¹R. J. Hopkins,¹A. D. Rogers,¹L. Ehm
Journal of Geophysical Research: Planets 131, e2025JE009299 Open Access Link to Article [https://doi.org/10.1029/2025JE009299]
¹Stony Brook University, Stony Brook, NY, USA
Published by arrangement with John Wiley & Sons

Throughout Gale crater on Mars, the Curiosity rover has found high abundances (15–73 wt%) of X-ray amorphous materials in the rocks and sediments. The composition of this amorphous fraction is primarily calculated by subtracting crystalline abundances measured by the Chemistry & Mineralogy X-Ray Diffractometer (CheMin) from bulk elemental abundances from the Alpha Particle X-Ray Spectrometer (APXS). If any crystalline phase was underrepresented in the CheMin data, the elemental components of that phase would be overestimated in the amorphous fraction. This study examines the possibility of underrepresented crystalline phases in X-ray diffraction data using mixtures of amorphous ferric sulfate (AFS) and crystalline Ca-sulfate. Two compositionally equivalent mixtures were made with different morphologies: first, a simple mixture of AFS and Ca-sulfate grains and second, Ca-sulfate grains with AFS coatings. Each mixture was characterized with Raman spectroscopy, and two X-ray diffractometers (XRDs): a Bragg-Brentano instrument with CuKα radiation and a Debye-Scherrer instrument with CoKα radiation. Raman peaks from Ca-sulfate dominate both mixtures, but are dampened when AFS coats the Ca-sulfate grains. In XRD data, AFS coatings cause an overestimation of the amorphous percentage, with a difference between the known and refined amorphous abundances of 29–34 wt%, compared to 2–2.8 wt% for the uncoated mixtures. The effects of the coatings were slightly amplified with the Debye-Scherrer XRD, primarily due to the increased scattering and absorption of the CoKα radiation. This has implications for interpreting the XRD data of mixed amorphous-crystalline samples on Mars, as any Fe-rich amorphous coating may cause an overestimation of the amorphous abundance.

^1,2Jitse Alsemgeest,¹Fraukje M. Brouwer,³Luis F. Auqué,¹Kirsten van Zuilen,⁴Natalia Hauser,⁴Wolf Uwe Reimold
Journal of Geophysical Research: Planets 131, e2025JE008966 Open Access Link to Article [https://doi.org/10.1029/2025JE008966]
¹Geology and Geochemistry Cluster, Department of Earth Sciences, VU Amsterdam, Amsterdam, The Netherlands
²Nowat GAIA, Faculty of Geo‐Information Science and Earth Observation, University of Twente, Enschede, The Netherlands
³Department of Geosciences, University of Zaragoza, Zaragoza, Spain
⁴Institute of Geosciences, University of Brasília,CEP, Brasília, Brazil
Published by arrangement with John Wiley & Sons

As hydrous minerals have been observed in impact craters on Mars, impact-generated hydrothermal systems (IGHSs) have been considered as potential habitats for life on that planet. The Vargeão Dome, a 12 km wide impact structure in southern Brazil, was formed in basalts with at least two hydrothermal alteration stages. This structure is a rare terrestrial analog for IGHS evolution on Mars. However, the thermochemical evolution of these stages and their relationship to the impact remain unresolved. Two vein-forming alteration stages were identified by multidisciplinary sample analysis of Vargeão Dome. Fractured and deformed white vein fragments from the first stage occur within red veins from the second. This suggests reactivation of the white vein set during the crater excavation and modification stages. Rare Earth Element and Rb-Sr isotope data indicate different fluid sources for the white and red veins and an evolving fluid system. Thermodynamic modeling indicates a cooling sequence from 100–250 to <25°C for the white vein set, whereas goethite and hematite within the red veins indicate that most IGHS activity occurred at temperatures below 40°C. Considering this and accounting for gravity differences, life-supporting IGHSs on Mars may preferentially form impact structures over 28 km in diameter. Furthermore, impact-reactivation suggests elevated habitat potential in structures with pre-existing fault, fracture, and vein systems. These occur in volcanic areas or terrain older than 3.5 Ga, when Mars was wetter and geologically active. Therefore, the search for evidence of IGHS-supported life should be focused on these kinds of terrains.

