P3X-584 is a planet which Anubis conducted experiments regarding Khalek, a genetically engineering human with Goa'uld DNA. SG-1 originally traveled to the planet to investigate a gravitational disturbance that Lt. Colonel Samantha Carter found. The disturbance was later discovered to be a normal black hole rather than a possible Ori Supergate.
Soon after arriving on the planet, however, they stumbled upon Anubis' lab. They discovered Khalek and brought him back to Earth. Dr. Daniel Jackson and Teal'c stayed on the planet and Daniel translated the logs (written in Ancient). By doing this he discovered that Khalek was not a prisoner of the Goa'uld like he said but was actually created by Anubis. While they were holding Khalek, Daniel, Carter and Teal'c ran a simulation using the DNA manipulation device and discovered that Khalek can't ascend until he has another few treatments in the machine. Before he could return to the planet Khalek was killed. (SG1: "Prototype")