^1,2K. K. Bhanot,^1,2,3H. Downes,⁴B. G. Rider-Stokes,^1,3E. S. Jennings,^2,4M. Anand,^5,6J. F. Snape,⁶M. J. Whitehouse
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.14269]
¹School of Natural Sciences, Birkbeck University of London, London, UK
²Natural History Museum, London, UK
³UCL/Birkbeck Centre for Planetary Sciences, University College London, London, UK
⁴School of Physical Sciences, The Open University, Milton Keynes, UK
⁵Department of Geosciences, Swedish Museum of Natural History, Stockholm, Sweden
⁶Department of Earth and Environmental Sciences, University of Manchester, Manchester, UK
Published by arrangement with John Wiley & Sons

Lunar dunite samples 72415–72417, collected by Apollo 17 astronauts from a South Massif boulder in the Taurus–Littrow valley, are crushed breccias composed of several types of olivine- and clinopyroxene-rich clasts, some of which are (or contain) intergrowths of Cr-spinel and pyroxenes or plagioclase. Among the clasts are ellipsoidal symplectites of Cr-spinel and pyroxene, up to 300 μm in diameter, which have bulk compositions consistent with those of olivine + garnet. These symplectites are inferred to originally have been olivine + Mg-Cr-rich garnet (pyrope–uvarovite) that formed deep in the lunar mantle and were subsequently transported closer to the lunar surface (spinel- or plagioclase-peridotite stability fields), perhaps during gravitationally driven overturn. Abundant microsymplectite (30 μm diameter) intergrowths of Cr-spinel and pyroxene inside olivine grains, many associated with inclusions of plagioclase and augite, formed during a later decompression event (perhaps excavation to the lunar surface). These inclusions have not previously been recorded in these samples and could be responsible for earlier reports of igneous zoning in olivine. Electron backscatter diffraction data show evidence of high shock pressures (>50 GPa), which are inferred to have occurred during the impact which excavated the dunites from the shallow anorthite-bearing lunar mantle. Apatite veinlets post-date the shock metamorphism and have been dated to 3983 ± 72 Ma and 3913 ± 118 Ma by the U–Pb method. This age is consistent with that inferred for the Imbrium impact basin, suggesting that the dunite was finally excavated from the mantle during formation of the Imbrium basin.

^1,2Guy Leckenby et al. (>10)
Nature 635, 321-326 Open Access Link to Article [DOI
https://doi.org/10.1038/s41586-024-08130-4]
¹TRIUMF, Vancouver, British Columbia, Canada
²Department of Physics and Astronomy, University of British Columbia, Vancouver, British Columbia, Canada

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

^1,2Mabel L. Gray,^1,2,3Michael K. Weisberg,^1,2,3Steven J. Jaret,^1,2Denton S. Ebel
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.14287]
¹Department Earth and Environmental Sciences, CUNY Graduate Center, New York, New York, USA
²Department Earth and Planetary Sciences, American Museum of Natural History, New York, New York, USA
³Department Physical Sciences, Kingsborough College CUNY, Brooklyn, New York, USA
Published by arrangement with John Wiley & Sons

The enstatite chondrite class is known to have complex thermal histories, often interpreted to include impact melting and shock metamorphism. Highly equilibrated (type 6) EH group enstatite chondrites are rare and thought to have formed through collisional heating. We studied two EH6 chondrites, NWA 7976 and NWA 12945, for their textural, chemical, and mineralogical characteristics. The samples we studied contain subhedral to anhedral grains of enstatite and plagioclase, suggesting solid-state recrystallization. They show low degrees of shock and no evidence of shock melting. Additionally, the ubiquitous occurrence of daubréelite exsolution lamellae in troilite and the Ni content of schreibersite suggest slow cooling at greater burial depths in the parent body, rather than rapid cooling as a result of an impact event. Based on the characteristics and scarcity of type 6 EH chondrites, and the ubiquitous shock effects and melt rocks in the enstatite chondrite class, we conclude that the unshocked NWA 7976 and NWA 12945 were formed by heat derived from impact melt sheets, analogous to contact metamorphism.

