¹Robert W. Nicklas,¹Melody Z.-A. Chen,¹Evan J. Saltman,¹Ethan F. Baxter,¹Andrew J. Lonero,¹Anthony B. Love
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.14356]
¹Department of Earth and Environmental Sciences, Boston College, Chestnut Hill, Massachusetts, USA
Published by arrangement with John Wiley & Sons

Brachinites, brachinite-like achondrites (BLA), and other similar primitive achondrites offer important constraints on differentiation processes of the earliest formed planetesimals, as they quenched amidst early differentiation processes on their parent body. Geochemical data for all major mineral phases in two previously poorly characterized meteorites, El Medano (EM) 395 and Northwest Africa (NWA) 12532, show that while EM 395 is a typical brachinite, NWA 12532 is more unusual, containing a high abundance of non-equilibrated apatite (1.26%) likely formed by a late-stage metasomatic event. These new data demonstrate that metasomatism by a P-Cl-Ca-rich fluid probably occurred on the brachinite parent body. This metasomatism may have occurred either during normal cooling of the asteroid or during later impact-related heating, consistent with the late formation of apatite in the paired andesitic achondrites Graves Nunatak (GRA) 06128 and 06129. These conclusions highlight that, while magmatism on small parent bodies ceased shortly after solar system formation, subsolidus processes may have continued much longer, and that metasomatism must be considered when interpreting bulk rock geochemical signatures of primitive achondrites.

¹Mohammad Tauseef,¹Ingo Leya,²Jérôme Gattacceca,³Sönke Szidat,²Régis Braucher,⁴Pascal M. Kruttasch,⁴Anna Zappatini,²ASTER Team
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.14355]
¹Physics Institute, Space Research and Planetology, University of Bern, Bern, Switzerland
²CNRS, Aix Marseille Université, IRD, INRAE, CEREGE, Aix-en-Provence, France
³Department of Chemistry, Biochemistry and Pharmaceutical Sciences & Oeschger Center for Climate Change
Research, University of Bern, Bern, Switzerland
⁴Institute of Geological Sciences, University of Bern, Bern, Switzerland
Published by arrangment with John Wiley & Sons

This study presents a refined approach to determine 14C saturation activities and 14C/10Be saturation activity ratios in chondritic meteorites with the goal to improve terrestrial age dating. By combining new model calculations for 10Be, 14C, and cosmogenic (22Ne/21Ne)cos, along with experimental data from 17 freshly fallen chondrites, we established reliable correlations for 14C production rates and 14C/10Be production rate ratios as a function of (22Ne/21Ne)cos. The experimental data agree with the model calculations, and they fully confirm that 14C production rates and 14C/10Be production rate ratios depend on shielding. Constrained correlations describe the experimental data for all shielding conditions and all ordinary chondrites mostly within the uncertainties given by the model. The new correlations therefore provide a significant improvement compared to the earlier approaches, in which average meteorite-type-dependent 14C production rates and average 14C/10Be production rate ratios were assumed. Ignoring the shielding dependence introduces a size-dependent bias into the terrestrial age database. This study enables the determination of shielding-corrected 14C saturation activities and 14C/10Be production rate ratios to calculate shielding-corrected terrestrial ages for meteorites reducing or eliminating a size bias in the database. In addition, this novel approach enables to give reliable uncertainty estimates of within 15% for the 14C and 14C-10Be terrestrial ages.

^1,2A. L. Knight,^1,2S. J. VanBommel,³R. Gellert,⁴J. A. Berger,^1,2J. G. Catalano,^5,6J. Gross,^1,2J. R. Christian
Journal of Geophysical Research (Planets) (in Press) Link to Article [https://doi.org/10.1029/2024JE008569]
¹Department of Earth, Environmental, and Planetary Sciences, Washington University in St. Louis, St. Louis, MO, USA
²McDonnell Center for the Space Sciences, Washington University in St. Louis, St. Louis, MO, USA
³Department of Physics, University of Guelph, Guelph, ON, Canada
⁴Jacobs JETSII at NASA Johnson Space Center, Houston, TX, USA
⁵NASA Johnson Space Center, Houston, TX, USA
⁶Department of Earth and Planetary Sciences, Rutgers University, Piscataway, NJ, USA
Published by arrangement with John Wiley & Sons

