P3X-042 was the planet from which the System Lord Yu reigned over his domain. Some time in 2001/2002, Jacob Carter/Selmak went undercover on this planet by impersonating a minor Goa'uld following Yu. When the Tok'ra got information about a large System Lord summit in the Hasara system, the Tok'ra informed Stargate Command to get their help. Selmak and Dr. Daniel Jackson infiltrated the planet and Jackson was able to convince Yu that he was his personal Lo'taur by using the Reol chemical on him. (SG1: "Summit")