^1,2Devan M. Nisson et al. (>10)
Journal of Geophysical Research: Planets (in Press) Open Access Link to Article [https://doi.org/10.1029/2025JE009395]
¹Department of Geosciences, Princeton University, Princeton, NJ, USA
²NASA Postdoctoral Program Fellow, NASA Ames Research Center, Moffett Field, CA, USA
Published by arrangement with John Wiley & Sons

Serpentinization produces hydrogen and methane through abiotic water-rock interactions, potentially supporting chemotrophic life in planetary subsurface environments. Serpentine deposits in the Martian Noachian landscapes of Nili Fossae and the Southern Highlands have been considered as potential paleo-habitable zones. However, the geochemical and physical conditions of Martian serpentinization fluids are poorly constrained because of limited data on serpentinite composition and formation environment. Furthermore, the co-occurrence of magnesite and magnesium-enriched serpentines on Mars remains enigmatic. To address such gaps, we investigated antigorite-magnesite paleo-serpentine bodies along the Highland-Vijayan suture of Sri Lanka as Martian analog sites, using thermodynamic batch reaction models to constrain alteration fluids and the production of primary (H2) and secondary (CH4) serpentinization products. Geochemist’s Workbench models combined field X-Ray Fluorescence (XRF) observations with varied protolith compositions (ultramafic or gneissic), precursor fluids (seawater or freshwater), temperatures (100–600°C), volumetric water-to-rock ratios (1–100,000), and CO2 partial pressures (0.01–1 bar). Models successfully reproduced the co-occurrence of antigorite and magnesite observed on Mars, with both minerals forming at 100°C across water-to-rock ratios. Despite their Mg-enriched composition, ultramafic protoliths produced H2 yields (up to 229 mmol/kg at W/R 1 at 100°C), supporting chemotrophic populations up to 107.5 cells/mL. Geochemical models indicate Mg enrichment from ultramafic mineralogy and Fe contribution from regional gneisses. Our thermodynamic equilibrium results show that Mg-rich serpentine systems with sufficient ferrous iron can produce biologically significant H2, establishing Sri Lankan serpentinites as valuable analogs for Noachian Mars habitability.

¹Neil E. Bowles et al. (>10)
Journal of Geophyiscal Research: Planets (in Press) Open Access Link to Article [https://doi.org/10.1029/2025JE009333]
¹Department of Physics, University of Oxford, Oxford, UK
Published by arrangement with John Wiley & Sons

The Lunar Thermal Mapper (LTM) instrument is a UK Space Agency funded infrared radiometer designed and built for the National Aeronautics and Space Administration Lunar Trailblazer mission launched in February 2025. LTM is a pushbroom imaging filter radiometer with 15 channels that cover the wavelength range from 6.25 to 100 μm with a 40–70 m/pixel ground sampling. Lunar Trailblazer’s mission is to understand the form, abundance and distribution of water across the lunar surface. LTM provides an independent measure of temperature to investigate thermal effects on water’s mapped distribution as well as an independent measure of surface mineralogy. The LTM instrument’s 15 infrared channels include four broadband temperature sensing channels (6.25–12.5, 12.5–25, 25–50 and 50–100 μm) plus 11 additional narrow band (∼40 cm−1) filters from ∼7–10 μm to map and discriminate silicate composition. We review the LTM design and calibration campaign at the University of Oxford’s Space Instrumentation facility and show that the instrument has sensitivity from 400 K with a Noise Equivalent Temperature Difference of <0.1 K to <1 K at 110 K for typical integration times (e.g., 30 Hz readout) from a nominal 70–130 km lunar orbit design altitude.

¹Ming Ma et al. (>10)
Journal of Geophysical Research: Planets (in Press) Open Access Link to Article [https://doi.org/10.1029/2026JE009657]
¹School of Surveying and Exploration Engineering, and Key Laboratory of Architectural Cold Climate EnergyManagement, Ministry of Education, Jilin Jianzhu University, Changchun, China
Published by arrangement with John Wiley & Sons

Space weathering substantially distorts the Christiansen feature (CF) observed by LunarReconnaissance Orbiter (LRO) Diviner thermal infrared radiometer, obscuring the intrinsic compositional andthermophysical signals of lunar surface silicate minerals. In this study, we develop a two‐step correctionframework designed to remove space weathering effects from a previously topographically corrected LRODiviner CF map. The method integrates Kaguya 750 nm reflectance, optical maturity (OMAT), FeO, H‐parameter, and npFe0 parameters to model nonlinear space weathering relationships across immature,moderately mature, and mature CF pixels. The corrected CF values exhibited reduced dependence on npFe0abundances, enhanced correlation with bulk FeO abundances, and improved internal consistency withincompositionally homogeneous regions. Comparisons with correction results based on Kaguya OMAT and FeOscale factors indicate that the proposed method more effectively suppresses space weathering inducedvariability while preserving compositionally diagnostic CF signatures. Persistent low CF anomalies in highlandregions suggest additional controls beyond npFe0 accumulation, potentially related to basaltic dustcontamination, subsurface compositional heterogeneity, and silicate amorphization processes. The resulting CFproduct offers a refined thermal infrared perspective on lunar surface composition, indicating clearer basalticdistributions, particularly within the South Pole Aitken basin.

