¹S. De Angelis, ^1,2F. Furnari, ¹M. Ferrari, ¹E. La Francesca, ¹C. Carli, ¹G. Piccioni, ¹S. Rubino, ¹S. Stefani, ¹F. Tosi
Journal of Geophysical Research: Planets, 131, e2026JE009723 Link to Article [DOI: 10.1029/2026JE009723]
¹Institute for Space Astrophysics and Planetology—INAF‐IAPS, Rome, Italy
²Sapienza University of Rome, Rome, Italy
Published by arrangement with John Wiley & Sons

Hexahydrite (MgSO₄·6H₂O) is among the possible candidates of the hydrated salts composing the “non-icy” materials on the surface of Europa. However, given the conditions of extreme vacuum characterizing the surfaces of icy and other airless Solar System bodies, a crucial aspect is to determine the conditions of stability of such hydrated salts in a wide range of pressures from ambient to high vacuum. The effect of varying temperatures in conjunction with variable vacuum is another important aspect to be considered. Studying the stability field of such compounds is crucial to establish the conditions of their presence on icy moons. In this work, we conducted an infrared (1–12 μm) and Raman spectral study on hexahydrite samples from ambient pressure to high vacuum, at ambient and low temperatures. We observe two main effects occurring upon lowering the pressure at which the sample is exposed, that is (a) de-hydration of the sample and consequent (b) loss of crystallinity and increase of structural disorder of the material. While the de-hydration is clear from the notable modification of H₂O absorption bands in the near-infrared, the effect of loss of crystallinity is observable in the mid-IR spectral region and also confirmed by Raman analyses. The transition is marked by the progressive loss of fine structure in the 1.5 and 2 μm hydration bands and by the collapse of the ∼9 μm Reststrahlen peak. Our measurements provide important laboratory constraints concerning the stability conditions of such hydrated materials that should provide aid in interpretation of mission data.

^1,2Lilin Huang, ^3,4Yanxue Wu, ¹Riqiang Wen, ⁵Chunwen Huang, ¹Chunmei Li, ¹Jiangmin Ma
Journal of Geophysical Research: Planets, 131, e2026JE010002 Link to Article [DOI: 10.1029/2026JE010002]
¹Hezhou University, Hezhou, China
²Key Laboratory of Planetary Geological Evolution at Universities of Guangxi Province, Institute of Meteorites and Planetary Materials Research, Guilin University of Technology, Guilin, China
³State Key Laboratory of Lunar and Planetary Sciences, Macau University of Science and Technology, Macau, China
⁴Analysis and Test Center, Guangdong University of Technology, Guangzhou, China
⁵Hezhou Information Network Center of Science and Technology, Hezhou, China
Published by arrangement with John Wiley & Sons

In this study, we report amorphous silica dendrites in three eucritic pyroxene grains from a howardite meteorite NWA 14701. These textures exhibit enhanced metasomatic features characterized by irregular or rounded amorphous silica containing numerous nanoscale ilmenite and chromian ulvöspinel inclusions distributed along both sides of fractures to form dendritic networks in the host pyroxene. These dendritic networks manifest as a discontinuous series of discrete, equant-shaped silica masses that project as embayments into the walls of the fractures. We propose that the formation mechanism of these amorphous silica dendrites was related to fluid-mediated alteration processes, as recorded by pyroxene decomposition to Fe–Ti–Cr oxides and amorphous silica along fractures. Such fluid preferentially leached and removed highly mobile cations (e.g., Mg, Ca, and Fe). Concomitantly, high field-strength elements (Cr and Ti) with extremely low mobility became passively enriched in situ due to their limited transportability within the fluid phase, subsequently crystallizing as ilmenite and chromian ulvöspinel at nanoscale dimensions. Meanwhile, the Si-O framework of the original host pyroxene, depleted in most interstitial cations, was preserved as a chemically inert amorphous silica framework. Our work suggests that the amorphous silica dendrites represent an unique type of secondary alteration texture on the HED parent asteroid that was previously undocumented, and they may also occur on other airless, differentiated planetary bodies.

