¹Eunjin Cho (>10)
Journal of Geophysical Research: Planets, 131, e2026JE009905
Open Access Link to Article [DOI: 10.1029/2026JE009905]
¹Korea Astronomy and Space Science Institute, Daejeon, Republic of Korea

Published by arrangement with John Wiley & Sons

The lunar surface is heterogeneous in grain size and metallic iron abundance due to diverse histories of space weathering. The spectral and polarimetric properties of the lunar regolith are strongly affected by both grain size and metallic iron particles. However, because physical and chemical alteration processes are closely coupled in their effects on optical properties, their combined influence remains poorly constrained. In this study, lunar simulants (JSC-1A and KLS-1) were sieved into two bulk-type and three size-separated fractions, and hydrogen reduction was conducted to produce metallic iron particles on grain surfaces. The spectral and polarimetric properties of these samples were then systematically measured. After reduction, reflectance decreases while the degree of positive polarization increases, consistent with Umov’s law. In addition, reflectance contrasts among grain sizes are reduced because fine grains preferentially darken, whereas the polarization–albedo relation remains sensitive to grain size. The reflectance of bulk-type fractions is intermediate, unlike that of natural bulk lunar soils, which resembles the finest fractions. In contrast, the polarization–albedo behavior of bulk-type fractions is close to that of the finest fraction. These differences from natural lunar soils suggest that agglutinates, which are absent in our reduced samples, may be important for the optical properties of natural bulk lunar soils. Further comparisons using natural lunar soils will help clarify the relative roles of agglutinates and grain-surface weathering products in controlling the optical properties of lunar regolith.

¹Fabrice Gaillard, ²Luiz Pereira, ¹Laurent Arbaret, ¹Giada Iacono-Marziano, ¹Emmanuel Le Trong, ^1,3Fabien Bernadou, ⁴Yves Marrocchi
Science, 394, 97–101 Link to Article [DOI: 10.1126/science.aef2542]
¹Institut des Sciences de la Terre d’Orléans, CNRS/Université d’Orléans/BRGM, Orléans, France
²GEOLAB, Hangzhou International Innovation Institute, Beihang University, Hangzhou, China
³CNRS, Géosciences Environnement Toulouse (GET), Observatoire Midi-Pyrénées, Toulouse, France
⁴Université de Lorraine, CNRS, CRPG, Nancy, France

Peprinted with permission from AAAS

Atmophile elements (carbon, hydrogen, and nitrogen) were thought to accrete late during planetary formation, yet cosmochemical and astrophysical evidence suggests that they were already present while small bodies, such as Vesta, were forming. High-temperature magmatic events on small bodies, however, should have outgassed these ultravolatile elements because gravity would have been insufficient to retain them. In this study, experiments reveal that gas bubbles strongly attach to metal droplets in magma ocean–like mixtures, forming compounds that resist segregation. Early flotation of such compounds would have enhanced mantle siderophile endowment, eliminating the need for late accretion. On small bodies, low gravity would have enabled millimeter- to centimeter-sized compounds to sink, trapping atmophiles in their interiors. This mechanism links core formation to the early entrapment of atmophile elements and provides a framework for reconciling volatile delivery across planetary bodies and planetary accretion models.

¹Jun Sakuma, ^2,3Hisashi Asanuma, ²Naoto Takahata, ^4,5Akira Yamaguchi, ¹Tsuyoshi Iizuka
American Mineralogist, 111, 1683–1692
Link to Article [https://msaweb.org/MSA/AmMin/TOC/2026/Abstracts/AM111P1683.pdf]
¹Department of Earth and Planetary Science, The University of Tokyo, Bunkyo, Tokyo 113-0033, Japan
²Atmosphere and Ocean Research Institute, The University of Tokyo, Kashiwa, Chiba 277-0882, Japan
³Graduate School of Human and Environmental Studies, Kyoto University, Sakyo, Kyoto 606-8501, Japan
⁴National Institute of Polar Research, Tokyo 190-8518, Japan
⁵Department of Polar Science, School of Multidisciplinary Science, SOKENDAI, Tokyo 190-8518, Japan

Copyright: The Mineralogical Society of America

Precise and accurate ages of asteroidal crusts are fundamental for reconstructing the timeline of magmatic, metamorphic, and impact events in the early Solar System. Zirconolite (CaZrTi2O7) is an accessory mineral found in a wide range of crustal rocks on both the Earth and Moon and has proven to be a potentially useful U-Pb chronometer. However, this mineral is rare in asteroidal meteorites, and its use for early Solar System chronology has been limited.

