^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

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

^1,2S. Iannini Lelarge, ^1,3M. Masotta, ^1,3L. Folco, ⁴T. Ubide, ^1,5M.D. Suttle, ^6,7L. Pittarello
Geochemistry (Chemie der Erde)(in Press) Link to Article [https://doi.org/10.1016/j.chemer.2025.126293]
¹Dipartimento di Scienze della Terra, Università di Pisa, Via Santa Maria 53, 56126 Pisa, Italy
²Institute of Geosciences and Earth Resources, Consiglio Nazionale delle Ricerche, Via Moruzzi 1, 56124 Pisa, Italy
³CISUP, Centro per l’Integrazione della Strumentazione Università di Pisa, Lungarno Pacinotti 43, Pisa 56126, Italy
⁴School of Earth and Environmental Sciences, The University of Queensland, Brisbane 4102, QLD, Australia
⁵School of Physical Sciences, The Open University, Walton Hall, Milton Keynes MK7 6AA, UK
⁶Naturhistorisches Museum, Mineralogisch-Petrographische Abteilung, Burgring 7, 1010 Vienna, Austria
⁷Department of Lithospheric Research, University of Vienna, Josef-Holaubek-Platz 2,1090 Vienna, Austria
Copyright Elsevier

We conducted high-pressure (1 GPa) melting experiments (1100–1400 °C) on the equilibrated ordinary chondrite DAV 01001 (L6) to investigate partial melting scenarios of planetary embryo in the early solar system. At 1100 °C, no melting of the silicate phase is observed, and the initial chondritic texture is preserved, but the metallic-sulphidic phases formed two immiscible Fesingle bondNi and S-rich liquids. Melting of silicate minerals began at 1200 °C, progressing from plagioclase to high-Ca and low-Ca pyroxene and olivine. As melting advanced, the formation of new olivine and low-Ca pyroxene resulted in the production of trachy-andesitic melt at 1200 °C, basaltic trachy-andesitic melt at 1300 °C, and andesitic melt at 1400 °C. These silicate melts have chemical similarities with some anomalous achondrites (e.g., GRA 60128/9). At the same time, minerals of new formation resemble those of primitive achondrites (e.g., brachinites, ureilites, IAB silicate inclusions, acapulcoites and lodranites). The rapid mineral-liquid re-equilibration suggests that basaltic liquids can form only above 1400 °C and that relatively high degrees of melting (>20 %) and crystallisation are necessary to explain the observed diversity of achondritic lithologies. These findings suggest that partial melting and recrystallization processes within planetary embryos could have played a critical role in the early solar system, contributing to the early differentiation of planetary bodies and the diversity of achondritic lithologies, including (but not limited to) alkali-rich achondrites.

¹Lee Saper,¹Yang Liu,²Michael A. Kipp,¹David Burney,³Chi Ma,²Francois L. H. Tissot,⁴Edward Young,³Jonathan Treffkorn,³Kenneth A. Farley
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.14345]
¹Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA
²The Isotoparium, Division of Geological & Planetary Sciences, California Institute of Technology, Pasadena, California, USA
³Division of Geological & Planetary Sciences, California Institute of Technology, Pasadena, California, USA
⁴Earth, Planetary, and Space Sciences, University of California, Los Angeles, Los Angeles, California, USA
Published by arrangement with John Wiley & Sons

