Since time immemorial, humans gazing up at the moon have asked grand questions. Where did it come from? Why does it wax and wane? Is it made of cheese?

We now have responses to most of these (“a giant impact,” “orbital phases” and “no, sadly,” respectively). But as an international 21st-century lunar race intensifies, one pragmatic query remains: How can you make money on the moon?

Helium-3 is spectacularly useful, and demand for it is soaring. A superlative coolant, helium-3 enables quantum computers to reach their operating temperatures, fractions of a degree above absolute zero. The precious substance is also vital for advanced medical imaging, as well as sniffing out smuggled nuclear material, and holds promise as a clean fuel for future fusion reactors. On terra firma, most of the available supply of helium-3 comes as a by-product of nuclear weaponry via the radioactive decay of tritium, a rare isotope of hydrogen that boosts the power of thermonuclear bombs. This process makes just a few kilograms of helium-3 per year worldwide, and a single kilogram currently costs about $20 million.

But scientists estimate that somewhere on the order of a billion kilograms of helium-3 are lacquered onto the lunar surface. So the moon-based mining of helium-3 could, it seems, someday become a multitrillion-dollar industry.