S1, E9: During an exploration of a planet with no apparent inhabitants Dr. McKay (David Hewlett) discovers that the planet's fog-like atmosphere is actually pure energy--enough to open a wormhole back to earth. Wanting to be sure they could return to Atlantis to continue their mission Dr. Weir (Torri Higginson) relays a message back to Stargate Command. They are told that the battleship Prometheus has been outfitted with a hyperdrive and they would be able to return to Atlantis within a month! Back on Earth the team is overjoyed to be with the things and people they love. However when the Prometheus' hyperdrive is accidentally destroyed their hopes of ever returning to Atlantis are suddenly dashed.