¹Chunjie Cao,¹Duojun Wang,¹Kenan Han,¹Kewei Shen,¹Kexuan Zhang
Journal of Geophysical Research: Planets (in Press) Link to Article [https://doi.org/10.1029/2026JE009722]

¹High Pressure Sciences Experiment Center, College of Earth and Planetary Sciences, University of Chinese Academy ofSciences, Beijing, China
Published by arrangement with John Wiley & Sons

The vesicles of meteorite fusion crusts offer a key window into transient processes during atmospheric entry, yet their formation mechanisms remain poorly constrained. In this study, we investigated the morphology, mineralogical composition, and evolutionary mechanisms of vesicles in the fusion crust and primary lithology of the meteorite NWA 10645 using micro-CT as the primary technique, complemented by SEM–EDS petrography. Vesicle nucleation in the fusion crust was likely driven by volatile supersaturation generated from multiple reservoirs, including apatite, pyroxene, melt inclusions, and mesostasis. After nucleation triggered by apatite devolatilization, isolated vesicles continued to grow and underwent three evolutionary stages: early growth, aggregation, coalescence, and critical rupture. Micro-CT 3D imaging shows that adjacent nucleated vesicles rapidly aggregated within a short time, forming bead-like alignments, then gradually coalesced into larger pores, and evolved into ellipsoidal shapes due to inertial tensile forces generated in the melt during high-velocity atmospheric entry, while near-surface vesicles approached critical rupture. Furthermore, Classical Nucleation Theory (CNT) is applied for the first time to predict a minimum nucleation radius of 23–70 nm, significantly smaller than the vesicle sizes resolved by micro-CT and SEM. This result indicates that vesicle nucleation occurs at a transient nanoscale stage. Diffusion-length estimates further suggest that volatile transport in the melt could support subsequent vesicle growth to experimentally observable micron-scale sizes.

¹J. R. Hill,¹P. R. Christensen
Journal of Geophysical Research: Planets (in Press) Open Access Link to Article [https://doi.org/10.1029/2026JE009775]
¹School of Earth and Space Exploration, Arizona State University, Tempe, Arizona, USA
Published by arrangement with John Wiley & Sons

Martian chloride salt deposits were first identified by Osterloo et al. (2008, https://doi.org/10.1126/science.1150690) and surveyed by Osterloo et al. (2010, https://doi.org/10.1029/2010je003613) primarily using thermal infrared data acquired by the Thermal Emission Imaging System (THEMIS) onboard the 2001 Mars Odyssey spacecraft. Over the subsequent 15 years, the THEMIS instrument has greatly expanded its areal and repeat coverage of the Martian surface. A principal component-based index was also developed to identify chloride salts and quantify the confidence level of their detection. Pairing the expanded data set with this improved analytical technique enabled a more accurate global survey of chloride salts, which identified 1,605 distinct deposits covering 11,974 km2. This includes 777 newly identified deposits, which represents a ∼20% increase in the surface area (∼1,997 km2) of identified chloride salts. The chloride salt deposits are primarily associated with Noachian-aged terrains, with a significant percentage occurring in Early Noachian terrains. A steep drop-off in chloride deposit occurrence was observed at the Noachian-Hesperian boundary. This pushes the period of chloride salt formation and deposition back to the earliest periods of Martian history, when the planet more closely resembled the Earth at the same time.

^1,2Pei Ma,³Hao Zhang
Journal of Geopyhsical Research: Planets (in Press) Link to Article [https://doi.org/10.1029/2026JE009863]
¹Planetary Environmental and Astrobiological Research Laboratory, School of Atmospheric Sciences, Sun Yat‐senUniversity, Zhuhai, China
²Now at Center for Lunar and Planetary Sciences, Institute of Geochemistry, Chinese Academy ofSciences, Guiyang, China
³School of Earth Sciences and Hubei Key Laboratory of Planetary Geology and Deep SpaceExplorations, China University of Geosciences, Wuhan, China
Published by arrangement with John Wiley & Sons

