Even a breakaway civilization of ancient Atlaneans living under Antarctica makes more sense than aliens. Do yourself a favor and look up how far away other stars are, consider how many times astronomers have looked into space and not seen aliens, and then ask yourself why aliens would be so good at cloaking themselves in space but would ostensibly let themselves be seen on Earth itself.

Spoilers: it's not Atlanteans either, it's just a big tangle of hoaxes and self-delusion from people who want to believe.