"P4M-399. It's a — it's a tiny little planet right on the very outskirts of our galaxy"
Bill Lee[src]

P4M-399 was a planet designated by the Tau'ri in the Milky Way galaxy. 399 is a small planet found on the outskirts of the Milky Way. A science team from Stargate Command was dispatched to this planet to set up and transmit a subspace message to the starship Daedalus, traveling in-between the Pegasus galaxy and the Milky Way. After successfully delivering the message, the Daedalus remained at a point where it could continue to pass messages between the SGC through the team on this planet and Atlantis and vice versa for a time before returning to Atlantis. (SGA: "Critical Mass")

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