¹Robin L. Haller,¹Martin R. Lee,²Mark E. Hodson
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.70145]
¹School of Geographical and Earth Sciences, University of Glasgow, Glasgow, UK
²Department of Environment and Geography, University of York, York, UK
Published by arrangement with John Wiley & Sons

Terrestrial weathering alters the chemical and isotopic composition, and mineralogy, of meteorites; its effects on ordinary chondrites are well-studied, but relatively little is known about the susceptibility of carbonaceous chondrites. We combined laboratory experiments, whereby Chwichiya 002 (C3-ung find), Murchison (CM2 fall) and Kolang (CM1/2 fall) were exposed to artificial rainwater for 30–180 days, with kinetic models to examine the effects of different weathering timespans and environments on mineralogy and petrologic (sub)type. Leachates derived from the Murchison and Kolang experiments were rich in S, Ca, Na, Cl, K, and Mg with less abundant Si and Fe. These results suggest that calcite and pyrrhotite, together with unknown Na-K-Cl bearing minerals, are particularly susceptible to terrestrial alteration. Chwichiya 002 was less reactive than anticipated, possibly due to earlier hot desert weathering. Models predict that primitive chondrites with amorphous material, including Chwichiya 002, oxidize within days when exposed to water, particularly in warm environments (e.g., hot deserts). Terrestrial weathering is expected to rapidly lower the petrologic (sub)type of CM3 chondrites, whereas CM2s react more slowly and their petrologic (sub)type does not change significantly.

^1,2,5Gabriel A. Pinto, ¹Vinciane Debaille, ²Jolantha Eschrig, ³Alexandre Corgne, ⁴Kevin Soto, ⁵Thierry Leduc, ⁵Sophie Decree, ²Steven Goderis
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2026.117102]
¹Laboratoire G-Time & Brussels Laboratory of the Universe (BLU), Université Libre de Bruxelles, 1050 Brussels, Belgium
²Archaeology, Environmental Changes, and Geo-Chemistry, Vrije Universiteit Brussel, 1050 Brussels, Belgium
³Instituto de Ciencias de la Tierra, Universidad Austral de Chile, Valdivia, Chile
⁴Departamento de Ciencias Geológicas, Universidad Católica del Norte, Antofagasta, Chile
⁵Institute of Natural Sciences, Geological Survey of Belgium, 1000 Brussels, Belgium
Copyright Elsevier

Evaporites are frequently reported in carbonaceous chondrites from hot and cold deserts, yet their origin remains debated between formation on the parent body or by post-fall terrestrial alteration. Here, we present a systematic characterization of Ca sulfate and Ca carbonate assemblages in four CO carbonaceous chondrites from different dense collection areas of the Atacama Desert (Los Vientos 123, El Médano 464, Calama 031, Paposo 088). We combine backscattered electron imaging, EDS, X-ray compositional mapping, Raman spectroscopy, and modal point counting to assess the distribution, mineralogy, and formation context of evaporites. Evaporites occur mainly as pore- and vein-filling phases and as replacements of Fe sulfides. Los Vientos 123 and El Médano 464 contain high abundances of Ca sulfates (~2.5 ± 0.35 vol%), Calama 031 is dominated by Ca carbonate veins (1.4 ± 0.26 vol%) with minor Ca sulfate, and Paposo 088 shows only low Ca sulfates contents (0.47 ± 0.15 vol%). These phases are systematically associated with Fe oxyhydroxides, jarosite-like phases, and strongly altered sulfides. The sulfate- and carbonate-rich assemblages in CO chondrites correlate with local soil geochemistry and microclimates. Limestone bedrock and more rain-influenced inland set different evaporite assemblages compared to coastal areas characterized by marine aerosols and salt-rich soils. Raman spectra indicate that the dominant Ca sulfate polymorph is anhydrite, lacking OH-stretching bands, consistent with precipitation from low-water activity, chloride-nitrate-rich brines and limited subsequent hydration. Disordered carbonaceous matter locally sheltered within sulfate-rich areas suggests that secondary evaporites can trap and preserve organic material, even if non-biological. Our results thus support (i) a terrestrial origin for Ca sulfates and Ca carbonates in Atacama CO chondrites; (ii) the stability of anhydrite as an indicator of extremely low water activity; and (iii) process analogues for evaporite formation in Martian settings, where anhydrite regions may be key targets to reconstruct aqueous conditions and assess organic preservation on Mars.

