Then there's always asteroid mining. That could be the major profit driver for early space colonization.
Discussion
The thing about mining that everyone forgets, is that its not enough for the desired element to be present, you also need an energy gradient to drive natural processes to concentrate it into ore.
Mars has this. Actually ALL the same processes as Earth.
Ceres and Luna had radioisotopic heat gradients and hydrothermal systems, so maybe.
Europa and Ganymede have tidal heating and hydrothermal systrems, plus fractional crystalisation of brines in ice diapirs. So maybe, but a bit weird.
Most asteroids are poorly differentiated and probably worthless.
Yup. Just the few that were part of proto planet cores that got blasted are useful, but those very much so.
My boss would love to dissolve Psyche in carbonyl. He has done some unpublished research on this, proving the practicality of separating iron, nickel and cobalt carbonyls.
Don't try this at home, though!
If you can get to the asteroids, though, couldn't you throw the rocks in a hot centrifuge or something to concentrate the elements into ores? Maybe not.
Worth a try!
You certainly can, there are many technologies we could use; but it costs energy, and wear and tear on precision machinery that is hard to repair and harder to replace.
Mars, by contrast, very likely has ores of a purity we mined out on Earth long ago; that mining engineers today can only dream of.
Luna and Ceres will have some too, but not the variety and mostly in deep hydrothermal systems hard to access.
Europa and Ganymede have stronger energy gradients than Earth or Mars ever did, but their geology is WEIRD. Most probably they have ores of amazing purity lying around, but they will be ones we don't see on Earth except in some evaporite sequences.
One of the biggest benefits of astroid (or lunar) mining is that most of its value derives from not being on earth. At Falcon 9 prices of roughly $3000/kg you'd lose most of the value by bringing it to earth.
We need in-space markets. Giant rotating stations preferably.