Complex sentence: The best-known portion of Scientology's space opera is the myth of Xenu, known as "Incident 2", in which Hubbard described a group of 76 planets, orbiting stars visible from Earth, organized in a Galactic Confederacy about 75 million years ago.
Split into simpler sentences: The best-known portion of Scientology's space opera is the myth of Xenu, known as "Incident 2". Hubbard stated that there was a group of 76 planets around stars that are visible from Earth that organized in a Galactic Confederacy about 75 million years ago.