The Book of Genesis is pretty explicit in addressing the issue actually.
Genesis 6 specifically.
Christians should consider “UFO’s” or “aliens” nothing more than Fallen Angels (Demons). It’s happened in the past over & over again, and it’ll happen again more than likely.
Sorry, disagree.
That chapter speaks of disobedient angels who interacted with men and, especially, women. So if “aliens” were to show up today, they might be of the same type. But I see no reason to assume from the biblical account that that rules out that “real” aliens might not also exist.