¹A. C. Zhang, ¹T. R. Du, ¹L. Zhang, ¹Z. G. Zhang, ²Q. Zhou, ¹R. C. Wang
Journal of Geophysical Research: Planets, 131, e2026JE009945 Link to Article [DOI: https://doi.org/10.1029/2026JE009945]
¹State Key Laboratory of Critical Earth Material Cycling and Mineral Deposits, School of Earth Sciences and Engineering, Nanjing University, Nanjing, China
²Key Laboratory of Lunar and Deep Space Exploration, National Astronomical Observatories, Chinese Academy of Sciences, Beijing, China
Published by arrangement with John Wiley & Sons

Lunar mantle material could have been excavated during the formation of South Pole-Aitken (SPA) basin and is potentially present in the Chang’e-6 lunar soil retrieved from the basin. Here, we report the petrography and mineral composition of highly magnesian olivine and enstatite in Chang’e-6 lunar soil. Most of the highly magnesian olivine grains have compositions consistent with source rocks from impact-related norites and Mg-suite rocks, while some lithic clasts containing highly magnesian olivine grains can be attributed to impact-induced melting and recrystallization with material contribution from chondrite meteorite. Some highly magnesian olivine grains display a high-Ni feature with high Al₂O₃, Cr₂O₃, and CaO contents, which could be attributed to impact origin rather than lunar mantle origin. Most of the highly magnesian enstatite grains have compositions comparable to those from impact-related SPA noritic clasts, indicating that they probably share similar source rocks; whereas, some highly magnesian enstatite grains in Chang’e-6 lunar soil are probably derived from Mg-suite rocks. The observations suggest that there are no unambiguous mantle minerals in Chang’e-6 lunar soil, which are instead potentially found in the regions surrounding the SPA basin in the future. We find that Chang’e-6 highly magnesian enstatite grains show systematically lower TiO₂ contents than those from the Moon’s near side and suggest that the relative Ti-depletion in highly magnesian enstatite from Chang’e-6 lunar soil could be due to high modal abundance of enstatite in their parent rocks, consistent with the orthopyroxene dominance in the far-side lunar mantle.

¹Chuansheng Xu, ^1,2Yifei Cui, ¹Ao Luo, ¹Guodong Wang, ^1,3Lu Jing, ⁴Jiayan Nie
Journal of Geophysical Research: Planets, 131, e2025JE009536 Link to Article [DOI: 10.1029/2025JE009536]
¹State Key Laboratory of Hydroscience and Engineering, Department of Hydraulic Engineering, Tsinghua University, Beijing, China
²Key Laboratory of Hydrosphere Sciences of the Ministry of Water Resources, Tsinghua University, Beijing, China
³Shenzhen International Graduate School, Institute for Ocean Engineering, Tsinghua University, Shenzhen, China
⁴School of Civil Engineering, Wuhan University, Wuhan, P. R. China
Published by arrangement with John Wiley & Sons

Lunar lithic fragments (micrometer–millimeter scale) mainly consist of basalt, breccia, agglutinates, leucocratic fragments, and glass. Their morphology, surface properties, and frictional behavior fundamentally control the mechanical characteristics of lunar regolith, which can be effectively characterized by the angle of repose (AoR)—a simple and intuitive parameter obtained through rapid experiments that reflects the frictional, flow, and stability features of granular materials. This study analyzes five representative lithic fragment types from Chang’e−6 samples (30 particles) to investigate how morphology, surface energy, and friction jointly influence the AoR and develops a predictive model coupling multi-scale particle parameters. Results show that for particles larger than 200 μm, complex shapes (Overall regularity 0.6) and high friction coefficients (0.55) increase AoR by 10°–20° through enhanced interlocking. For smaller particles, surface energy dominates interparticle forces but is constrained by surface roughness, reducing its effective range. Under lunar gravity, the effects of morphology and friction are weakened, and the threshold size separating friction-shape-dominated and adhesion-dominated regimes shifts from ∼100 μm on Earth to ∼200 μm on the Moon. In coarse-grained assemblages, agglutinates dominate the variation in AoR, while glass content is weakly negatively correlated with it. The model reveals intrinsic mechanisms of lunar soil behavior and provides a theoretical basis for regolith handling and construction in future lunar missions.

