¹A.M. Lee, ^1,2I.B. Smith, ¹J.A. Isen, ¹M.G. Daly
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2026.117127]
¹Centre for Research in Earth and Space Science, York University, Canada
²Planetary Science Institute, USA
Copyright Elsevier

MARSIS detected bright basal reflections at Ultimi Scopuli, near the south pole of Mars, which could imply the presence of liquid water or water saturated sediments. The dielectric permittivity was originally modelled to have a median value of 33 at 4 MHz, which is lower than expected for water in liquid form. Later investigations estimated values as high as 40 or as low as 4, where basal interface roughness is not considered. Besides roughness and water, alternative materials were suggested, such as brines or smectite clays. Two previous studies measured hydrated smectites at cold temperatures and found an apparent permittivity of 39 and 8.4. The larger number could explain the anomalous reflections, but the lower number would not. To review this discrepancy, we conducted experiments using a well-established smectite simulant at various hydration states at 230 K and 4 MHz, used for comparison to previous measurements. Our results show an apparent permittivity between 7 and 12 at 230 K, however, 180 K is considered a more reasonable estimation of basal South Polar Layered Deposits (SPLD) conditions. Our results at 180 K are close to 4, ruling out the presence of smectites as a potential source of the reflections. This study refines the techniques from a past study at York University, especially related to temperature control and gradients, and demonstrates the increasing capabilities of the MARVIN chamber.

¹Robin L. Haller, ¹Martin R. Lee, ²Mark E. Hodson
Geochimica et Cosmochimica Acta (in Press) Open Access Link to Article [https://doi.org/10.1016/j.gca.2026.04.022]
¹School of Geographical and Earth Sciences, University of Glasgow, Glasgow G12 8QQ, UK
²Department of Environment and Geography, University of York, York YO10 5NG, UK
Copyright Elsevier

Mighei-like (CM) meteorites are the most abundant group of hydrated carbonaceous chondrites. They display a wide range of degrees of aqueous alteration, from very mild to near complete, as demonstrated by the relative abundances of phyllosilicates and surviving anhydrous silicates. The reasons for differences in the extent of alteration are debated, and probably reflect variations within the CM parent body/bodies of one or more of water/rock ratio, temperature, and timescale. The least understood is timescale, and so to constrain the duration of aqueous alteration and to investigate precipitation conditions of key CM minerals, we created kinetic models with the software PHREEQC. These models simulated a mineralogically detailed alteration of the CM3 proxy Dominion Range 08006 by an aqueous fluid for different values of water/rock (W/R) ratio (by mass) and temperature over the timespan of 10−5–105 years with incremental time steps. Additional laboratory experiments in which chips of Dominion Range 08006 were reacted with either pure water or a carbonated aqueous solution under reducing conditions were undertaken to validate parts of the models and to evaluate formation conditions of calcite, as the study of calcite in CM chondrites provides invaluable information on aqueous alteration timings and conditions. The models suggest that regardless of their petrologic type, CM chondrites could have been altered from a CM3 over timescales ranging from months to ∼10,000 years depending on temperature. The more highly altered CM1 chondrites that contain magnetite instead of cronstedtite would have needed to react at temperatures of at least 100°C but not necessarily different W/R ratios compared to less altered CM2s. Some of the modelled systems suggest that minimally altered CM chondrites like Asuka 12169 could have been exposed to aqueous solutions at ∼1°C and W/R ratios (by mass) of ∼3 or higher. Significant quantities of calcite only form in laboratory experiments with a carbonated solution, suggesting that at least for early formed calcite, aqueous carbonate was sourced from accreted C-bearing ice instead of indigenous organic carbon. According to the models, a typical CM2 chondrite could have been altered from a CM3 lithology within ∼1,000 years at 50°C and 0.8 W/R ratio (by mass).