¹Cyrena A. Goodrich et al. (>10)
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2026.02.019]
¹Lunar and Planetary Institute, USRA, 3600 Bay Area Blvd, Houston, TX 77058, USA
Copyright Elsevier

Xenoliths of carbonaceous chondrites (CC) in meteoritic breccias can provide samples of primitive solar system materials that are not represented by individual meteorites and thus expand our knowledge of chemical and isotopic reservoirs in the early solar system and early geologic processes on CC parent bodies. The Almahata Sitta (AhS) polymict ureilite contains one such xenolith, referred to here as AhS 202. Hamilton et al. (2020) discovered that, unlike any other known CC, the AhS 202 xenolith contains abundant (∼12–14 vol%) amphibole, a hydrous mineral that characteristically forms in greenschist to amphibolite facies metamorphism and requires a significantly larger parent body than typically inferred (≤100 km diameter) for CC meteorite bodies. Building on that initial work, we report additional analyses of the mineralogy and petrology, and new analyses of the chemical composition, oxygen and chromium isotope compositions, and physical properties of this xenolith that further constrain its petrogenesis and provenance. Our results show that the AhS 202 precursor was chondritic and experienced aqueous alteration similar to many low petrologic type CC meteorites at temperatures of ∼ 30–100 °C and fluid pressures of PH2O < 0.1 kbar, leading to formation of serpentines, magnetite, and chlorite. However, unlike any known CC meteorite, AhS 202 was heated further under water-saturated conditions similar to prograde metamorphism of terrestrial serpentinites, leading to formation of chemically pure diopside, secondary olivine, and tremolite amphibole. Peak metamorphic conditions determined from thermodynamic modeling, constrained by olivine-magnetite oxygen isotope thermometry, were ∼ 380–430 °C and ∼ 0.5–2.25 kbar. Based on our measured density of 2.27 g/cc for AhS 202, these conditions imply parent body sizes of 600–1875 km diameter, confirming the previous estimate (640–1800 km) of Hamilton et al. (2020). The fluid-assisted metamorphic conditions experienced by AhS 202 cannot be represented in current classification systems of meteorite petrologic type, which recognize only anhydrous metamorphism; we discuss an alternative approach to the classification of such materials. Oxygen and chromium isotope compositions show an affinity between AhS 202 and CR chondrites and/or CR-related achondrites, suggesting derivation from a common reservoir. However, petrology, refractory element composition, and extremely low carbon content indicate that it did not form on the same parent body as known CR chondrites or CR-related achondrites. The existence of this sample, in combination with several even higher-pressure clasts observed in CR chondrites (Kimura et al., 2013; Hiyagon et al., 2016), suggests that this reservoir contained multiple large planetesimals.

¹Alexander M. Kling, ¹Michelle S. Thompson
Geochimica et Cosmochimica Acta (in Press) Open Access Link to Article [https://doi.org/10.1016/j.gca.2026.02.016]
¹Department of Earth, Atmospheric, and Planetary Sciences, Purdue University, West Lafayette, IN 47907, USA
Copyright Elsevier

Solar wind neon is incorporated into lunar regolith grains and other planetary materials via solar wind implantation. Understanding the abundance of neon relative to other solar wind gases and its trapping and storage within planetary materials can inform on both parent body processing and volatile cycling. Microstructural defects in lunar regolith grains, including vesicles formed by space weathering processes, have previously been identified to store other solar wind-derived volatiles such as hydrogen, water, and helium. Here, we use transmission electron microscopy and electron energy loss spectroscopy to identify the presence of solar wind neon and quantify its abundance in vesicles within a space weathered lunar regolith grain. The direct observation of solar wind neon trapped in vesicles offers a new understanding of the space weathering history of lunar regolith grains and other planetary materials rich in solar wind gases. The storage of solar wind neon in nanoscale vesicles also has implications for its retention, diffusivity, and fractionation which may affect interpretations of the exposure and processing histories of lunar and other planetary materials as derived from noble gas analyses.

¹Anna Zappatini et al. (>10)
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.70110]
¹Institute of Geological Sciences, University of Bern, Bern, Switzerland
Published by arrangement with John Wiley & Sons

A fireball camera system installed in 2022 by the Oman Meteorite MonitoringProject (OMMP) as part of the Global Fireball Observatory (GFO) recorded a 3.2 s fireballon March 8, 2022 at 8:15 p.m. UTC. A meteoroid of 4 2 kg entered the atmosphere at14.0 km/s. Its trajectory, with a slope of 68.4°, started at 67.6 km and ended at 30.2 kmwhere the meteoroid traveled at 7.36 km/s. Approximately 50 g survived atmospheric entry.On February 7, 2023, two meteorites of 13.85 g and 8.21 g were recovered at the predictedsite. Gamma spectrometry confirmed their young terrestrial age via short-lived cosmogenicradionuclides 54 Mn and 22 Na. Al-Khadhaf is thus the first camera-observed meteorite fallfrom Oman. Petrography and mineral composition classify it as an ordinary H5–6 S2 W1chondrite. Its pre-impact orbit (a = 1.72 AU, e = 0.45, i = 4.36°) is consistent withasteroid-belt delivery, with both inner-belt and Koronis-family sources remaining plausible.The cosmic ray exposure age of 8.57 1.2 Ma coincides with an exposure-age peak observedamong H chondrites. Al-Khadhaf adds to the record of camera-observed falls, linkingmeteorite compositions to their solar system context via orbit calculations.

