¹Timothy J. McCoy,¹Catherine M. Corrigan
Meteoritics & Plantetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13613]
¹Department of Mineral Sciences, National Museum of Natural History, Smithsonian Institution, Washington, District of Columbia, 20560‐0119 USA
Published by arrangement with John Wiley & Sons

Alevtina A. Maksimova et al. (>10)
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13597]
¹Institute of Physics and Technology, Ural Federal University, Ekaterinburg, 620002 Russian Federation
²The Zavaritsky Institute of Geology and Geochemistry of the Ural Branch of the Russian Academy of Sciences, Ekaterinburg, 620016 Russian Federation
Published by arrangement with John Wiley & Sons

We report the results of the complex study of the bulk interior of Bursa L6 ordinary chondrite using optical microscopy, scanning electron microscopy with energy dispersive spectroscopy, electron microprobe analysis (EMPA), X‐ray diffraction (XRD), magnetization measurements, and Mössbauer spectroscopy. The main and minor iron‐bearing phases and their chemical compositions were determined by these techniques. The detected iron‐bearing phases in the bulk interior of Bursa L6 are the following: olivine; orthopyroxene; Ca‐rich clinopyroxene; troilite; chromite; hercynite; ilmenite; the α2‐Fe(Ni, Co), α‐Fe(Ni, Co), and γ‐Fe(Ni, Co) phases; and ferrihydrite resulting from meteorite terrestrial weathering. Using the EMPA, the values of fayalite and ferrosilite were obtained as ~25.2% and ~21.4%, respectively. The unit cell parameters for silicate crystals were determined from XRD, then the Fe2+ and Mg2+ occupations of the M1 and M2 sites in these crystals were estimated. Further calculations of the ratios of the Fe2+ occupancies in the M1 and M2 sites in olivine and orthopyroxene based on XRD and Mössbauer spectroscopy appeared to be in a good agreement. The temperatures of equilibrium cation distributions for olivine and orthopyroxene obtained from these techniques are consistent: 623 K (XRD) and 625 K (Mössbauer spectroscopy) for olivine and 1138 K (XRD) and 1122 K (Mössbauer spectroscopy) for orthopyroxene.

¹A. V. Stennikov,¹V. S. Fedulov,¹S. G. Naimushin,¹N. V. Dushenko,¹S. A. Voropaev
Solar System Research 54, 150-154 Link to Article [DOI
https://doi.org/10.1134/S0038094620020070%5D
¹Vernadsky Institute of Geochemistry and Analytical Chemistry, Russian Academy of Sciences, 119991, Moscow, Russia

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¹Siraj, A.,¹Loeb, A.
New Astronomy 84, 101545 Link to Article [DOI: 10.1016/j.newast.2020.101545]
¹Department of Astronomy, Harvard University, 60 Garden Street, Cambridge, MA 02138, United States

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¹S.Baliyan,²H.Moitra,³S.Sarkar,¹D.Ray,¹D.K.Panda,¹A.D.Shukla,³S.Bhattacharya,²S.Gupta
Chemie der Erde (Geochemistry)(in Press) Link to Article [https://doi.org/10.1016/j.chemer.2020.125729]
¹Physical Research Laboratory, Ahmedabad, 380009, India
²Indian Institute of Technology, Kharagpur, 721302, India
³Space Application Centre, Ahmedabad, 380015, India
Copyright Elsevier

We report the textures, mineralogy and mineral chemistry of the Mukundpura matrix component, a clast-bearing, brecciated, new CM2 carbonaceous chondrite. Like other CMs, Mukundpura is matrix-enriched and has experienced different degrees of aqueous alteration with evidences of fracturing and compaction of clasts due to the impact. A few relict chondrule clasts and CAIs (diopside and spinel) survived despite of the alteration amidst accessory phases of olivine, magnetite, sulphides and calcite. X-Ray Diffraction (XRD), Visible Near Infrared (VNIR) and Fourier Transform Infrared (FTIR) spectroscopic studies reveal higher phyllosilicate content (∼90%) comprising of both Mg and Fe-serpentine and abundant serpentine-sulphide intergrowths. Even then, the presence of accessory olivine as relict clasts can be interpreted from the presence of certain typical olivine absorptions in the FTIR spectra. The non-stoichiometric, Tochilinite-Cronstedtite occurrences probably relate to broadening of XRD and FTIR spectra and can be explained by coupled Al–Si and Mg–Al substitutions in talc and serpentine. The FTIR spectra suggest widespread transformation of olivine to serpentine, unlike the largely unaltered chondrules. The correlations of mineralogical alteration index with FeO/SiO2 and S/SiO2 in different domains of matrix suggest different extent of alterations. Thus, the aqueous alteration is extensive but not pervasive. The majority of alteration seems to have occurred within the asteroidal parent body. The Mukundpura CM2 thus preserves a unique combination of relict chondrules and highly aqueous altered variegated matrix clasts, although the surface mineralogy resembles the C-type asteroids recently probed by OSIRIS-REx and Hayabusa-2 missions.

