Multiple sources of water preserved in impact glasses from Chang'e-5 lunar soil

Lunar dichotomy in surface water storage of impact glass beads

Water is the one of most precious resources for planetary utilisation. Lunar nearside impact glass beads (IGBs) have been demonstrated to contain abundant solar wind-derived water (SW-H2O); however, little is known about its farside counterpart. Here, we report the water abundances and hydrogen isotope compositions and their distribution in farside IGBs collected by the Chang'e-6 mission to investigate the role of IGBs in the lunar surface water cycle. Farside IGBs are found to have water abundances of ~10-1,070 μg.g-1 with hydrogen isotopes (δD) ranging from -988‰ to >2000‰ and display typical SW-H2O hydration profiles. The SW-H2O hydration depths in farside IGBs are strikingly shallower than in nearside IGBs. Moreover, the hydration profiles are only found in mare IGBs, with none observed in non-mare IGBs, indicating that SW-H2O hydration in IGBs is likely composition dependent. These findings indicate that SW-H2O storage of IGBs exhibits a dichotomy distribution in lunar soils.

A potential mantle origin for precursor rocks of high-Mg impact glass beads in Chang'e-5 soil

The chemical compositions of most lunar impact glass beads reflect mixing of crustal components including mare basalts, highlands rocks, and KREEP [from high concentrations of K, REE (rare earth element), and P]. However, a few glass beads in the soil from the Chang'e-5 mission have unusually high MgO contents that require distinct target compositions. The young age of these high-MgO glass beads suggests an origin through impact melting of ultramafic target rocks with abundant pyroxene and olivine. While such targets might represent cumulates of mare basalts, impact melts, or Mg-suite rocks, they appear unlike any sampled lunar lithologies. Alternatively, these high-Mg beads might be sampling the upper mantle brought to the surface by the Imbrium basin-forming event.