¹Laura B. Seifert et al. (>10)
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.70093]
¹Astromaterials Research and Exploration Science Division, NASA Johnson Space Center, Houston, Texas, USA
Published by arrangement with John Wiley & Sons

Calcium phosphates are ubiquitous in planetary materials, including samples returned from asteroid Bennu by the OSIRIS-REx mission. We characterized apatite [Ca5(PO4)3(F,Cl,OH)] grains in Bennu samples by scanning electron microscopy, electron microprobe analysis, and transmission electron microscopy to investigate their compositions, mineral associations, and microstructures. We find that Bennu apatite is halogen-poor, consistent with a composition of hydroxyapatite, and can be separated into two main structural types: single crystals, which often exhibit etched crystal faces, and anhedral polycrystalline assemblages. Both types exhibit zoning in cathodoluminescence imaging that results from incorporation of trace Mn2+ and rare earth elements into the apatite structure during crystal growth. Transmission electron microscopy of a single phosphate crystal and a polycrystalline assemblage reveals close association between apatite and phyllosilicates in the surrounding matrix. Phyllosilicates are either oriented parallel to intact apatite crystal facets or radiating from altered crystal faces. We interpret that single crystals with or without etched crystal faces are among the least aqueously altered of the observed apatites, whereas polycrystalline assemblages exhibiting a porous texture, consistent with successive dissolution–reprecipitation reactions, represent assemblages that experienced more extensive aqueous alteration. These microstructural data suggest that several stages of aqueous alteration likely occurred on Bennu’s parent body, leading to the mineral assemblages observed here.

¹Pal Patel et al. (>10)
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2026.117000]
¹Department of Computer Science and Engineering, Institute of Technology, Nirma University, Ahmedabad, Gujarat, 382481, India
Copyright Elsevier

This paper presents a methodology for analyzing hyperspectral data obtained from the imaging infrared spectrometer (IIRS) onboard ISRO (Indian Space Research Organisation)’s Chandrayaan-2 mission. The method uses unsupervised learning and classical spectral unmixing techniques to process hyperspectral data from the Mare Crisium region. The processing starts with the identification and removal of bad spectral bands using auxiliary metadata. This is followed by total variation (TV) based denoising to reduce noise and improve data quality. The denoising performance is measured using the peak signal-to-noise ratio (PSNR), with a minimum value of 36 dB, showing effective noise reduction while preserving important spectral information. The main focus of the methodology is endmember extraction. Vertex component analysis (VCA) is used for this purpose and its performance is compared with five existing methods: N-FINDR, automatic target generation process (ATGP), fast iterative pixel purity index (FIPPI), pixel purity index (PPI), and
-norm based pure pixel identification (TRI-P). Abundance estimation is carried out using fully constrained least squares (FCLS). The results are evaluated using spectral similarity measures such as normalized cross-correlation (NormXCorr), spectral angle mapper (SAM), spectral information divergence (SID), normalized euclidean distance (NED), spectral correlation measure (SCM), and spectral gradient angle (SGA). The VCA method shows the best performance with values of NormXCorr = 0.999, SAM = 0.006, SID = 0.00061, NED = 0.0312, SCM = 0.999, and SGA = 0.066. The results show that the validation of the TV-VCA-FCLS pipeline over Mare Crisium confirms its ability to deliver clear spectral endmembers, geologically meaningful abundance maps, and strong spectral fidelity with high computational efficiency, making it a reliable and practical approach for IIRS hyperspectral data analysis.

