Possible records of space weathering on Vesta: Case study in a brecciated eucrite Northwest Africa 1109

Shu-Zhou WANG1, Ai-Cheng ZHANG1,2, Run-Lian PANG1, Yang LI3, and Jia-Ni CHEN1
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13254]
1State Key Laboratory for Mineral Deposits Research, School of Earth Sciences and Engineering, Nanjing University,Nanjing 210046, China
2Lunar and Planetary Science Institute, Nanjing University, Nanjing 210046, China
3Center for Lunar and Planetary Sciences, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, China
Published by arrangement with John Wiley & Sons

Records of space weathering are important for understanding the formation and evolution of surface regolith on airless celestial bodies. Current understanding of space weathering processes on asteroids including asteroid‐4 Vesta, the source of the howardite–eucrite–diogenite (HED) meteorites, lags behind what is known for the Moon. In this study, we studied agglutinates, a vesicular glass‐coating lithic clast, and a fine‐grained sulfide replacement texture in the polymict breccia Northwest Africa (NWA) 1109 with electron microscopy. In agglutinates, nanophase grains of FeNi and FeS were observed, whereas npFe0 was absent. We suggested that the agglutinates in NWA 1109 formed from fine‐grained surface materials of Vesta during meteorite/micrometeorite bombardment. The fine‐grained sulfide replacement texture (troilite + hedenbergite + silica) should be a result of reaction between S‐rich vapors and pyroxferroite. The unique Fe/Mn values of relict pyroxferroite indicate a different source from normal HED pyroxenes, arguing that the reaction took place on or near the surface of Vesta. The fine‐grained sulfide replacement texture could be a product of nontypical space weathering on airless celestial bodies. We should pay attention to this texture in future returned samples by asteroid exploration missions.

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