What, exactly, does Scientology say about space aliens?

In the materials for OT III (Operating Thetan level 3), L. Ron Hubbard writes that, 75 million years ago, the head of the Galactic Federation, made up of 76 planets, was a being named Xenu. Faced with an overpopulation problem, he brought beings to this planet, blew them up with hydrogen bombs, and packaged them. Their spirits now infest our bodies: he says "One's body is a mass of individual thetans stuck to oneself or to the body." Scientologists at this level try to rid themselves of these thetans (spirits) by helping each one to remember the painful experiences of being blown up like that.

There are other Scientology teachings that relate to space aliens. The book "Have You Lived Before This Life?", described in Scientology advertisements as "a cold-blooded account of your last years", contains dozens of case histories of memories experienced by Scientologists, some of which include adventures in outer space.

Even the glossary in Scientology's What Is Scientology? contains a definition for the phrase " space opera", which, according to Scientology, relates to periods on "the whole track" (that is, our whole history, going back through many lives and millions of years), and it contains "space travel, spaceships, spacemen" and so on.