Iris (Stargate)
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In the sci-fi television show, Stargate SG-1, the iris is a large, metal protective device that opens and closes over Earth's Stargate. The iris was designed by Stargate Command (SGC) to prevent unwanted travelers from emerging through the Stargate's wormhole.
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[edit] Earth's Iris
The iris appears to have 20 overlapping blades that swing outwards to form a near-circular opening, and then close again afterwards. This is similar to the way a multi-bladed leaf shutter works in a camera. Other structures that are similar in appearance are iris diaphragms in cameras and the iris of the human eye. 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.<ref name="enemy">"The Enemy Within." Stargate SG-1. | Transcript</ref> 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 original iris was installed the pilot episode, "Children of the Gods". It was first seen when Jack O'Neill and his team returned from Abydos. General George Hammond described it as Earth's "insurance against any more surprises," referring to Apophis' attack earlier in the episode. Despite the fact that it was pure titanium, it was unable to stand up to a black hole's gravitational pull which was transmitted through the Stargate.<ref name="matter of time">"A Matter Of Time." Stargate SG-1. | Transcript</ref> It was replaced with a new iris made of a trinium alloy.
The iris is controlled from either the control room palm scanner, or the manual control down in the Gate room on the left wall. The palm scanners were installed as a security measure after a Re'tu, an invisible alien, came through the Stargate and overrode the computer system, which opened the iris.<ref name="Show and Tell">"Show and Tell." Stargate SG-1. | Transcript</ref> The manual control appears to have been added sometime after the episode "The Fifth Race" where it was stated that because the SGC's systems were down, they had lost control of the iris.<ref name="Fifth Race">"The Fifth Race." Stargate SG-1. | Transcript</ref> Since the iris was installed by the SGC, Earth's Stargate is one of the 'Gates known with such protection,' and the only 'Gate known with a mechanical way of quickly alternating between preventing and allowing travel.'
[edit] Breaching the Iris
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.<ref name="serpant song">"Serpent's Song." Stargate SG-1. | Transcript</ref> 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.<ref name="100 days">"A Hundred Days." Stargate SG-1. | Transcript</ref>
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.<ref name="2 fires">"Pretense." Stargate SG-1. | Transcript</ref> 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.<ref name="2 fires">"Between Two Fires." Stargate SG-1. | Transcript</ref>
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.<ref name="Redemption">"Redemption." Stargate SG-1. | Transcript Part 1, Transcript Part 2</ref>
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.<ref name="Chain Reaction">"Chain Reaction." Stargate SG-1. | Transcript</ref> Thankfully, the thirty-eight minute window managed to shut down the gate.
Replicators once breached the iris somehow and stormed the SGC, trying to get out of the base to infest Earth. But they were permanently deactivated by the Dakara Superweapon.
[edit] 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 Earth, such as the Tok'ra<ref name="serpant song"/> and Master Bra'tac,<ref name="Lost City">"Lost City." Stargate SG-1. | Transcript Part 1, Transcript Part 2</ref> have IDCs.
[edit] 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"<ref name="Rising">"Rising." Stargate Atlantis. </ref> 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.<ref name="Rising"/> 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.<ref name="The Storm">"The Storm." Stargate Atlantis. </ref>
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 being killed by the Genii.<ref name="The Storm"/>
It is also notably able to withstand a nuclear blast, as it was raised after Ladon Radim of the Genii launched a nuclear device on the planet where Chief Cowen and his battalion were stationed. Thus intiating a coup d'etat over the Genii.<ref name="Coup D'etat">"Coup D'etat." Stargate Atlantis. </ref>
It has been speculated by fans that if the Ancient shield were part of the gate's original design, as seems likely, then it might materialise so close to the event horizon that not even subatomic particles would have space to reintegrate. This would make the shield completely unbreachable.
[edit] Other shielded gates
There have been a few examples of planets (mostly Goa'uld ones) that use a gate shield similar to the one in place on Atlantis.
Erebus, which was a forced labor camp for rebel Jaffa to construct Goa'uld Ha'tak vessels until they were worked to death had a gate shield which also required a signal to deactivate it. The SGC was able to acquire the signal during a failed attempt by Bra'tac and Rya'c to escape to the Alpha Site, a fact that was witnessed by Daniel Jackson during his Ascension, allowing him to relay this information to the others following his return.<ref name="Orpheus">"Orpheus." Stargate SG-1. | Transcript</ref>
Tartarus, which was a planet under the control of Anubis was a base used for the making of Kull Warriors also possessed a gate shield. A Kull Warrior, with his energy-absorbing suit, can easily pass through the shield can return without requiring an IDC.<ref name="Evolution">"Evolution." Stargate SG-1. | Transcript Part 1, Transcript Part 2</ref>
Dakara, although unconfirmed, it was stated by Teal'c that Dakara would most likely be shielded in "Threads".
[edit] Making of the iris
Image:Iris prop.jpg When a shot of Earth's iris opening and closing is needed, the actual animation of it is added in post-production, as the mechanics of it opening and closing would be very difficult to build. In order to save time and money, however, it is sometimes implied that the iris closes. In other words, the iris is not shown closing on camera. In these cases, a jar-lid shaped prop is just inserted into the Stargate prop. The Atlantis shield is created totally through the use of computer animation.
[edit] References
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