¹Hiroto Tokumon, ¹Yohei Noji, ²Keisuke Fukushi, ^2,3Yasuhito Sekine
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2025.07.021]
¹Division of Natural System, Graduate School of Natural Science, Kanazawa University, Kakuma, Kanazawa, Ishikawa 920-1192, Japan
²Institute of Nature and Environmental Technology, Kanazawa University, Kakuma, Kanazawa, Ishikawa 920-1192, Japan
³Earth-Life Science Institute (ELSI), Institute of Science Tokyo, Meguro, Tokyo 152-8550, Japan
Copyright Elsevier

A key step in understanding prebiotic chemistry in the Solar System is to predict and reconstruct the speciation and solid–liquid partitioning of inorganic nitrogen species, such as ammonium and ammonia, in icy planetesimals—including C-type asteroids, the dwarf planet Ceres, and Saturn’s moon Enceladus. Smectite, a common constituent of these bodies, can regulate the chemical behavior of NH₄⁺ through cation exchange reactions. Accurate reconstruction of ammonium and ammonia speciation and distribution therefore requires appropriate selectivity coefficients for these exchange processes. In this study, we measured the NH₄⁺–Na⁺ selectivity coefficients (K_Na-NH4) of montmorillonite and saponite under varying initial NH₄⁺ and Na⁺ concentration, solid concentration, and pH. Cation exchange was confirmed by stoichiometric NH₄⁺ uptake and Na⁺ release. Montmorillonite exhibited log K_Na-NH4 ranging from −0.06 to 0.41, while saponite showed systematically lower values, from −0.46 to 0.07, likely reflect a difference in hydration retention capacity between the two smectites. Selectivity coefficients for both smectites showed a pH dependence with a maximum around pH 8, and well-described by second-order polynomial fits. Speciation modeling incorporating these coefficients demonstrates that NH₄⁺ interlayer occupancy and the aqueous concentrations of NH₄⁺ and NH₃ are highly sensitive to pH, salinity, and water–rock ratio under plausible geochemical conditions. Modeling results suggest that the aqueous solutions surrounding the Ryugu and Bennu samples during aqueous alteration were highly alkaline (pH > 9.5), favoring NH₃ over NH₄⁺ in solution and resulting in limited NH₄⁺ retention on solids. In the ancient Ceres ocean, NH₄⁺ was abundant in solution due to moderately alkaline conditions (pH ∼ 8) and a high water–rock ratio. For Enceladus, the results indicate that its rocky core may serve as a reservoir of NH₄⁺, with up to 60–70 % of total NH₃ in Enceladus present as interlayer NH₄⁺. These findings provide a quantitative framework for interpreting nitrogen speciation in icy Solar System bodies, including Europa, and their returned or observed materials.

¹Martin R. Lee,²Tobias Salge,¹Ian Maclaren
Meterotics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.70018]
¹School of Geographical and Earth Sciences, University of Glasgow, Glasgow, UK
²Imaging and Analysis Centre, Natural History Museum, London, UK
Published by arrangement with John Wiley & Sons

Hydrous Mg-phosphate was first described from astromaterials in particles returned from the C-type asteroid Ryugu, and has subsequently been found in samples of the B-type asteroid Bennu and CI1 carbonaceous chondrites. This phase may have been highly significant as a source of bioessential compounds for early Earth. Here, we describe Mg-phosphate from a petrologic type 1 clast (called “C1MP”) in the Cold Bokkeveld CM2 carbonaceous chondrite. This clast has a fine-grained serpentine–saponite matrix that in addition to the Mg-phosphate contains magnetite, Mg-Fe carbonate, calcite, pentlandite, transjordanite, eskolite, and daubréelite/zolenskyite. The Mg-phosphate grains are 7–36 μm in size and together constitute 0.27% of the clast by area. They have a “cracked” texture in scanning electron microscope images, and scanning transmission electron microscopy (STEM) shows that they are highly porous suggesting alteration of originally hydrous grains. The Mg-phosphate has Mg/P and Na/P ratios (atom%) of 1.02 and 0.25, respectively, along with minor concentrations of C, S, Cl, K, Ca, and Fe. Nitrogen was sought because ammonia has been reported from Ryugu Mg-phosphate, but none was detected by X-ray or electron spectroscopy. 4D-STEM shows that the C1MP clast’s Mg-phosphate is amorphous, and radial distribution function analysis of electron diffraction patterns reveals that its P-O and Mg-P bonding distances are comparable to newberyite (MgHPO4.3H2O). The C1MP clast’s Mg-phosphate formed from late-stage alkaline brines and subsequently underwent dehydration, amorphization, and partial loss of Na in response to heating in its parent body and/or during laboratory analysis.