Lunar-like space weathering causes spectral darkening, reddening, and the attenuation of absorption bands due to metallic iron particles. The commonly cited iron size boundary, particles smaller than 40–50 nm redden spectra, while larger ones only darken, comes mainly from measurements of silica gel powders, and does not reflect the true particle-size effects. Using rigorous Mie theory to calculate absorption efficiencies of metallic iron spheres, we find that particles smaller than 80 nm primarily induce reddening with moderate darkening across the 0.4–2.6 μ⁢m$$ wavelengths, and the Hapke and Lucey‒Riner space weathering models are equivalent in this size range. Particles larger than ∼2 μ⁢m$$ cause darkening with only minor reddening. The upper size limit for reddening is wavelength-dependent; for 0.5–2.6 μ⁢m$$ wavelengths, particles <120 nm always redden the spectrum. Accounting for the polydisperse nature of metallic iron in lunar and laboratory samples, we incorporate the size distribution into the Lucey‒Riner space weathering model and validate it with laboratory data. We also discuss UV bluing, NIR reddening, and spectral brightness induced by metallic iron particles.

^1,2S. Ottaviani,^1,3L. Folco,^1,4M. D. Suttle,⁵R. Repič,⁵L. Mancini,⁵T. Battiston,^1,6S. Iannini Lelarge,^1,3M. Masotta
Journal of Geophysical Research: Planets (in Press) Open Access Link to Article [https://doi.org/10.1029/2026JE009650]
¹Dipartimento di Scienze della Terra, Università di Pisa, Pisa, Italy
²Dipartimento di Fisica e Geologia, Università degliStudi di Perugia, Perugia, Italy
³CISUP, Centro per l’Integrazione della Strumentazione dell’Università di Pisa, Pisa, Italy
⁴School of Physical Sciences, The Open University, Milton Keynes, UK
⁵Slovenian National Building and CivilEngineering Institute ‐ ZAG, Ljubljana, Slovenia
⁶Consiglio Nazionale delle Ricerche, Istituto di Geoscienze e Georisorse,Pisa, Italy
Published by arrangement with John Wiley & Sons

We estimate the cosmic dust flux to Earth through the study of rare micrometeorites that preserve part of their precursor features during atmospheric entry heating, namely unmelted and scoriaceous subtypes. Combining high-precision mass balance measurements, X-ray computed microtomography and scanning electron microscopy, we studied mass, size and petrography of 207 micrometeorites recovered from sediment traps in the Transantarctic Mountains (TAM), ranging from ∼170 to ∼1650 µm. Chondrules were identified in ∼14% of the micrometeorites, particularly among coarse-grained and composite particles. The analysed population shows a bimodal size-frequency distribution, with peaks at ∼305 µm and ∼470 µm. A similar bimodal distribution was previously reported from the TAM cosmic spherule population, yet shifted towards lower sizes. This size-shift is consistent with an average mass loss of ∼87% during atmospheric entry heating. The mass-size relationship follows a power-law, where the spherical equivalent diameter (d_µm) and mass (m_µg) of the micrometeorite are related by: 𝑚 =1.07 ×10−6 𝑑2.96$$. The size-frequency distribution of the fine- and coarse-grained micrometeorites reveals two well-separated clusters, with peaks at ∼315 µm and ∼550 µm, respectively. These observations suggest that the bimodal distribution in the micrometeorite flux reflects contrasting lithological end-member components with different physical properties and fragmentation behaviours during dust production in space. Based on earlier mass flux estimates from TAM melted micrometeorites and accounting for the mass loss due to atmospheric entry derived here, we calculate a time-averaged pre-atmospheric mass flux of ∼12,000 (±6,000) t/yr over the Quaternary, suggesting that the influx has remained stable over the last few million years.

