The Moon’s surface contains water in glass beads formed by the impact of meteorites, according to a study based on samples brought back to Earth by China’s Chang’e 5 lunar probe.
There is little doubt that most of the Moon’s surface harbours water in some form, a team of Chinese researchers said in the study, published on Monday in Nature Geoscience.
The team examined about 100 tiny glass beads brought back in 2020 and ranging in size from the thickness of a hair to a millimetre. The beads, dating back as much as two billion years ago, were created by meteoroid impacts that melted the lunar material.
US lunar missions had brought back samples of them, but this is the first time they have been studied in detail, according to the study.
The tiny receptacles contain as much as two millionths of a gramme of water equivalent per gramme of bead. This water comes from different processes than those resulting from lunar volcanism or falling comets (which contain ice).
The team, led by researchers from the Chinese Academy of Sciences, speculates that the glass beads formed during a meteoroid impact would have initially lost most of their water. They were then bombarded by solar winds, delivering hydrogen which then combined with the oxygen atoms contained in the beads.
The study concludes that these glass beads could constitute the “dominant reservoir” involved in the water cycle on the Moon, “usable in situ in future lunar explorations,” especially since this water would be “fairly easy to extract.”