Profitable space mining is easily 100+ years out. So, IMO your best bet is to invest in an existing company you expect to get into the field in the long term.

PS: We could extract gold from sea water, and there is a lot of gold in the sea. That does not mean it's a good investment.

Per my other comment in this thread, you could perhaps provide funding for researcher studying mining techniques in exchange for a partial interest in any patents that arose out of that work. But beyond that I don't think there is a way to participate yet as an outside investor, lots of ways to participate if you're just jumping in and doing the work yourself right?

Perhaps you could invest a few thousand in an S&P500 ETF with instructions to use the account value to buy into the first space mining company to go public? Might take awhile but you're investment would grow while it was waiting to be put to work.

Get your ass to work.

What other "entry point" do you truly expect for emerging worlds?

#kidstoday

Simple supply and demand: Sell commodity futures. If there really are huge influxes of an existing scarce resource on the horizon (the article mentions platinum), prices will drop.

Mutual funds of some sort, I'd guess. Assuming there are any.