Question:
Would the discovery of ETs (extra-terrestrials) threaten organized religion?
Answer:
The discovery of ETs would pose no more of a threat to Judaism than would the discovery of a new species of rabbit.
It would be limiting G‑d's power to say that He could not have placed life on other planets. In fact, there is a reference in the biblical Book of Judges (5:23) to an inhabited place called Maroz, which the Talmud identifies as a star.
But Jewish thought has always believed that the most weird and wonderful creatures are to be found right here on earth. We can explore the remotest extremities of space but still remain alien to our own humanity. The real secrets of the universe lie hidden in the depths of the human soul.
Moses received the Torah from G-d to deliver to us, not to other 'beings'. No mention of G-d delivering the Torah to aliens on other planets...
Isn't it possible to say that just as there are gentiles on this planet that do not accept the Torah..but are intelligent...there could be gentiles on other planets but they don't have the Torah...yet....science seems to say there could be millions of planets with life...maybe Hashem found us worthy of the Torah but not others in the universe
Interestingly, any non-human species that pursues science is attempting to cobble together an understanding of the universe, of Creation, which is one and the same with Torah.
Keep in mind that if Moses hadn't brought down Torah from Sinai, we would have had to learn Torah lessons from the animals (see my favorite text, the Perek of Shira).
This is to say that Torah is not unknown or unknowable to non-humans. But such Torah learning doesn't involve the letters, words, chapters and books, which are tailored to human perception, sensory capabilities, cognition and understanding.
Of relevance is the idea of other "sensory worlds," that exist for other animals. In the sensory world of human beings, we have Tanakh as we know it and understand it. Which is to say that when G-d dictated the Torah to Moshe, that it was compressed into a form that humans would be able to understand. Torah may take different form for other species, but we may not be exclusive to revelation.