^1,2Gustavo P. Maia, ²Laurent Remusat, ^2,3Kana Amano, ²Jean-Christophe Viennet, ^4,5,6Jason P. Dworkin, ^4,5,6Hannah L. McLain, ¹José A.L. da Silva
Earth and Planetary Science Letters, 692, 120237 Open Source Link to Article [DOI: 10.1016/j.epsl.2026.120237]
¹Centro de Química Estrutural, Institute of Molecular Sciences, Instituto Superior Técnico, University of Lisbon, Lisbon, Portugal
²Institut de Minéralogie, Physique des Matériaux et Cosmochimie, UMR CNRS 7590, Sorbonne Université, Muséum National d’Histoire Naturelle, Paris, France
³Institut d’Astrophysique Spatiale (IAS), Université Paris-Saclay, Orsay Cedex, 91405, France
⁴Solar System Exploration Division, NASA Goddard Space Flight Center, Greenbelt, USA
⁵Center for Space Science and Technology, University of Maryland Baltimore County, Baltimore, Maryland, USA
⁶Center for Research and Exploration in Space Science and Technology, NASA/GSFC, Greenbelt, MD, 20771, USA
Copyright Elsevier

Carbonaceous chondrites contain up to 4 wt% organic matter, likely inherited from precursors synthesised during preaccretion events. This organic inventory was later altered by hydrothermal and radiative processes, though the role of shock-induced impacts remains unclear. In this study, we examine the solid-state mechanochemical reactivity of hexamethylenetetramine (HMT) with sodium-rich montmorillonite (MMT) as an analogue to investigate the influence of shock- or impact-induced processes on organic matter evolution. HMT is reactive under mechanical stress, particularly when the clay mineral structure is disrupted, resulting in a wide range of molecules, including HMT-related compounds (as HMT-CH₃, HMT-OH, among others), pyrazine and triazinane/triazine derivatives. Notably, the incorporation of oxygen in N-rich species was also observed, despite the absence of liquid water. Conversely, when the clay mineral remains intact, mechanical input promotes the solid-state insertion of HMT-like molecules (as HMT, HMT-CH₃ and triazinane derivative) within its interlayer space, thereby protecting it from further reaction. The “cyclic mechanical input” delivered by laboratory milling (i.e., MM 200) and grinding (i.e., McCrone) is relevant to shock processes at an asteroid surface through repeated micrometeorite and IDPs impacts (i.e., space gardening). This work highlights shock/impact as a key factor driving both transformation and protection of extraterrestrial organics, offering new insights on how impact processes might have shaped extraterrestrial organic matter and consequent exogenous delivery of possibly prebiotic compounds to planetary surfaces.

¹E. Caminiti, ²P. Beck, ¹A. Wargnier, ²L. Bonal, ²B. Schmitt, ¹T. Usui
Icarus, (in Press) Link to Article [DOI: 10.1016/j.icarus.2026.117286]
¹Institute of Space and Astronautical Science (ISAS), Japan Aerospace Exploration Agency (JAXA), 3-1-1 Yoshinodai, Sagamihara 252-5210, Kanagawa, Japan
²Université Grenoble Alpes, CNRS, Institut de Planétologie et d’Astrophysique de Grenoble (IPAG), 414 rue de la piscine, 38400 Saint-Martin d’Hères, France
Copyright Elsevier

The spectroscopic properties of airless bodies are influenced by the space environment, including extreme temperatures. In this work, we study how low temperatures affect the spectral properties of meteorites in the visible to near-infrared wavelength range. We selected a Howardite-Eucrite-Diogenite meteorite, an ordinary chondrite, as well as seven carbonaceous chondrites of four different groups. Low-temperature reflectance spectroscopy measurements were acquired from 280 K down to 70 K over the 0.5–4 μm spectral range. We used spectral parameters to investigate changes during the cooling phase, including the position, depth, and full width at half maximum of the main absorption bands, as well as the position of interband peaks and spectral slope. We observed significant modifications in the position, amplitude, and width of absorption bands around 0.7, 1, 2, and 3 μm, as well as modifications of the position of interband peaks and average slope. The magnitude and trend of spectral modifications vary depending on the meteorite type. Spectral changes can influence the interpretation of the composition and the degree of hydration of meteorites and planetary objects. Moreover, even if CV and CO chondrites show comparable spectral properties, they exhibit different changes under temperature variations which may be used to distinguish their parent bodies. The effects of cryogenic temperatures on spectral properties must be considered when interpreting remote sensing data and comparing laboratory measurements with remote sensing observations. In the golden age of small body exploration, numerous space missions are affected, including but not limited to the Martian Moons eXploration (MMX, JAXA), Hera (ESA), Lucy (NASA), Tianwen-2 (CNSA), and Emirates Mission to the Asteroid Belt (EMA, UAE).