¹Martin R. Lee,^1,2,3Luke Daly,¹Cameron Floyd,¹Pierre‐Etienne Martin
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13607]
¹School of Geographical & Earth Sciences, University of Glasgow, Glasgow, G12 8QQ UK
²Space Science and Technology Centre, School of Earth and Planetary Sciences, Curtin University, GPO BOC U1987, Perth, Western Australia, 6845 Australia
³Australian Centre for Microscopy and Microanalysis, The University of Sydney, Camperdown, New South Wales, 2006 Australia
Published by arrangement with John Wiley & Sons

The CM carbonaceous chondrites provide unique insights into the composition of the protoplanetary disk, and the accretion and geological history of their parent C‐complex asteroid(s). Of the hundreds of CMs that are available for study, the majority are finds and so may have been compromised by terrestrial weathering. Nineteen falls have been recovered between 1838 and 2020, and there is a hint of two temporal clusters: 1930–1942 and 2009–2020. Falls are considered preferable to finds to study because they should be near pristine, and here this assumption is tested by investigating their susceptibility to alteration before recovery and during curation. CMs falling on the land surface are prone to contamination by organic compounds from soil and vegetation. Where exposed to liquid water prior to collection, minerals including oldhamite can be dissolved and most fluid mobile elements leached. Within days of recovery, CMs adsorb water from the atmosphere and are commonly contaminated by airborne hydrocarbons. Interaction with atmospheric water and oxygen during curation over year to decadal timescales can produce Fe‐oxyhydroxides from Fe,Ni metal and gypsum from indigenous gypsum and oldhamite. Relationships between the petrologic (sub)types of pre‐1970 falls and their terrestrial age could be due to extensive but cryptic alteration during curation, but are more likely a sampling bias. The terrestrial history of a CM fall, including circumstances of its collection and conditions of its curation, must be taken into account before it is used to infer processes on C‐complex parent bodies such as Ryugu and Bennu.

¹L. J. Hicks,¹J. C. Bridges,²T. Noguchi,³A. Miyake,¹J. D. Piercy,¹S. H. Baker
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13611]
¹Space Research Centre, School of Physics & Astronomy, University of Leicester, Leicester, LE1 7RH UK
²Faculty of Arts and Science, Kyushu University, 744 Motooka, Nishi‐ku, Fukuoka, 819‐0395 Japan
³Division of Earth and Planetary Sciences, Kyoto University, Kitashirakawaoiwake‐cho, Kyoto, 606‐8502 Japan
Published by arrangement with John Wiley & Sons

Synchrotron Fe‐K X‐ray absorption spectroscopy and transmission electron microscopy have been used to investigate the mineralogy and Fe‐redox variations in the space‐weathered (SW) rims of asteroidal samples. This study focuses on the FIB lift‐out sections from five Itokawa grains, returned by the Hayabusa spacecraft, including samples RB‐QD04‐0063, RB‐QD04‐0080, RB‐CV‐0011, RB‐CV‐0089, and RB‐CV‐0148. Each of the samples featured partially amorphized SW rims, caused by irradiation damage from implanted low mass solar wind ions, and the impacting of micrometeorites. Using bright‐field and HAADF‐STEM imaging, vesicular blistering and nanophase Fe metal (npFe0) particles were observed within grain rims, and solar flare tracks were observed in the substrate host grain, confirming the presence of SW zones. We use Fe‐K XANES mapping to investigate Fe‐redox changes between the host mineral and the SW zones. All SW zones measured show some increases in the ferric‐ferrous ratio (Fe3+/ΣFe) relative to their respective host grains, likely the result of the implanted solar wind H+ ions reacting with the segregated ferrous Fe in the surface material.

¹Larry R. Nittler,¹Conel M. O’D. Alexander,^1,2Andrea Patzer,^1,3Maximilien J. Verdier‐Paoletti
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13618]
¹Earth and Planets Laboratory, Carnegie Institution of Washington, 5241 Broad Branch Rd NW, Washington, District of Columbia, 20015 USA
²Geosciences Center Göttingen, University of Göttingen, Goldschmidtstr. 1, 37077 Göttingen, Germany
³Institut de Minéralogie, de Physique des Matériaux, et de Cosmochimie (IMPMC), Sorbonne Université, Muséum national d’Histoire naturelle, UPMC Université Paris 06, UMR CNRS 7590, IRD, UMR 206, 75005 Paris, France
Published by arrangement with John Wiley & Sons

