China's Chang'e-5, which touched down on the Moon in December 2020, found water at its landing site using spectral reflectance measurements of soil and rocks.
Now, researchers at the Chinese Academy of Sciences (CAS) found that impact glass beads in Chang'e-5's lunar soils also contain some water.
Detailed studies suggest that these glass beads are likely to be a new water reservoir on the Moon reflecting the movement of water into and away from the surface due to solar wind.
Solar winds originating from the Sun are capable of changing the chemical composition of the Moon's surface by causing it to eject oxygen which then combines with hydrogen ions in the same solar winds to create water.
Many lunar missions have confirmed the presence of structural water or water ice on the Moon and there is little doubt that most of the Moon's surface harbours water, though the amount is much less than on Earth.
Surface water on the Moon has been shown to be lost to space during its daily rotations. This indicates that there should be a water reservoir at depth in lunar soils to sustain the retention, release, and replenishment of water on the surface.
However, previous studies of water inventory of fine mineral grains in lunar soils, impact-produced agglutinates, volcanic rocks, and pyroclastic glass beads have been unable to explain the retention, release, and replenishment of water on the surface of the Moon.
The researchers proposed that impact glass beads, a ubiquitous component in lunar soils, were a potential candidate for investigation of the unidentified hydrated layer or reservoir in lunar soils.
The glass beads returned by the CE5 mission were studied in depth to discover their composition and the abundance of water within them. The 'hydration profiles' compiled by the team showed that much of the water was derived from the solar wind.
The impact glass is assumed to act as a sponge for buffering the lunar surface water cycle.
"These findings indicate that the impact glasses on the surface of the Moon and other airless bodies in the solar system are capable of storing solar-wind-derived water and releasing it into space," said team leader Professor Hu Sen.
In August, Nasa unveiled a high-powered laser which it intends to use to discover new patches of water on the Moon.