^1,2Matthew J. Genge,²Natasha Almeida,³Matthias Van Ginneken,⁴Lewis Pinault,⁵Louisa J. Preston,³Penelope J. Wozniakiewicz,^6,7Hajime Yano
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.14288]
¹Department of Earth Science and Engineering, Imperial College London, London, UK
²Planetary Materials Group, Natural History Museum, London, UK
³Centre for Astrophysics and Planetary Science, Dept. Physics and Astronomy, University of Kent, Canterbury, Kent, UK
⁴Department of Earth and Planetary Sciences, Birkbeck College, London, UK
⁵Department of Space and Climate Physics, Mullard Space Science Laboratory, University College London, Surrey, UK
⁶Department of Interdisciplinary Space Science, Institute of Space and Astronautical Science (ISAS), Japan Aerospace Exploration Agency (JAXA), Sagamihara, Kanagawa, Japan
⁷Space and Astronautical Science, Graduate Institute for Advanced Studies, SOKENDAI, Sagamihara, Kanagawa, Japan
Published by arrangement with John Wiley & Sons

The presence of microorganisms within meteorites has been used as evidence for extraterrestrial life, however, the potential for terrestrial contamination makes their interpretation highly controversial. Here, we report the discovery of rods and filaments of organic matter, which are interpreted as filamentous microorganisms, on a space-returned sample from 162173 Ryugu recovered by the Hayabusa 2 mission. The observed carbonaceous filaments have sizes and morphologies consistent with microorganisms and are spatially associated with indigenous organic matter. The abundance of filaments changed with time and suggests the growth and decline of a prokaryote population with a generation time of 5.2 days. The population statistics indicate an extant microbial community originating through terrestrial contamination. The discovery emphasizes that terrestrial biota can rapidly colonize extraterrestrial specimens even given contamination control precautions. The colonization of a space-returned sample emphasizes that extraterrestrial organic matter can provide a suitable source of metabolic energy for heterotrophic organisms on Earth and other planets.

^1,2,3Yuri Amelin, ⁴Qing-Zhu Yin, ^2,5Piers Koefoed, ^2,6Renaud Merle, ^7,8Yuki Hibiya, ^4,9Magdalena H. Huyskens, ⁷Tsuyoshi Iizuka, ¹⁰Julia A. Cartwright
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2024.11.008]
¹Research School of Earth Sciences, The Australian National University, Australia
²Division of Earth and Environmental Sciences, Korea Basic Science Institute, Ochang, 28119, South Korea
³State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry CAS, Guangzhou, 510640, China
⁴Department of Earth and Planetary Sciences, University of California-Davis, Davis, CA 95616, USA
⁵Department of Earth, Environmental, and Planetary Sciences and McDonnell Center for the Space Sciences, Washington University in St. Louis, MO, USA
⁶Department of Earth Sciences, Uppsala University, Villavägen 16, 75236 Uppsala, Sweden
⁷Department of Earth and Planetary Science, The University of Tokyo, Japan
⁸Research Center for Advanced Science and Technology, The University of Tokyo, Japan
⁹Geological Survey of Norway, Leiv Eirikssons vei 39, 7040 Trondheim, Norway
¹⁰Institute for Space, University of Leicester, UK
Copyright Elsevier