¹Yukari Yamaguchi, ¹Akiko M. Nakamura
Icarus (in Press) Link to Article [https://doi.org/10.1016/j.icarus.2026.117005]
¹Graduate School of Science, Kobe University, 1-1 Rokkodaicho, Nada-ku, Kobe 657-8501, Japan
Copyright Elsevier

Hypervelocity impacts play a key role in material transport among planetary bodies. To investigate how target material properties influence high-velocity ejecta, we conducted impact experiments using aluminum projectiles at velocities of about 7 km s−1, with serpentinite, dolerite, and pyrophyllite as targets. Ejecta were impacted onto polycarbonate plates and analyzed using high-speed imaging and crater measurements. Ejecta velocities ranged from 5 to 13 km s−1, with maximum fragment sizes decreasing from 100 to 7 μm as velocity increased. Ejecta with velocities exceeding twice the particle velocity existed, consistent with previous numerical simulations. No clear differences in size–velocity or ejection angle–velocity relationships were observed among the targets. The largest sizes of high-velocity ejecta in this study may suggest that near the impact point, the material may behave as if it were in a fully cracked state. The axial ratios of the craters, which are considered to reflect those of the ejecta, were approximately 0.6–0.7. Although direct extrapolation to planetary scales is not straightforward, these results provide new experimental constraints on the influence of target properties on high-velocity ejecta production, contributing to a better understanding of material transport between planetary bodies.

^1,2Sergey N. Britvin,¹Oleg S. Vereshchagin,¹Natalia S. Vlasenko,¹Maria G. Krzhizhanovskaya,³Marina A. Ivanova,¹Irina A. Volkova
American Mineralogist 111, 335-344 ink to Article [https://doi.org/10.2138/am-2025-9851]
¹Saint Petersburg State University, Universitetskaya Nab. 7/9, 199034 St. Petersburg, Russia
²Kola Science Center, Russian Academy of Sciences, Fersman Str. 14, 184209 Apatity, Russia
³Vernadsky Institute of Geochemistry of the Russian Academy of Sciences, Kosygin St. 19, Moscow 119991, Russia
Copyright: The Mineralogical Society of America

The enigma of ammonium mineral speciation in the solar system has no proven solution due to the lack of data on the real minerals serving as space ammonium carriers. We herein report on the discovery of the first ammonium mineral in meteoritic substance and show its relevance to compositional and spectral characteristics ascribed to hypothetical ammonium phases in cometary and asteroidal bodies. Chemically distant from previously inferred volatile organics or ammoniated phyllosilicates, the mineral is an aqueous metal-ammonium sulfate related to the picromerite group—a family of so-called Tutton’s salts. Nickeloan boussingaultite, (NH4)2(Mg,Ni)(SO4)2·6H2O, was discovered in Orgueil, a primitive carbonaceous chondrite closely related to (162173) Ryugu and (101955) Bennu, the C-type asteroids. The available spectroscopic, chemical, and mineralogical data signify that natural sulfates related to boussingaultite-nickelboussingaultite series perfectly fit into the role of bound ammonia carriers under conditions of cometary nuclei and carbonaceous asteroids. The potential technogenic contamination of astromaterial samples and the difficulties in electron microprobe determination of ammonium are discussed in the context of recently published reports on the discovery of lunar and asteroidal ammonium-containing minerals.

¹Jiaming Zhu, ¹Bo Wu, ²Zikang Li, ²Yiliang Li
Earth and Planetary Science Letters 680, 119904 Open Access Link to Article [https://doi.org/10.1016/j.epsl.2026.119904]
¹Planetary Remote Sensing Laboratory, Department of Land Surveying and Geo-Informatics, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong
²Department of Earth & Planetary Sciences, The University of Hong Kong, Pokfulam Road, Hong Kong
Copyright Elsevier

The behavior of volatiles is critically important for understanding crustal fluids and the potential existence of a subsurface biosphere on Mars. However, our knowledge of the volatile cycle on Mars is limited by insufficient data from landed rovers and orbiter sensors. Halite salt crusts are widespread in the Qaidam Basin on the northern Tibetan Plateau due to strong evaporation under hyperarid climate conditions. We observed that the halite-dominated salt crust in the desiccated playa area diverts fluids percolating from depth to the surface, leading to the formation of raised polygonal rims enriched in gypsum. We drilled through the salt crust using a hand mill and measured the instantaneous gas concentrations and compositions. Beneath the halite salt crust, significantly higher concentrations of H2O, CO2, and CH4 were detected compared with levels in the atmospheric background and at the polygonal rims. The thickness of the salt crust ranges from approximately 0.3 to 1 m, with halite content primarily between 5 and 30 wt%, and is comparable in scale to the thickness (typically ❤ m) and abundance (10–25 wt%) of chloride deposits on Mars. These results suggest that similar salt crust formation should also be common in Martian crater basins subjected to long-term evaporation under hyperarid conditions. Furthermore, such salt crusts could trap deep volatiles, including potential biogenic gases, which may be detectable by gas spectrometers aboard Mars landers.