^1,2Liying Huang et al. (>10)
Journal of Geophysical Research (Planets) (in Press) Link to Article [https://doi.org/10.1029/2023JE007955]
¹State Key Laboratory of Space Weather, National Space Science Center, Chinese Academy of Sciences, Beijing, China
²College of Earth and Planetary Sciences, University of Chinese Academy of Sciences, Beijing, China
Published by arrangement wth John Wiley & Sons

Baddeleyite (ZrO2) is widespread in lunar basalts and frequently used for U-Pb geochronology of magmatic and impact events. The formation of baddeleyite involves two primary mechanisms: (a) crystallization from late-stage magma, and (b) decomposition of zircon under high-temperature (high-T) conditions. Baddeleyite with distinct formation mechanisms commonly displays different morphologies. In a Chang’e-5 lunar basalt, we report baddeleyite with two different morphologies, termed “singular type” and “aggregate type.” Petrographic and crystallographic analyses were conducted on both types of baddeleyite to understand their formation conditions and evolution processes. Despite the similarity in the morphology and mineral assemblages between the aggregate type baddeleyite and zircon decomposition products, the petrographic characteristics and the rarity of zircon in lunar basalts tend to suggest that both types of baddeleyite are derived from magma crystallization. Crystallographic relationships observed in both types indicate a phase transformation from the precursor tetragonal-ZrO2/cubic-ZrO2 or orthorhombic-ZrO2 phase. Two potential scenarios are proposed for the formation of these microstructures: (a) direct crystallization of high symmetry ZrO2 from magma, and (b) crystallization of baddeleyite from magma followed by a high-pressure (high-P) event causing its phase transition. However, due to unresolved scientific issues in both scenarios, an accurate evolutionary process cannot currently be determined. Therefore, extensive thermodynamic experiments are necessary to enhance our understanding of baddeleyite microstructures as indicators of P-T processes, providing insights into magmatism and the impact history of planetary bodies.

¹Toshihiro Tada,^2,3Kosuke Kurosawa,⁴Naotaka Tomioka,^5,6Takayoshi Nagaya,³Junko Isa,⁷Christopher Hamann,⁸Haruka Ono,⁹Takafumi Niihara,³Takaya Okamoto,^1,3Takafumi Matsui
Journal of Geophysical Research (Planets) (in Press) Open Access Link to Article [https://doi.org/10.1029/2024JE008409]
¹Institute for Geo-Cosmology, Chiba Institute of Technology, Chiba, Japan
²Department of Human Environmental Science, Graduate School of Human Development and Environment, Kobe University, Hyogo, Japan
³Planetary Exploration Research Center, Chiba Institute of Technology, Chiba, Japan
⁴Kochi Institute for Core Sample Research, X-star, Japan Agency for Marine-Earth Science and Technology, Kochi, Japan
⁵Department of Environmental Science, Tokyo Gakgei University, Tokyo, Japan
⁶Department of Earth and Planetary Science, The University of Tokyo, Tokyo, Japan
⁷Museum für Naturkunde, Leibniz-Institut für Evolutions- und Biodiversitätsforschung, Berlin, Germany
⁸Research Organization of Science and Technology, Ritsumeikan University, Kyoto, Japan
⁹Department of Applied Science, Okayama University of Science, Okayama, Japan
Published by arrangement with John Wiley & Sons

Feather features (FFs) in quartz consist of a planar fracture (PF) and associated fine lamellae (FF lamellae; FFL) and have been observed in various natural impact structures. However, the mechanisms and conditions of FF formation are poorly understood. We conducted shock recovery experiments on granite using decaying compressive pulses to investigate the formation conditions of FFs. We characterized the recovered samples using an optical microscope equipped with a universal stage, a scanning electron microscope combined with an electron back-scattered diffraction detector, and a transmission electron microscope. We found that FFs are formed over a wide range of peak pressures (2–18 GPa) and that FFs can be divided into at least three types (I–III) based on the crystallographic orientation of the PFs and FFL, the angle between the orientation of the FFL and the propagation direction of the compression wave, and the presence/absence of amorphous silica in the FFL. The peak pressures that produce type I–III FFs are estimated to be <12, 12–14, and >16 GPa, respectively. We propose that FFs can be used as a shock barometer for quartz-bearing rocks.

¹Ninna K. Jensen, ²Alexander A. Nemchin, ³Gavin Kenny, ³Martin J. Whitehouse, ¹James N. Connelly, ⁴Takashi Mikouchi, ¹Martin Bizzarro
Geochimica et Cosmochimica Acta (in Press) Open Access Link to Article [https://doi.org/10.1016/j.gca.2024.11.014]
¹Centre for Star and Planet Formation, Globe Institute, University of Copenhagen, 1350 Copenhagen, Denmark
²School of Earth and Planetary Sciences (EPS), Curtin University, GPO Box U1987, Perth, WA 6845, Australia
³Swedish Museum of Natural History, SE-104 Stockholm, Sweden
⁴The University Museum, The University of Tokyo, 118-0033 Tokyo, Japan
Copyright Elsevier

Impact events were frequent in the early history of our Solar System, and the dynamics of planetary crust formation were, consequently, substantially different from the processes that dominate today. Mars, a planet with stagnant lid tectonics and a unique preservation of ancient surface terrains, provides an outstanding opportunity to investigate the early processes related to the formation and reshaping of the first crust. Northwest Africa (NWA) 7034 and paired meteorites (such as NWA 7533) are fragments of polymict, regolith breccia that provide a tangible record of the ancient, brecciated crust on Mars. Zircon and baddeleyite from NWA 7034/7533 record evidence for two events of intense crustal reworking at 4442 ± 17 and 4474 ± 10 million years ago (Ma) triggered by impacts, placing important constraints on the timing and the dynamics of early crust formation on Mars. To date, only few studies have focussed on the geochronology of the igneous clasts present within NWA 7034 and its pairs. Although these studies consistently report ancient ages (∼4.4 Ga) for basaltic, basaltic andesitic and monzonitic clasts, the associated precisions are generally too low to link the different lithologies with the two age peaks inferred from NWA 7034/7533 zircon and baddeleyite. Here, we conduct an isotopic and petrographic study of igneous clasts from NWA 7533 to shed further light on the timing and nature of crustal reworking in the early history of Mars. We show that six out of seven investigated igneous clasts, representing at least four distinct types, record undisturbed Lu-Hf isotope systematics that indicate contemporaneous formation. Together with two zircons hosted in basalt and basaltic andesite clasts, these igneous clasts yield an isochron age of 4440 ± 41 Ma (2SE, MSWD = 2.1). This isochron age is consistent with clast ages inferred from zircon U-Pb geochronology, and altogether the available age constraints for the lithic components in NWA 7533 indicate that they derive from the younger of the two peaks of intense crustal reworking on early Mars (4442 ± 17 Ma). The initial εHf values (the 176Hf/177Hf ratio in the sample normalised to that of the chondritic uniform reservoir at the time of crystallisation in parts per ten thousand) of the igneous clasts range between −2.07 and −0.74, consistent with crystallisation from enriched source melts deriving from impact-induced reworking of the crust. The mean Lu-Hf isotope composition of the igneous clasts constrains the timing of primordial crust formation and reveal planet formation and differentiation within the first 10 Myr of the history of the Solar System, in consistence with the conclusions in earlier reports. The results presented here suggest a 176Lu/177Hf ratio of ∼ 0.0135 or higher in the primordial martian crust.

^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.