¹Jasmijsn Van der Graaf, ²John F. Mustard, ¹Annemiek C. Waajen, ³Frank J.A. Van Ruitenbeek, ^4,5Christopher S. Romanek, ^1,4Mónica Sánchez-Román
Icarus (in Press) Open Access Link to Article [https://doi.org/10.1016/j.icarus.2026.117262]
¹Geobiology Lab, Earth Sciences Department, Vrije Universiteit Amsterdam, De Boelelaan 1100, 1081HV Amsterdam, the Netherlands
²Department of Earth, Environmental and Planetary Sciences, Brown University, Providence, RI, USA
³Department of Applied Earth Sciences, Faculty of Geo-Information Science and Earth Observation, University of Twente, Drienerlolaan 5, 7500 AE Enschede, the Netherlands
⁴NASA Astrobiology Institute, USA
⁵Department of Earth and Environmental Sciences, Furman University, Greenville, SC, USA
Copyright Elsevier

Microbial activity plays a crucial role in the precipitation of carbonate minerals, mediated by bacterial cells and their secreted extracellular polymeric substances (EPS). Traditional detection of such biosignatures often requires invasive chemical treatments. This study explores the potential of Fourier Transform Infrared (FTIR) spectroscopy as a non-destructive tool to identify compositional features and microbial imprints in mixed-cation carbonates, providing a new pathway for remote sensing applications and in situ mineralogical studies. Carbonate samples from natural settings and laboratory experiments, under both biotic and abiotic conditions were analyzed to reveal their distinct spectral characteristics. The minerals studied include dolomite, siderite, ankerite, (hydro)magnesite, and various carbonate hydroxides, with varying amounts of the cations Ca2+, Mg2+ and Fe2+.
Distinct FTIR spectral characteristics were observed: dolomites, in particular, exhibited consistent clustering in overtone band positions around 2300 nm and 2500 nm. While this clustering was less apparent in other carbonate types, Fe2+ content could be reliably traced through a unique near-infrared absorption feature, whose intensity correlated with Fe2+ abundance following a square root function.
Despite the overlap of biosignature and mineral spectral features, specific markers emerged in biogenic samples. These included weak absorptions near 3310 nm (indicative of alkene bonds) and enhanced OH− bands around 1400 nm and 2760 nm, possibly related to phenols, alcohols, or structural water-components often associated with microbial EPS. FTIR spectroscopy is sensitive to trace amounts of water and organic compounds, making it a promising tool for evaluating precipitation conditions and the diagenetic history of mixed-cation carbonates.

¹Sophie Benaroya, ¹Christopher D.K. Herd
Earth and Planetary Science Letters 691, 120176 Open Access Link to Article [https://doi.org/10.1016/j.epsl.2026.120176]
¹Department of Earth and Atmospheric Sciences, 1-26 Earth Sciences Building, University of Alberta, Edmonton, AB T6G 2E3, Canada
Copyright Elsevier

Constraining the oxygen fugacity (fO2) of the mantle of Mars is critical for understanding planetary differentiation processes and magmatic evolution. The degree to which the shergottite martian meteorites faithfully record the redox states of their mantle sources remains obscured by several factors. One of these factors is the various methods used to estimate fO2: Fe-based oxybarometers require multiple minerals to be found in chemical equilibrium, which can be challenging to obtain, while previous V-based values rely on estimated parental melt compositions. Here, we present new, mineral-specific V/Sc oxybarometers calibrated for olivine and pyroxene in shergottites using experimentally determined partition coefficients. This method obviates the need for parental melt V concentrations and allows for fO2 determination from single mineral phases, bypassing the equilibrium constraints that limit Fe-oxybarometry. We applied these calibrations to a petrologically diverse suite of geochemically depleted, intermediate, and enriched shergottites. Our results reveal that: (1) basaltic shergottites, previously estimated at fO2 ∼FMQ-1, record a significantly lower initial/magmatic fO2 of ∼FMQ-1.7; (2) the magmatic fO2 of shergottites is correlated with their geochemical enrichment; and (3) all shergottites show oxidation of a magnitude of >0.5 log units with progressive crystallization. The V/Sc oxybarometers provide a robust tool for estimating the magmatic fO2 of shergottites and tracking their redox changes throughout their petrogenetic histories.