¹Sébastien Charnoz,²Jérôme Aléon,¹Marc Chaussidon,³Paolo A. Sossi,⁴Yves Marrocchi,¹Patrick Franco
Nature 652, 925-930 Open Access Link to Article [DOI https://doi.org/10.1038/s41586-026-10257-5]
¹Université Paris Cité, Institut de Physique du Globe de Paris, CNRS, Paris, France
²Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie, UMR 7590, Sorbonne Université, Museum National d’Histoire Naturelle, CNRS, Paris, France
³Institute of Geochemistry and Petrology, ETH Zürich, Zürich, Switzerland
⁴Université de Lorraine, CRPG, CNRS, UMR 7358, Nancy, France

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¹Inès Torres Auré, ^2,3John Carter, ¹Cathy Quantin-Nataf, ^2,4Damien Loizeau, ¹Erwin Dehouck, ¹Matthieu Volat
Icarus (in Press) Open Access Link to Article [https://doi.org/10.1016/j.icarus.2026.117113]
¹Laboratoire de Géologie de Lyon : Terre, Planètes, Environnement (LGL-TPE), Université Claude Bernard Lyon 1, CNRS, Villeurbanne, France
²Institut d’Astrophysique Spatiale (IAS), Université Paris Saclay, CNRS, Orsay, France
³Laboratoire d’Astrophysique de Marseille (LAM), Université Aix-Marseille, CNRS, Marseille, France
⁴Qualisat, Bièvres, France
Copyright Elsevier

The Fe/Mg-phyllosilicate-bearing units at Oxia Planum and Mawrth Vallis, two key Noachian sites along the martian dichotomy, exhibit distinct compositions despite their proximity. Using novel spectral criteria developed in this study, we distinguish two clay types: Type-1 (Mg-rich smectites/Fe2+-bearing saponite/vermiculite) and Type-2 (Fe3+-rich nontronite). Hyperspectral (OMEGA/CRISM) and textural (HiRISE/CTX) analyses reveal a regionally extensive basal Type-1 unit continuous across both sites, overlain by a Type-2 unit limited to Mawrth Vallis and southeast of Oxia Planum (above main delta fan elevations). A cratered paleosurface, with a Type-1 spectral signature, marks their boundary, indicating a depositional hiatus. The Type-1 unit’s lateral extent (>600 km) and elevation range (>1300 m) suggest a large-scale aqueous process, while the Type-2 unit’s absence below Oxia Planum’s delta fan implies either post-depositional erosion or environmental controls during deposition at Oxia Planum. Our results constrain early Mars’ climate models, challenging localized deposition/alteration hypotheses and ocean scenarios. These findings reveal that Type-1 clays extend over a much broader area than previously assumed, indicating that the ExoMars Rosalind Franklin rover will not investigate a localized phenomenon but rather a process with significant regional–and potentially global–implications for the geological and climatic history of Mars.

¹Veronika Pazderová, ¹Pavol Matlovič, ^2,3Hadrien Devillepoix
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2026.117107]
¹Faculty of Mathematics, Physics and Informatics, Comenius University, Mlynská Dolina, Bratislava, 842 48, Slovakia
²Space Science and Technology Centre, School of Earth and Planetary Sciences, Curtin University, Kent Street, Perth, 6102, WA, Australia
³International Centre for Radio Astronomy Research, Curtin University, Perth, 6845, WA, Australia
Copyright Elsevier

Meteor spectroscopy is a key method for probing the composition of meteoroids, providing insights into both their overall composition and the relative abundances of individual species. In this study, we present a comparison of meteor spectra recorded simultaneously from multiple observing sites within the Australian segment of the AMOS (All-sky Meteor Orbit System) network. We examine the origins of spectral discrepancies between the respective systems, considering factors such as focusing, spectrum extraction geometry, calibration, and observing geometry. This work represents one of the few detailed examinations of such effects. Our results show that factors such as observing geometry, focusing, calibration procedures, instrument characteristics, and specific data-processing approaches can introduce uncertainties in relative line intensities that are typically unresolved in conventional single-station observations. The four case studies presented in this work demonstrate that the sources of discrepancy in relative line intensities can be identified and potentially accounted for, ensuring that meteoroid composition estimates based on these intensities remain robust.

