1Y. Fu, 1H. Z. Wang, 1J. Zhang, 1Q. Q. Shi, 1R. L. Guo, 1A. M. Tian, 2C. Yue
The Astrophysical Journal, 1008, 141
Open Access Link to Article [DOI: 10.3847/1538-4357/ae9098]
1Shandong Key Laboratory of Space Environment and Exploration Technology, School of Space Science and Technology, Institute of Space Sciences, Shandong University, Key Laboratory of Eco-Environment and Population Health of Xizang Autonomous Region, Weihai, Shandong, 264209, People’s Republic of China
2School of Earth and Space Sciences, Institute of Space Physics and Applied Technology, Peking University, Beijing, People’s Republic of China
Solar wind ion irradiation and micrometeoroid impacts are two primary agents of lunar space weathering, but their relative contributions remain unclear. This study provides new constraints by analyzing optical maturity (OMAT) asymmetries of crater walls in the lunar polar regions (latitude > 50°). Using OMAT derived from Kaguya Spectral Profiler observations, we analyze the equator facing–pole facing (EF–PF) and east–west (E–W) space weathering asymmetries of polar crater walls. After excluding craters significantly affected by geological processes, such as crater degradation, impact ejecta mixing, and impact excavation, the EF–PF asymmetry increases toward polar regions at latitudes above 50°, whereas previous studies reported the opposite trend at latitudes below 50°, indicating a latitudinal trend reversal occurring around 50°. The E-W asymmetry is similar to that observed at low latitudes. Simulations based on real crater morphology show that solar wind alone (even with the shielding effect of the Earth’s magnetosphere) cannot explain the latitude of this trend reversal, which may be due to the increasing importance of micrometeoroid flux at high latitudes. However, by including micrometeoroid impacts, which have a more isotropic flux, our models successfully reproduce the observations. The simulations suggest that micrometeoroid impacts should contribute at least 70% as much as the solar wind to space weathering in the lunar equatorial region. This work demonstrates that micrometeoroid impacts are a significant process in lunar space weathering comparable in importance to the solar wind.