The Mars Exploration Rovers (MER) Spirit and Opportunity, sent to Gusev crater and Meridiani Planum, respectively, determined the chemical composition of martian materials with their Alpha Particle X-ray Spectrometers (APXS). The MER APXS was effective at routinely quantifying major, minor, and select (Ni, Zn, Br) trace elements at levels down to ∼50 ppm but often reached detection limits for other trace elements (e.g., Ga and Ge during typical individual analyses of a single sample). To enable precise quantification of additional trace elements, a database of MER APXS target properties (e.g., location, feature, target, formation, target type, sample preparation) was created, enabling the construction of a library of composite (i.e., summed) spectra with improved statistics. Composite spectra generated from individual spectra with shared characteristics have a higher potential for resolving and thus quantifying trace element peaks. Analyses of composite spectra from Meridiani Planum and Gusev crater indicate that the molar Ga to Al ratio is relatively constant throughout both regions and is in line with predicted values for the martian crust and measured values in martian meteorites. Gallium and aluminum likely do not volatilize and instead remain together during volcanism and aqueous alteration. In contrast, Ge is enriched at least an order of magnitude relative to martian meteorites, and the molar Ge to Si ratio is much more variable across Meridiani Planum and Gusev crater. Enrichment of Ge may be a global phenomenon resulting from volcanic outgassing of volatiles and subsequent overprinting by local mobilization and enrichment via hydrothermal fluids.

^1,2K. Hirata,¹T. Usui,^3,4E. Caminiti,⁵J. Wright,⁶S. Besse
Journal of Geophysical Research (Planets)(in Press) Open Access Link to Article [https://doi.org/10.1029/2024JE008788]
¹Institute of Space and Astronautical Science (ISAS), Japan Aerospace Exploration Agency (JAXA), Sagamihara, Japan
²Department of Earth and Planetary Science, The University of Tokyo, Tokyo, Japan
³LIRA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Université de Paris, Meudon, France
⁴Université Grenoble Alpes, CNRS, Institut de Planétologie et d’Astrophysique de Grenoble (IPAG), Saint-Martin-d’Hères, France
⁵School of Physical Sciences, The Open University Walton Hall, Milton Keynes, UK
⁶European Space Astronomy Centre (ESAC), European Space Agency (ESA), Madrid, Spain
Published by arrangement with John Wiley & Sons

The observed geochemical heterogeneity on the surface of Mercury is key to understanding the planet’s volcanic activity and mantle conditions. The Caloris basin shows a diversity in elemental composition, spectral properties, and geomorphology, both within and around it. However, the relationship among these characteristics has not been well understood due to the mismatch in spatial resolutions of the available observation data. This study investigates the geochemical end-members around the Caloris basin, overcoming the limitation of the low spatial resolution of MESSENGER’s X-Ray Spectrometer (XRS) data. End-member units are defined using spectral and geomorphological units from MESSENGER’s VIS-NIR spectral data and high-resolution images, with the assumption of homogeneous elemental compositions within each unit. A mixing model is constructed to reproduce the XRS data by mixing the end-members, and we solve the inverse problem to calculate the respective end-member compositions. Five end-member compositions were determined, including those corresponding to the post-Caloris volcanic smooth plains interior and exterior to the basin and surrounding pre-Caloris crust. Two smooth plains units, which are geomorphologically indistinguishable but spectrally distinct, showed a compositional variation consistent with magma evolution through fractional crystallization. This suggests that they originated from parent magmas with a common composition. The pre-Caloris crust units showed a large compositional variation, ranging from low- to high-Mg content, implying the potential existence of high-Mg crusts comparable to the HMR. The observed crustal diversity could be explained by relatively minor heterogeneity in source mantle compositions and/or conditions of partial melting within the mantle.

^1,2Ronghua Pang,^1,3Zhuang Guo,¹Chen Li,^1,4Sizhe Zhao,^1,5Xiongyao Li,¹Yuanyun Wen,⁶Shuangyu Wang,¹Rui Li,^1,5Yang Li
Journal of Geophysical Research (Planets)(in Press) Link to Article [https://doi.org/10.1029/2024JE008611]
¹Center for Lunar and Planetary Sciences, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang, China
²University of Chinese Academy of Sciences, Beijing, China
³Department of Geology, NWU-HKU Joint Center of Earth and Planetary Sciences, Northwest University, Xi’an, China
⁴State Key Laboratory of Lunar and Planetary Sciences, Macau University of Science and Technology, Macau, China
⁵Center for Excellence in Comparative Planetology, Chinese Academy of Sciences, Hefei, China
⁶Laboratory for Space Environment and Physical Sciences, Harbin Institute of Technology, Harbin, China
Published by arrangement with John Wiley & Sons

