Bitcoin in the far future
The extraterrestrial mining problem is the prospect of Bitcoin mining occurring on bodies other than the Earth.
Mining bitcoins on the moon is feasible, as transactions and blocks between it and the Earth would only be delayed by a few seconds. The worst that this would cause is the occasional orphaned block when a block is solved on both the Earth and the Moon within this several-second timeframe. Transactions could occur when broadcast from either body and nodes would be able to communicate with other nodes on either body.
Mining on Mars is a bigger problem, because it would take several minutes for communication from the Earth to reach Mars, depending on their distance at the time of broadcast. As such, it is uncertain that a block solved on Mars would reach the terrestrial block chain in time for a block to be solved on Earth instead.
Where faster-than-light technology is required to reach somewhere in a reasonable amount of time, faster-than-light technology would be required to communicate with anyone there in the first place without significant delay. Whether bitcoin will be able to function under these conditions depends on what kind of technology will exist when they will be reproducible.