I first heard about helium-3 (He-3) from the geologist Harrison "Jack" Schmitt, the only scientist among the 12 Americans who walked on the moon between 1969 and 1972, and a tireless campaigner for a US return. He understood a 21st-century programme would never happen without an economic rationale, and he hoped that He-3, which is deposited on the surface by the solar wind, might provide one. If the necessary fusion technology could be made to work, he said, this compound would be a source of clean energy for Earth.Against Schmitt's enthusiasm were the facts that, a) no one had made the technology work, b) the US had to get up there first, and c) mining He-3 would involve ripping up the lunar surface to a depth of one metre. So the idea of mining moon dust has gained little support in the US. Now it seems China might be with Jack on this one - and where they go, everyone else will try to follow.
Whether it turns out to be He-3, solar energy, or some as yet unknown technology that draws humanity back to the moon, there's an irony here. In 1968, Apollo 8 brought back the first shimmering image of an "Earthrise" as seen from the moon. Four years later, Apollo 17 came home with the famous whole Earth picture. These new views of our fragile, heartbreakingly isolated planet are often credited with having helped to kickstart the environmental movement - even with having changed the way we see ourselves as a species.
At present, nations are forbidden under international treaty from making territorial claims to the moon, but the same has hitherto been true of Antarctica, of which the UK government is trying to claim a chunk. Earth's sister has played a role in teaching us to value our environment: how extraordinary to think that the next giant leap for the environmental movement might be a campaign to stop state-sponsored mining companies chomping her up in glorious privacy, a quarter of a million miles from our ravaged home.