In a spin-off of a law forum question ("Can an extra terrestrial be legally adopted?"), I ask:
"Can an extraterrestrial be a Christian?"
Like all short questions, however, it might have a long answer and implies answers to a lot of subordinate questions.
Whose Christian Doctrine?
I don't believe that this particular doctrinal question is denomination specific because I think that the core parts of the answer pre-date doctrinal schism in Christianity and weren't addressed in later diversification of Christian doctrines. But, to the extent that it is relevant, I would be most interested in Protestant doctrine, and to the extent that there is a distinction, with Methodist doctrine.
This is because having grown up in small town rural Kansas, if Superman and his parents were affiliated with a Christian church in the early 20th century when he arrived on Earth, it would probably have been a Methodist church (I'm not sure that the modern United Methodist Church denomination existed in the early 20th century, but if it didn't it would probably have eventually absorbed the church in question).
For what it is worth, so far as I know, the comic book canon about Superman doesn't actually resolve the question of whether Superman was religiously affiliated one way or the other and simply abstains from discussing the issue (I may be wrong about that, but it doesn't really matter for these purposes). But, I am assuming for the purposes of this question that his parents were devout Methodists and tried to raise their adopted child in their own faith and that Superman even after discovering his true origins wanted to be a Christian and a Methodist.
Thus, this question is quite distinct from the question of the afterlife of non-Christians, because in this case we are talking about a specific individual who wants to be a Christian and is familiar with Christianity, rather than a heathen (who has never been exposed to Christianity since the "Great Commission" has not been fulfilled) or a heretic (who has been exposed to little "o" orthodox Christianity and rejected it).
For what it is worth, the Roman Catholic church has analyzed this issue in some depth for hundreds of years and reached a generally strongly pro-ET conclusion. But, perhaps there is something in Methodist doctrine, or in the Anglican doctrine from which Methodism emerged, or the broad Protestant movement that gave rise to the Anglican church, that might lead it in a different direction than the Roman Catholic Church on this point.
Yes. Seriously. Why Care?
I elaborate on and frame this question at some length below to confirm that it is a legitimately serious question about Christian doctrine asked with an open mind, and to suggest some of the issues underlying the question that might not be obvious if it was stated in unelaborated form, as well as to suggest a branch of Christianity whose opinion matters most, to the extent that there is a diversity of opinion in Christian doctrine on the question between different branches of Christianity.
It is easiest to answer unusual questions when you know why they are asked.
While this question does have a rather fanciful dimension to it and no current direct application, it isn't a joke either. I know that it has receive some serious theological treatment in Christian seminaries and from Christian theological thinkers. I have seen the question addressed by theologians in a number of religious denominations both Christian and non-Christian in my life but don't have any references at hand and most were either in print newspapers or audiovisual formats that I would have no means of linking to (and I never followed any of the discussions to their conclusion to see how they came out on the issue).
And, of course, even if this is a question that never will and never can come up because humans are the only living sentient beings with souls in the universe, how one goes about thinking about an answer has intrinsic value because it provides a means to think about the important elements of what Christian doctrine has to say about what it means to be human and what it means to be Christian, which could also have applications to other issues relating to life and death and how humans should treat non-humans.
The law question focused on a particular extraterrestrial, "Superman", assuming that someone with his characteristics existed in what was otherwise the real world, and this one basically does too, although perhaps this level of specificity isn't as important for a theological answer as it is for a legal one (where detailed context always matters).
Incidentally, the theological issue isn't entirely irrelevant to the legal issue, because denying person status to someone who is considered by a particular religious denomination of which the someone is a member that considers that someone to be a person potentially has First Amendment free exercise and establishment clause implications that would favor treating the someone recognized as a person by a church as a person under the law.
Subordinate Questions That May Be Relevant Or Necessary In An Answer.
Who Is A Christian?
Right at the heart of the question is the more general question, "Who is a Christian?", and you really can't answer it without having an answer to that.
What makes you a Christian and not just someone who knows something about Christianity or agrees with some of what Christianity has to say? What disqualifies you from being a Christian?
I assume that Methodists have an answer to these questions, but having never been one myself, I don't know that answer.
Does The Scope Of The New Covenant Matter?
I don't discount the possibility that Christian doctrine makes Superman's status as a homo sapien irrelevant given that God had jurisdiction over the whole universe, although that in part depends upon the question of whether the New Covenant between God and humanity as a result of the sacrifice of Jesus was specific to Earth humans only or was more universal than that.
Do Superman's people need their own Messiah, or can they share ours?
Is There An Answer In Christology?
One relevant point in this analysis and discussion is that another individual with some mysterious form of extraterrestrial paternity, Jesus, is definitively "fully human" in addition to being fully divine, under the doctrines of all significant extant denominations of Christianity of which I am aware (Roman Catholic, Eastern Orthodox, Protestants, Mormons and IIRC, Ethiopian Orthodox as well), although a few almost dead heresies that died out in the Roman era (e.g. Gnostic Christianity) took a different position historically (other heretics took the position that Jesus was fully human but was not any more divine than any other human interpreting his status as "son of God" either metaphorically or as a statement about what it means to be human or what it means to be human who supports God as opposed to rebelling against God).
Of course, maybe Jesus is a "dual citizen" of Heaven and Earth who also got a vistor's visa to Hell, while Superman doesn't have an analog to Mary, mother of Jesus, only to Joseph, husband of Mary mother of Jesus, so maybe the analogy doesn't apply.
Does It Matter If He Has A Soul?
One closely related question to who can be a Christian is "who has a soul?"
The issues posed by this question could have been explored historically in theological discourse in related questions such as "do animals have souls?", "can angels be Christians?", and "can demons be Christians?".
Many people seem to think that having a soul and being a Christian are close corollaries of each other based upon the treatment this issue has had in fiction.
Another similar issue was addressed in a science fiction setting in a series of teen fiction books by S.J. Kincaid, starting with The Diabolic in which a genetically modified human who very much wants to be an adherent of the predominant faith (a fictional stand in for Christianity) is told by the clergy that she cannot because she doesn't have a soul.
Also along the same lines, a key issue in the Twilight series by Stephanie Meyer (herself a Mormon, but explored in the books from the Anglican and Roman Catholic and Baptist perspectives held by the members of her vampire family before they were turned) is whether the belief of male protagonist and vampire Edward that he should not turn female protagonist and human Bella into a vampire, because this would cause her to lose her soul and be denied eternal salvation and by association her humanity, is well founded in Christian doctrine.
On the other hand, angels, demons and vampires have theological aspects to them that an extraterrestrial like Superman does not. Angels and demons have origins outside the dimension of Earth, while vampires are associated with witchcraft and/or demons.
But, Superman is just an ordinary sentient being from the same dimension as humans on Earth who just happens to be from out of town and can even produce children with Earth humans so is probably part of the same biological species as humans somehow, perhaps Created that way by God and wasn't really all that special on his home world. So, maybe it is obvious that he has a soul.