¹Devin L.Schrader,²Kazuhide Nagashima,¹Jemma Davidson,³Timothy J.McCoy,⁴Ryan C.Ogliore,⁵Roger R.Fu
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2020.05.014]
¹Center for Meteorite Studies, School of Earth and Space Exploration, Arizona State University, 781 East Terrace Road, Tempe, AZ 85287, USA
²HIGP/SOEST, University of Hawai‘i at Mānoa, Honolulu, HI 96822, USA
³Department of Mineral Sciences, National Museum of Natural History, Smithsonian Institution, 10th & Constitution Avenue NW, Washington, DC 20560-0119, USA
⁴Department of Physics, Washington University in St. Louis, St. Louis, MO 63130, USA
⁵Department of Earth and Planetary Sciences, Harvard University, 20 Oxford St., Cambridge, MA 02138, USA
Copyright Elsevier

Determining the origins of chondrule precursors is key to constraining how material migrated in the early Solar System. Chondrules that were only partially melted during their formation retain portions of their solid precursors, termed relict grains. By measuring the chemical and O-isotopic compositions of relict grains in chondrules from an unequilibrated ordinary chondrite (UOC), and Renazzo-like carbonaceous (CR) and Mighei-like carbonaceous (CM) chondrites we constrain their origins and discuss implications for disk transport within the first 4 million years of the Solar System. For all three chondrite groups, the chemical and O-isotopic compositions of dusty olivine grains are sometimes consistent with the reduction of type I (FeO-poor) and/or type II (FeO-rich) chondrules from the same meteorite group. However, other dusty olivine grains from the CM chondrites and the UOC are found to be xenocrysts that require an origin from a source distinct from the host meteorite. This material plausibly originated as fragments of earlier-formed chondrules from another chondrite group or of partially or fully differentiated planetesimals that migrated into an active chondrule-forming region. Multiple CM chondrite dusty olivine chondrules have O-isotope compositions that match those of UOC chondrule olivine (Δ¹⁷O ∼ 0‰), suggesting an origin from an UOC source. This implies that UOC chondrules and/or chondrule fragments migrated from the inner Solar System outwards to CM chondrite chondrule-forming region, likely beyond the orbit of Jupiter. These UOC chondrules or chondrule fragments could have migrated outwards in the protoplanetary disk before the formation of the Jupiter Gap, or <300 μm diameter fragments could have migrated outwards after Gap formation as CM chondrite chondrule dusty olivine grains with Δ¹⁷O ∼ 0‰ were small enough to pass through Jupiter Gap. The identification of xenocrysts in each meteorite group studied here argues for widespread migration of material in the early Solar System, potentially crossing the Jupiter Gap.

^1,2Zoltán Váci,¹Carl B. Agee,²Christopher D. K. Herd,^2,3Erin Walton,⁴Oliver Tschauner,¹Karen Ziegler,⁵Vitali B. Prakapenka,⁵Eran Greenberg,⁴Sylvia Monique‐Thomas
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13479]
¹Department of Earth and Planetary Sciences, Institute of Meteoritics, University of New Mexico, Albuquerque, New Mexico, 87106 USA
²Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton, Alberta, T6G 2E3 Canada
³Department of Earth and Planetary Sciences, MacEwan University, Edmonton, Alberta, T5J 4S2 Canada
⁴Department of Geoscience, University of Nevada, Las Vegas, Las Vegas, Nevada, 89154 USA
⁵GSECARS, Argonne National Laboratory, Lemont, Illinois, 60439 USA
Published by arrangement with John Wiley & Sons

Hydrous alteration of olivine macrocrysts in a Martian olivine phyric basalt, NWA 10416, and a terrestrial basalt from southern Colorado are examined using SEM, EPMA, TEM, and µXRD techniques. The olivines in the meteorite contain linear nanotubes of hydrous material, amorphous areas, and fluid dissolution textures quite distinct from alteration identified in other Martian meteorites. Instead, they bear resemblance to terrestrial deuteric alteration features. The presence of the hydrous alteration phase Mg‐laihunite within the olivines has been confirmed by µXRD analysis. The cores of the olivines in both Martian and terrestrial samples are overgrown by unaltered rims whose compositions match those of a separate population of groundmass olivines, suggesting that the core olivines are xenocrysts whose alteration preceded crystallization of the groundmass. The terrestrial sample is linked to deep crustal metasomatism and the “ignimbrite flare‐up” of the Oligocene epoch. The comparison of the two samples suggests the existence of an analogous relatively water‐rich magmatic reservoir on Mars.