^1,2Shuya Tan et al. (>10)
Geochimica et Cosmochimica Acta (in Press) Open Access Link to Article [10.1016/j.gca.2026.06.034]
¹Earth and Space Exploration Center, Ritsumeikan University, Kusatsu, Japan
²Institute for Extra-cutting-edge Science and Technology Avantgarde Research of Life (X-star), Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Yokosuka, Japan
Copyright Elsevier

The geochemical effects of freezing are becoming important in the investigation of closed aqueous environments, such as inland water on Earth and early Mars, and liquid water on planetesimals. Carbonate-bearing alkaline saline lakes in Mongolia are frozen in the cold season, with chemical species being partitioned among surface ice, lake water, and sediments. Freezing of the lakes leads to the accumulation of dissolved carbonate species, thereby decreasing the pH. The lakes are enriched not only in heavy metals, such as As, Mo, and U, but also in phosphorus. However, little is known about how metals and phosphorus are affected by chemical changes during freezing. Moreover, the mechanisms of major chemical changes are poorly understood and reproduced. Here we performed field surveys to investigate the behavior of these elements during lake freezing. Heavy metals and phosphorus accumulate in lake water during freezing, similar to major elements such as Cl−, with Mo and U concentrations reaching ∼1 mg/L. On the other hand, As and P accumulations are limited. Concentrations of heavy metals and phosphorus in ice increase with depth in the ice. We interpret the observed behavior using a geochemical model that accounts for their adsorption reactions coupled with water removal by freezing and carbonate precipitation. The model successfully reproduces the major chemical changes, including the decrease in pH, achieving quantitative accuracy by accounting for the combined effects of freezing and the revised solubility of carbonate minerals. The pH decrease promotes the adsorptions of As and P on sedimentary ferrihydrite particles, suppressing their accumulation in lake water. However, the decrease in pH is insufficient to promote adsorptions of Mo and U, resulting in their accumulations as major dissolved species. Adsorptions of heavy metals and phosphorus by iron oxides may be an important factor in their behaviors at low temperatures near the freezing point of water. Based on our model and observations, we discuss phosphate/carbonate precipitation in freezing porewater of icy planetesimals and phosphate availability in lake water on early Mars.

^1,2Juliana G. Peckenpaugh, ²Meryem Berrada, ¹Peng Jiang, ²Bin Chen
Geochimica et Cosmochimica Acta (in Press) Link to Article [10.1016/j.gca.2026.06.033]
¹Department of Earth Sciences, University of Hawaiʻi at Mānoa, Honolulu, HI 96822, USA
²Hawaiʻi Institute of Geophysics and Planetology, University of Hawaiʻi at Mānoa, Honolulu, HI 96822, USA
Copyright Elsevier

Mercury’s highly reduced formation conditions likely promoted the incorporation of silicon into its metallic core during planetary differentiation. The resulting Si-rich core composition would reduce the capacity of the metallic liquids to dissolve carbon, making carbon saturation more likely as the core cooled and crystallized. Determining the solubility of carbon in Fe-Si liquids under Mercury’s core conditions is therefore essential for evaluating whether graphite or diamond could precipitate from the core and influence Mercury’s thermal and magnetic evolution. In this study, high-pressure and high-temperature experiments were conducted on carbon-saturated Fe-Si alloys with varying silicon content from 4 to 27 wt% using a multi-anvil press at 5–20 GPa and 1673–1873  K. The analyses of the recovered samples by Scanning Electron Microscope (SEM) and Raman spectroscopy show the Fe-Si-C liquids with precipitated carbon phases in the form of graphite or diamond. Quantitative electron probe microanalysis (EPMA) results demonstrate a trend of decreasing carbon content in the Fe-Si-C alloys with increasing silicon content, described by the following equation: CFe-Si = 8.45–––0.663[Si] + 0.0134[Si]2. Higher initial silicon content within Mercury’s core due to the highly reduced conditions may result in lower solubility of carbon, suggesting a potential mechanism for the preferential exsolution of carbon-rich materials, such as graphite or diamonds. This finding suggests that carbon could precipitate within Mercury’s cooling, solidifying core under Mercurian core compositions and conditions. The segregation and accumulation of carbon could modify heat flux across the core-mantle boundary, affecting both the strength of Mercury’s early magnetic field and the longevity of dynamo action. Such compositional convection could sustain a dynamo, contributing to Mercury’s present-day magnetic field.