¹E.A. Cloutis et al. (>10)
Icarus (in Press) Link to Article [DOI: 10.1016/j.icarus.2026.117289]
¹Centre for Terrestrial and Planetary Exploration (C-TAPE), University of Winnipeg, 515 Portage Avenue, Winnipeg R3B 2E9, Manitoba, Canada
Copyright Elsevier

We measured reflectance spectra (250–2500 nm) of a 200 mg aliquot (sample id OREX-800029-0) of aggregate (unsorted) regolith particles returned from asteroid Bennu by the OSIRIS-REx mission). Our measurements include spots centered on small (<0.5 mm), medium (0.5–1 mm), and large particles (1–2 mm), as well as spots dominated by larger individual particles, including angular, hummocky, and mottled examples. The ultraviolet (UV) spectra (250–450 nm) are characterized by low reflectance (<3%), slightly red spectral slopes, absorption features near 270 and 320 nm attributable to Fe²⁺-O charge transfers, and Fe³⁺-associated absorption features, respectively. The 450–2500 nm region spectra are of low reflectance (<3% at 550 nm), red-sloped, and exhibit variable but weak absorption features, the most ubiquitous being a broad region of absorption in the 1000 nm region (<~2%), attributable to magnetite and Fe²⁺-bearing phyllosilicates. The low albedo, weak absorption features, and red-sloped spectra can be attributed to the presence of carbonaceous components. Overall, we confirm the spectral similarities between Bennu aggregate material and powders of the rare CI1 chondrite meteorites. The spectra we measured are generally red-sloped, in contrast to the blue-sloped global-average spectra measured by ground-based telescopes and the OSIRIS-REx spacecraft. This difference is consistent with Bennu’s boulder-dominated surface and limited fine-grained dust, in combination with compositional contributions from optically efficient minor phases.

¹Poula Eyðbjørnsdóttir, ¹Anders Johansen, ¹Elishevah van Kooten
Geochimica et Cosmochimica Acta (in Press) Open Access Link to Article [DOI: 10.1016/j.gca.2026.07.028]
¹Center for Star and Planet Formation, Globe Institute, University of Copenhagen, Øster Voldgade 5-7, 1350 Copenhagen, Denmark.
Copyright Elsevier

Chondrules and their associated fine-grained rims (FGRs) record fundamental processes operating in the early protoplanetary disk, yet the relationship between chondrule chemistry, morphology, and matrix complementarity remains incompletely understood. Here we investigate the major, minor, and trace element compositions of 66 chondrules and associated FGRs from relatively unaltered CM carbonaceous chondrites Asuka 12236, Paris and Maribo in relation to their three-dimensional morphology, using a multi-analytical approach including femtosecond LA-ICP-MS and X-ray tomography. Our results show that CM chondrules record a systematic process of metal loss and evaporation of Si-rich mesostasis, driving initially CI-like precursor compositions toward more Mg- and Si-rich bulk compositions along the CI ratio line and toward increasingly Si-poor forsteritic mineral assemblages. GEMS-like materials in pristine CM matrices appear to mirror chondrule compositions and likely represent complementary condensates derived from evaporated Si-rich mesostasis. The dust accreted to chondrules is dominantly CI-like but incorporates ∼ 14 wt% complementary condensate material represented by chondritic amorphous silicates, reconciling the observed Mg/Si complementarity between chondrules and matrix with the preservation of primordial organics and presolar grains.

Morphological observations further reveal no significant sectioning bias in chondrule size or plane, consistent with CM chondrule populations being dominated by agglomerates of ∼ 100 μm sized microspherules rather than larger primary melt droplets. Many chondrules display grape-bunch textures formed by welding of smaller primary chondrules with metal-rich or CI-like rims. This structure may explain the moderate volatile element plateau at ∼ 0.3 × CI observed for average CM chondrule compositions, reflecting incorporation of primary fine-grained rim material into these aggregates. We propose a “micro-chondrule-first” formation scenario in which localized heating events produced small molten droplets that subsequently accreted CI-like dust and ice, aggregated, and experienced limited in situ aqueous alteration. These observations place new constraints on chondrule formation mechanisms in the outer disk and highlight the importance of localized melting and aggregation processes.