We report a NanoSIMS search for presolar grains in the CM chondrites Asuka (A) 12169 and A12236. We found 90 presolar O‐rich grains and 25 SiC grains in A12169, giving matrix‐normalized abundances of 275 (+55/−50, 1σ) ppm or, excluding an unusually large grain, 236 (+37/−34) ppm for O‐rich grains and 62 (+15/−12) ppm for SiC grains. For A12236, 18 presolar silicates and 6 SiCs indicate abundances of 58 (+18/−12) and 20 (+12/−8) ppm, respectively. The SiC abundances are in the typical range of primitive chondrites. The abundance of presolar O‐rich grains in A12169 is essentially identical to that in CO3.0 Dominion Range 08006, higher than in any other chondrites, while in A12236, it is higher than found in other CMs. These abundances provide further strong support that A12169 and A12236 are the least‐altered CMs as indicated by petrographic investigations. The similar abundances, isotopic distributions, silicate/oxide ratios, and grain sizes of the presolar O‐rich grains found here to those of presolar grains in highly primitive CO, CR, and ungrouped carbonaceous chondrites (CCs) indicate that the CM parent body(ies) accreted a similar population of presolar oxides and silicates in their matrices to those accreted by the parent bodies of the other CC groups. The lower abundances and larger grain sizes seen in some other CMs are thus most likely a result of parent‐body alteration and not heterogeneity in nebular precursors. Presolar silicates are unlikely to be present in high abundances in returned samples from asteroids Ryugu and Bennu since remote‐sensing data indicate that they have experienced substantial aqueous alteration.

^1,2,3Hong Tang,^1,2,3XiongyaoLi,¹Xiaojia Zeng,^1,2,3Yang Li,^1,2,3Wen Yu,^1,2,3Bing Mo,^1,2,3Jianzhong Liu,⁴Shijie Wang,⁵Yongliao Zou
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2021.114322]
¹Center for Lunar and Planetary Sciences, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, China
²CAS Center for Excellence in Comparative Planetology, China
³Key Laboratory of Space Manufacturing Technology, Chinese Academy of Sciences, Beijing 100094, China
⁴State Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, China
⁵National Space Science Center, Chinese Academy of Sciences, Beijing 100190, China
Copyright Elsevier

The possibility of OH/H2O formation on the lunar surface has been proposed because of the interaction between protons from the solar wind and oxygen in the regolith. In this study, we examined olivine, pyroxene, plagioclase, and volcanic glass samples together irradiated with 7 keV H+ at a dose of 1017 ions/cm2 under the same experimental conditions to simulate the solar-wind proton implantation process on the moon. By comparing the infrared spectral characteristics of these samples before and after H+ implantation through an infrared spectrometer, we confirm that OH forms in all minerals and glass after H+ implantation, with a remarkable amount of OH/H2O found in plagioclase. This indicates that plagioclase can capture more H+ than other silicate phases to form the OH/H2O. The absorption characteristics of OH/H2O formed by H+ implantation are distinct and associated with the mineral structure. The efficiency of OH/H2O formation by H+ implantation is affected by crystal structure. We conclude that OH/H2O formed by solar-wind implantation in the lunar soil is likely to be mainly preserved in plagioclase, and the estimated OH/H2O absorption strength from 0.7 to 3.6% at 3356 cm−1 and from 0.9 to 4.8% at 3622 cm−1 of plagioclase is consistent with those found by recent lunar spacecraft missions

¹Thomas M.McCollom,^1,2Brian Hynek
Earth and Planetary Science Letters 557, 116729 Link to Article [https://doi.org/10.1016/j.epsl.2020.116729]
¹Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, CO 80309, United States of America
²Department of Geological Sciences, University of Colorado, Boulder, CO 80309, United States of America
Copyright Elsevier

The hematite-bearing, sulfate-rich sandstones of the Burns formation at Meridiani Planum are underlain by a thin stratigraphic unit referred to as the Grasberg formation. The sulfate-bearing Grasberg rocks are fine-grained and lack bedding structures, and were previously interpreted to be a distinct lithologic unit based on morphological and chemical differences from the overlying Burns formation. However, reanalysis of the data indicates that, except for variable amounts of Mg, Ni, SO3 and Mn, the chemical compositions of the Grasberg and Burns rocks are very similar. The relatively low levels of Mg, Ni, and SO3 in the Grasberg rocks indicates that they have experienced diagenetic loss of Mg sulfates similar to that observed in a subset of eleven Burns formation rocks depleted in the same elements, including two Burns rocks immediately above the Grasberg contact. The Grasberg formation and Burns rocks near the contact have also evidently lost Mn during diagenesis. When compensated for diagenetic losses, rocks from the Grasberg and Burns formations are found to have nearly identical chemical compositions, albeit Grasberg rocks contained a few wt.% less SO3. These observations suggest that the sediment sources for the Grasberg and Burns formations are genetically related, and that both formations experienced some of the same diagenetic processes after deposition. Furthermore, the apparent loss of Mg, Ni, SO3, and Mn from the Grasberg formation and immediately overlying Burns rocks is mirrored by enrichments of these same elements in fractures within the underlying Shoemaker formation, suggesting downward movement of fluids during some diagenetic events.