Extraterrestrials/aliens form a major part of science fiction. I know there are myths going back to ancient times of aliens, but I was wondering what the first reference in the actual science-fiction literature (ancient is accepted) is to life existing on another planet (not necessarily visiting Earth)? They cannot be considered to be Gods in that particular piece of literature. The only other restriction is that they did not originate on Earth.
Just for your interest, here is a related question, but not a dupe; I'm specifically asking about the first sci-fi story to introduce the concept of aliens where they weren't considered to be Gods.