Wouldn’t discovering a massive supply of gold on Mars instantly devalue it?
Note that there is already a huge amount of gold in the oceans, but it's very diluted so it's too expensive to extract. You don't want to just know that there is gold. You want to know how much profit you would get after the gold bars arrive to Fort Knox.
edit: this is assuming we're not allowed to set up nuclear reactors there
Oxygen atoms are easy to find, sand and rust (and water) have a lot of them. The problem is isolating them to produce molecular oxygen that can be used to burn the fuel.
Eventually it should be possible to build such things in space and then they can be huge. There are already semi-serious proposals to solve the Earth's energy problems with space based solar collectors. Of course they would have to a lot bigger further out. Perhaps Jupiter's flux tubes could be tapped.
Feasible? No.
https://www.youtube.com/watch?v=Wum8_8sWdeU
We really lucked out with all of that ancient unmetabolized biomass.
Without that, we might not have had our fancy computers by this point.
I'm genuinely curious: why do you say this?
What's the price of gold on Earth? Is it the same as now? What if I could email someone on Mars and buy 50oz of gold? Could I sell it to someone here? What if it's cost prohibitive to move all of the gold to Earth? Or any of the gold to Earth? How refined does the Martian gold have to be before someone on Mars can say the own it?
The answers to all of those are clear (or at least only marginally unclear) for materials that are intrinsically valuable but for the "store of vaule" as opposed to industrial use of something like gold it gets weird for me.
I guess the answer to all of those questions is - whatever someone will pay.
In Micronesia there was a practice of carving massive "coins" out of stone. These "Rai stones" were often too large to move. Yet individuals could "own" them and they were traded often for things of great value. I believe I even read an account of one that had sunk in a shipwreck, but the owners went on to trade it even though it was at the bottom of the sea.
Just cause a physical item cannot be possessed physically doesn't mean it is valueless.
However, for gold specifically, part of what makes it valuable is that it has some manufacturing uses and people like making jewelry out of it. There is no doubt a much larger supply of gold throughout the universe than on earth and it has no effect on the price here.
So I think while you can buy and sell gold on another planet (provided people can widely agree on it's transfer of ownership), that would be a completely separate market from the terrestrial gold market.
We'd need something much more valuable, although the usual go-to, diamonds, also wouldn't work since it's a highly controlled market.
At that point you're in exotic materials territory. Maybe a natural source of Californium which on Earth is only produced in reactors or particle accelerators, and actually has industrial uses? Even if its price dropped substantially, we'd probably find new uses for the new supply and the stuff costs millions of USD per gram.