We present the in situ occurrence, U-Pb chronology, and chemistry of zirconolite in the andesitic meteorite Erg Chech 002, which represents a sample of the oldest known asteroidal crust. Zirconolite occurs as needle- and fiber-shaped and stubby crystals with widths of ∼3 μm and lengths up to ∼30 μm. Electron and ion microprobe analyses yielded concordant U-Pb data with a weighted mean 207Pb/206Pb age of 4557.9 ± 4.3 Ma (2σ), rendering it the Solar System’s oldest known zirconolite. Yet, this age is distinctly younger than reported high-precision 207Pb/206Pb ages varying from 4565.6 to 4566.2 Ma, which were obtained by acid leaching of pyroxene and whole-rock samples of the meteorite.

From its mineralogical and REE–(U Th)–(Nb Ta) characteristics, we argue that the zirconolite age represents the timing of a shock metamorphism of the parent asteroid’s crust. Our results suggest that 207Pb/206Pb dating for acid-leached samples can be affected by including even a tiny amount of metamorphic zirconolite, calling for caution in interpreting the high-precision 207Pb/206Pb age data. On the basis of thermodynamic and geochemical considerations, we infer further occurrences of zirconolite in alkali-silica-rich asteroidal rocks that rapidly cooled from high temperatures.

^1,2Xiaorong Qin, ^1,3,4Jianxi Zhu, ^1,3,4Hongping He, ⁵Yiliang Li
American Mineralogist, 111, 1537–1546
Link to Article [https://msaweb.org/MSA/AmMin/TOC/2026/Abstracts/AM111P1537.pdf]
¹State Key Laboratory of Deep Earth Processes and Resources, Guangzhou Institute of Geochemistry/Guangdong Provincial Key Laboratory of Mineral Physics and Materials, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China
²National Key Laboratory of Deep Space Exploration/School of Earth and Space Sciences, University of Science and Technology of China, Hefei 230026, China
³Center for Advanced Planetary Science (CAPS), Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China
⁴University of Chinese Academy of Sciences, Beijing 100049, China
⁵Department of Earth & Planetary Sciences, the University of Hong Kong, Hong Kong 999077, China
Copyright: The Mineralogical Society of America

In Gale crater, the Curiosity rover has documented a sequence of ∼3500 million year old sedimentary rocks containing smectite, indicating the presence of liquid water. However, the paleoenvironment in Gale crater, particularly the question of whether a paleolake ever existed, remains hotly debated.

Here, we compare the interlayer cations of smectite from terrestrial basalt weathering sequences and marine environments. Marine smectites are considered key analogs for smectites detected in martian paleolakes due to perceived similarities in formation processes and geochemical contexts between terrestrial marine settings and ancient lacustrine environments on Mars. Numerous observations show that K/Na-rich smectite is associated with marine environments, whereas Ca2-rich smectite is typical of terrestrial basalt weathering sequences.

We find that the basal spacings of K- and Na-smectite are ∼10.0 Å, whereas the basal spacings of Ca2- and Mg2-smectite range from 13.1 to 13.8 Å at a relative humidity (<1%) equivalent to that of the Curiosity rover on Mars. The XRD profiles measured by Curiosity in Gale crater show a basal spacing of ∼10.0 Å, which is attributed to K/Na-rich smectites. Our results support the idea that the presence of K/Na-rich smectites from Yellowknife Bay to Glen Torridon indicates that a lake existed in the 3500 million-year-old Gale crater, confirming that the habitable state lasted longer than previously thought.