^1,2Naoya Imae,¹Makoto Kimura
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13491]
¹National Institute of Polar Research, 10‐3 Midori‐cho, Tachikawa‐shi, Tokyo, 190‐8518 Japan²Department of Polar Science, the Graduate University for Advanced Studies, SOKENDAI, 10‐3 Midori‐cho, Tachikawa‐shi, Tokyo, 190‐8518 Japan
Published by arrangement with John Wiley & Sons

Identification and characterization of small extraterrestrial samples, such as small Antarctic meteorites <~1 cm, require the development of convenient laboratory‐based nondestructive analytical techniques using X‐ray diffraction (XRD). We explore the characterization criteria using an X‐ray diffractometer with a Gandolfi attachment using sub‐mm small fragments and powder aggregates for various kinds of stony meteorites and develop a new analytical technique. We primarily focus on olivine and pyroxene because they are the most abundant and important minerals for stony meteorite classification. A new calibration is performed to estimate the FeO content of the olivine in unequilibrated ordinary chondrites, which is useful for determining the meteorite chemical group irrespective of powder aggregate diameter but dependent on fragment grain diameter. This is because X‐ray intensity absorption is more effective for grains than for powders. Clinoenstatite (Cen) and orthoenstatite (Oen) were distinguished using the presence or absence of the isolated Oen 511 index peak. The method is also applied to other stony meteorites including carbonaceous chondrites and achondrites. The XRD results are consistent with studies based on polished sections involving textural observations by scanning microscope and chemical compositions of the constituent minerals. The new measurement technique presented here is convenient because of its use in air by the laboratory‐based X‐ray diffractometer, which makes it useful for the initial analyses of restricted extraterrestrial sample characterization.

¹N.M.Abreu,^2,3J.C.Aponte,⁴E.A.Cloutis,⁵A.N.Nguyen
Geochemistry (Chemie der Erde) (in Press) Link to Article [https://doi.org/10.1016/j.chemer.2020.125631]
¹Earth Science, Pennsylvania State University – DuBois Campus, DuBois, PA, 15801, USA
²Solar System Exploration Division, Code 691, NASA Goddard Space Flight Center, Greenbelt, Maryland 20771, USA
³Department of Chemistry, Catholic University of America, Washington, DC 20064, USA
⁴Department of Geography, University of Winnipeg, 515 Portage Avenue, Winnipeg, MB R3B 2E9, Canada
⁵Jacobs Engineering Group Inc., NASA Johnson Space Center, Houston, Texas 77058, USA
Copyright Elsevier

We present here a review of the characteristics of CR carbonaceous chondrite meteorites. Over the past three decades, our knowledge and understanding of the scientific value of the CR chondrites have increased dramatically, as more samples from cold and hot deserts have become available for analysis. Based on a variety of compositional, mineralogical, isotopic, and spectroscopic studies, we have come to understand that CR chondrites are excellent samples of asteroidal meteorites to look for virtually unaltered solar nebula material and to observe asteroidal processes in progress. This paper summarizes these investigations, their similarities, and differences with other chondritic groups, their relationships to asteroids, and the questions yet to be addressed.