¹Alvaro Penteado Crósta,²Neivaldo Araújo de Castro,³Marcos Alberto Rodrigues Vasconcelos,⁴Airton Natanael Coelho Dias,^5,6Ludovic Ferrière,⁷Wolf Uwe Reimold,⁸Ana Maria Góes,⁹Jackson Alves Martins,²Liliana Sayuri Osako,⁹Raimundo Mariano Gomes Castelo Branco
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.70144]
¹Institute of Geosciences, Universidade Estadual de Campinas, Campinas, Brazil
²Geology Department, Federal University of Santa Catarina-UFSC, Florianopolis, Brazil
³Institute of Geosciences, Federal University of Bahia, Salvador, Brazil
⁴Physics, Chemistry and Mathematics Department, Federal University of Sao Carlos, Sorocaba, Brazil
⁵Natural History Museum Abu Dhabi, Abu Dhabi, United Arab Emirates
⁶Department of Lithospheric Research, University of Vienna, Vienna, Austria
⁷Instituto de Geociencias, Universidade de Brasilia, Brasilia, Brazil
⁸Institute of Geosciences, University of Sao Paulo, Sao Paulo, Brazil
⁹Geophysics Laboratory, Centro de Ciencias, Federal University of Ceara, Fortaleza, Brazil
Published by arrangement with John Wiley & Sons

The São Miguel do Tapuio structure (SMT) is a remarkable, nearcircular feature of about 21 km diameter, centered at 5°37.6′ S, 41°23.3′ W in Piauí state, northeastern Brazil. The structure is located within the sedimentary strata of the Paleozoic–Mesozoic Parnaíba Basin and predominantly comprises sandstones of the Devonian Pimenteiras and Cabeças formations. SMT exhibits a rugged morphology, in contrast to the smoother surrounding terrain. An impact origin has been suggested for SMT since the 1980s based on indirect aspects, such as the structure’s morphology with an annular outer rim, inner rings, and an elevated central area. Some of the sandstones found in the inner region were structurally deformed and recrystallized, in contrast to the undeformed equivalent strata outside the structure. A field survey conducted in 2017 yielded a few samples of sandstone and monomict sandstone breccia from near the center of the structure. Here we report the discovery of multiple shocked quartz grains with planar fractures (PFs), feather features (FFs), and planar deformation features (PDFs) in four thin sections of two samples from this central area. Universal stage measurements on all shocked quartz grains (25 grains in total; 16 with PFs, five with PDFs, and four with both PFs and PDFs) confirm that these planar microstructures occur in distinct crystallographic orientations that are indicative of shock pressures up to 20 GPa. Our investigations, thus, have confirmed the impact origin of the SMT. It represents the ninth confirmed impact structure in Brazil and, at 21 km diameter, is the second largest of its kind in South America.

¹S.P. Goudy, ¹M. Telus, ²K. Nagashima, ²G.R. Huss
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2026.04.014]
¹Earth and Planetary Sciences, University of California at Santa Cruz, 1156 High Street, Room A232, Santa Cruz, CA 95064, United States
²Hawaii Institute of Geophysics and Planetology, University of Hawai’i at Mānoa, 1680 East-West Road, POST Building, Office 602, Honolulu, HI 96822, United States
Copyright Elsevier

Here we present petrographic, O isotope, and C isotope data on calcite and petrographic and O isotope data on magnetite in Aguas Zarcas (CM2) and Miller Range (MIL) 13005 (CM1/2) in an effort to test CM aqueous alteration models. Our O and C isotope data for Aguas Zarcas and MIL 13005 are within the ranges reported in previous work for calcite in CMs. Using O isotope data from Δ17O-matched calcite and magnetite grains in our samples, we calculated equilibrium-model formation temperatures for the analyzed calcites in each meteorite. Combining our isotopic and temperature data with literature data, we sort the data into less altered (CM2) and more altered (CM1/2 and CM1) categories, and examine that data for differences between the categories by analyzing the δ18O-δ17O, δ18O-δ13C, and model formation temperature data of the categories. We find potential differing cluster patterns between δ18O and δ13C in calcites between our two CM alteration categories, and find that sparse extant temperature data imply that more altered CMs (types 1 and 1/2) may have undergone alteration at a lower average temperature than CM2s. We also find that the O isotopic compositions between CM1s, CM2s, and CM1/2s do not differ significantly. Through use of a novel mass-balance model, we infer a pre-alteration ice Δ17O within the range of 5.3–13.3‰. We find two generations of calcite formation in MIL 13005 with different proportions of their O being sourced from ices and anhydrous silicates, and one generation of calcites within Aguas Zarcas. We created concentration mixing models through an original machine-learning-based analytical approach, which show that the calcite data can be readily explained using three optimally determined C- and O-bearing sources.

