[keep_reading]

> Not on Earth, or anywhere in the Solar System except the interior of the Sun, as far as I know

There are helium-3 deposits on the moon. That's what the new space race is about. Bezos wants to mine helium on the moon...

https://www.popsci.com/blue-origin-moon-lander/

[pdonis]

Hm, interesting. Helium-3 would be better than Helium-4 (which is what I assumed in the numbers I gave), its weight is halfway between Helium-4 and Hydrogen gas.