¹Farshid Nozarian,²Suzette Timmerman,¹Ingo Leya
Meteoritics & Planetary Science (in Press) Open Access Link to Article [https://doi.org/10.1111/maps.70201]
¹Physics Institute, Space Science and Planetology, University of Bern, Bern, Switzerland
²Institute of Geological Sciences, University of Bern, Bern, Switzerland
Published by arrangement with John Wiley & Sons

The 40K-K cosmic-ray exposure (CRE) dating system offers a promising method for determining exposure ages of iron meteorites by combining the radioactive cosmogenic 40K with the stable cosmogenic isotopes 39K and 41K. However, earlier applications relied on semi-empirical production models and inconsistent analytical data sets, limiting their reliability. This study presents a comprehensive reassessment of the 40K-K and 4He/21Ne system using state-of-the-art model calculations. Production rates of 39K, 40K, and 41K were simulated with the GEANT4–INCL++6 framework, incorporating updated excitation functions and fully considering depth-dependent shielding effects. The resulting model yields physically robust relationships between K isotopes and noble gas shielding proxies, such as 4He/21Ne. In addition to revisiting the classical approach used by Voshage and co-workers, we introduce two new alternative strategies for calculating CRE ages: a two-component mixing model and a native-K correction approach that mitigates contamination effects. Overall, these developments establish a more accurate and physically consistent framework for future applications of the 40K–K system in cosmochemistry and studies of galactic cosmic rays.

¹C.L. Kirkland, ²M. Brown, ³P. Sutton, ¹T.E. Johnson
Earth and Planetary Science Letters 691, 120201 Open Access Link to Article [https://doi.org/10.1016/j.epsl.2026.120201]
¹Timescales of Mineral Systems Group, School of Earth and Planetary Sciences, Curtin University, Perth, WA, 6845, Australia
²Laboratory for Crustal Petrology, Department of Geological, Environmental, and Planetary Sciences, University of Maryland, College Park, MD, 20742-4211, USA
³School of Engineering and Physical Sciences, University of Lincoln, Lincoln, LN6 7TS, UK
Copyright Elsevier

The pock-marked surface of the Moon provides a stark reminder of the impact flux endured by the early Earth. Notwithstanding, the role of exogenic (impact-driven) processes in the generation and evolution of Earth’s continental crust has attracted relatively little attention compared to endogenic processes driven by loss of heat from the planet’s interior. Here we explore various isotope time series inferred to track crust production within the context of changing local mass density for the Solar System over the duration of its orbit through the Milky Way galaxy. Using a global dataset of zircon Hf isotopes during the Archean, we find an enhanced probability of a step change in composition during entry into the galactic spiral arms, on a periodicity of ∼190 Myr. Fluctuations in zircon oxygen isotopes between normal and non-normal distributions also reveal periods of less normality corresponding to spiral arm entry, implying the production of a greater volume of buoyant lithosphere due to an enhanced flux of energetic impacts. Additionally, the age distributions of post-Archean terrestrial hypervelocity impact craters and lunar impact-melt clasts show elevated probabilities during the predicted phases of spiral-arm crossing. For a Sun–spiral-arm recurrence interval of ∼190 Myr, the local Galactic rotation model predicts a radial epicyclic period of approximately ∼150 Myr, which is also resolved in the zircon Hf change-point record for the ancient Earth. Both frequencies have been related to periodic disturbance of the Oort cloud and modifications to the impact flux in the inner Solar System. Together, these correlations suggest that some episodes of production and reworking of continental crust during the Archean were triggered by large impacts, some of which were probably comets. That there seems to be a fundamental connection between events on Earth and the galactic tide supports a role for periods of catastrophism through Earth’s history.

¹Xi Deng, ¹Jinting Kang, ²Pei-Yi Li, ²Yun Jiang, ¹Haolan Tang, ³Yang Xiao, ^1,4Fang Huang
Geochimica et Cosmochimica Acta (in Press) Link to Article [10.1016/j.gca.2026.07.022]
¹State Key Laboratory of Lithospheric and Environmental Coevolution, University of Science and Technology of China, Hefei 230026, China
²Purple Mountain Observatory, Chinese Academy of Sciences, Nanjing 210023, China
³Sichuan Chuangyuan Weipu Analytical Technology Co., Ltd, Chengdu 610300, China
⁴Deep Space Exploration Laboratory, Hefei 230026, China
Copyright Elsevier

