Some day in the future we will have human settlements in Mars can they use bitcoin?
Earth-Mars transactions would currently not be so fast. The distance to mars is about 1.5 lightyears, If I am not mistaken. Faster than light is necessary for crypto to work on such an enormous scale - nobody wants to wait about 2 years for a transaction.
On Mars itself - of course. But to mix the economies into a space economy, faster than light is necessary. For now, moon-earth crypto is about the largest we can do.
I suggest you take a class on astronomy. Mars is not 1.5 lightyears from Earth. At its farthest from Earth, it's something like 22 light minutes.
At 22 light minutes, would the slowing of confirmation times cause an issue in the blockchain?