Due to the lack of an atmosphere and a global magnetic field on the Moon, its surface is extensively subject to space weathering. One of the important products of space weathering is the iron particle, which has significant impacts for planetary exploration. Research on Apollo samples suggests that iron particles primarily form through vapor deposition processes during meteorite impacts. The Chang’e-5 (CE5) samples are the youngest samples collected so far, and the phenomenon of surface vapor deposition has not been studied in depth. Anorthite stoichiometrically free of Fe minerals, is highly suitable for studying the vapor deposition process of iron particles. Five anorthite grains from CE5 were analyzed using transmission electron microscope (TEM). Results show that the iron particle on the surface of anorthite formed from impact sputtering glass, and lack vapor-deposited nanophase iron particles (np-Fe0, <100 nm) on its surface. Additionally, residual Fe from Fe-Mg silicate impactors on the anorthite surface did not form np-Fe0. The dominant mechanism of np-Fe0 formation due to space weathering differs between the CE5 and Apollo landing sites. Impact melting rather than vapor deposition may be the dominant mechanism of np-Fe0 formation at the CE5 landing site due to impact. This indicates that the meteorite impact environment of CE5 landing site is weak. It is not possible to generate a large amount of vapor deposition-derived np-Fe0 like in Apollo samples.

¹Baoliang Wang, ¹Frédéric Moynier, ²Yan Hu
Geochimica et Cosmochimica Acta (in Press) Open Access Link to Article [https://doi.org/10.1016/j.gca.2025.04.007]
¹Université Paris Cité, Institut de Physique du Globe de Paris, CNRS, 1 Rue Jussieu, 75005 Paris, France
²Department of Geoscience, University of Nevada, Las Vegas, Las Vegas, NV 89154, USA
Copyright Elsevier

Enstatite meteorites, including enstatite chondrites and enstatite achondrites (e.g., aubrites), formed under highly reducing conditions in the solar system. Enstatite chondrites underwent progressive thermal metamorphism from petrologic type 3 to type 6, potentially leading to vaporization and redistribution of volatile elements. Coupled Rb and K isotopic analyses of enstatite meteorites could provide complementary insights into the inherent isotopic variability and volatile depletion processes. In this study, we present Rb and K isotopic compositions for a suite of enstatite meteorites, including sixteen enstatite chondrites spanning metamorphic grades from 3 to 6, as well as four aubrites. Type 3 enstatite chondrites exhibit isotopic compositions similar to those of Earth for both Rb and K, which further underscores the isotopic resemblance between Earth and enstatite chondrites. From type 3–4 to type 5–6, the examined enstatite chondrites generally show a trend towards heavier Rb and K isotopic compositions, indicating volatilization and redistribution of Rb and K during open system thermal metamorphism of the parent body(ies). One EH5 (St. Marks) and two EL6 (Pillistfer and Atlanta) samples deviate from this trend with light K isotope compositions, which may result from an interplay of evaporation, vapor transport and recondensation. On the other hand, the Rb and K isotopic variations in aubrites—which originated from the melting and fractional crystallization of enstatite chondrite-like parent body(ies)—likely reflect more complex processes, possibly involving a combination of plagioclase-bearing melt extraction, magmatic differentiation, core segregation, and the back-condensation of volatiles after impact volatilization.

¹William S. Cassata
Earth and Planetary Science Letters 660, 119307 Link to Article [https://doi.org/10.1016/j.epsl.2025.119307]
¹Berkeley Geochronology Center, 2455 Ridge Road, Berkeley, CA 94709, USA
Copyright Elsevier

The origins of Earth’s volatiles, including water, remain uncertain. Noble gases can be used to constrain volatile sources as they exhibit significant chemical and isotopic variations amongst Solar System materials that Earth may have accreted. Here, I refine the isotopic composition of cometary xenon (Xe) measured during the Rosetta mission by optimizing its fit to isotopically similar presolar grains in meteorites. Using this composition, I show that Earth’s atmosphere can be explained as a mixture of 83.6 ± 3.2% meteoritic, 15.3 ± 2.8% cometary, and 1.1 ± 0.7% fission Xe (1σ; percentages are with respect to 132Xe). This same approach applied to Kr indicates Earth’s atmosphere is 72.1 ± 9.5% meteoritic and 27.9 ± 9.5% cometary Kr (1σ; percentages are with respect to 84Kr). Carbonaceous chondrites are likely the predominant source of meteoritic Xe. A carbonaceous chondrite accretion mass of 1.8– 5.2 wt.-% of Earth at the 95% confidence interval explains the relative abundances of meteoritic and fission Xe in Earth’s atmosphere. Such accretion may have delivered up to 6 – 18 oceans of water to Earth. Conversely, a cometary ice accretion mass of less than 5 × 10–5 wt.-% of Earth explains the relative abundance of cometary Xe. This would have delivered less than 0.2% of Earth’s water. The data further imply a more linear temporal variation in the mass dependent fractionation of atmospheric Xe throughout the first two billion years of Earth history than previously thought.

