There are billions of planets even in our own galaxy, and millions of galaxies in the universe. Discovering other inhabitable planets and possibly extraterrestrial life is inevitable , it’s simply a question of when. Andrew Fiala wrote a great article for the Council For Secular Humanism in which he predicts that discovering either other inhabitable planets and/or extraterrestrial life would be the end of terrestrial religions. For at least 4 main reasons:
1. Popular religions were created by people with an only ancient knowledge of the cosmos. Religions would have to adapt to the new world and/or life
“At the very least, traditional religions will have to reinterpret themselves in such a way as to explain how the geocentric focus of the past is to be understood in light of our expanded astronomical knowledge.
…We are on the cusp of another phase in the evolution of religion. Religions will have to evolve beyond an exclusive focus on the earth.”
All of the popular religions are written with the assumption that the Earth is the only inhabited planet and so holy books and perhaps entire religions would have to reinterpreted away from their Earthly focus.
2. The special relationship between humans and God(s) would also have to change.
It is human beings that are supposed to have a special relationship with God, having been created in God’s image. Some traditions do speak of transmigration of souls across the species divide. But it is usually held that there is something special and unique about the human phase of the soul’s journey. In religion, the interests of human beings on this planet are the primary concern.
Obviously once life is discovered on other planets religions can no longer claim we are the sole creation of God or Gods. Nor could religions claim that we the primary concern for God (s) without being transparently egotistical.
3. Life on other planets would mean the death of the creation stories of various religions.
In that case, religious traditions will have to revise their creation stories in such a way as to provide for a creation event that includes other planets
Of course, the world’s religious traditions will have to find ways to explain the embarrassing lack of knowledge among ancient prophets who knew nothing of these other planets.
Creation stories are having a hard time being taken seriously as it is, life on other planets would likely be the final nail in creationism’s coffin.
4. The goals and purposes of the prophets change.
And claims about saviors and redemption will have to be reinterpreted to explain the possibility of redemption for inhabitants of exoplanets.
Once again the stories of the prophets are human centered, making the assumption that only human beings and life on Earth exist. These stories would be rendered logically inconsistent without a radical retelling.
In summary Fiala sumamrizes:
But mainstream terrestrial religions—as they exist today—provide scant guidance for dealing with the possibility of life on distant planets. Traditional religions provide no answer to the question of whether extraterrestrial life would have moral value. Would it make sense to say that extraterrestrial beings are created in the image of God or that they are endowed by their (or our) creator with inalienable rights? And how would extraterrestrials be incorporated into religious eschatology? Are extraterrestrials afflicted by original sin? Can they be saved? And so on.
Fiala goes on to explain why sciences like evolution and thinking like Kantian philosophy and existentialism better serves us for dealing with the discovery of extraterrestrial life. It seems certain that discovering other inhabitable planets would mean either the end of most major religions or they would have t0 make changes so vast and radical that they become too absurd to be popular.