^1,2Samuel Ebert,¹Kazuhide Nagashima,¹Alexander N.Krot,²Addi Bischoff
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2020.05.012]
¹School of Ocean, Earth Science and Technology, Hawai’i Institute of Geophysics and Planetology, University of Hawai‘i at Mānoa, USA
²Institut für Planetologie, Westfälische Wilhelms-Universität Münster, Germany
Copyright Elsevier

The nature of oxygen-isotope heterogeneity in refractory inclusions [Ca,Al-rich inclusions (CAIs) and amoeboid olivine aggregates (AOAs)] from weakly metamorphosed chondrites is one of the outstanding problems in cosmochemistry. To obtain insights into possible processes resulting in O-isotope heterogeneity of refractory inclusions, we investigated the mineralogy, petrology, and oxygen isotopic compositions of six CAIs and two AOAs and aqueously formed fayalite grains within the matrix of the H3.1 chondrite Northwest Africa (NWA) 3358. Most of the refractory inclusions studied appear to be unmolten solar nebula condensates; some may have experienced partial melting and/or high-temperature annealing. The NWA 3358 refractory inclusions nearly completely avoided metasomatic alteration on the H-chondrite parent body: nepheline grains replacing anorthite and/or melilite are either very minor or absent. Five out of eight refractory inclusions studied have heterogeneous O-isotope composition: Δ17O ranges from ∼ −25‰ to ∼ 3.5±2‰ (2σ). This O-isotope heterogeneity appears to be mineralogically controlled with melilite and anorthite being systematically 16O-depleted compared to hibonite, spinel, Al,Ti-diopside, and forsterite all having similar solar-like Δ17O of ∼ −24±2‰. In contrast to NWA 3358 refractory inclusions, the previously studied AOAs and a fine-grained CAI from the LL3.00 chondrite Semarkona have uniform Δ17O of ∼ −25‰ (McKeegan et al., 1998; Itoh et al., 2007). Because the mineralogically-controlled O-isotope heterogeneity in refractory inclusions from ordinary chondrites appears to correlate with petrologic type of a host meteorite experienced by aqueous alteration, we suggest O-isotope exchange in NWA 3358 CAIs and AOAs resulted from aqueous fluid-rock interaction on the H-chondrite parent asteroids. This is supported by the presence of 16O-depleted anorthite (Δ17O ∼ 3.5±2‰) and aqueously formed fayalite similar depleted in 16O (Δ17O ∼ 4±2‰). The Δ17O of NWA 3358 fayalite is comparable to that of magnetite and fayalite in Semarkona and other weakly metamorphosed L3 and LL3 chondrites (Choi et al., 1998; Doyle et al., 2015) suggesting similar Δ17O of aqueous fluids on the H, L, and LL chondrite parent asteroids.

¹Yuri Shimaki et al. (>10)
Icarus (in Press) Link to article [https://doi.org/10.1016/j.icarus.2020.113835]
¹Institute of Space and Astronautical Science, Japan Aerospace Exploration Agency, Sagamihara 252-5210, Japan
Copyright Elsevier

TIR, the thermal infrared imager on Hayabusa2, acquired high-resolution thermal images of the asteroid 162173 Ryugu for one asteroid rotation period on August 1, 2018 to investigate the thermophysical properties of the asteroid. The surface temperatures of Ryugu suggest that the surface has a low thermal inertia, indicating the presence of porous materials. Thermophysical models that neglect or oversimplify surface roughness cannot reproduce the flat diurnal temperature profiles observed during daytime. We performed numerical simulations of a thermophysical model, including the effects of roughness on the diurnal brightness temperature, the predictions of which successfully reproduced the observed diurnal variation of temperature. The global thermal inertia was obtained with a standard deviation of 225 ± 45 J m⁻² s^−0.5 K⁻¹, which is relatively low but still within the range of the value estimated in our previous study (Okada et al., Nature 579, 518–522, 2020), confirming that the boulders on Ryugu are more porous in nature than typical carbonaceous chondrites. The global surface roughness (the ratio of the variance of the height relative to a local horizontal surface length) was determined as 0.41 ± 0.08, corresponding to a RMS surface slope of 47 ± 5°. We identified a slightly lower roughness distributed along the equatorial ridge, implying a mass movement of boulders from the equatorial ridge to the mid-latitudes.

