May sound strange, but yes I believe that Aliens exist and the answer is in the bible. What do you think in the 21.century are Angels, that can descend from heaven and then ascend again?
For instance read the book of Hesekiel. What did he describe there?
Furthermore in the bible is mentioned that Henoch was the greatest of all prophets. Today his prophecy is not part anymore in the bible, a few centuries ago it still was. So google a bit and you will find the book of Henoch.
He described the beginning of mankind till Noah. He wrote that the Angels descended and build cities next to that of humans and started to take human women as wifes.
So Angels building citties and mating? Doesn´t this sound pretty weird if they are what the churches tell us or does it sound understandable if we think of aliens who came to Earth and build a colony?
Well in addition as German I have to point out, that in the 1920´s the Thule society declared that the Angels of the bible were extraterrestrials and that the Thule society established contact.
In this context it is pretty odd, that the Thule society 10 years later was the mother organization of the German Nazi party. What do you think was all this second world war about?
They then started to build not only the V-Rockets, but also flying disc shaped aircrafts. Just google for Haunebu.
So there was a an occult group one century ago that claimed being in contact with Aliens and managed to build aircrafts which look like UFO´s in todays science fiction movies.
Decide yourself if they were just weirdos with genious knowledge in aeronautics or well if somebody really told them how to build such things.