Future human bases on the Moon could produce water in situ melting lunar regolith (i.e. the surface layer of our natural satellite) at temperatures above 1100 °Cpossibly through mirrors that collect and focus sunlight. A recent study (accepted for publication in the journal The Innovation) where some samples of lunar regolith brought to Earth in 2020 by the Chinese mission were brought to melting temperature Chang’e 5 (The next mission, Chang’e 6, brought the first samples of the far side of the Moon to Earth in June 2024.) This discovery is important because the water production It will be a crucial factor for the permanence of humans on the Moon: it will be used for drinking, for irrigating plants in greenhouses and for producing – through electrolysis – oxygen to breathe and hydrogen as a source of energy. In addition to water, the fusion of lunar regolith also produces iron which can be used as a building material.
The study, conducted by a team of researchers led by Xiao Chenbrought a sample of lunar regolith to temperatures above the melting point (about 1100 °C) and through microscopic analysis discovered that the heating triggered chemical reactions that led to the production of water. The researchers estimated that in this way 1 gram of regolith can produce between 5.62 and 8.43 milligrams of water: in proportion, from one ton of regolith can yield more than 50 kg of water.
But how is it possible to obtain water by melting rocks? This happens because the minerals of the lunar regolith contain a certain amount of “trapped” hydrogen in their structure, which at high temperatures reacts with the iron oxides present in the regolith to form water and “free” iron. Hydrogen comes from the Sun through the so-called solar windsthat is, streams of charged particles (mainly protons and electrons) that our star continuously disperses into the surrounding space. When protons and electrons arrive on the lunar surface, they can combine to form hydrogen atoms, which in turn can remain trapped in the crystalline structures of the minerals present there.
According to the study, among the minerals that make up the lunar regolith, the one that proportionally contains the most “useful” hydrogen isilmenitea compound of iron, titanium and oxygen that has the chemical formula FeTiO3. Its crystalline structure presents micro-voids ideal for hosting hydrogen atoms. This mineral constitutes only 6% of the lunar regolith by weight but contains 38% of exogenous hydrogen. In particular, according to the researchers, the two main reactions that produce water are:
FeO + 2H → Fe + H2OR
Faith2OR3 + 6 H → 2 Fe + 3 H2OR
The reaction would be catalyzed by the flow of electrons present in the solar wind. Transmission electron microscope analyses clearly show that pairs of water “bubbles” and iron nanocrystals form in ilmenite even at temperatures of about 700 °C.
The study shows that it is possible to obtain water by melting regolith, but there is a whole series of obstacles between saying and doing. engineering and technological challenges not a small thing. While mirror systems can be used for temperature (a solution that is far from simple to implement), extracting water from a huge number of nano-bubbles is very complicated from a technical point of view.
