¹Shounak Dutta, ¹Paul D. Asimow, ¹Kenneth A. Farley, ²Arya Udry, ³Nicholas Randazzo, ⁴Kenneth H. Williford
Journal of Geophysical Research: Planets, 131, e2026JE009746
Link to Article [DOI: 10.1029/2026JE009746]
¹Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA, USA
²Department of Geoscience, University of Nevada, Las Vegas, NV, USA
³University of Alberta, Edmonton, AB, Canada
⁴Blue Marble Space Institute of Science, Seattle, WA, USA
Published by arrangement with John Wiley & Sons

The Margin Unit, explored by the Mars 2020 Perseverance rover in Jezero crater, is a distinctolivine‐rich lithology whose origin has remained unresolved due to extensive alteration and lack of preservedprimary textures. While hypotheses for its formation range from sedimentary to igneous, recent geochemicaldata allow for quantitative testing of these scenarios. To test the igneous hypothesis, we applied Markov ChainMonte Carlo simulations with MELTS thermodynamic modeling to assess whether the observed olivine andspinel compositions in the Margin Unit are consistent with igneous fractional crystallization. Our simulationsreproduce the observed systematic increase in spinel TiO2/Cr2O3 with decreasing olivine forsterite content, apattern difficult to reconcile with sedimentary mixing processes, providing strong evidence for an igneousorigin for the Margin Unit. Furthermore, continuing evolution of the same magma leads to coexisting olivineand clinopyroxene compositions that suggest a genetic link between the Margin Unit and the crater floor olivine‐rich unit, Séítah, pointing toward the existence of an extensive igneous complex within Jezero crater. Modeledmagma compositions for the Margin Unit are comparable to the parental melt compositions of the chassignitegroup of Martian meteorites, implying conditions necessary to produce chassignite‐like melts were alreadyestablished early in Noachian Mars

^1,2E. L. Cardarelli, ³T. M. Present, ⁴P. M. Vasconcelos, ⁵L. C. Kah, ^3,6C. Swindle, ³S. Bhattacharjee, ³K. Farley
Journal of Geophysical Research: Planets, 131, e2026JE009660 Open Access
Link to Article [DOI: 10.1029/2026JE009660]
¹Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, CA, USA
²Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA
³Division of Geologic and Planetary Sciences, California Institute of Technology, Pasadena, CA, USA
⁴The University of Queensland, Brisbane, QLD, Australia
⁵Department of Earth, Environmental and Planetary Sciences, University of Tennessee, Knoxville, TN, USA
⁶Department of Materials Science and Engineering, University of California, Los Angeles, CA, USA
Published by arrangement with John Wiley & Sons

Magnesite (MgCO₃) is a magnesium (Mg) carbonate mineral that records the aqueous environmental conditions of its formation. On Earth, magnesite forms in metamorphic, diagenetic or pedogenic environments, and distinguishing between these environments is critical for understanding the fluid chemistry during magnesite precipitation. Mg carbonates have been observed across the Nili Fossae region on Mars and in Jezero crater by orbital spectroscopy as well as in situ by the Perseverance rover. Rover acquired core samples with Mg carbonates may provide constraints on the chemical conditions of the ancient aqueous environments of Jezero crater, and may also be an important target for the preservation of potential biosignatures. This work explores magnesite phases found in Vertisols of the Kunwarara Mine, Australia, as a potential analog environment for magnesite on Mars. We document the principal microtextures, mineralogical context, and elemental compositions. We investigate the processes involved in the formation and diagenesis of magnesite nodules and a magnecrete. Kunwarara hosted magnesite shows complex textural relationships at the outcrop scale, and these relationships extend down to the nanoscale in samples that were collected along a depth profile. By characterizing textural and chemical variations in magnesite at different scales, this work reveals a continuum between diagenetic and pedogenic magnesites. It illustrates that diagenetic reactions produce magnesite from ascending Mg²⁺-rich groundwater interacting with detrital phases; groundwater interaction with descending meteoric solutions result in the conversion of magnesite into authigenic dolomite. Overall, this work shows how the superposition of textures and elemental compositions permits reconstruction of pedogenic processes leading to magnesite authigenesis.