¹W. Rapin (>10)
Journal of Geophysical Research: Planets, 131, e2026JE009783
Open Access Link to Article [DOI: 10.1029/2026JE009783]
¹Institut de Recherche en Astrophysique et Planétologie, Université de Toulouse, CNRS UMR 5277, CNES, Toulouse, France

Published by arrangement with John Wiley & Sons

Changing surface conditions on Mars during the Hesperian eon (∼3.6–3.0 billion years ago) produced widespread stratal sequences transitioning from clay to sulfate-bearing according to orbital data. Using data collected in situ at Gale crater by the Curiosity rover, we examined both the sedimentology and geochemistry of a 210-m-thick succession across a reference clay-sulfate transition. Four intervals (A–D) are defined based on both sedimentary structures and nodule distribution and composition, reflecting changes in depositional setting and diagenetic parameters. Large trough cross-beds, which become prevalent within interval A and dominate intervals B and C, are interpreted to indicate eolian processes, whereas dark-toned lens-shaped sandstone bodies in interval C point to recurring fluvial incursions. Planar bedding in uppermost interval D suggests damp or wet interdune conditions. ChemCam analyses show nodules are enriched in calcium and magnesium sulfates. The highest observed nodule densities coincides with strata interpreted to reflect damp or wet depositional environments (A, C, D), whereas their near-absence corresponds to the interval interpreted as the driest (B). We propose that this stratigraphic partitioning of the type, density, and sulfate-content of nodules indicates that they mostly formed during early diagenesis via capillary evaporation in the shallow subsurface, with only subordinate late-stage remobilization. The preserved strata record fluctuations in water availability and sediment supply, driven by repeated changes in climate, rather than by a single drying trend. These observations suggest new constraints on the fate of sulfur on early Mars and sulfate evaporite formation within sedimentary basins.

¹Hunter Vannier, ¹Briony H. N. Horgan, ²Michael Phillips, ¹Michael Eddy, ³Rebecca Greenberger, ⁴Arya Udry
Journal of Geophysical Research: Planets, 131, e2026JE009705
Open Access Link to Article [DOI: 10.1029/2026JE009705]
¹Purdue University, West Lafayette, IN, USA
²University of Arizona, Tucson, AZ, USA
³California Institute of Technology, Pasadena, CA, USA
⁴University of Nevada Las Vegas, Las Vegas, NV, USA

Published by arrangement with John Wiley & Sons

Widespread plagioclase detections on Mars using orbital visible to near infrared (VNIR) reflectance spectra have led to multiple interpretations of “feldspathic” terrain, ranging from ancient crustal material and evolved plutons to volcanic lava flows. A systematic, laboratory-based study of plagioclase detectability in whole igneous rocks is needed to contextualize these detections. We analyzed 42 feldspar-bearing igneous rocks (∼50–77 wt.% SiO₂; ∼25–60 vol.% plagioclase) using VNIR and mid-infrared (MIR) laboratory spectra, bulk chemistry/mineralogy, microscopic analyses of rock texture, and plagioclase chemistry to assess the characteristics influencing plagioclase signatures in whole-rock spectra. We find that 1.25 μm absorption bands are common in intrusive samples, and that plagioclase can be spectrally detected at abundances <40 vol.%, even in the presence of ∼20 vol.% mafic hydrous minerals. We find that large (mm-scale) grain size is a driver of plagioclase detection, and that oxides are highly effective at subduing absorption bands. Plagioclase with a wide range of compositions (An_25–47,90) can produce a 1.25 μm absorption, unless iron-depleted (<0.13 wt.% FeO). Alteration can obscure the 1.25 μm absorption, causing rocks with similar plagioclase abundances and chemistries to exhibit different bulk VNIR spectra. Unambiguous detection of feldspathic rocks on Mars is only likely for: (a) plagioclase-rich crust (e.g., anorthosites or other plagioclase cumulates), (b) intrusive felsic rocks with limited alteration and plagioclase with iron >0.13 wt.%, and (c) plagioclase-phyric effusive rocks with little or no mafic phenocrysts. MIR spectra can distinguish felsic (granite, granodiorite, monzonite) and mafic (anorthosite, basalts) rocks with similar 1.25 μm absorptions.

