Although the Moon was previously thought to be dry, samples taken by the Apollo missions in the 1970s already revealed the existence of water trapped in minerals in the lunar interior. Orbiters also detected it across the lunar surface, especially at the poles.
Scientists considered that the interaction of the solar wind with materials in the soil of our satellite could produce water and maintain a cycle of this element there. However, no aqueous reservoir has been identified on the lunar surface. Now, an international team led by China believes it has found, as reported in the journal nature geoscience.
The results reveal that water stored in impact glass ‘beads’ (IGB) collected from the lunar soil by the Chang’e 5 spacecraft is consistent with the origin of the solar wind.
These are the ‘impact glass balls’ (IGBs), formed by the cooling of molten material ejected after the constant bombardment of asteroids that, in the form of meteorites, fall on the Moon. This granular material is spread over its entire surface and can store substantial amounts of water due to the effects of solar winds.
Researcher Huicun He, from the Chinese Academy of Sciences, along with other colleagues from his country and the United Kingdom, analyzed the water content of these IGBs thanks to samples of lunar soil collected by the Chang’e 5 spacecraft. This probe landed on the planet. lua in December 2020 and that same month brought the collected material to Earth for analysis.
After measuring the abundance, hydrogen isotopic composition, and core-to-water-edge variations in IGBs extracted from lunar soil, the results reveal that the water they store is consistent with the origin of the solar wind. For example, the characteristic signature of a positively charged isotope of hydrogen (H+) appears.
Accumulation of water by diffusion
Furthermore, the distribution of water into individual ‘beads’ indicates that H2O can rapidly accumulate in them by diffusion, on timescales of just a few years, and be rapidly released. The authors suggest that this presents an efficient recharge mechanism to drive an active water cycle on the Moon’s surface.
“The IGBs preserve hydration signatures and show water abundance consistent with internal diffusion of water derived from the solar wind,” write Huicun He and colleagues. “Diffusion modeling estimates diffusion times of less than 15 years at a temperature of 360 K (86.85 °C). These short diffusion times suggest an efficient water recharge mechanism that could sustain the water cycle on the lunar surface.”
The amount of water stored in these impact glass balls on lunar soils can reach 2.7 × 1014 kg
The researchers note in their study: “We estimate that the amount of water stored in these impact glass beads on lunar soils could reach 2.7 × 1014 kg. Our direct measurements of this reservoir of lunar surface water show that IGBs can store substantial amounts of water derived from the solar wind on the Moon.”
The authors note that the water trapped in these impact glass “beads” could represent a potential water resource for future exploration of the Moon, as it is relatively easy to extract, they say. They also concluded that this type of glassy material might harbor similar water deposits on other airless bodies.
References:
Hejiu Hui et al. “A reservoir of water derived from the solar wind on the Moon hosted by impact glass spheres”. Nature Geoscience, 2023.