^1,2Xiaojia Zeng, ³Chenkun Sun, ²Mingchao Xiong, ^1,2Xiongyao Li
Journal of Geophysical Research: Planets, 131, e2026JE009807 Link to Article [DOI: 10.1029/2026JE009807]
¹State Key Laboratory of Critical Mineral Research and Exploration, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang, China
²Center for Lunar and Planetary Sciences, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang, China
³State Key Laboratory of Lunar and Planetary Sciences, Macau University of Science and Technology, Macau, China
Published by arrangement with John Wiley & Sons

Hypervelocity impacts from micrometeorites or asteroids are a dominant long‐term geologicalprocess that modifies the mineralogical and elemental components of surface regolith on the Moon and otherairless planetary bodies. However, the pathways by which impacts drive elemental redistribution on the Moonremain poorly understood. Here, we report the discovery of thousands of chromite (FeCr2O4) nanoparticlesdeposited on a space‐weathered olivine fragment from Chang’e

¹Yoshio Kono (>10)

Journal of Geophysical Research: Planets, 131 e2026JE009944 Link to Article [DOI: 10.1029/2026JE009944]
¹Department of Physics and Astronomy, Kwansei Gakuin University, Sanda, Japan
Published by arrangement with John Wiley & Sons

Oxidation state of magma ocean is one of the most important factors, which influence its nature and dynamics. Since iron is the most abundant redox-sensitive element, understanding the effect of ferrous (Fe²⁺) and ferric (Fe³⁺) iron on the physical properties and structure of peridotite melts are fundamental to discuss geophysical and geochemical evolutions of magma ocean. In this study, we investigate the viscosity of Fe³⁺-bearing peridotitic melts under Ar gas environment by utilizing an electrostatic levitation furnace at the International Space Station. The results show strong increase of the viscosity of the Fe³⁺-bearing peridotitic melts with increasing iron content, which is in contrast to previous reports of lower viscosities of iron-abundant peridotitic melts than iron-poor peridotitic melts under reduced environment. Our structural investigations show that Fe³⁺ causes polymerization of melt structure with increasing iron content, while Fe²⁺-dominant peridotitic melts under reduced environment show almost no change in the melt structure. These results indicate that polymerization of melt structure by Fe³⁺ strongly increases the viscosity of peridotitic melt, while simple replacement of Mg²⁺ with Fe²⁺ decreases the viscosity of peridotitic melt. Since deep magma ocean is considered to be enriched in Fe³⁺, due to disproportionation reaction to form metallic iron and Fe³⁺ at high pressures, strong increase of the viscosity of peridotitic melt by the formation of Fe³⁺ would be important to discuss nature and dynamics of magmas at deep planetary interiors, such as formation and stability of the basal magma ocean at the core-mantle boundary in Mars.

^1,2Liyu Shan, ¹Heng-Ci Tian, ¹Yangting Lin, ¹Wei Yang, ¹Xu Tang, ¹Lixin Gu
Icarus (in Press) Open Access Link to Article [DOI: 10.1016/j.icarus.2026.117330]
¹Key Laboratory of Planetary Science and Frontier Technology, Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China
²University of Chinese Academy of Sciences, Beijing 100049, China
Copyright Elsevier

Recent studies of the returned Chang’e-5 (5CE) and Chang’e-6 (6CE) lunar soils have revealed differences in space weathering between the nearside and farside of the Moon, yet the relative roles of meteorite impacts and solar wind (SW) irradiation remain debated. Here we report new microstructural observations of eleven 6CE lunar soils, which were previously shown to contain SW-derived water contents within their grain rims. Combined with published data from 6CE and 5CE soils at similar latitudes, our results demonstrate that despite variations among mineral types, the average solar flare track density and mean amorphous layer thickness of 6CE samples are both comparable to those of 5CE samples, implying similar exposure ages at the two landing sites. Moreover, water contents in the grain rims are also comparable between the two sample suites. These similarities in exposure ages, amorphous layer thicknesses, and rim water contents suggest that the contribution of SW to space weathering is remarkably consistent between the two landing sites. In addition, we find that lunar surface water content reaches a time-dependent dynamic equilibrium after ~0.5 Myr, with higher water contents at mid-latitudes than at low latitudes. Meanwhile, long-term micrometeoroid impacts play an important role in modulating the total water content of SW-derived water within the bulk lunar regolith.

¹Zoë E. Wilbur (>10)
Earth and Planetary Science Letters, 695, 120296 Open Access Link to Article [DOI: 10.1016/j.epsl.2026.120296]
¹Department of Mineral Sciences, National Museum of Natural History, Smithsonian Institution, WA, DC, USA
Copyright Elsevier

Exogenous fragments in brecciated planetary materials offer direct evidence of mixing among planetary bodies in the Solar System. Fragments of undifferentiated carbonaceous material are frequently identified in differentiated meteorites. However, differentiated fragments are rarely observed in carbonaceous material. An exception is the exogenous basalt observed by the OSIRIS-REx spacecraft on the carbonaceous asteroid (101955) Bennu, which motivated a search for differentiated material in the returned samples. We report a pyroxene grain in a brecciated Bennu sample that is texturally and compositionally like pyroxene from cumulate eucrites — basaltic meteorites linked to the differentiated asteroid (4) Vesta — but oxygen isotopic measurements indicate that it is likely sourced from a basaltic asteroid not clearly represented among known basaltic achondrites. This grain may have been delivered to a precursor to Bennu in the main asteroid belt. Whether this grain is representative of the pyroxene-rich boulders observed remotely on Bennu’s surface remains unconstrained. Nevertheless, extending spacecraft observations to the grain scale reveals that Bennu serves as an archive for uncharacterized basaltic asteroids, documenting a history of planetary mixing that is otherwise elusive in current meteorite records.