¹Alison R. Santos, ²Mikhail Yu. Zolotov, ¹Martha S. Gilmore, ³Craig Motil, ³Kyle Phillips, ⁴Valerie Tu
Journal of Geophysical Research: Planets, 131, e2025JE009457
Open Access Link to Article [DOI: 10.1029/2025JE009457]
¹Department of Earth and Environmental Sciences, Wesleyan University, Middletown, CT, USA
²School of Earth and Space Exploration, Arizona State University, Tempe, AZ, USA
³NASA Glenn Research Center, Cleveland, OH, USA
⁴Texas State University, Amentum JETSII Contract at NASA Johnson Space Center, Houston, TX, USA

Published by arrangement with John Wiley & Sons

Investigations of the venusian surface suggest chemical alteration (weathering) of rocks in contact with a hot, high-pressure atmosphere. This alteration was anticipated based on mineral stability considerations and has been supported by laboratory experiments conducted under Venus surface conditions. Here, we exposed iron-bearing samples (oxides, sulfides, iron-metal) to a simulated venusian environment (93 bars, 733 K, and a 9-gas mixture) for 60 days at the NASA Glenn Extreme Environments Rig (GEER). Iron metal, pyrrhotite, and troilite were altered to pyrite and magnetite. Some magnetite formed at the expense of hematite. Neither magnetite nor pyrite was altered. Measured concentrations of CO₂, SO₂, and OCS during the run suggest rapid OCS-SO₂ equilibration and drawdown of sulfur-bearing gases through reactions with the vessel and sample materials. The observed alteration assemblages and the gas composition in the vessel suggest experimental gas-phase fugacities (fO₂, fS₂, fSO₂, fOCS, fCO, fCO₂) in the vicinity of the magnetite-pyrite phase boundary and within the uncertainty of the magnetite-hematite boundary. Fugacities (log₁₀fO₂ of −22.5 to −21.5; log₁₀fS₂ of −5.4 to −4.6) and mineralogy in the Fe-O-S system are consistent with observation-based models for the near-surface conditions on Venus. This experiment supports both gas-phase chemical equilibrium and equilibration between gases and minerals in the Fe-O-S system on the surface of Venus, as proposed six decades ago.

¹Sang Woo Kim, ^1,2Kyeong Ja Kim
Journal of Geophysical Research: Planets, 131, e2026JE009892 Link to Article [DOI: 10.1029/2026JE009892]
¹Korea Institute of Geoscience and Mineral Resources (KIGAM), Daejeon, Republic of Korea
²University of Science and Technology (UST), Daejeon, Republic of Korea

Published by arrangement with John Wiley & Sons

The Dynamic Albedo of Neutrons (DAN) instrument on the Curiosity rover has mapped subsurface hydrogen along an extensively analyzed 27-km segment of its traverse in Gale Crater, revealing water-equivalent hydrogen (WEH) of 1–6 wt%. Neutron die-away measurements alone, however, cannot determine whether this hydrogen resides in adsorbed water, hydrated minerals, or ice. Here we use Geant4 Monte Carlo simulations (1⁢08$$ source neutrons per configuration) to quantify what a pulsed neutron generator with time-resolved prompt gamma-ray neutron activation analysis (PGNAA) adds to neutron-only measurements, for eight representative Martian regolith compositions under idealized detection. The model reproduces the established first-order sensitivity of the epithermal die-away constant to WEH (𝜏epi =57$$–77 𝜇$$s for WEH =15$$–1 wt%; power-law 𝑅2 =0.87$$)—an internal benchmark. The central experiment holds WEH fixed at 3 wt% across six compositionally distinct host endmembers: 𝜏epi$$ compresses to 61.4–67.0 µs, whereas simultaneously measured PGNAA ratios (Fe/Cl, apparent Si/Ca, Fe/H) provide complementary elemental constraints: for every host pair, at least one of the three ratios gives ≥7.6⁢𝜎$$ separation under the present idealized uncertainties. In a native-WEH benchmark, 27 of 28 pairs are separated at >5𝜎$$ by 𝜏epi$$ alone, driven largely by the broad assigned WEH range. Fe (Si) capture-to-inelastic ratios decrease monotonically by 36% (44%) for a 20 cm dry overburden, giving model-dependent depth information. These results define the information content of pulse-synchronized neutron–gamma-ray packages and modeling priorities for future Mars, Titan, and lunar volatile payloads.

