^1,2,3Damanveer S. Grewal, ³Surjyendu Bhattacharje, ³Gabriel-Darius Mardaru,
³Paul D. Asimow
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2024.11.011]
¹School of Molecular Sciences, Arizona State University, Tempe, AZ 85281, USA
²School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85281, USA
³Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA
Copyright Elsevier

Understanding the relationships between the nitrogen (N) isotope ratios of early solar system planetesimals and terrestrial reservoirs is crucial for tracing the origin of volatiles on Earth. The Earth primarily grew from planetesimals and planetary embryos that accreted rapidly (within ∼1–2 Ma after CAIs) in the inner solar system, also known as the non-carbonaceous (NC) reservoir. Magmatic iron meteorites, which sample the metallic cores of the earliest solar system planetesimals, have emerged as a promising proxy in this exercise. NC irons are distinctly ¹⁵N-poor compared to their CC (carbonaceous or outer solar system) counterparts. However, the utility of this proxy is limited by the lack of knowledge of N isotope fractionation during core crystallization. Using high pressure-high temperature experiments, we show that equilibrium N isotopic fractionation between solid and liquid metal (Δ¹⁵N^{solid–liquid} = δ¹⁵N^solid − δ¹⁵N^liquid) is limited (≤1.2 ‰) under conditions relevant for core crystallization. This, combined with the siderophile character of N and limited equilibrium N isotope fractionation during core-mantle differentiation, suggests that the δ¹⁵N values of iron meteorites accurately represent the N isotopic composition of their parent bodies. Unlike the variation in the N isotope ratios of NC and CC chondrites, which can be attributed to the effects of parent-body processes acting on organic precursors, the ¹⁵N-poor nature of NC irons relative to CC irons likely offers the most definitive evidence for the distinct N isotopic compositions of the earliest inner and outer solar system planetesimals. The N isotopic composition of Earth’s primordial mantle (δ¹⁵N = <−40 ‰) suggests that it retains the memory of the early accretion of ¹⁵N-poor NC iron meteorite parent body-like planetesimals. The early accreted ¹⁵N-poor nitrogen may be stored in the deep mantle, segregated into the core, or lost to space during atmospheric loss caused by impacts. This signature was overprinted by the subsequent accretion and admixing of CC materials, which is reflected in the relatively ¹⁵N-rich nature of Earth’s atmosphere (δ¹⁵N = 0) and convecting mantle (δ¹⁵N = −5 ‰).

¹Francis Nimmo, ²Thorsten Kleine, ³Alessandro Morbidelli, ⁴David Nesvorny
Earth and Planetary Science Letters 648, 119112 Link to Article [https://doi.org/10.1016/j.epsl.2024.119112]
¹Dept. Earth & Planetary Sciences, University of California Santa Cruz, Santa Cruz CA 95064, United States
²Max Planck Institute for Solar System Research, Gottingen 37077, Germany
³College de France, Paris Cedex 05 75 231, France
⁴Dept. Space Studies, Southwest Research Institute, Boulder CO 80302, United States
Copyright: Elsevier

The nucleosynthetic isotope signatures of meteorites and the bulk silicate Earth (BSE) indicate that Earth consists of a mixture of “carbonaceous” (CC) and “non-carbonaceous” (NC) materials. We show that the fraction of CC material recorded in the isotopic composition of the BSE varies for different elements, and depends on the element’s tendency to partition into metal and its volatility. The observed behavior indicates that the majority of material accreted to the Earth was NC-dominated, but that CC-dominated material enriched in moderately volatile elements by a factor of ∼10 was delivered during the last ∼2–10% of Earth’s accretion. The late delivery of CC material to Earth contrasts with dynamical evidence for the early implantation of CC objects into the inner solar system during the growth and migration of the giant planets. This, together with the NC-dominated nature of both Earth’s late veneer and bulk Mars, suggests that material scattered inwards had the bulk of its mass concentrated in a few, large CC embryos rather than in smaller planetesimals. We propose that Earth accreted a few of these CC embryos while Mars did not, and that at least one of the CC embryos impacted Earth relatively late (when accretion was 90–98% complete). This scenario is consistent with the subsequent Moon-forming impact of a large NC body, as long as this impact did not re-homogenize the entire Earth’s mantle.

^1,2Yuki Masuda, ²Martin Schiller, ²Martin Bizzarro, ¹Tetsuya Yokoyama
Geochimica et Cosmochimica Acta (in Press) Open Access Link to Article [https://doi.org/10.1016/j.gca.2024.11.010]
¹Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Meguro, Tokyo 152-8551, Japan
² Centre for Star and Planet Formation, Globe Institute, University of Copenhagen, DK-1350 Copenhagen, Denmark
Copyright Elsevier

Calcium-aluminum rich inclusions (CAIs) are the oldest condensates in the Solar System. Previous studies have revealed that moderately heavy and trace element isotope anomalies (e.g., Ti, Sr, Mo, and Nd) in CAIs record large nucleosynthetic isotope variations compared to bulk meteorites. Calcium is a major element in CAIs that has six stable isotopes with multiple nucleosynthetic origins. As such, Ca isotopes in CAIs have been an important target of isotopic analysis since the 1970s. However, the Ca isotope compositions of CAIs measured by previous-generation mass spectrometers are less precise than recent isotopic data of heavy elements, which complicates their direct comparisons. Obtaining high-precision Ca isotopic data provides a stronger link between CAI-formation processes from nebular gas and the origin of their source materials.
In this study, we report high-precision Ca isotopic compositions of CAIs, amoeboid olivine aggregates, and an Al-rich chondrule from Vigarano-type carbonaceous chondrites. The obtained µ43Ca and µ48Ca values range from +5.8 ± 1.4 to +40.2 ± 5.2 and +181.2 ± 44.8 to +743.1 ± 8.3 ppm, respectively (µXCa represents the mass bias corrected relative deviation in the XCa/44Ca ratio of the sample from a standard material in parts per million). The improved precision of our measurements reveals that the Ca isotopic compositions of CAIs vary over a narrower range than previously thought. Our precise data also show that µ43Ca and µ48Ca values in CAIs are anti-correlated, which cannot be explained by analytical artifacts such as matrix effects. Additionally, the µ43Ca and µ48Ca values of CAIs increase and decrease, respectively, with increasing Ca abundances of the inclusions. These observations suggest the presence of two distinct gaseous reservoirs from which CAIs condensed, one of which was more enriched in 43Ca but depleted in 48Ca, while the other reservoir was more depleted in 43Ca but enriched in 48Ca. Given the distinct nucleosynthetic sources of 43Ca and 48Ca, this change in isotopic signature is best understood if the two reservoirs inherited material derived from distinct nucleosynthetic sites. As such, our results suggest the presence of more than two compositionally distinct gas reservoirs for Ca isotopes in the early Solar System. If correct, this suggests that the infalling material contributing to the CAI-forming reservoirs was not fully mixed.

^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.