In this study we test the possibility that radiogenic 207Pb/206Pb ratios (207Pb*/206Pb*) in meteorites can be fractionated during partial dissolution, and explore the consequences of this fractionation for Pb-isotope chronology of meteorites. We report the results of experiments tailored to detect Pb-isotope fractionation, induced by partial dissolution through acid leaching, in plutonic angrite Northwest Africa (NWA) 4801 and ungrouped achondrites NWA 10132 and Erg Chech (EC) 002. We also re-examine previously published U-Pb data for other achondrites and for Ca-Al-rich refractory inclusions (CAIs), to seek evidence of such fractionation. We observe that, in primitive achondrite NWA 10132, differences in 207Pb*/206Pb* ratios, corresponding to the age bias of ca. 1–2 Ma, exist between the 0.5 M hydrofluoric acid leachates of pyroxene or crushed rock, and the residues after such leaching. In angrite NWA 4801, similar acid treatment of pyroxene separates did not cause a resolvable age bias. In EC 002, three steps of partial dissolution in 0.2 M – 5 M HF caused irregular 207Pb*/206Pb* fractionation between leaching steps, and generally higher 207Pb*/206Pb* ratios in the residues than in HF leachates. These age biases were observed in leaching pairs with highly radiogenic Pb, and cannot be explained by mixing between radiogenic Pb, primordial Pb, and Pb introduced by terrestrial contamination. Instead, the observed isotope fractionation is attributed to the combined effects of the size difference between α-recoil tracks in the decay chains of 238U and 235U, and exsolution of primary pigeonite, leading to the formation of a lamellar structure consisting of augite and low-Ca pyroxene by either slow-cooling or subsequent metamorphic reactions. Where extensive acid leaching intended for removal of non-radiogenic Pb causes fractionation of radiogenic Pb isotopes, its detrimental effect can be reversed by performing a numeric recombination of partial leachate and residue data. Currently, it is unclear how common leaching-induced isotopic fractionation is in Pb-isotopic chronology to meteoritic materials. Acid leaching is an essential step for removal of non-radiogenic Pb in the precise Pb-isotopic dating of meteorites, which currently does not have viable alternatives. However, it is important to be aware of its possible side effects, and to continue search for new non-radiogenic Pb removal techniques that do not cause radiogenic 207Pb* and 206Pb* fractionation.

^1,2Zhipeng Xia,^1,2Baochen Yang,^1,2Bowen Si,^1,2Guozhu Chen,^1,2Xi Wang,^1,3Hongyi Chen,^1,2Chuantong Zhang,^1,2Bingkui Miao
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.14285]
¹Institution of Meteorites and Planetary Materials Research, Key Laboratory of Planetary Geological Evolution, Guilin University of Technology, Education Department of Guangxi Zhuang Autonomous Region, Guilin, China
²Guangxi Key Laboratory of Hidden Metallic Ore Deposits Exploration, Guilin University of Technology, Guilin, China
³Collaborative Innovation Center for Exploration of Nonferrous Metal Deposits and Efficient Utilization of Resources in Guangxi, Guilin University of Technology, Guilin, China
Published by arrangement with John Wiley & Sons

We present petrology and mineralogy for two lunar granulitic breccia meteorites that were detected in Northwest Africa (NWA), the samples NWA 15062 and NWA 15063. The fragments primarily consist of plagioclase and olivine mineral clasts, with minor amounts of anorthosite clasts and one troctolite clast. The anorthosite clasts are dominated by plagioclase/maskelynite, with minor olivine and pyroxene. A troctolite clast, composed of olivine and maskelynite, occurs in NWA 15063. The olivine clasts display mosaic extinction and usually have a homogeneous Mg-rich composition. However, all olivine mineral clasts exhibit two distinct ranges of their major element composition (Mg#: 85–88 and 77–78, respectively). Large individual plagioclase clasts show heterogeneous compositions (Ab content: 2.5–4.8) and have different Raman peak positions in different domains. The matrix of the meteorites appears semitransparent and is composed of olivine and pyroxene aggregates associated with maskelynite, constituting a granoblastic texture. Pyroxenes of the matrix are dominantly enstatites, associated with a few augites. Both meteorite samples exhibit shock-induced melt veins ranging from 50 to 200 μm width. These melt veins traverse the entire samples and contain rare, very fine-grained (2–3 μm) Mg-rich olivine clasts (Mg# = 90–93) and mafic silicate glass. Some Cr-spinel grains exhibit slight compositional zonation, characterized by a magnesium-rich core (Mg# = 56, Cr# = 23) and Cr-rich rims (Mg# = 50, Cr# = 28), with decomposition at the edges. The significantly differing Mg# contents of the mafic silicate minerals in the matrix, lithic clasts, and mineral clasts of the two meteorites indicate a diverse origin of the clasts. Based on their petrology, mineral chemistry, and bulk composition, NWA 15062 and NWA 15063 are classified as anorthositic troctolitic granulitic polymict breccia. Textural evidence suggests that the parent rocks of NWA 15062 and NWA 15063 were affected by high pressure of up to 30 GPa during impact-induced shock metamorphism, causing crystal structure deformation in olivine and the transformation of plagioclase to maskelynite. During cooling from peak temperatures of 1600–1700°C, the coarse-grained maskelynite mineral clasts were partially devitrified, and the granoblastic texture of the matrix was developed. Mg-rich anorthosite was formed before this shock event. Cr-spinel was formed in a troctolitic melt, which was probably differentiated after the crystallization of anorthite and magnesium-rich olivine. However, the possibility of the formation of the Mg-rich melt through interaction with the lunar anorthositic crust cannot be ruled out. The meteorite NWA 15062/15063 strongly resembles the textural, chemical, and mineralogical characteristics of the NWA 5744 meteorite group. Therefore, we interpret the two samples as a new member of the NWA 5744 meteorite group.