¹L. J. Riches,^1,2M. D. Suttle,¹I. A. Franchi,¹X. Zhao,^1,2M. M. Grady
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.70150]
¹School of Physical Sciences, The Open University, Milton Keynes, UK
²Planetary Materials Group, Natural History Museum, London, UK
Published by arrangement with John Wiley & Sons

Bells is an ungrouped carbonaceous chondrite that has in recent years been proposed as a CR-an. This link to CR chondrites has previously been identified through the analysis of anhydrous silicates, for example, oxygen isotopic compositions of olivine (Marrocchi et al., 2023). In this study, the aqueous alteration extent of Bells has been analyzed through the use of carbonate minerals to see whether Bells’ aqueous history supports a CR origin. The carbonates identified were calcite grains that had O-isotope compositions showing a single generation trend ranging from δ18O = +20.7 to +40.3‰, δ17O = +6.9 to +23.4‰ and Δ17O = −4.1 to +2.4. These are isotopically similar values to carbonates found in other CR-an meteorite Al Rais (δ18O = +28.8 to +34.8‰ Jilly-Rehak et al., 2018). Oxygen isotope compositions plot along a mass-independent slope of 0.75 ± 0.12, which indicates that isotopic evolution is controlled primarily by mixing of fluid and rock reservoirs. Starting temperatures for calcite precipitation are estimated to be ~14°C. These observations here help support a potential reclassification of Bells as a CR-an meteorite.

^1,2M. R. Boyd,¹M. J. Genge
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.70142]
¹Department of Earth Science and Engineering, Imperial College London, London, UK
²Grantham Institute—Climate Change and the Environment, Imperial College London, London, UK
Published by arrangement with John Wiley & Sons

Natural microspherules are important tracers of geologic and environmental processes in modern and ancient deposits. However, anthropogenic contamination can dilute natural collections by releasing synthetic microspherules into the environment. We report on a collection of microspherules from Pikes Peak, a granitic batholith mountain in Colorado, USA. Most particles are smooth, glassy spheres and are compositionally homogeneous, while some particles do not indicate formation via a molten or vapor phase and are interpreted as erosional products. The glassy microspherules are compared to spheres found in road paint from London, United Kingdom, and show strong textural and compositional similarities. In particular, Na content is high, which is unexpected in natural spherules. The Pikes Peak spherules are interpreted as microspherules eroded from road markings, illustrating local contamination on the summit. In addition, two microspherules with potential natural origins were found. We propose criteria for distinguishing paint microspherules from their natural counterparts, which is vital when investigating ancient spherule-forming processes as well as the impact of human activity on the environment. Quantifying the mass of microspherules found indicates high erosion rates of road paint, leading to microspherule abundances that could dominate the local microspherule flux.

^1,2L. Folco,^1,2M. Masotta
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.70149]
¹Dipartimento di Scienze della Terra, Università di Pisa, Pisa, Italy
²Centro per la Integrazione della Strumentazione dell’Università di Pisa CISUP, Università di Pisa, Pisa, Italy
Published by arrangement with John Wiley & Sons

We report on a petrographic and geochemical study of coated impact melt lapilli and bombs from the ejecta blanket of the Wabar crater field (Saudi Arabia), which formed ~300 years ago by the hypervelocity impact of an iron asteroid against sand dunes. These objects, up to 15 cm across and with aerodynamic shapes, characteristically consist of a thin coat of vesicular Fe-Ni-rich siliceous black glass enveloping a core of pumiceous silica-rich white glass. Both glasses are geochemically indistinguishable from the white or black glass masses found earlier in the ejecta blanket and interpreted as the product of impact melting of the target material and of the mixing of target and impactor impact melts, respectively. The black glass coating studied here contains high concentrations of Fe (8.7 wt%), Ni (4770 μg g−1), and Co (463 μg g−1), indicating high impactor contamination (4–17 wt%) typical of impactor–target interface melts. We propose a qualitative model for the formation of the coated lapilli and bombs within the context of the contact and excavation stages of a crater-forming event, thereby contributing to the understanding of the physical–chemical interactions between impactor and target impact melts during the formation of impact craters in rocky planetary surfaces.

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.