Aliens And Christianity - An Unlikely Tango In Space:

From a theological perspective, The Covenant of Grace is exclusive to humans, and neither Aliens (if they exist) nor angels can be added to it. It's theoretically possible that aliens never would have sinned and thus never would have any need of Divine Mercy. But if they were sinners, there would be no hope of salvation for them.

I'll also note that Scripture gives no indication that any creatures other than Angels and Humans have moral responsibility to God. If Aliens do exist throughout the universe, they wouldn't think of things as right or wrong, but as beneficial or maleficial.

I tend to agree with CULDOOD

That is a good question, my estimated guess would be that many would celebrate that an entire race of extraterrestrial being changed to the Christian Faith. But of course, like all of society, there would be a lot of people saying that it's a religious thing, so it is a bad thing. So the social can be changed for the better, or for the worse.
Theological, an entire race conversion would be a feat humans have never seen before.
Cultural, it, like social, could go both ways. It could help people, and show them new possibilities for our race. But some will fight against it, it always happens.
We cannot guess how the aliens would react. We cam only make guesses since no one has ever made contact with an alien. And if they are anything like us humans, there would be those who would fight against it. But if they all converted and accepted it, then we humans might not be as good as we thought.

I have proposed numerous times that, usually in the context of an alien species, we break "animal" away from encompassing humanity and put humanity into it's own box, where sentient alien species may also exist- I often refer to this new grouping as the "People Box", desperate from an "Animal Box"

I then think it is arguable that this new "person" box can also be defined in a religious term as the "humanity" box, as "person" and "human" usually carry the same definition. At which point, unlike Culedood's claim, an Alien species can indeed be considered in divine interpretation just as "human" as you and me.

I understand that my argument makes a lot of assumptions and huge stretches of the definitions of various key words, and my points can be used to argue against my message just as well as they can fit it. Still, I don't think it right to decide that "all aliens are beyond salvation" as that goes against just about everything else in Christianity.