They’re both so near zero as to be hardly worth considering.

The thing to think about is the fact that, in either case, ghost or alien are in any way especially indicated by the evidence. People don’t see something strange and conclude aliens because they have good reason to believe from the evidence that something traveled vast distances across space, but rather they simply don’t have anything good to believe right now.

Having unusual evidence that doesn’t seem to point at the simple, mundane explanation isn’t the same as having evidence that does point at a supernatural or extraterrestrial explanation