^1,2M. D. Suttle, ¹B. Brabrián
Earth and Planetary Science Letters, 697, 120415
Open Access Link to Article [DOI: 10.1016/j.epsl.2026.120415]
¹School of Physical Sciences, The Open University, Walton Hall, Milton Keynes, MK7 6AA, UK
²Dipartimento di Scienze della Terra, Università di Pisa, Pisa, 56126, Italy

Copyright Elsevier

We investigate three unresolved questions in CM chondrite research: (1) what was the initial O-isotope composition of their accreted water? (2) How much water was accreted? And (3) Did aqueous alteration proceed under open or closed-system conditions? We approach this problem through numerical modelling of the aqueous alteration process using an O-isotope perspective. Our model simulates dissolution and mixing between dry rock and the fluid reservoir, secondary mineralisation (phyllosilicate and calcite) and, in some scenarios open-system evaporative loss. Previously published O-isotope measurements (CM chondrite bulk rock, and T1 and T2 calcite) and a suitable alteration extent (65–85 vol%) are used as constraints against which viable alteration scenarios must match. We find the most likely conditions for alteration were the accretion of water-ice with an approximately Earth-like composition (plotting on or close to the intersection between the TFL and the PCM) and with a δ¹⁸O value <30‰ and likely at ∼5‰, prograde conditions (increasing temperature with time), T1 formation before significant protolith was dissolved, an initial water-to-rock (mass) ratio of ∼0.6 and moderate open system evaporative water loss. The most surprising result of this study is the isotopically light (relatively ¹⁶O-rich) initial water composition. We show that this is consistent with fluid compositions independently determined from several other studies. This implies that outer Solar System water was not ubiquitously ¹⁶O-poor, as might have been expected based on the composition of isotopically anomalous cosmic symplectite found in Acfer 094.

¹Andrei Yakovlev, ¹Dmitriy Beloborodov
Icarus (in Press) Link to Article [DOI: 10.1016/j.icarus.2026.117363]
¹St. Petersburg State University, 28, Universitetskaya prospekt, St. Petersburg, 198504, Russia

Copyright Elsevier

We investigate the dynamics of levitation and horizontal transport of lunar regolith particles in the vicinity of the terminator, taking into account the radiation pressure of solar irradiation. In contrast to earlier simplified models, the radiation pressure efficiency factor Q_pr(R) is calculated based on Mie theory using experimental data for the complex refractive index of vitreous silicate that is characteristic of lunar soil. We consider a two-dimensional model of particle motion in the near-surface photoelectron sheath that incorporates electrostatic, gravitational and radiation forces. Within this framework, the dependence of the minimum levitation angle θ_min(R) on particle radius is analyzed, and numerical calculations of the maximum horizontal transport distance L_max(R) during sunrise and sunset periods are performed. Our results show that incorporating the real optical properties of particles leads to quantitative changes in the dependence of L_max(R) compared to earlier estimates. At sunset, the transport maximum is attained for particle radii of approximately 0.075 μm, whereas at sunrise a non-monotonic dependence L_max(R) appears, along with significantly larger transport distances for small particles. Our findings show that the realistic optical properties of particles have a significant impact on the spatial scales over which lunar regolith is redistributed horizontally.

¹Ai-Cheng Zhang, ¹Tian-Ran Du, ¹Lang Zhang, ¹Xiao-Wen Liu, ²Li-Ping Qin
Meteoritics & Planetary Science (in Press)
Link to Article [DOI: 10.1111/maps.70260]
¹State Key Laboratory of Critical Earth Material Cycling and Mineral Deposits, School of Earth Sciences and Engineering, Nanjing University, Nanjing, China
²State Key Laboratory of Lithospheric and Environmental Coevolution, School of Earth and Space Sciences, University of Science and Technology of China, Hefei, China

Published by arrangement with John Wiley & Sons

Late veneer hypothesis involves a process whereby material with a generally bulk chondritic composition is added to the silicate shell of a differentiated planetary body, subsequent to core formation. Understanding the origin and extent of the putative late veneer is critical for understanding the late stages of planetary accretion and evolution. The late veneer concept was originally proposed based on the absolute and relative abundances of highly siderophile elements in whole-rock samples of Earth’s mantle, and supported by data for several other planetary bodies. No supporting mineralogical evidence, however, has been reported. Here, we report the discovery of an Ir,W,Ru,Rh-rich metal grain in early-formed unbrecciated cumulate eucrite Northwest Africa 8326. We suggest that the W-rich nature of this grain could not be a result of eucrite parent melt evolution, or due to exsolution from a pre-existing sulfide phase during cooling or S degassing. Instead, it is best explained with the addition of a chondrite-related component. The survival of this W-rich metal grain during high-temperature melting processes could be related to its high melting point. The W-rich grain in NWA 8326 represents the first mineralogical evidence, supporting the late veneer hypothesis. Refractory metal grains in unbrecciated achondrites like that reported here potentially have important impacts on the highly siderophile element patterns and isotopic modal ages of their host rocks.