¹Richard J. Anslow,²Maylis Landeau,¹Amy Bonsor,^1,3Jonathan Itcovitz,^1,4Oliver Shorttle
Journal of Geophysical Research: Planets (in Press) Open Access Link to Article [https://doi.org/10.1029/2025JE009328]
¹Institute of Astronomy, University of Cambridge, Cambridge, UK
²Université de Paris, Institut de Physique du Globe deParis, CNRS, Paris, France
³Department of Civil and Environmental Engineering, Imperial College London, London, UK
⁴Department of Earth Sciences, University of Cambridge, Cambridge, UK
Published by arrangement with John Wiley & Sons

The excess abundance of highly siderophile elements (HSEs), as inferred for the terrestrial planets and the Moon, is thought to record a “late veneer” of impacts after the giant impact phase of planet formation. Estimates for total mass accretion during this period typically assume all HSEs delivered remain entrained in the mantle. Here, we present an analytical discussion of the fate of liquid metal diapirs in both a magma pond and a solid mantle, and show that metals from impactors larger than approximately 1 km will sink to Earth’s core, leaving no HSE signature in the mantle. However, by considering a collisional size distribution, we show that to deliver sufficient mass in small impactors to account for Earth’s HSEs, there will be an implausibly large mass delivered by larger bodies, the metallic fraction of which lost to Earth’s core. There is therefore a contradiction between observed concentrations of HSEs, the geodynamics of metal entrainment, and estimates of total mass accretion during the late veneer. To resolve this paradox, and avoid such a mass accretion catastrophe, our results suggest that large impactors must contribute to observed HSE signatures. For these HSEs to be entrained in the mantle, either some mechanism(s) must efficiently disrupt impactor core material into
0.01 mm fragments, or alternatively Earth accreted a significant mass fraction of oxidized (carbonaceous chondrite-like) material during the late veneer. Estimates of total mass accretion accordingly remain unconstrained, given uncertainty in both the efficiency of impactor core fragmentation, and the chemical composition of the late veneer.

¹Oleg S. Vereshchagin,¹Maya O. Khmelnitskaya,¹Natalia S. Vlasenko,¹Elena N. Perova,¹Mikhail N. Murashko,²Yevgeny Vapnik,¹Elena S. Sukharzhevskaya,³Albina G. Kopylova,^1,4Sergey N. Britvin
Journal of Geophysical Research: Planets (in Press) Link to Article [https://doi.org/10.1029/2025JE009396]
¹Saint Petersburg State University, University Embankment 7/9, St. Petersburg, Russian Federation
²Department ofGeological and Environmental Sciences, Ben‐Gurion University of the Negev, Beer‐Sheva, Israel
³Diamond and PreciousMetal Geology Institute, Siberian Branch, Russian Academy of Sciences, Yakutsk, Russia
⁴Nanomaterial Research Center,Kola Science Centre, Russian Academy of Sciences, Apatity, Russia
Published by arrangement with John Wiley & Sons

Iron is one of the most common elements on Earth and is present in the modern crust mainly in the form of (hydro)oxides and silicates, whereas terrestrial (telluric) native Fe is extremely rare. It is generally assumed that telluric Fe differs greatly in its chemical composition and mineralogy from the metal of iron meteorites, indicating different modes of formation. We uncover haxonite (NiFe22C6) and uakitite (VN) within telluric iron assemblages in terrestrial crustal rocks (volcanic rocks of the Norilsk ore region, Russia and metamorphic rocks of the Hatrurim Basin, Israel, respectively). Both minerals were previously discovered in iron meteorites and were thought to be absent in Earth’s crustal rocks. Consequently, we analyzed available data on terrestrial rocks containing native iron and iron meteorites and compared their oxygen-free mineral assemblages. The resemblance in mineralogy suggests that at least some metal-rich asteroids may have formed in a manner similar to telluric iron. We suggest that heating at low pressures (T ≈ 1000°C, P < 10 MPa) of the primary Fe-bearing silicates in the presence of organic matter led to the formation of an iron melt at low oxygen fugacity (up to 5 units below Fe-FeO buffer). Significant differences in the geochemistry of terrestrial and extraterrestrial iron are associated with different degrees of evolution of the primary minerals involved in their formation.

