The iris is a metal covering on the Earth Stargate which is used to screen incoming traffic. It prevents anything larger than an atom from being reconstructed, thereby destroying it. It dilates and contracts to cover or expose the central part of the Stargate where the wormhole connects. Friendly travelers are identified by the correct GDO code, while unfriendly or hostile aliens are identified, usually by an unrecognizable signal, or lack thereof.
Following the Raid on Atlantis where the Wraith are able to breach the Stargate shield with the help of the now-Wraith Doctor Rodney McKay, an iris is installed on the Atlantis' Stargate. (SGA: "Allegiance")
The iris was designed by Stargate Command to prevent unwanted travelers from emerging through the Stargate's event horizon. It appears to have 20 overlapping blades that swing outwards to form a near-circular opening, and then close again afterward. This is similar to the way a multi-bladed leaf shutter works in a camera. When closed, the iris forms a barrier less than 3 μm from the wormhole's event horizon, thereby preventing most forms of matter from properly reintegrating. Objects coming through the wormhole are destroyed instead, accompanied by a ringing thud against the iris. Radio signals are able to penetrate, however, allowing SG teams to request the opening of the iris using their GDOs. (SG1: "The Enemy Within")
The original iris was installed in 1997. It was first seen when Colonel Jack O'Neill and his team returned from Abydos. Major General George S. Hammond described it as Earth's "insurance against any more surprises," referring to Apophis' recent attack on Earth. The original iris, made of titanium, was later destroyed by the gravitational pull of a black hole being transmitted through the Stargate. It was replaced with a new iris made of a trinium alloy. (SG1: "Children of the Gods", "A Matter of Time")
The iris is controlled from either the control room palm scanner, or the manual iris control on the left wall of the Embarkation room. The palm scanners were permanently installed as a security measure after a Reetou, an invisible alien, came through the Stargate and overrode the computer system to open the iris. (SG1: "Show and Tell")
Breaching the iris
Although Earth's iris provides it with a far greater degree of protection than most Stargates possess, it is not infallible, and has been circumvented or overcome on several occasions.
Certain types of weapons can breach the iris, albeit inefficiently. The System Lord Sokar devised a means to breach the iris by firing a Particle accelerator through the wormhole, the subatomic particles being small enough to reintegrate in the space between the iris and the event horizon, thus heating the iris up. Stargate Command used this technique themselves during a later incident to penetrate a "natural iris" that had formed over Edora's Stargate after it had been hit by an asteroid and buried while still active. Major Samantha Carter constructed her own particle accelerator and used it to save O'Neill, who had been trapped on Edora by the asteroid strike; the plasma weapon was able to create enough of a gap for Earth to dial the Edoran Stargate, creating a cavern above the now-buried gate via the 'kawoosh' effect that gave Teal'c enough space and oxygen to dig to the surface. (SG1: "Serpent's Song", "A Hundred Days")
The Tollan possessed phase-shifting technology that allowed them to walk through solid matter, including Earth's iris. This technology was almost turned against Earth with the use of phase-shifting weapons, created on the orders of Tanith acting as the agent of Anubis after Anubis demonstrated his advanced defences against the Tollans' usual technological advantage, but the cache was destroyed before they could be put to use. (SG1: "Pretense", "Between Two Fires")
Certain types of dangerous energy can also pass through the iris. When Major General Henry Bauer (then commander of the SGC) detonated a naquadah-enhanced nuclear warhead on a planet that the SGC was connected to through a Stargate, radiation was transmitted through the Stargate. Closing the iris temporarily decreased the radiation in the gate room, but the iris would have overheated and melted had the Stargate not shut down at its 38-minute limit. Anubis fired an Ancient energy weapon into the Earth Stargate which caused energy to build up in the naquadah, eventually overloading the gate's capacity and causing a massive explosion. The iris significantly reduced the rate of energy buildup, but couldn't stop it. (SG1: "Chain Reaction", "Redemption, Part 1", "Redemption, Part 2")
The Stragoth managed to breach the iris and establish a Foothold situation on the base by masquerading as SG-6. They took over the base and started plans to take over the world. Thanks to their encounters with the Goa'uld, Teal'c and Carter were immune to their technology. Carter managed to escape the base and get help. Most of the remaining aliens escaped through the Stargate and the rest self-destructed to prevent capture. Countermeasures were employed to negate any further attempts at intrusion by that unknown species. (SG1: "Foothold")
Replicators once breached the iris by remotely hacking into the control system through an incoming wormhole and stormed the SGC, trying to get out of the base to infest Earth. The Asgard were also capable of doing this, though defenses were presumably employed against it following the capture of Thor by Anubis. (SG1: "The Fifth Race", "Small Victories", "Reckoning, Part 2")
In a less harmful type of breach, Asgard holographic projectors are capable of bypassing the Stargate's iris, allowing the user to appear a short distance in front of the gate. The nanoscopic space between the shutters of the iris are enough for the holographic material to reintegrate. (SG1: "Redemption, Part 1", "Reckoning, Part 1")
The Wraith were able to bypass the iris through the use of the Midway space station, which Stargate Command believed to be secure against intrusion and thus recognized automatically from the dialing sequence. The Wraith sent a stun bomb through, knocking everyone out and infiltrating the base. Fortunately, Teal'c and Ronon Dex had also been on the Midway station when the attack took place, and were able to follow the Wraith to Earth and kill the entire invasion force before they could get to the surface. In the process, the Midway Station was destroyed by a self-destruct that prevented such an attack from happening again. (SGA: "Midway")
- GateWorld's article on
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