¹Scott A. Sandford (>10)
Meteoritics & Planetary Science (in Press)
Open Access Link to Article [DOI: 10.1111/maps.70221]
¹NASA Ames Research Center, Moffett Field, California, USA

Published by arrangement with John Wiley & Sons

Regolith samples from the carbonaceous asteroid Bennu were stowed and delivered to Earth in the OSIRIS-REx spacecraft’s Sample Return Capsule (SRC). We applied multiple analytical techniques to study the components of the post-flight SRC, with a focus on assessing the conditions and any contaminants to which the Bennu samples were exposed. Examination of the passive temperature sensors placed inside the SRC, in combination with thermal modeling results, indicate that the samples were not heated above the 75°C limit imposed by OSIRIS-REx mission requirements. The sample canister air filter was found to contain Bennu particulates that had escaped from the sample collector, as well as a range of contaminants likely associated with the original filter component materials. No indications of terrestrial soils were found in the filter. Isotopic analyses of organic compounds and noble gases trapped in the filter show values consistent with terrestrial origins, and there are no indications of trapped asteroidal volatiles. Organic compounds found in the flight filter that were not present in a non-flight control filter include aromatic hydrocarbons, alkylated aromatic hydrocarbons, phenolic-related compounds, aliphatic hydrocarbons, and alcohols. The abundances of these organic compounds typically decrease from outer layers of the filter toward the canister interior, suggesting that they are external contaminants. We conclude that the majority of these organic compounds are chemical byproducts associated with outgassing of the SRC heatshield and backshell following the ablation portion of SRC atmospheric entry. Overall, our findings show that the OSIRIS-REx SRC performed excellently in containerizing the asteroidal samples obtained at Bennu, delivering them safely to the ground at the UTTR, and preventing most, though perhaps not all, external contaminants from reaching them. We discuss lessons learned from the flight and recovery of the OSIRIS-REx SRC that can benefit future sample return missions.

¹Gary R. Huss (>10)
Meteoritics & Planetary Science (in Press) Open Access Link to Article [DOI: 10.1111/maps.70231]
¹Hawai‘i Institute of Geophysics and Planetology, School of Ocean and Earth Science and Technology, University of Hawai‘i at Mānoa, Honolulu, Hawaii, USA

Published by arrangement with John Wiley & Sons

We report on the petrography and oxygen isotopic compositions from in situ analyses of carbonates (Ca-carbonate, dolomite, and Fe-rich magnesite), magnetite, and apatite in particles from asteroid Bennu. Using oxygen isotope thermometry of Ca-carbonate, dolomite, and magnetite, we estimated crystallization temperatures and the oxygen isotopic compositions of the aqueous fluids from which they precipitated. The Ca-carbonate–magnetite pairs formed at lower temperatures (−5 to 20°C) than the dolomite–magnetite pairs (5–89°C); the uncertainties are ±10–16°C. The inferred fluid compositions for Ca-carbonate–magnetite pairs are δ¹⁸O = 0.6‰–9‰ and Δ¹⁷O = 1.8‰–2.7‰, whereas for dolomite–magnetite pairs, they are δ¹⁸O = −2.2‰ to 7.6‰ and Δ¹⁷O = −0.1‰ to 0.9‰. On a three-isotope oxygen diagram (δ¹⁷O vs. δ¹⁸O), 11 out of 13 of our inferred aqueous fluid compositions plot along a single line with a slope of ~0.8, potentially indicating precipitation from a single isotopically evolving fluid. Two dolomite–magnetite pairs appear to be outliers and may have formed from fluids with different oxygen isotopic compositions. The oxygen isotope data presented herein overlap with those reported from samples of asteroid Ryugu, supporting a possible close genetic relationship between these asteroids.