Northwest Africa 13134 is a coarse-grained gabbro with an oxygen isotopic composition consistent with a Martian origin and is classified as an enriched shergottite based on its bulk trace element abundances and bulk La/Yb ratio of 1.53. The meteorite is composed of a framework of large pyroxene rods up to 6 mm in longest dimension (64% by area) with interstitial maskelynite (formerly plagioclase; 28% by area). Minor phases include merrillite and apatite, Fe-Ti oxides, and Fe-sulfides; trace phases such as baddeleyite, tranquillityite, fayalitic olivine, silica, and a felspathic phase are observed in evolved mesostasis pockets and partially crystallized magmatic inclusions in minerals. Individual pyroxene rods display a distinctive patchy Ca zoning pattern of juxtaposed low-Ca (pigeonite) and high-Ca (augite) patches with a common crystallographic orientation indicating epitaxial growth. Low-Ca pigeonite is the volumetrically dominant pyroxene phase (~70% of exposed pyroxene) and was the primary liquidus phase, followed closely by augite. Plagioclase crystallized along with the other minor phases from the residual melt between cumulus pyroxene rods. Pyroxenes display ubiquitous exsolution lamellae with typical widths and spacings of 1–2 μm. Sulfide grains are characterized by flame-shaped lamellar intergrowths of hexagonal pyrrhotite (Fe0.90S) and slightly metal-deficient pyrrhotite (Fe0.98S), along with minor pentlandite and chalcopyrite. The pyroxene and sulfide microtextures suggest that the gabbro experienced slow and protracted subsolidus cooling. Ilmenite-oxide pairs imply an oxygen fugacity of ~1 log unit below the fayalite–magnetite–quartz buffer at a closure T ≈ 875°C. Collectively, the texture and bulk composition suggest that Northwest Africa 13134 represents a slowly cooled and coarsely crystalline portion of a solidified magma body similar to the source of the enriched basaltic shergottites. Magnetite occurs locally as veins crosscutting pyrrhotite grains and in oxide–phosphate symplectites observed at merrillite–apatite phase boundaries. The presence of magnetite in the sample suggests that at various stages of cooling, the gabbro interacted with relatively oxidized fluids, which could be of deuteric or exogeneous origin. A cosmic-ray exposure age of 2.8–4.0 Ma was calculated based on 3He measured in pyroxene grain separates and overlaps with other shergottites. Finally, we present the first bulk uranium isotope measurement of a Martian meteorite: δ238U = −0.22 ± 0.10‰ and δ234Usec = +9.57 ± 0.35‰. These values indicate slight excesses in heavy U but overlap with the distribution of U isotope compositions of the Earth and other solar system materials.

¹Mireia Leon-Dasi, ²Sebastien Besse, ³Camille Cartier, ⁴Océane Barraud, ⁴Alessandro Maturilli, ¹Alain Doressoundiram, ⁵Johannes Benkhoff, ^3,6Laurie Llado
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2025.116582]
¹LESIA, Observatoire de Paris, Université PSL, CNRS, 5 Place Jules Janssen, Meudon, 92195, France
²European Space Agency (ESA), European Space Astronomy Centre (ESAC), Camino Bajo del Castillo s/n, Villanueva de la Canada, 28692, Spain
³Centre de Recherches Pétrographiques et Géochimiques, Université de Lorraine, 15 Rue Notre Dame des Pauvres, Vandœuvre-lès-Nancy, 54501, France
⁴German Aerospace Center DLR, Institute of Planetary Research, Rutherfordstr. 2, Berlin, 12489, Germany
⁵European Space Agency (ESA), European Space Research and Technology Centre (ESTEC), Keplerlaan 1, Noordwijk, 2200 AG, The Netherlands
⁶Department of Geology, University of Liège, 4000 Sart Tilman, Belgium
Copyright Elsevier

The temperature of Mercury varies greatly across different latitudes due to the planet’s spin/orbit resonance, leading to modifications in the surface spectral properties. The upcoming BepiColombo mission will map the surface of the planet in the UV-TIR range, providing a more comprehensive understanding of the surface alteration. However, comparing the spectral measurements between BepiColombo and the past MESSENGER mission could be challenging due to the large differences in observation geometry. Laboratory experiments with close surface analogs in viewing conditions similar to the space-based observations are necessary to understand the effect of the space environment and interpret the orbital spectral measurements. This study presents the UV-NIR spectroscopy of a Mercury simulant to understand the impact of observation geometry and temperature on the spectral properties of the planet’s surface. The simulant (a mixture of aubrites, albite, and synthetic sulfides) and its endmembers are measured under six geometries that sample the viewing conditions of both missions. The samples are measured fresh and after heating to 450 °C during three cycles. This study finds that the observation geometry modifies the reflectance spectrum of the samples differently depending on the wavelength and composition. The analog presents a darkening, reddening, and flattening with increasing phase angle in the UV-NIR domain. The heated samples present a brightening and reddening, with a deepening of absorption bands. The spectral changes associated with observation geometry and heating are stronger with increasing Mg abundance.