¹Ling-Zhi Hu, ¹Maxence Regnault, ¹Philipp Gleißner, ¹Ninja Braukmüller, ²Ashley J. King, ¹Anne Lindner, ¹Harry Becker
Earth and Planetary Science Letters, 695, 120270 Open Access Link to Article [DOI: 10.1016/j.epsl.2026.120270]
¹Institut für Geologische Wissenschaften, Freie Universität Berlin, Malteserstrasse 74-100, Berlin, D-12249, Germany
²Planetary Materials Group, Natural History Museum, Cromwell Road, London, SW7 5BD, UK
Copyright Elsevier

Carbonaceous chondrites (CCs) exhibit profound non-systematic heterogeneity in their elemental and isotopic compositions, both within individual meteorite splits and among bulk samples of the same group, providing opportunities for a better understanding of early solar system processes. This variability also poses significant challenges for constraining bulk compositions of the parent bodies. We report new mass-independent Ti and Cr isotope data, integrated with major and trace element abundances for a suite of CC bulk rocks, to better understand the origin of this multiscale heterogeneity. Some bulk CCs (e.g., Yamato chondrites and Allende) exhibit elemental or isotopic compositions consistent with the literature, while others display significant differences.

Simple binary or ternary mixtures, using ε⁵⁰Ti, ε⁵⁴Cr and chemical data from the present study and literature as constraints, cannot reproduce the full range of isotopic and elemental data. The data are best explained by a multi-component mixing model with a minimum of four endmembers, involving CI-like matrix, heterogeneous non-carbonaceous (NC) dust, and two distinct refractory inclusion populations. The latter are similar to the average composition of calcium-aluminium-rich inclusions (CAIs) and amoeboid olivine aggregates (AOAs) and a CAI-like component found in some chondrules. Crucially, the model constraints reveal that NC dust, which migrated into the CC region, contained chemically fractionated material, characterized by a significant depletion in siderophile elements. This result suggests that some NC dust in CC may represent silicate-rich debris derived from the collision of early differentiated planetesimals in the inner solar system. Thus, carbonaceous chondrites record a multi-stage history of early transport of variably ⁵⁰Ti- and ⁵⁴Cr-enriched CAIs and subsequent migration of chondritic and differentiated planetary debris into CI chondrite-like icy dust of the outer disk.

¹Nicole X. Nie, ²Damanveer S. Grewal, ¹Zhe J. Zhang
Earth and Planetary Science Letters, 695, 120321 Link to Article [DOI: 10.1016/j.epsl.2026.120321]
¹Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA, 02139, USA
²Department of Earth and Planetary Sciences, Yale University, New Haven, CT, 06511, USA
Copyright Elsevier

High-temperature evaporation is a fundamental process shaping the chemical and isotopic signatures of planetary materials, yet the specific physical laws governing isotopic fractionation during evaporation remain debated. We investigated the mass-dependent isotope fractionation of Fe and Ni during vacuum evaporation of metallic melts. The residues exhibit large isotope fractionation, reaching up to 11.4 ‰ for δ^56/54Fe and 2.9 ‰ for δ^60/58Ni. Determining the isotope fractionation factors for Fe and Ni [$\alpha ={\left(m_{i1}/m_{i2}\right)}^{\beta }$] using the Rayleigh distillation model yielded a $\beta$ value of 0.5 for both Fe and Ni. Further, the evaporation coefficients of Fe and Ni were found to be similar (${\gamma }_{\text{Fe}}\simeq {\gamma }_{\text{Ni}}$). These results suggest that Fe and Ni evaporation from metallic melts is ideal and uninhibited by kinetic barriers.

We used high-precision three-isotope plots to constrain the mass fractionation law governing the evaporation process. Both Fe and Ni in the evaporation residue strictly follow the law of $n=-0.5$, distinct from the exponential law ($n=0$) typically assumed for kinetic processes. We propose a theoretical framework to reconcile this observation with kinetic gas theory: while the intrinsic instantaneous isotope fractionation between vapor and melt follows the exponential law, the apparent law observed in the residue is shifted by the Rayleigh distillation process. We derive a general relationship showing that the divergence between the apparent law and the intrinsic law during a Rayleigh distillation process is controlled by the magnitude of isotope fractionation ($\beta$), $n_{\text{appr}}\simeq \left[1+\frac{{\beta }_{i2/i1}}{2}\text{ln}\left(\frac{m_{i1}}{m_{i2}}\right)\right]n_{\text{inst}}-{\beta }_{i2/i1}$. This framework unifies conflicting observations regarding mass fractionation laws in previous evaporation experiments. The implications of these results for the evaporation history of Type-I cosmic spherules and for identifying nucleosynthetic isotopic anomalies are discussed.