^1,2Xiaolong Guo,^1,2Peixin Du,³Hongmei Liu,⁴Jiacheng Liu,⁵Shangying Li,^1,2Xinyi Xiang,⁶Shun Wang,⁷Peng Yuan
Journal of Geophysical Research: Planets (in Press) Link to Article [https://doi.org/10.1029/2025JE009644]
¹State Key Laboratory of Lunar and Planetary Sciences, Macau University of Science and Technology, Macau, China
²CNSA Macau Center for Space Exploration and Science, Macau, China
³Guangdong Provincial Key Laboratory ofMineral Physics and Materials, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou, China
⁴Department of Earth Sciences and Laboratory for Space Research, The University of Hong Kong, Hong Kong, China
⁵School of Land Engineering, Chang’an University, Xi’an, China
⁶Qinghai Provincial Key Laboratory of Geology andEnvironment of Salt Lakes, Qinghai Institute of Salt Lakes, Chinese Academy of Sciences, Xining, China
⁷School ofEnvironmental Science and Engineering, Guangdong University of Technology, Guangzhou, China
Published by arrangement with John Wiley & Sons

Poorly ordered Al/Si phases are widely distributed across the surface of Mars, among which allophane and amorphous silica are the two main constituents. Both allophane and amorphous silica can form in Al-Si systems through surface chemical weathering or subsurface hydrothermal alteration of volcanic materials. Nevertheless, our comprehension of the products derived from Al-Si hydrolysis systems remains poorly constrained. Hydrolysis experiments were conducted on Al-Si systems across an unprecedentedly wide range of Si/(Al + Si) molar ratios (n, 0 ≤ n ≤ 0.9), followed by characterizing the products using multiple techniques. At n ≤ 0.1, the products consist predominantly of Al30 (an Al polycation with a Keggin structure) and poorly ordered Al hydroxides. The introduction of Si resulted in formation of a small amount of proto-allophane. At n = 0.2 and 0.3, poorly ordered materials were still dominant, along with the presence of well-crystallized bayerite and gibbsite. The proto-allophane increased in quantity and began to assemble into allophane. At n = 0.5, well-crystallized minerals were absent and allophane dominated the product. At n = 0.7, the amount of allophane decreased significantly and at n = 0.8 and 0.9, allophane was probably absent, although proto-allophane still formed. Meanwhile, an increasing amount of amorphous silica was formed. X-ray diffraction, Fourier transform infrared, and VNIR provide information for differentiating Al-rich phases and Si-rich phases but show limited capability in identifying poorly ordered Al/Si-rich phases. NMR is powerful for identifying poorly ordered Al/Si phases, although widespread iron on the martian surface and the large instrument pose challenges to its application on Mars.

^1,2,3Fengke Cao et al. (>10)
Journal of Geophysical Research: Planets (in Press) Link to Article [https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2025JE009228]
¹Research Center for Planetary Science, College of Earth and Planetary Sciences, Chengdu University of Technology,Chengdu, China
²Department of Earth Sciences, Western University, London, ON, Canada
³Institute for Earth & SpaceExploration, Western University, London, ON, Canada
Published by arrangement with John Wiley & Sons

