effects in the plume, which resulted in light and heavy isotope signatures, respectively. Textural differences between CH and CBb are most pronounced in the mean grain size, which may be attributed to grain-size sorting. Such a process could also explain the lack of zoned metals in CBa chondrites, as zoned metal grains in CBb and CH chondrites are by more than a magnitude smaller than the mean metal grain size of CBa chondrites.

In CR chondrites, metal within chondrules likely formed by fractional condensation from a solar type gas followed by subsequent melting leading to equilibration with chondrule silicates. Larger isolated metal grains from the matrix are less processed, and apparently escaped silicate equilibration. Those metal grains are indistinguishable from unzoned grains in CH and CB chondrites in trace elements and Fe and Ni isotopic compositions albeit with a slightly narrower compositional range. Based on these findings we conclude that metal precursors in CR chondrites are strongly related to unzoned metal in CH, and CB chondrites and possibly share a common origin. This metal component would be smallest in CR chondrites, larger in CH and dominant in CB chondrites which is also consistent with age constraints and isotopic anomalies observed in CR clan chondrites.

¹A.Moreras-Marti,^1,2M.Fox-Powell,¹E.Stueeken,^1,3T.Di Rocco,¹T.Galloway,^4,5G.R.Osinski,¹C.R.Cousins,¹A.L.Zerkle
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2021.06.007]
¹School of Earth and Environmental Sciences and Centre for Exoplanet Science, University of St Andrews, Irvine Building, North Street, KY169AL, UK
²Current address: AstrobiologyOU, Open University, Walton Hall, Milton Keynes MK7 6AA, UK
³Current address: Isotope Geology Department, Georg-August-Universitat Gottingen, Wilhelmsplatz 1, 37073 Gottingen, Germany
⁴Department of Earth Sciences, University of Western Ontario, London, Ontario, Canada
⁵Institute for Earth and Space Exploration, University of Western Ontario, London, Ontario, Canada
Copyright Elsevier

In this study, we present quadruple sulfur isotope values (QSI: ³²S,³³S,³⁴S,³⁶S) measured in sediments from two sulfur-rich Mars analogue environments: i) the glacially-fed hydrothermal pools in Iceland (Kerlingarfjöll and Kverkfjöll), and ii) the Lost Hammer hypersaline spring from Axel Heiberg Island, Nunavut, Canada. The localities host different physical and geochemical characteristics, including aqueous geochemistry, volcanic input, temperature, pH and salinity. The δ³⁴S values of sulfur compounds from the Lost Hammer hypersaline spring exhibit large fractionations typical of microbial sulfate reduction (MSR) with or without additional oxidative sulfur cycling and microbial sulfur disproportionation (MSD) (³⁴ε_SO4-CRS from -49.5 to -43.5 ‰), contrary to the small S isotope fractionations reported for the Icelandic hydrothermal sites (³⁴ε_SO4-CRS from –9.9 to -0.7 ‰). Lost Hammer minor S isotope values (Δ³³S and Δ³⁶S), interpreted within the context of a sulfur cycling box model, are consistent with a biogeochemical S cycle including both MSR and MSD. In contrast, the small range in δ³⁴S values within the Iceland hydrothermal pools are consistent with a large volcanic H₂S flux and minimal biological S cycling. The minor S isotope values recorded in the hydrothermal pools, however, indicate further biogeochemical sulfur cycling. Our results demonstrate that contrasting physical and chemical characteristics between sites support different microbial S cycling processes, as recorded in the QSI sedimentary values. The QSI data and the derived models support the strong potential for QSI values to be used as biosignatures in the search for life in Martian S-rich environments. These results also suggests that extreme, metabolic energy-limited environments with low abiotic sulfur fluxes could be more likely to produce unequivocal biological QSI signals than those with more moderate conditions or abundant available energy. This finding carries significant implications for targeting sites on Mars for in situ measurements or future sample return missions.

^1,2AlSalhi M.S.,²Masilamani V.,³Alarifi N.,^1,2Aslam Farooq W.,^1,2Atif M.,¹Ramay S.,¹Saeed Althobaiti H.,⁴Anwar S.,³Elkhedr I.,³Abuamarah B.A.
Journal of King Saud University 33, 101341 Link to Article [DOI
10.1016/j.jksus.2021.101341]
¹Physics and Astronomy Department, College of Science, King Saud University, Riyadh, Saudi Arabia
²Research Chair for Laser Diagnosis of Cancer, King Saud University, Riyadh, Saudi Arabia
³Department of Geology and Geophysics, College of Science King Saud University, Riyadh, Saudi Arabia
⁴Industrial Engineering Department, College of Engineering, King Saud University, P.O. Box 800, Riyadh, 11421, Saudi Arabia

We currently do not have a copyright agreement with this publisher and cannot display the abstract here