Rubidium (Rb) is a moderately volatile element (MVE), and its isotopic system has been widely applied to constrain evaporation and condensation processes during solar nebular evolution and planetary accretion. Tektites, natural glasses formed by the rapid melting and quenching of terrestrial crustal materials during hypervelocity impacts of extraterrestrial bodies, serve as critical geological archives for quantifying impact-driven volatile loss, particularly for MVE. Here, we report high-precision Rb isotopic data for tektites from the Australasian, North American, Central European, and Ivory Coast strewn fields, obtained via both micro-drilling (in-situ) and bulk dissolution analyses. In-situ edge–center–edge profile analyses of three australasites reveal negligible Rb concentration variations (<10%) and remarkable isotopic homogeneity, with δ87Rb ranging from –0.16 ± 0.01‰ to –0.09 ± 0.03‰ (2SD). The absence of resolvable elemental or isotopic zoning across these profiles rules out diffusion-limited evaporation as the dominant control on Rb behavior during tektite formation. Bulk δ87Rb for all analyzed tektites range from –0.22 ± 0.05‰ to –0.12 ± 0.03‰, yielding a weighted mean of –0.16 ± 0.06‰ (2SD, n = 14). This uniformity indicates no resolvable Rb isotopic fractionation and is consistent with the composition of the upper continental crust (δ87Rb = –0.14 ± 0.01‰). To further evaluate the volatility behavior of MVE under Earth-surface conditions, we perform thermodynamic modeling at ambient atmospheric pressure and oxidizing conditions. The model predicts a volatility sequence of Zn ≫ Rb ≥ K, consistent with the well-documented large Zn isotopic fractionations in tektites and the absence of measurable isotopic shifts in Rb and K. Collectively, these results may imply that Rb isotope fractionation is effectively suppressed during impact-induced evaporation under the oxidized, near-surface conditions of Earth.

¹Dafilgo Fernandes,^1,2N. G. Rudraswami,^1,2V. P. Singh
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.70206]
¹National Institute of Oceanography (Council of Scientific and Industrial Research), Dona Paula, India
²Academy of Scientific and Innovative Research (AcSIR), Ghaziabad, India
Published by arrangement with John Wiley & Sons

We report 14 Antarctic and 15 deep-sea partially melted micrometeorites containing ~71 to 458 μm rounded, porous, and intact igneous objects. These objects likely represent non-porphyritic igneous chondrules. Analyzing these objects allows us to better relate them to the constituents of their parent bodies, thereby improving our understanding of the chondrule properties inherent to micrometeorite precursors. Seven identified Antarctic spherules and all deep-sea spherules primarily exhibit radial pyroxene (Rp) textures; one Antarctic composite spherule contains an Rp object embedded within an olivine matrix. Additionally, four Antarctic spherules show barred olivine (Bo) textures, two of which are surrounded by igneous rims, while two other Antarctic spherules show cryptocrystalline (Cc) textures. The bulk major and minor element oxides for the Rp objects vary significantly: MgO ~25.4 to 39.0 wt%, Al₂O₃ ~ 0.03 to 3.23 wt%, SiO₂ ~ 44.7 to 55.1 wt%, CaO ~0.02 to 2.72 wt%, Cr₂O₃ ~ 0.18 to 1.44 wt%, MnO ~0.18 to 1.51 wt%, and FeO ~11.4 to 22.1 wt%. The chemical compositions of the pyroxene within the Rp spherules suggest they originate primarily from unequilibrated–equilibrated ordinary chondrites (UOC–EOC) rather than carbonaceous chondrites. Conversely, the glass chemical compositions of the Cc spherules (MgO ~32.9 to 42.4 wt% and FeO ~0.73 to 10.5 wt%; En98-83) largely support an origin from chondritic carbonaceous materials. Atmospheric entry heating has progressively altered the chemical composition of the Bo spherules beyond recognition from their original chondrule states. Ultimately, their collective chemical compositions suggest that these spherules may consist of chondrules similar to non-porphyritic chondrules in carbonaceous and ordinary chondrites. Based on their textures and mineralogy, these spherules indicate that the parent sources of these micrometeorites are chondrule-bearing asteroid bodies.