^1,2Chen Li et al. (>10)
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2024.10.035]
¹Center for Lunar and Planetary Sciences, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, China
²Faculty of Metallurgical and Energy Engineering, Kunming University of Science and Technology, Kunming 650093, China
Copyright Elsevier

The formation of a unique microstructure of minerals on the surface of airless bodies is attributed to space weathering. However, it is difficult to distinguish the contributions of meteorite impacts and solar wind to the modification of lunar soil, resulting in limited research on the space weathering mechanism of airless bodies. The thermochemical reactivity of troilite can be used to distinguish the contributions of impact events and solar wind to the modification of lunar soil and provide evidence for space weathering of lunar soil. We examined the structure of a single particle of troilite in the Chang’e-5 lunar soil and determined whether an impact caused the thermal reaction. Microanalysis showed that troilite underwent substantial mass loss during thermal desulfurization, forming a crystallographically aligned porous structure with iron whiskers, an oxygen-rich layer, and other crystallographic and thermochemical evidence. We used an ab initio deep neural network model and thermodynamic calculations to conduct experiments and determine the anisotropy and crystal growth of troilite. The surface microstructure of troilite was transformed by the thermal reaction in the vacuum on the lunar surface. Similar structures have been found in near-Earth objects (NEOs), indicating that small bodies underwent the same impact-induced thermal events. Thus, thermal reactions in a vacuum are likely ubiquitous in the solar system and critical for space weathering alterations of the soil of airless bodies.

^1,2Zhuang Guo,¹Yu Zhu,^2,3Yang Li,⁴Ian M. Coulson,^2,3Xiongyao Li,^2,3Jianzhong Liu
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.14283]
¹State Key Laboratory of Continental Dynamics & NWU-HKU Joint Center of Earth and Planetary Sciences, Department of Geology, Northwest University, Xi’an, China
²Center for Lunar and Planetary Sciences, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang, China
³Center for Excellence in Comparative Planetology, Chinese Academy of Sciences, Hefei, China
⁴Solid Earth Studies Laboratory, Department of Geology, University of Regina, Regina, Canada
Published by arrangement with John Wiley& Sons

Basaltic shergottites are the most abundant rock type of Martian meteorites, and pyroxene grains within shergottites commonly show a zoned structure. Here, the detailed microscopic mineralogical characteristics of patchy zoned pyroxene in basaltic shergottite NWA 12522 were investigated by a combination of scanning electron microscopy, electron microprobe, Raman spectroscopy, and transmission electron microscopy. The results show that the cores of zoned pyroxene in NWA 12522 have a homogeneous Mg# value and consist mainly of augite and pigeonite. By contrast, the rim of zoned pyroxene is extremely ferroan and can be further divided into two regions based on quite distinct mineralogy and textures (i.e., far-core and near-core pyroxene rims). The near-core rim shows narrow exsolution lamellae (~35 nm) that were cross-cut by thin pigeonite veinlets and contain abundant nano-sized particles of metastable pyroxferroite and pigeonite. Only relatively coarse exsolution lamellae (~80 nm) were observed in the far-core pyroxene rim regions. The distinct mineralogical characteristics of the pyroxene rims and cores in NWA 12522 imply different crystallization conditions, and the homogeneous Mg-rich pyroxene cores should have slowly crystallized from magma within a deep-seated chamber, followed by an overgrown evolved melt on these pyroxene cores during their ascent to the Martian surface, and disequilibrium crystallization of nano-sized metastable phase (pyroxferroite) occurred in the near-core region. The abnormally low ΣREE contents and steep REE pattern (high Yb/La ratio) of the pyroxene rims in NWA 12522 imply that merrillite should have crystallized prior to the pyroxene rims, making the residual melt become REE-depleted and HREE-enriched.

