If we find tons of gold on mars will that affect gold prices here on earth?
Yes it will, all that gold has to come here. There are no buyers sitting there on Mars.
Will it be economical to bring all the golds here and sell here? We barely can send a piece of metal there.
I think a more viable threat to gold prices might be the ability to produce it artificially.
This happened with Diamonds (Some references - https://money.stackexchange.com/questions/79848/is-it-true-that-the-price-of-diamonds-is-based-on-a-monopoly, https://www.forbes.com/sites/pamdanziger/2019/12/15/mined-diamond-sales-decline-as-the-future-is-in-laboratory-grown-diamonds/, and https://www.bbc.com/future/article/20200207-the-sparkling-rise-of-the-lab-grown-diamond)
There are ways to produce gold artificially currently in existence (https://en.wikipedia.org/wiki/Synthesis_of_precious_metals#Gold) but each of those has some kind of shortcoming (either more expensive than mining gold or the gold produced is radioactive). If progress happens in that field, then things might change
If somehow we can bring to earth at low cost , maybe scarcity which drives the value of gold will diminish and price would crash. This is one of the thing which could happen
Synthesizing Gold is not as simple as Diamonds.
For curious minds:
Trading is only activity that gets you learn chemistry, physics, spiritual consciousness and alchemy all at same time 
1 Like