Iris (Stargate)

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.

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. 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 in the pilot episode, . 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. The original iris, made of titanium, was destroyed when a black hole's gravitational pull was transmitted through the Stargate. 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. The manual control appears to have been added sometime after the episode where it was stated that because the SGC's systems were down, they had lost control of the iris. 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.'

Breaching the Iris

Although it provides the Earth Stargate with a greater degree of protection than any of the other Gates (with the exception of Atlantis), 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 accelerator through the wormhole, the subatomic particles being small enough to reintegrate in the space between the iris and the event horizon (three micrometers), thus heating the iris up with the intent of eventually heating the naqahdah and causing a thermonuclear explosion. The SGC used this technique themselves in a later episode to penetrate a "natural iris" that had formed over Edora(P5C-768)'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.

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 the iris was losing integrity.

Anubis fired an Ancient energy weapon into the Earth Stargate (the Antarctic gate) which caused it to heat up and cause the unstable Naqahdah to overload and 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 Naqahdah 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. Thankfully, the thirty-eight minute window managed to shut down the gate.

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. But each individual block was broken down to its basic elements. The basic concept of the weapon was derived from Colonel O'Neill's replicator Blaster. Anubis (in Redemption) and Ba'al (in several episodes) are seen communicating with the SGC via the use of a hologram, which projects user's image into the gate room despite the iris being closed. The nanoscopic space between the shutters of the iris are enough for the holographic material to reintegrate.

Iris Deactivation Code

The Iris Deactivation Code (IDC) 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), a small device carried by SG team members. The Atlantis expedition uses a different kind of GDO which is smaller, and used to identify individuals instead of teams. Each SG team has a unique multi-digit IDC.

In addition, certain allies of Earth, 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 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 the purpose was never stated explicitly, this entry method to the SGC was generally given to off-world allies who were too technologically inexperienced to understand the computerized GDO.

Atlantis Stargate shield

Installed by the Ancients, the Stargate in Atlantis is protected by a force field that fulfills the same role as the metal iris on Earth. While it was likened to the SGC's iris in "Rising", this force field has since only been referred to as the "shield" by Atlantis personnel, not the "iris". 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, in the season 3 episode "The Return, Part Two", a "back-door" that was previously coded into the shield's control system by Dr. McKay allowed him to deactivate it remotely from an off world location and prevented anyone else (including the inhabitants of Atlantis itself) from reactivating it.

GDOs and IDCs are still used in Atlantis; they are used by both Atlantis offworld teams and Athosians. It is important to note that the GDOs used by the Atlantis expedition members have been modified from the original.

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. On the other hand, Anubis himself used an almost, if not identical technology to protect his Kull Warrior manufacturing facilities. The Kull's energy absorbing suit in turn did allow travel through the iris forcefield without deactivation.

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.

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. However, Kull Warriors, with their energy-absorbing suit, can easily pass through the shield without requiring an IDC.

Although unconfirmed, it was stated by Teal'c that Dakara would most likely be shielded in "Threads".

Making of the iris

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 scenes where movement of the iris is not required, a jar-lid shaped prop is just inserted into the Stargate prop. The Atlantis shield is created totally through the use of computer animation.

References

cs:Iris (Stargate) it:Iride (Stargate)