¹A. C. Stadermann,²T. M. Erickson,¹L. B. Seifert,³Y. Chang,³Z. Zeszut,³T. J. Zega,⁴Z. D. Michels,³J. J. Barnes
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.14282]
¹NASA Johnson Space Center, Houston, Texas, USA
²Jacobs JETS Contract at NASA Johnson Space Center, Houston, Texas, USA
³Lunar and Planetary Laboratory, University of Arizona, Tucson, Arizona, USA
⁴Department of Geosciences, University of Arizona, Tucson, Arizona, USA
Published by arrangement with John Wiley & Sons

The temperature and pressure conditions experienced by rocks during an impact event can be constrained using petrologic and microstructural analysis and is crucial to providing ground truth to the impact cratering process. Suevite is a polymict, impact melt-bearing breccia, specific to Ries crater in Germany. There are competing models for suevite formation and emplacement, such as clastic flows pushed out of the crater rim or ejecta plume fallback. Knowledge of the temperature and pressure pathways recorded by grains within the suevite can help distinguish between these and other models. The accessory phase zircon (ZrSiO4) and its high-pressure polymorph reidite are particularly useful in such circumstances as they are highly refractory minerals that can record the high-temperature and/or high-pressure conditions of an impact event. Here, we present evidence for a wide array of temperature and pressure conditions recorded in zircon grains within a single thin section of suevite. Zircons in this study range from unshocked to highly shocked (>53 GPa), and record temperatures more than 1673°C. These findings confirm previous studies concluding that suevites contain material exposed to very diverse pressure and temperature conditions during initial shock compression and excavation but do not, as a whole, experience extreme temperatures (>1673°C) or pressures (>30 GPa).

^1,2Alan E. Rubin
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.14284]
¹Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, California, USA
²Maine Mineral & Gem Museum, Bethel, Maine, USA
Published by arrangement with John Wiley & Sons

H, L, and LL chondrites all exhibit positive correlations between mean shock stage and petrologic type. At a given shock energy, hot samples exhibit more intense shock features than cold samples. After the ordinary-chondrite (OC) parent asteroids were collisionally disrupted, jumbled, and gravitationally reassembled, the correlations between mean shock stage and petrologic type may have resulted from stochastic collisions into material of different temperatures that were randomly distributed in the near-surface regions of the rubble-pile asteroids. Late-stage processes including shock events and post-shock annealing affected the preexisting correlations to only minor degrees. This model, combined with literature data, permits the following scenario: Each principal OC asteroid initially had an onion-shell structure with deeply buried type 6 materials cooling slowly, yielding young closure ages in Pb-phosphate data. The OC bodies were disrupted at ~60 Ma, locking in the Pb-phosphate record of the onion-shell structure. The H-chondrite parent body was collisionally disrupted somewhat later than the L or LL bodies and was thus somewhat cooler at the time of disruption. In the OC asteroidal rubble piles, materials of different petrologic types cooled at similar rates through ~500°C, precluding a correlation between petrologic type and metallographic cooling rate. Shortly after rubble-pile formation, materials of higher petrologic types remained hotter than materials of lower petrologic types. The hotter materials recorded more intense shock features from the common meteoroid flux, leading to positive correlations in each OC asteroid between petrologic type and mean shock stage. The cooler H-chondrite materials manifested a lower range in mean shock stage.