Northwest Africa (NWA) 7034 and its paired meteorites represent polymict regolith breccias derived from the ancient Martian crust. We employed micro-X-ray diffraction and Raman spectroscopy to quantitatively assess impact-induced metamorphism in plagioclase and alkali feldspar. Strain-related mosaicity (SRM) was measured via full width at half maximum in the Debye ring or chi (χ) dimension (FWHMχ) from 2D XRD images. A total of 149 plagioclase and 21 alkali feldspar grains were analyzed. Plagioclase exhibits FWHMχ values from 0.5° to 10.9°, and alkali feldspar shows a range of 2.1°–9.7°. Plagioclase grains record peak shock pressures from 0 GPa (unshocked) to 28–30 GPa based on calibrations for experimentally shocked andesine. Approximately 26% of grains show no detectable shock deformation (<1.0 GPa), while ∼4% preserve evidence of severe shock (>21.0 GPa), indicative of exposure to at least moderate shock metamorphism prior to ejection from Mars. Alkali feldspar records higher apparent peak pressures, possibly spanning 4.7–28.5 GPa. Martian crustal minerals experienced highly heterogeneous shock effects, which highlights the complex and varied impact histories of feldspar minerals during the impact-induced brecciation process. Pressure differences between plagioclase and alkali feldspar may reflect distinct source regions, pre-lithification shock events, or differing shock responses. This study highlights the importance of multi-mineral analytical approaches to enhance the accuracy of shock pressure quantification in Martian regolith breccias and to reconstruct the planet’s impact processes. This methodology should also be applied to other extraterrestrial samples to characterize shock effects across planetary bodies in the solar system.

¹Pengyu Ren,¹Changqing Liu,¹Yuzhen Wang,¹Enming Ju,¹Xin Wang,¹Ruize Zhang,¹Yanqing Xin,¹Ying-Bo Lu,¹Zongcheng Ling
Journal of Geophysical Research: Planets (in Press) Link to Article [https://doi.org/10.1029/2025JE009532]
¹Shandong Key Laboratory of Space Environment and Exploration Technology, School of Space Science and Technology,Institute of Space Sciences, Shandong University, Weihai, China
Published by arrangement with John Wiley & Sons

The Mars Mineralogical Spectrometer (MMS) onboard the Tianwen-1 orbiter can obtain high-resolution visible and infrared reflectance spectra of the Martian surface, that supports detailed analysis of mineral types and their spatial distribution across Mars. However, raw MMS data cannot be directly applied to scientific analysis. To address this limitation, this paper develops a processing pipeline for MMS data, including radiance to I/F conversion, photometric correction, inhomogeneity correction, and geometric correction. Three global maps of ferric oxides were obtained using the processed MMS data. Results reveal that the ferric oxides are nearly ubiquitous across the Martian surface, and they primarily exist in the form of nanophase ferric oxides in the bright regions of Mars (e.g., Amazonis Planitia, Tharsis Montes, and Arabia Terra). Subsequently, the distribution of gray crystalline hematite is identified in Meridiani Planum and Aram Chaos using data from MMS. Additionally, a new deposit of red crystalline hematite is detected in the southeastern part of Aram Chaos. These findings provide crucial evidence for the existence of past aqueous environments in these regions, including Fe-rich aqueous fluids under ambient conditions, hydrothermal fluids, and in-place oxidative weathering of Fe-bearing rocks under the influence of surface water. Notably, the processing pipeline and methods established in this study are critical for advancing our understanding of the ferric oxide distribution across the Martian surface using MMS data.

^1,2Robert Platt,^1,2Rossella Arcucci,^1,3Cédric M. John
Journal of Geophysical Research: Planets (in Press) Open Access Link to Article [https://doi.org/10.1029/2025JE009473]
¹Department of Earth Science and Engineering, Imperial College London, London, UK,
²Data Science Institute, ImperialCollege London, London, UK,
³Digital Environment Research Institute (DERI), Queen Mary University of London,London, UK
Published ny arrangement with John Wiley & Sons

Orbital remote sensing observations are a lynchpin of planetary science research. Hyperspectral infrared spectroscopy in particular is key for planetary mineralogical exploration, for example, CRISM for Mars, as this underpins our understanding of the distribution of specific lithologies and the geological process leading to their formation. Yet routine analysis workflows involving summary parameters have significant limitations and are highly time-consuming. This work presents a novel methodology and framework for the analysis and classification of CRISM SWIR reflectance spectroscopy, leveraging Machine Learning (ML). We train a model to classify 37 minerals previously manually identified on the planet. We show this model is highly performant, with test data across Mars and a case study within Jezero crater, where ML results match previous manual analyses and rover observations. We also adapt Expected Cost (EC) to remote sensing data for use in geological context for the first time. We demonstrate that EC can be used to dynamically weight misclassification penalties based on geological context, as a rigorous measure of automated classification methods. We envision this model to make analysis of CRISM data more accessible to the planetary science community, allowing rapid searches for a vast range of minerals across a global/regional scale. As a result, areas of interest for further satellite or rover exploration can be quickly identified, leading to greater understanding of geological processes on Mars.