Iris (Stargate)
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Image:StargateIris.jpg In the sci-fi television show, Stargate SG-1, the "iris" (of the Stargate) is a large, metal protective device, similar to the leaf shutter of a camera, which was invented by Stargate Command to prevent unwanted travelers from emerging through the Stargate's wormhole.
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Overview
When closed, the iris forms a barrier within 3 μm of 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. The iris also suppresses the destructive "kawoosh" (the unstable vortex) generated when the Stargate opens, apparently as a side effect.
The original titanium iris, instituted in the pilot episode, was destroyed in the episode "A Matter of Time" by a black hole's gravitational pull, which leaked through from the other end of the wormhole. It was replaced with a new iris made of a trinium alloy.
The iris is controlled from either the control room Iris Hand Scanner, or the manual control down in the Gate room on the left wall. Since the iris was installed by the SGC, Earth's Stargate is the only one with such protection. However, the Stargate in the Ancient city of Atlantis, as well as some Stargates controlled by the advanced Goa'uld Anubis, possess force fields that serve the same function.
The palm scanners were installed in the Season 2 episode "Show and Tell", after a Re'tu, who is invisible, came through the Stargate and overrode the computer system, which opened the iris.
Breaching the Iris
Image:StargateIrisAnimation.gif Although it provides the Earth Stargate with a greater degree of protection than any of the other Gates, the iris is not infallible, and several enemies of SG-1 have devised ways around it.
The System Lord Sokar devised a means to breach the iris by firing a particle beam 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 with the intent of eventually melting it (Season 2 "Serpent's Song"). The SGC used this technique themselves in a later episode to penetrate a "natural iris" that had formed over a distant world's Stargate after it had been buried while still active (Season 3 "A Hundred Days").
The Tollan possessed technology that allowed them to walk through solid matter, which also allowed them to reintegrate their particles through the iris, appearing as though they were stepping through it. Anubis attempted to arm warheads with this technology and send them through the iris to destroy Earth, but this plan was foiled by SG-1.
The iris cannot block out certain types of energy. The original iris was destroyed by the gravitation pull of a black hole. Later, Anubis fired an Ancient energy weapon into the Earth Stargate (the Antarctic gate) which caused it to overload and eventually cataclysmically explode. It is noted that, although it did not completely deflect the Ancient energy weapon's discharge, it dissipated the energy enough to significantly prolong the time until the gate would explode.
Also, when Major General Bauer (then commander of the SGC) detonated a naqahdah-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, however it would be a matter of time before the iris melted and the radiation transmitted freely.
Iris Deactivation Code
The Iris Deactivation Code is a code transmitted through an open stargate to request that the iris be opened to allow travellers through. IDCs are transmitted using a GDO (Garage Door Opener). Each SG team has a unique IDC. In addition, certain allies of the SGC, such as the Tok'ra and Master Bra'tac have IDCs.
Some early allies of the SGC (such as the people from the Land of Light in the first season episode "The Broca Divide") were given boxes (according to Samantha Carter, made by the Sagan Foundation) made out of an alloy with a unique mixture of isotopes, whose residue could be detected and identified after being sent through the Stargate and destroyed by the Iris. This would act as a non-computerized IDC, prompting SGC to open the iris just as if an IDC had been sent. While never stated explicitly, this entry method to the SGC was generally given to off-world allies who might have been too technologically inferior to understand the computerized GDO.
Atlantis Iris shield
Image:Stargate-shield.jpg The stargate in Atlantis is protected by a force field that fulfills the same role as the metal iris on Earth. This force field, often called the "iris shield" or simply the "shield" was installed by the Ancients. Unlike the iris, however, it is transparent and one can clearly see the suppressed "kawoosh" and the impact of objects prevented from rematerializing. The Atlantis Shield has yet to be breached by anything. However random malfunctions have made it flicker off and then on again.
GDOs and IDCs are still used in Atlantis; they are used by both Atlantis offworld teams and Athosians.
There are indications that the GDOs used in the Pegasus Galaxy may be more advanced than those used for SG teams based on Earth; one Athosian farmer told Acastus Kolya and his Genii strike force that it had to be in his hands to work; however, the farmer was clearly intoxicated at the time and attempting to avoid an opportunity to allow the Genii to kill him.
Some Goa'uld worlds, such as the Ha'tak-assembly planet Erebus and the Kull Warrior homeworld Tartarus, are also protected by energy shields. The Erebus shield is, like the Earth iris, deactivated by transmitting a special code, whereas it is assumed that a Kull Warrior, with his energy-absorbing suit, can easily pass through the shield. Why more Goa'uld worlds are not also protected by shields is a mystery; it may have to do with the cost of doing so or possibly an agreement among the System Lords.