^1,2Wouters M.,¹Rahman S.,³Myamoto H.,^1,4Tran N.N.,^1,5Hessel V.
Separation and Purification Technology 260, 118238 Link to Article [DOI
10.1016/j.seppur.2020.118238]
¹School of Chemical Engineering and Advanced Materials, University of Adelaide, Australia
²Department of Chemical Engineering and Chemistry, Eindhoven University of Technology, Netherlands
³Department of Systems Innovation, The University of Tokyo, Japan
⁴Department of Chemical Engineering, Can Tho University, Viet Nam
⁵School of Engineering, University of Warwick, United Kingdom

We currently do not have a copyright agreement with this publisher and cannot display the abstract here

¹Kalpana M.S.,¹Babu E.V.S.S.K.,²Mani D.,³Tripathi R.P.,⁴Bhandari N.
Planetary and Space Science 198, 105177 Link to Article [DOI
10.1016/j.pss.2021.105177]
¹National Geophysical Research Institute (Council of Scientific and Industrial Research), Hyderabad, 500007, India
²Centre for Earth, Ocean and Atmospheric Sciences (CEOAS), University of Hyderabad, Gachibowli, Hyderabad, 500046, India
³78, BGKT Extension, Jodhpur, 342005, India
⁴Science and Spirituality Research Institute, Navrangpura, Ahmedabad, 380009, India

We currently do not have a copyright agreement with this publisher and cannot display the abstract here

¹Fredrik Terfelt,^1,2Birger Schmitz
Proceedings of the National Academy of Sciences of teh United States of America 118, e2020977118 Link to Article [https://doi.org/10.1073/pnas.2020977118]
¹Astrogeobiology Laboratory, Department of Physics, Lund University, 221 00 Lund, Sweden;
²Robert A. Pritzker Center for Meteoritics and Polar Studies, Negaunee Integrative Research Center, Field Museum of Natural History, Chicago, IL 60605

The meteoritic material falling on Earth is believed to derive from large break-up or cratering events in the asteroid belt. The flux of extraterrestrial material would then vary in accordance with the timing of such asteroid family-forming events. In order to validate this, we investigated marine sediments representing 15 time-windows in the Phanerozoic for content of micrometeoritic relict chrome-spinel grains (>32 μm). We compare these data with the timing of the 15 largest break-up events involving chrome-spinel–bearing asteroids (S- and V-types). Unexpectedly, our Phanerozoic time windows show a stable flux dominated by ordinary chondrites similar to today’s flux. Only in the mid-Ordovician, in connection with the break-up of the L-chondrite parent body, do we observe an anomalous micrometeorite regime with a two to three orders-of-magnitude increase in the flux of L-chondritic chrome-spinel grains to Earth. This corresponds to a one order-of-magnitude excess in the number of impact craters in the mid-Ordovician following the L-chondrite break-up, the only resolvable peak in Phanerozoic cratering rates indicative of an asteroid shower. We argue that meteorites and small (<1-km-sized) asteroids impacting Earth mainly sample a very small region of orbital space in the asteroid belt. This selectiveness has been remarkably stable over the past 500 Ma.

^1,2Gözen Ertem,³Daniel P.Glavin,⁴Robert P.Volpe,⁵Christopher P.McKay
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2021.114540]
¹SETI Institute, Carl Sagan Center, Mountain View, CA 94043, USA
²Department of Atmospheric and Oceanic Science, University of Maryland, College Park, MD 20742, USA
³NASA Goddard Space Flight Center, Solar System Exploration Division, Greenbelt, MD, USA
⁴Uniformed Services University of the Health Sciences, Bethesda, MD 20814, USA
⁵Space Science Division, NASA Ames Research Center, Moffett Field, CA 94035, USA
Copyright Elsevier

Organic compounds have been delivered to the surface of Mars via meteorites, comets and interplanetary dust particles for billions of years. Determining the effects of high energy radiation and galactic cosmic radiation (GCR) on these organic compounds is critical for understanding the potential for the preservation of organic molecules associated with past or present life, and where to look for possible chemical bio- signatures during future Mars missions. Understanding how these effects are attenuated by the mineral matrix and the depth at which they are buried have been challenging to determine in situ on Mars. There have been very few experimental studies on the survival of organic compounds under radiation from a gamma source under realistic conditions, and their interpretation until now has been difficult due to the lack of data for actual radiation levels on Mars. Using the in-situ data obtained by the MSL/RAD instrument to anchor the dose calculations, here we show that the N-heterocycles purine and uracil, crucial components of biochemical processes in extant living systems, mixed with calcite, anhydrite, and kaolinite as Mars analogue minerals can survive the effects of radiation with a dose corresponding to ~500,000 years on Martian surface. The extent of survival varied not only with the nature of the organic compound, but its depth from the surface. These results provide new experimental data for the degree of protection offered by the regolith, in conjunction with minerals, for organic compounds that may be present on Mars.