Revealing Space Weathering of the Moon Farside via Soft X-ray Emission Spectroscopy

The Chang'e-6 (CE-6) mission successfully brought the precious lunar soil from the South Pole-Aitken (SPA) basin on the Moon's farside, providing a unique opportunity to investigate space weathering in this region. Herein, to the best of our knowledge, we first combined soft X-ray emission spectroscopy (SXES) technique with scanning electron microscopy (SEM) to analyze micromorphology and electronic structure of the lunar sample. The results demonstrate that both O-<i>K</i> and Si-<i>L</i> SXES spectra exhibit a systematic low-energy shift, along with significant broadening of the O-<i>K</i>. Thus, the lunar sample has been predominantly transformed into a highly reduced and amorphous state, which is due to the combined effects of solar wind hydrogen ion irradiation and micrometeorite impacts. Our study elucidates space weathering mechanisms on the lunar farside at an electronic scale, providing a novel analytical method and key evidence for understanding the material evolution on the Moon and other airless celestial bodies.