Chinese scientists have found signs of water in samples retrieved by China from a lava plain on the moon, bringing them closer to understanding its origin there - a crucial question for future lunar exploration.

In a paper published in Nature Communications this week, the scientists said they had analysed remnants of solidified lava retrieved by an uncrewed Chinese mission from the plain known as the "Ocean of Storms" and found evidence of water in the form of hydroxyl encased in a crystalline mineral known as apatite.

Hydroxyl, comprising a single hydrogen atom and an oxygen atom versus two hydrogen to one oxygen in a water molecule, was also found in samples retrieved by NASA decades ago.

It was widely held that most of the water on the moon was the result of chemical processes triggered by the bombardment of charged particles from the sun on the lunar surface.

The source of hydroxyl in minerals such as apatite is very likely indigenous, the scientists said.

"The hydroxyl contents in foreign materials produced by the impact processes are probably negligible," the scientists said.

The Chinese samples suggest that little or none of the hydroxyl in them was from "extraneous sources", they said.

China's Chang'e-5 mission, named after the mythical Chinese goddess of the moon, brought back 1,731 grammes of samples in December 2020 after retrieving the soil and rock from a previously unvisited part of the Oceanus Procellarum plain.

China is expected to launch more uncrewed lunar missions in coming years, with the study of water one of the objectives.

The presence of water on the moon could shed more light on the evolution of the solar system. It could also point the way to in-situ water resources vital to any long-term human habitation.

"The sources and distributions of water on the moon are still an open question with no consensus," the scientists said.