^1,2Chen Li et al. (>10)
Geochimica et Cosmochimica Acta (in Press) Link to Article [https://doi.org/10.1016/j.gca.2024.10.035]
¹Center for Lunar and Planetary Sciences, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, China
²Faculty of Metallurgical and Energy Engineering, Kunming University of Science and Technology, Kunming 650093, China
Copyright Elsevier

The formation of a unique microstructure of minerals on the surface of airless bodies is attributed to space weathering. However, it is difficult to distinguish the contributions of meteorite impacts and solar wind to the modification of lunar soil, resulting in limited research on the space weathering mechanism of airless bodies. The thermochemical reactivity of troilite can be used to distinguish the contributions of impact events and solar wind to the modification of lunar soil and provide evidence for space weathering of lunar soil. We examined the structure of a single particle of troilite in the Chang’e-5 lunar soil and determined whether an impact caused the thermal reaction. Microanalysis showed that troilite underwent substantial mass loss during thermal desulfurization, forming a crystallographically aligned porous structure with iron whiskers, an oxygen-rich layer, and other crystallographic and thermochemical evidence. We used an ab initio deep neural network model and thermodynamic calculations to conduct experiments and determine the anisotropy and crystal growth of troilite. The surface microstructure of troilite was transformed by the thermal reaction in the vacuum on the lunar surface. Similar structures have been found in near-Earth objects (NEOs), indicating that small bodies underwent the same impact-induced thermal events. Thus, thermal reactions in a vacuum are likely ubiquitous in the solar system and critical for space weathering alterations of the soil of airless bodies.

^1,2Zhuang Guo,¹Yu Zhu,^2,3Yang Li,⁴Ian M. Coulson,^2,3Xiongyao Li,^2,3Jianzhong Liu
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.14283]
¹State Key Laboratory of Continental Dynamics & NWU-HKU Joint Center of Earth and Planetary Sciences, Department of Geology, Northwest University, Xi’an, China
²Center for Lunar and Planetary Sciences, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang, China
³Center for Excellence in Comparative Planetology, Chinese Academy of Sciences, Hefei, China
⁴Solid Earth Studies Laboratory, Department of Geology, University of Regina, Regina, Canada
Published by arrangement with John Wiley& Sons

Basaltic shergottites are the most abundant rock type of Martian meteorites, and pyroxene grains within shergottites commonly show a zoned structure. Here, the detailed microscopic mineralogical characteristics of patchy zoned pyroxene in basaltic shergottite NWA 12522 were investigated by a combination of scanning electron microscopy, electron microprobe, Raman spectroscopy, and transmission electron microscopy. The results show that the cores of zoned pyroxene in NWA 12522 have a homogeneous Mg# value and consist mainly of augite and pigeonite. By contrast, the rim of zoned pyroxene is extremely ferroan and can be further divided into two regions based on quite distinct mineralogy and textures (i.e., far-core and near-core pyroxene rims). The near-core rim shows narrow exsolution lamellae (~35 nm) that were cross-cut by thin pigeonite veinlets and contain abundant nano-sized particles of metastable pyroxferroite and pigeonite. Only relatively coarse exsolution lamellae (~80 nm) were observed in the far-core pyroxene rim regions. The distinct mineralogical characteristics of the pyroxene rims and cores in NWA 12522 imply different crystallization conditions, and the homogeneous Mg-rich pyroxene cores should have slowly crystallized from magma within a deep-seated chamber, followed by an overgrown evolved melt on these pyroxene cores during their ascent to the Martian surface, and disequilibrium crystallization of nano-sized metastable phase (pyroxferroite) occurred in the near-core region. The abnormally low ΣREE contents and steep REE pattern (high Yb/La ratio) of the pyroxene rims in NWA 12522 imply that merrillite should have crystallized prior to the pyroxene rims, making the residual melt become REE-depleted and HREE-enriched.