The Emperor of Mankind
Currently the galaxy's spookiest paraplegic
Most certainly.
Unfortunately, yes... seeing as how NASA is based in a country that's HEAVILY religious in its culture.
Probably, at least on those other worlds.
Possibly, but I doubt it. Pretty much all extant religions are dependent upon a single-planet experience, even the ones that deal in aliens and space.
I think it more likely that new religions will be born, out of the new cultures that form in these new worlds. Religion is, first and foremost, an expression of a culture's collective experience, and so you'll find different religions in places where that collective experience is different.
Since we haven't had any of these experiences, I'm not sure we can accurately speculate on exactly what those religions will look like.
Another possibility is that current religions will shift into new forms, going by the same names and having some shared stories and rituals, but being functionally quite different.
Probably a combination of both of these will be what happens, perhaps together with other things.
Good answer. The way I see it, I think Paganism, as an umbrella, will probably do the best out of space travel. We might see the descendants of humans sent to Mars establishing religions centred around the worship of Father Mars or, if there's a sense of nostalgia and longing for our species' birth world, worship & reverence of Mother Earth. Perhaps these two cults might even become mingled. Actually, a show that made what I feel is some pretty good guesses is Babylon 5 with its references to both insular, human-purist religions like Adamism and more eclectic movements like Foundationism.
1. Can't see much changing here. Though from a Christian point of view, I'd wonder how Jesus' return will work if we have humans all over the galaxy on different planets.
2. Same as number 1 really, otherwise can't see much of a change or effect on religion.
3. This is the big one, really big. If the alien life is unintelligent, non-sapient, that can be explained away fairly easily. If there are other actual intelligent alien civilisations however, that would certainly raise a lot of questions, and from a Christian view especially about salvation and how these other people fit in, and if Jesus died for them too, and why didn't God tell us about other people He created, etc.
Another good answer, thanks. It would make a great deal of difference if those civilisations we encountered didn't have a concept of a Messianic religion. It could challenge the proposed universalism Christianity claims.
I think religions more prone to traditional, conservative views like Islam or Zoroastrianism wouldn't change that much - and might even fade with time. Even if Muslim scholars were to suddenly start liberally interpreting jinns as meaning 'aliens'.