^1,2Lixin Gu, ^1,3Yangting Lin, ⁴Yongjin Chen, ⁵Yuchen Xu,^1,2Xu Tang, ^1,3Jinhua Li
Geochimica et Cosmochimica Acta (in Press) Open Access Link to Article [https://doi.org/10.1016/j.gca.2025.04.004]
¹Key Laboratory of Earth and Planetary Physics, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China
²Institutional Center for Shared Technologies and Facilities, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China
³College of Earth and Planetary Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
⁴Center for High Pressure Science and Technology Advanced Research, Beijing 100094, China
⁵State Key Laboratory of Space Weather, National Space Science Center, Chinese Academy of Sciences, Beijing 100190, China
Copyright Elsevier

Hyper-velocity impacts are dominant agents in the physical and chemical alteration of lunar surface materials. Natural small-scale craters on lunar soils provide an opportunity to understand the impact process and specific space weathering effects on minerals, however, they have not been systematically studied. Here, we report the morphology and microstructure of submicron-scale craters on Chang’e-5 lunar soils. Craters are found only on a few soil grains. Most identified craters exhibit large diameter-to-depth (D/d) ratios (>3) or are spatially clustered, indicating that they are formed by secondary ejecta rather than primary micrometeoroid impacts. Advanced electron microscopy investigations revealed that the microstructures of these craters are complex. Craters on the surfaces of two pyroxenes and one olivine have continuous nanophase iron (npFe0)-bearing rims that extend over the crater and beyond over the crystal substrate, even when covered by an impact-produced redeposition layer. These features provide reliable evidence of solar wind exposure prior to the impact events that formed the craters. The possibility cannot be ruled out that the npFe0 particles present in these craters were previously produced by solar wind irradiation and not by impact. However, no clear signs are observed to establish the chronological order of formation of npFe0 particles in other craters studied. Furthermore, a crater on ilmenite has a minimum D/d value of 2.6, suggesting that this crater is likely formed by a primary micrometeoroid impact. Some unusual euhedral and elongated npFe0 particles observed on the crater floor may also have been produced earlier by solar wind irradiation and retained in the crater during subsequent impact. Shock melting and vapor deposition may also contribute to npFe0 formation by reduction during impact. Our findings imply that secondary impacts can also have a high velocity (1–2.38 km/s lunar escape velocity) and play a more crucial role in the microstructural and chemical changes of lunar soils than previously recognized. Moreover, the formation of npFe0 particles in submicron-scale craters may involve multiple processes, such as solar wind irradiation, shock melting, and vapor deposition, and their effects can be superimposed. These new formation processes of npFe0 particles are universal and fundamental to the evolution of materials on the Moon and other airless planetary bodies.

¹E.S. Kite et al. (>10)
Earth and Planetary Science Letters 660, 119347 Open Access Link to Article [https://doi.org/10.1016/j.epsl.2025.119347]
¹University of Chicago, Chicago, IL, USA
Copyright Elsevier

Early Mars was habitable, at least intermittently, but major questions remain about how much water flowed and for how long. The paleoclimate evolution of Mars is captured by the stratigraphic record in Gale crater (Milliken et al. 2010). Climbing through mostly aeolian deposits reflecting arid conditions within Gale crater, the Mars Science Laboratory Curiosity rover encountered wave-rippled lake sediments of the basin-spanning Amapari Marker Band (AMB) that have very high metal enrichments (Fe, Mn, Zn). What caused the association between relatively wet primary depositional environment, and metal enrichment? Tentative, but reasonable extrapolation of rover metal data across the AMB suggests an excess Fe mass of 0.2 Gt. Transporting this Fe likely required ∼10,000 km³ of water flow, much more than the volume of the lake, across >10³ yr. Deposition of the Fe could be due to a redox or pH front within or just beneath the lake. One possible basin-scale synthesis involves a climate excursion consisting of initial cooling then subsequent warming: initial cooling permits wind scour in Gale basin and ice build-up on Gale’s rim, while subsequent melting fills the lake and mobilizes Fe. Alternatively, the data can be explained by water-table fluctuations. In either case, the metal enrichment likely contributed to the hardness of these rocks, aiding wave-ripple preservation.

¹Simon Turner,²Bernard Wood,³Tim Johnson,⁴Craig O’Neill,⁵Bernard Bourdon
Nature 640, 390–394 Link to Article [DOI https://doi.org/10.1038/s41586-025-08719-3]
¹School of Natural Sciences, Macquarie University, Sydney, New South Wales, Australia
²Department of Earth Sciences, University of Oxford, Oxford, UK
³School of Earth and Planetary Sciences, Curtin University, Perth, Western Australia, Australia
⁴School of Earth and Atmospheric Sciences, Queensland University of Technology, Brisbane, Queensland, Australia
⁵Laboratoire de Géologie de Lyon Terre Planète Environnement, ENS Lyon, CNRS and Université Lyon I, Lyon, France

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