¹Xhonatan Shehaj et al. (>10)
Earth, Planets and Space 77, 108 Open Access Link to Article [DOI https://doi.org/10.1186/s40623-025-02245-2]
¹Dipartimento di Fisica, Università degli Studi di Trento, Trento, Italy

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¹K.K. Hoch et al. (>10)
Nature 643, 938-942 Link to Article [DOI https://doi.org/10.1038/s41586-025-09174-w]
¹Space Telescope Science Institute, Baltimore, MD, USA

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¹Semenenko, V. P.,¹Shkurenko, K. O.,²Starik, S. P.,¹Kychan, N. V.
Mineralogical Journal 47, 33-42 Link to Article [DOI: 10.15407/mineraljournal.47.02.033]
¹Institute of Geochemistry, Mineralogy and Ore Formation of the NAS of Ukraine 34, Acad. Palladin Ave., Kyiv, Ukraine, 03142
²V.М. Bakul Institute for Superhard Materials of the NAS of Ukraine 2, Avtozavodska Str., Kyiv, Ukraine, 04074

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¹Noriyuki Kawasaki,²Sota Arakawa,¹Yushi Miyamoto,³Naoya Sakamoto,⁴Daiki Yamamoto,⁵Sara S. Russell,¹Hisayoshi Yurimoto
Communications Earth & Environment 6, 537 Open Access Link to Article [DOI
https://doi.org/10.1038/s43247-025-02511-x%5D
¹Department of Earth and Planetary Sciences, Faculty of Science, Hokkaido University, Sapporo, Japan
²Center for Mathematical Science and Advanced Technology, Japan Agency for Marine-Earth Science and Technology, Yokohama, Japan
³Institute for Integrated Innovations, Hokkaido University, Sapporo, Japan
⁴Department of Earth and Planetary Sciences, Kyushu University, Fukuoka, Japan
⁵Department of Earth Sciences, Natural History Museum, London, UK

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¹Michael C. Bouchard, ¹Bradley L. Jolliff
Icarus (in Press) Open Access Link to Article [https://doi.org/10.1016/j.icarus.2025.116752]
¹Department of Earth and Planetary Sciences, Washington University in St. Louis, Campus Box 1169, 1 Brookings Drive, St. Louis, MO 63130-4899, United States of America
Copyright Elsevier

Perseverance Valley is an erosional feature with the appearance of an eroded gully, located in the western wall of the Noachian aged Endeavour crater in Meridiani Planum, Mars. It is the most lithologically diverse location investigated by the Opportunity rover other than Cape York, where the rover first characterized the pre-, post-, and syn-depositional lithologies of Endeavour crater. We use hierarchical clustering and a similarity index combined with examination of Panoramic camera and Microscopic Imager images to classify these rock suites in Perseverance Valley, and contextualize them with comparison to rocks examined previously along the rim of Endeavour crater. The Perseverance Valley lithologies are classified into four rock suites, a clast-poor impact breccia that forms the “walls” of the valley, a competent basaltic outcrop of rocks that appear “blue” in false color Panoramic camera imagery, an outcrop of pitted rocks that has among the highest silica concentrations investigated by Opportunity, and a loose regolith mixture of martian soil, impact breccia, and local “blue” rocks that makes up the valley floor. Macro and micro textures indicate that the valley is currently being eroded by wind exiting the crater basin from west to east. Units that are offset both within and across Perseverance Valley indicate that the valley location and structure is likely influenced by a system of radial impact faults. Lithologies such as the co-located “blue” (in false color) and silica-rich pitted rocks, and observations of aqueous alteration such as “red” (in false color) zones, show similarities between Perseverance Valley and both Marathon Valley and the Spirit of St. Louis feature. We explore multiple working hypotheses to explain the formation mechanisms of Perseverance Valley, but can now say: the valley is likely structurally controlled including an ~80 m vertical offset by a graben; the valley hosted local aqueous alteration; the floor material of the valley consists of mass-wasted local materials; and the current topographic expression was overprinted by modern aeolian erosion.

¹Shiori Inada, ²Tetsuya Hama, ^1,3Shogo Tachibana
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2025.07.018]
¹Department of Earth and Planetary Science, The University of Tokyo, 7-3-1 Hongo, Tokyo 113-0033, Japan
²Komaba Institute for Science and Department of Basic Science, The University of Tokyo, 3-8-1 Komaba, Tokyo 153-8902, Japan
³UTokyo Organization for Planetary and Space Science, The University of Tokyo, 7-3-1 Hongo, Tokyo 113-0033, Japan
Copyright Elsevier