^1,2Wei Dai, ¹Julien Siebert, ³Alexandre Corgne, ¹Nicolas Wehr, ⁴Yunke Song, ¹Frederic Moynier
Earth and Planetary Science Letters (in Press) Open Access Link to Article [DOI: 10.1016/j.epsl.2026.120342]
¹Université Paris Cité, Institut de Physique du Globe de Paris, CNRS, 1 rue Jussieu, Paris, 75005, France
²Centre for Star and Planet Formation, Globe Institute, University of Copenhagen, DK-1350 Copenhagen K, Denmark
³Instituto Ciencias de la Tierra, Universidad Austral de Chile, Valdivia, Chile
⁴Bayerisches Geoinstitut, University of Bayreuth, Bayreuth, 95440, Germany
Copyright Elsevier

Considerable isotopic variation between Earth and major chondritic materials implies a possible fractionation in the early differentiate stage of the Earth. However, it is challenging to study isotopic fractionation at the high pressures relevant to the deep Earth due to the lack of natural samples. We present Ca isotopic fractionation (Δ^44/40Ca_pv-melt) between calcium perovskite (Ca-Pv, CaTiO₃) and co-existing silicate glass (melt fraction) from experimental samples. The Δ^44/40Ca_pv-melt varies in experiments with different pressure, yields equilibrium fractionation factor [10³lnα(1000K)] of $0.{04}_{-0.08}^{+0.06}$ at 1 atm and $0.{50}_{-0.07}^{+0.07}$ at 3 GPa, respectively. The variation on Ca isotope fractionation is likely caused by Ca-Pv phase structure transition from orthorhombic/tetragonal (coordination number (CN) = 8) to cubic (CN = 12) with the increase of pressure and temperature. Our model calculation shows that Ca perovskite is enriched in heavy Ca isotopes relative to silicate melts by 0.02 to 0.08 ‰ in the lower mantle. It suggests that the Ca isotope fractionation in the deep magma ocean is less than 0.05 ‰, regardless of the variation of isotopic fractionation factor caused by phase transition. We conclude that no considerable Ca isotope variation occurred in the deep mantle and the Ca isotope composition of upper mantle could be representative of the bulk silicate Earth. Considering the Nd isotopic differences between Earth and Moon, we suggest that the Moon formed primarily from a partly molten proto-Earth with advanced crystallization of perovskites in its lower mantle.

^1,2Seamus L. Anderson (>10)
Meteoritics & Planetary Science (in Press), Link to Article [DOI: 10.1111/maps.70232]
¹Space Science and Technology Centre, School of Earth and Planetary Sciences, Curtin University, Perth, Western Australia, Australia
²Solar System Exploration Division, Code 690, NASA Goddard Space Flight Center, Greenbelt, Maryland, USA
Published by arrangement with John Wiley & Sons

The Dingle Dell meteorite fell in the wheat belt of Western Australia on Halloween night (October 31st) in 2016 and was observed by multiple cameras from the Desert Fireball Network, being recovered less than a week later. In this paper, we report the in-depth characterization and reclassification of this meteorite, from its original LL6 class to an updated L6 chondrite. Dingle Dell is an unbrecciated L6 chondrite with low shock features (S2) and no weathering (W0). The silicate mineral chemistry is typical of an L chondrite (Fa = 24.4 ± 0.3; Fs = 20.5 ± 0.2; Wo = 1.6 ± 0.3; all mol%), while the kamacite-Co concentration is on the high end of the L-chondrite range. The measured oxygen isotopes (δ¹⁷O = 3.809 ± 0.068; δ¹⁸O = 5.102 ± 0.126; Δ¹⁷O = 1.115 ± 0.011) are slightly more consistent with an LL chondrite classification, though on the border shared by L and LL chondrites. The chromium isotopic anomaly measured in Dingle Dell also places it among both L and LL chondrites (ɛ⁵⁴Cr = −0.37 ± 0.09). Analyses of cosmogenic radionuclides and noble gases indicate that Dingle Dell existed as a small meteoroid (10–15 cm radius) for 9.3 ± 1.3 Myr before impacting the Earth. Ideal gas pycnometry indicates a grain density of 3.61 ± 0.01 g cm⁻³ and a bulk density of 3.23 ± 0.02 g cm⁻³, revealing a calculated porosity of 10.5% ± 0.5%. Dingle Dell’s likely source region near the 3:1 mean motion resonance may constitute meteoritic sampling from an asteroid not associated with the Massalia or Flora families, the proposed sources for many L chondrites.