¹Jiawei Wang, ^1,2Nicole M. Fernandez
Journal of Geophysical Research: Planets, 131, e2025JE009493 Open Access Link to Article [DOI: 10.1029/2025JE009493]
¹Department of Earth and Atmospheric Sciences, Cornell University, Ithaca, NY, USA
²Department of Earth and Planetary Sciences, ETH Zürich, Zürich, Switzerland
Published by rrangement with John Wiley & Sons

Oxidized clays and the widespread Al/Si-over-Fe/Mg stratigraphy on Mars imply prolonged water-rock interactions and efficient oxidative weathering despite the largely anoxic conditions of Early Mars when most deposits formed during the climate optimum. Oxychlorine species are now known to be common on Mars, and laboratory kinetics show that chlorate oxidizes Fe(II) orders of magnitude faster than O2$$ at low temperatures, motivating a chlorate-centered oxidative weathering framework. We develop a 1-D reactive transport model that explicitly includes Fe(II) oxidation by chlorate to evaluate whether low-temperature alteration of basalt can produce oxidized Fe(III)-rich smectites (nontronite) and associated weathering-derived minerals commonly observed on Mars. Model simulations span oxidant supply (chlorate 1⁢0−10$$–1⁢0−3 M$$; oxygen partial pressure (p⁢O2$$, 1⁢0−5$$–0.21 bar), climate (0–25 °C$$; 30–800 m⁢m y⁢r−1$$), and parent basalt mineralogy. Across this space, only saponite, nontronite, kaolinite, and amorphous silica consistently formed. Dissolved chlorate on the order of 1⁢0−5$$–1⁢0−4 M$$ reproduces the canonical Al/Si cap over Fe/Mg-smectites within ∼200 kyr and builds clay-bearing intervals approaching 100 m. Clay-bearing unit accumulation is nonlinear, with most deposition occurring in the early stages of oxidative weathering, highlighting limitations of constant net-rate assumptions for long-term thickness. An intermediate climate window ( ∼10$$–15 °C$$; 50–100 m⁢m y⁢r−1$$) preserves thick sections with an Al-rich cap. Certain clay phases are sensitive to parent basalt mineralogy (plagioclase favors kaolinite; olivine/pyroxene favor saponite), whereas nontronite reflects oxidant capacity and amorphous silica marks cool–dry conditions. These findings provide a testable chlorate-driven framework that reconciles oxidized clays under anoxic conditions and links stratigraphy to redox, climate, and bedrock composition.

¹Joanna V. Egan, ^1,2Wuhu Feng, ¹Alexander D. James, ³James Manners, ^1,4Daniel R. Marsh, ⁵Sébastien Lebonnois, ⁶Franck Lefèvre, ⁷Aurélien Stolzenbach, ¹John M. C. Plane
Journal of Geophysical Research: Planets, 131, e2025JE009634 Open Access Link to Article [DOI: 10.1029/2025JE009634]
¹School of Chemistry, University of Leeds, Leeds, UK
²NCAS, University of Leeds, Leeds, UK
³Met Office, Exeter, UK
⁴School of Physics and Astronomy, University of Leeds, Leeds, UK
⁵Laboratoire de Météorologie Dynamique, Sorbonne Université, ENS, PSL Research University, École Polytechnique, Institut Polytechnique de Paris, CNRS, Paris, France
⁶LATMOS, Sorbonne Université, UVSQ Paris-Saclay, CNRS, Paris, France
⁷Instituto de Astrofisica de Andalucia (IAA/CSIC), Granada, Spain
Published by arrangement with John Wiley & Sons

Near-ultraviolet imaging of the planet Venus reveals inhomogeneous absorption features in the otherwise bright clouds. This absorption has been studied for nearly 100 years, but identification of the near-UV absorber remains one of the largest open questions in Venusian research. Based on a multiple scattering radiative transfer model, the observed absorption between 300 and 600 nm can be produced by 1.0–1.2 wt% ferric chloride (FeCl₃) in the mode 1 (∼0.2 μm radius) sulfuric acid cloud droplets—less than the in-cloud iron mass loading measured during the Venera-12 mission. We present a novel chemical network within a global chemistry-climate model, which provides the required source of FeCl₃ in the upper cloud region from the reaction of Fe-containing molecules, produced by the ablation of cosmic dust particles, with atmospheric HCl. A residence lifetime of ∼3,000 years is required to provide sufficient optical absorption from a purely meteoric source of FeCl₃.

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.