IIsotopic fractionation resulting from kinetic isotope effects (KIEs) in evaporation is a key to investigating high-temperature evaporation events in the early Solar System. The magnitude of the KIEs is represented by the kinetic isotope fractionation factor , which is predicted as  (: the mass ratio of the isotopic evaporated gas species) to a first approximation based on the Hertz-Knudsen equation. However, the experimentally measured  are often closer to 1 than this prediction to various degrees. In this study, we investigated the reason for this observation based on the transition state theory. To evaluate the classical (high-temperature) limit of , which is given by the isotopic ratio of the imaginary frequencies representing the evaporative motion at the transition state, we constructed a simple model for the vibrational normal mode analysis. In this model, we included the effects of the interaction of the evaporating species with the condensed phase surface, as well as the degrees of freedom of atoms in the condensed phase. The present theory clarified the relationship between the magnitude of the evaporative KIEs and the properties of the potential energy surface: the classical limit of  becomes closer to 1 than  due to the effect of the condensed-phase degrees of freedom when there exists a potential energy barrier, which is related to unstable interaction between the evaporating species and the condensed phase surface. This result is consistent with the previous experimental data and provides general insights into classical KIEs in chemical reactions.

¹S.A. Singerling, ¹F.E. Brenker, ¹B. Tkalcec, ²S.S. Russell, ³T.J. Zega, ⁴T.J. McCoy, ^3,5,6H.C. Connolly Jr., ³D.S. Lauretta
Geochimica et Cosmochimica Acta (in Press) Open Access Link to Article [https://doi.org/10.1016/j.gca.2025.06.028]
¹Schwiete Cosmochemistry Laboratory, Goethe University, Frankfurt, Germany
²Planetary Materials Group, Natural History Museum, London, UK
³Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA
⁴Department of Mineral Sciences, National Museum of Natural History, Smithsonian Institution, Washington, DC, USA
⁵Department of Geology, Rowan University, Glassboro, NJ, USA
⁶Department of Earth and Planetary Sciences, American Museum of Natural History, New York, NY, USA
Copyright Elsevier

We describe nanoscale observations obtained via transmission electron microscopy of Na,Ca carbonates in OSIRIS-REx samples of asteroid Bennu. Four Na,Ca carbonate grains were observed (including the one briefly described in McCoy and Russell et al., 2025), ranging in size from 140 nm to 2.36 µm. The stoichiometry of the grains and electron diffraction data best match gaylussite (Na2Ca(CO3)2·5H2O) or pirssonite (Na2Ca(CO3)2·2H2O). The grains rapidly amorphized under the electron beam. We also found that the grains are reactive to the terrestrial atmosphere, with their compositions and textures changing over six months of storage in a standard desiccator. NaCl salts grew on the exteriors of the grains, and the compositions of the carbonates became richer in C, F, Cl, and Ca and poorer in O and Na.
Neither gaylussite nor pirssonite have been observed in planetary materials other than samples from Bennu. On Earth, these phases occur in evaporites or shales from alkali lakes and, less commonly, as veins in alkaline igneous rocks. Thermodynamic modeling has shown that both phases require a low-temperature (<55 °C), Na-rich (>140 g/kg Na2CO3) brine, and their presence in the Bennu samples supports a model of salt formation on the parent body during syndepositional back-reaction of a briny fluid (McCoy and Russell et al., 2025). We argue that these minerals have not been previously observed owing either to their rare formation conditions or their susceptibility to degradation from sample preparation and analysis (e.g., electron/ion beam imaging), terrestrial weathering, and/or storage in a terrestrial environment. This study highlights the importance of collecting and carefully preserving pristine samples from planetary bodies.

¹T. Cuppone,²C. Carli,¹M. Casalini,^1,3A. Stephant,³C. R. Greenwood,^1,2G. Pratesi
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.70007]
¹Dipartimento di Scienze della Terra, Università degli Studi di Firenze, Florence, Italy
²Istituto di Astrofisica e Planetologia Spaziali—INAF, Rome, Italy
³School of Physical Sciences, The Open University, Milton Keynes, UK
Published by arrangement with John Wiley & Sons

NWA 13489 is a meteorite that has been classified as a brachinite. Brachinites are olivine-rich primitive achondrites representing residual products after a variable degree of silicate melt extraction on a barely differentiated, noncarbonaceous asteroid. Nevertheless, NWA 13489 displays petrographic and mineralogical characteristics that are anomalous when compared with other meteorites of that group. The petrography and thermometric data of this sample are compatible with a high metamorphic grade origin. NWA 13489 results in intermediate between type 6 and 7 chondrites, with a thermal regime broadly straddling the FeNi-FeS eutectic and the onset of silicate melting, resembling other meteorites defined as primitive achondrites. Evidence from mineral chemistry, bulk trace element geochemistry, and oxygen and chromium isotope systematics shows a “carbonaceous” composition and, therefore, NWA 13489 is not a brachinite. Rather, together with an ungrouped chondrite (the NWA 11961 C3-ungrouped) and other ungrouped achondrites (the paired NWA 10503/10859), NWA 13489 supports the existence of a distinct carbonaceous-like meteorite grouplet.