China discovers water-loaded beads on Moon, offering huge reservoir

Scientists already suspect that there should be a hydrated layer or reservoir at depth in the lunar soils to support the retention, release, and replenishment of water on the Moon's surface, given that surface water on the Moon exhibits diurnal cycles and loss to space.

Still, prior investigations into the water content - of lunar soils' small mineral grains, agglutinates created by impacts, volcanic rocks, and pyroclastic glass beads - have been unable to explain this lunar surface water cycle.

Now, doctorate candidate HE Huicun, under the guidance of Prof. HU Sen, proposed that impact glass beads, a common component in lunar soils with a non-crystalline form, were a suitable candidate for examination of the unexplained hydrated layer or reservoir in lunar soils. 

The researchers examined the water content of glass beads generated by impact events using Chang'e-5 lunar soil samples. They discovered water consistent with a solar wind origin is stored within the impact glass.

Additionally, water distribution within individual beads suggests that water can quickly build up in glass beads through diffusion over a few years and then be rapidly released.

The researchers estimated that the amount of water glass beads contributes to lunar soils varies from 3.0 × 1011 kilograms to 2.7 × 1014 kilograms. 

"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 Prof HU Sen in a press release. 

According to the authors, this offers a powerful recharge mechanism to support an active water cycle on the lunar surface.

They also argue that impact glass may contain comparable water reservoirs on other airless worlds and that the water trapped in impact glass beads may constitute a potential water resource for future lunar exploration that is relatively simple to extract.

Study abstract:

The past two decades of lunar exploration have seen the detection of substantial quantities of water on the Moon’s surface. It has been proposed that a hydrated layer exists at depth in lunar soils, buffering a water cycle on the Moon globally. However, a reservoir has yet to be identified for this hydrated layer. Here we report the abundance, hydrogen isotope composition and core-to-rim variations of water measured in impact glass beads extracted from lunar soils returned by the Chang’e-5 mission. The impact glass beads preserve hydration signatures and display water abundance profiles consistent with the inward diffusion of solar wind-derived water. Diffusion modelling estimates diffusion timescales of less than 15 years at a temperature of 360 K. Such short diffusion timescales suggest an efficient water recharge mechanism that could sustain the lunar surface water cycle. We estimate that the amount of water hosted by impact glass beads in lunar soils may reach up to 2.7 × 1014 kg. Our direct measurements of this surface reservoir of lunar water show that impact glass beads can store substantial quantities of solar wind-derived water on the Moon and suggest that impact glass may be water reservoirs on other airless bodies.