^1,2Shuya Tan et al. (>10)
Geochimica et Cosmochimica Acta (in Press) Open Access Link to Article [DOI: 10.1016/j.gca.2026.06.034]
¹Earth and Space Exploration Center, Ritsumeikan University, Kusatsu, Japan
²Institute for Extra-cutting-edge Science and Technology Avantgarde Research of Life (X-star),
Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Yokosuka, Japan
Copyright Elsevier

The geochemical effects of freezing are becoming important in the investigation of closed aqueous environments, such as inland water on Earth and early Mars, and liquid water on planetesimals. Carbonate-bearing alkaline saline lakes in Mongolia are frozen in the cold season, with chemical species being partitioned among surface ice, lake water, and sediments. Freezing of the lakes leads to the accumulation of dissolved carbonate species, thereby decreasing the pH. The lakes are enriched not only in heavy metals, such as As, Mo, and U, but also in phosphorus. However, little is known about how metals and phosphorus are affected by chemical changes during freezing. Moreover, the mechanisms of major chemical changes are poorly understood and reproduced. Here we performed field surveys to investigate the behavior of these elements during lake freezing. Heavy metals and phosphorus accumulate in lake water during freezing, similar to major elements such as Cl−, with Mo and U concentrations reaching ∼1 mg/L. On the other hand, As and P accumulations are limited. Concentrations of heavy metals and phosphorus in ice increase with depth in the ice. We interpret the observed behavior using a geochemical model that accounts for their adsorption reactions coupled with water removal by freezing and carbonate precipitation. The model successfully reproduces the major chemical changes, including the decrease in pH, achieving quantitative accuracy by accounting for the combined effects of freezing and the revised solubility of carbonate minerals. The pH decrease promotes the adsorptions of As and P on sedimentary ferrihydrite particles, suppressing their accumulation in lake water. However, the decrease in pH is insufficient to promote adsorptions of Mo and U, resulting in their accumulations as major dissolved species. Adsorptions of heavy metals and phosphorus by iron oxides may be an important factor in their behaviors at low temperatures near the freezing point of water. Based on our model and observations, we discuss phosphate/carbonate precipitation in freezing porewater of icy planetesimals and phosphate availability in lake water on early Mars.

¹Valentine Megevand, ¹Sylvain Bernard, ²Corentin Le Guillou, ²Roberto Conconi, ¹François Guyot
Meteoritics & Planetary Science (in Press) Open Source Link to Article [DOI: 10.1111/maps.70214]
¹Institut de Minéralogie, Physique des Matériaux et Cosmochimie, Muséum National d’Histoire Naturelle, Centre National de la Recherche Scientifique UMR 7590, Sorbonne Université, Paris, France
²Université de Lille, CNRS, INRA, Centrale Lille, UMR 8207 – UMET – Unité Matériaux et Transformations, Villeneuve d’Ascq, France
Published by arrangement with John Wiley & Sons

Carbonaceous chondrites contain phosphorus, whose speciation and thus history remain to be investigated. Phosphorus/sulfur-bearing assemblages have been reported in carbonaceous CM chondrites, but there is no consensus about their exact compositions and origins. Here, we present submicrometer-scale investigations by analytical transmission electron microscopy of phosphorus/sulfur-bearing assemblages from the CM chondrites Murray and Murchison. Results indicate that, in CM chondrites, phosphorus associated with sulfides occurs under distinct oxidation states. In Murray, we identified a pyrrhotite–schreibersite nanocrystalline assemblage associated with carlsbergite and chromite. Its reduced nature and petrographic context are indicative of a nebular formation mechanism, possibly through kamacite sulfidation. In contrast, Murchison contains nanocrystalline pentlandite assemblages associated with carlsbergite and likely with phosphate phases that we interpret as being produced via interactions with an oxidizing fluid under asteroidal conditions. Thermodynamic modeling suggests that such complex assemblages hosting reactive forms of both phosphorus and nitrogen could promote the synthesis of activated phosphate species such as diamidophosphate, an efficient phosphorylation reagent, thereby underscoring their potential prebiotic significance.