What is the importance of the Proxima system in the novel, The Three Stigmata of Palmer Eldritch?

The Proxima system is a planetary system located around the star Proxima Centauri. Ten years before the narrative, Palmer Eldritch departed to explore the Proxima System. He returns at the beginning of the story and begins to spread his essence through the spread of Chew-Z. Some characters theorize that Eldritch may have been replaced by an alien life form while in the Proxima System.