^1,2L. F. White,^1,2,3A. Černok,⁴J. R. Darling,⁵M. J. Whitehouse,⁶K. H. Joy,⁷C. Cayron,⁴J. Dunlop,^1,2 K. T. Tait,^3,8M. Anand
Nature Astronomy (in Print) Link to Article [DOIhttps://doi.org/10.1038/s41550-020-1092-5]
¹Centre of Applied Planetary Mineralogy, Department of Natural History, Royal Ontario Museum, Toronto, Ontario, Canada
²Department of Earth Sciences, University of Toronto, Toronto, Ontario, Canada
³School of Physical Sciences, The Open University, Milton Keynes, UK
⁴School of Earth and Environmental Sciences, University of Portsmouth, Portsmouth, UK
⁵Swedish Museum of Natural History, Stockholm, Sweden
⁶Department of Earth and Environmental Science, University of Manchester, Manchester, UK
⁷Laboratory of ThermoMechanical Metallurgy (LMTM), PX Group Chair, École Polytechnique Fédérale de Lausanne (EPFL), Neuchâtel, Switzerland
⁸Department of Earth Sciences, The Natural History Museum, London, UK

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^1,2Michaël Marsset et al. (>10)
Nature Astronomy (in Press) Link to Article [DOIhttps://doi.org/10.1038/s41550-019-1007-5]
¹Department of Earth, Atmospheric and Planetary Sciences, MIT, Cambridge, MA, USA
²Astrophysics Research Centre, Queen’s University Belfast, Belfast, UK

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¹Miyamoto, H.,¹Niihara, T.
Natural Resources Research (in Press) Link to Article [DOI: 10.1007/s11053-020-09626-2]
¹Department of Systems Innovation, Graduate School of Engineering, University of Tokyo, Tokyo, Japan

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¹Thomas S.Kruijer,¹Lars E.Borg,¹Josh Wimpenny,¹Corliss K.Sio
Earth and Planetary Science Letters 542, 116315 Link to Article [https://doi.org/10.1016/j.epsl.2020.116315]
¹Nuclear and Chemical Sciences Division, Lawrence Livermore National Laboratory, 7000 East Avenue (L-231), Livermore, CA 94550, USA
Copyright Elsevier

The mantle of Mars probably differentiated through the crystallization of a magma ocean during the first tens of million years (Ma) of Solar System evolution. However, the exact timescale of large-scale silicate differentiation of the martian mantle is debated, and in particular, it remains unclear when differentiation commenced. Here we applied the short-lived 53Mn-53Cr system to martian meteorites in order to date the onset of large-scale mantle differentiation on Mars. The new Cr isotope data demonstrate that martian meteorites exhibit no resolvable radiogenic 53Cr variations, and instead have a uniform +20.2±1.2 (95% conf.) parts-per-million excess in 53Cr/52Cr relative to the terrestrial mantle. The investigated groups of martian meteorites are lithologically varied and derive from diverse mantle sources that probably had variable Mn/Cr. Hence, the lack of 53Cr variability among martian meteorites demonstrates that silicate differentiation on Mars occurred after the extinction of 53Mn. Provided that the sources of the martian meteorites have Mn/Cr variations that are typical of the terrestrial planets, this result implies that the onset of large-scale silicate differentiation must have occurred later than 20±5 Ma after Solar System formation. The onset of silicate differentiation on Mars inferred here is significantly later than time estimates for segregation of the martian core which conservatively occurred within <10 Ma after Solar System formation. Thus, the new Mn-Cr data imply that there was a small, but resolvable, time gap of at least 5 Ma between core formation and magma ocean solidification on Mars. If the age of core segregation is taken at face value, our results imply that the martian magma ocean remained mostly molten over several Ma. This inferred longevity of the magma ocean is inconsistent with thermal models predicting rapid (<1 Ma) solidification of the martian magma ocean. Although there is currently no unique solution to this conundrum, our results can potentially be explained by a protracted history of impact bombardment that delayed differentiation in a shallow magma ocean on Mars, or perhaps more readily, by the presence of an early and dense atmosphere that acted as an insulator and prevented the magma ocean from cooling quickly.