While there is, as of yet, no evidence that there are other intelligent beings in the universe, it seems reasonable to think that there could be such beings. After all, the universe is a rather big place and if God exists it seems likely that He would not just create a big, empty universe. After all, any reasons He had to create us would also seem to give Him reasons to create other beings. Then again, perhaps we are all alone because our creation sufficed for His purposes. Maybe all that empty space is reserved for us or maybe it just exists to give us something to look at at night (other than YouTube and internet porn).
But, let us suppose that there are other worlds with other mortal beings like us. If they sinned (as we supposedly did), then presumably God would extend His mercy to them and send Jesus to die for their sins. Of course, unless this is a Star Trek style universe, the aliens will not be humans and hence the alien Jesus will be just that-a combination of God and alien. Of course, alien is a relative thing-our Jesus would be an alien Jesus to the others.
From a metaphysical standpoint, there is no more problem with an alien Jesus than there is for the human Jesus. After all, however the metaphysics supposedly worked with the human Jesus can work the same way for alien Jesus-only the biology would be different.
Of course, there are some reasons why there might not be an alien Jesus. First, there might not be any Jesus at all, and hence no alien Jesus. Second, there might not be an aliens and hence no alien Jesus. Third, aliens might be without sin. Perhaps all other beings were created without sin or managed to pass the sin test and never fell from grace. So, if we ever build star ships, we might find Eden after Eden. Fourth, perhaps God does not care about aliens and is content to let them all toast in Hell. Fifth, maybe there are aliens, but they do not have an afterlife and hence have no need of an alien Jesus. There are, of course, other