^1,2Ronghua Pang,^1,3Zhuang Guo,¹Chen Li,^1,4Sizhe Zhao,^1,5Xiongyao Li,¹Yuanyun Wen,⁶Shuangyu Wang,¹Rui Li,^1,5Yang Li
Journal of Geophysical Research (Planets)(in Press) Link to Article [https://doi.org/10.1029/2024JE008611]
¹Center for Lunar and Planetary Sciences, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang, China
²University of Chinese Academy of Sciences, Beijing, China
³Department of Geology, NWU-HKU Joint Center of Earth and Planetary Sciences, Northwest University, Xi’an, China
⁴State Key Laboratory of Lunar and Planetary Sciences, Macau University of Science and Technology, Macau, China
⁵Center for Excellence in Comparative Planetology, Chinese Academy of Sciences, Hefei, China
⁶Laboratory for Space Environment and Physical Sciences, Harbin Institute of Technology, Harbin, China
Published by arrangement with John Wiley & Sons

Due to the lack of an atmosphere and a global magnetic field on the Moon, its surface is extensively subject to space weathering. One of the important products of space weathering is the iron particle, which has significant impacts for planetary exploration. Research on Apollo samples suggests that iron particles primarily form through vapor deposition processes during meteorite impacts. The Chang’e-5 (CE5) samples are the youngest samples collected so far, and the phenomenon of surface vapor deposition has not been studied in depth. Anorthite stoichiometrically free of Fe minerals, is highly suitable for studying the vapor deposition process of iron particles. Five anorthite grains from CE5 were analyzed using transmission electron microscope (TEM). Results show that the iron particle on the surface of anorthite formed from impact sputtering glass, and lack vapor-deposited nanophase iron particles (np-Fe0, <100 nm) on its surface. Additionally, residual Fe from Fe-Mg silicate impactors on the anorthite surface did not form np-Fe0. The dominant mechanism of np-Fe0 formation due to space weathering differs between the CE5 and Apollo landing sites. Impact melting rather than vapor deposition may be the dominant mechanism of np-Fe0 formation at the CE5 landing site due to impact. This indicates that the meteorite impact environment of CE5 landing site is weak. It is not possible to generate a large amount of vapor deposition-derived np-Fe0 like in Apollo samples.

¹Baoliang Wang, ¹Frédéric Moynier, ²Yan Hu
Geochimica et Cosmochimica Acta (in Press) Open Access Link to Article [https://doi.org/10.1016/j.gca.2025.04.007]
¹Université Paris Cité, Institut de Physique du Globe de Paris, CNRS, 1 Rue Jussieu, 75005 Paris, France
²Department of Geoscience, University of Nevada, Las Vegas, Las Vegas, NV 89154, USA
Copyright Elsevier

Enstatite meteorites, including enstatite chondrites and enstatite achondrites (e.g., aubrites), formed under highly reducing conditions in the solar system. Enstatite chondrites underwent progressive thermal metamorphism from petrologic type 3 to type 6, potentially leading to vaporization and redistribution of volatile elements. Coupled Rb and K isotopic analyses of enstatite meteorites could provide complementary insights into the inherent isotopic variability and volatile depletion processes. In this study, we present Rb and K isotopic compositions for a suite of enstatite meteorites, including sixteen enstatite chondrites spanning metamorphic grades from 3 to 6, as well as four aubrites. Type 3 enstatite chondrites exhibit isotopic compositions similar to those of Earth for both Rb and K, which further underscores the isotopic resemblance between Earth and enstatite chondrites. From type 3–4 to type 5–6, the examined enstatite chondrites generally show a trend towards heavier Rb and K isotopic compositions, indicating volatilization and redistribution of Rb and K during open system thermal metamorphism of the parent body(ies). One EH5 (St. Marks) and two EL6 (Pillistfer and Atlanta) samples deviate from this trend with light K isotope compositions, which may result from an interplay of evaporation, vapor transport and recondensation. On the other hand, the Rb and K isotopic variations in aubrites—which originated from the melting and fractional crystallization of enstatite chondrite-like parent body(ies)—likely reflect more complex processes, possibly involving a combination of plagioclase-bearing melt extraction, magmatic differentiation, core segregation, and the back-condensation of volatiles after impact volatilization.