Mass Relay

For information on launching trans-relay fleet assaults, see Codex/Ships and Vehicles.

Mass Relays are mass transit devices scattered throughout the galaxy, usually located within star systems. They form an enormous network allowing interstellar travel. Hailed as one of the greatest achievements of the extinct Protheans, a mass relay can transport starships instantaneously to another relay within the network, allowing for journeys that would otherwise take years or even decades with only FTL drives.

Overview

Specifications

Mass relays consist of two fifteen-kilometer long curved metal arms surrounding a set of revolving, gyroscopic rings five-kilometers across. These rings contain a massive, blue-glowing core of element zero. The relays are made of an unknown but incredibly resilient material, the same material that the Citadel is built from, and are protected by a quantum shield that renders them nearly impervious to damage by locking their structure in place at the subatomic level. They are even capable of surviving a supernova's wake without being damaged. They are "cold" objects that don't emit heat or radiation, unlike starships, making them difficult to find if their position changes. Some relays, like the Charon Relay, are "gravitationally anchored" to planets; others appear to be out in space and are carefully tracked.

An active mass relay

Mass relays function by creating a virtually mass-free "corridor" of space-time between each other. This can propel a starship across enormous distances that would take centuries to traverse, even at FTL speeds. Before a vessel can travel, the relay must be given the amount of mass to transit by the ship's pilot before it is moved into the approach corridor. When a relay is activated, it aligns itself with the corresponding relay before propelling the ship across space.

There are two kinds of mass relay, primary and secondary. Primary relays can propel a ship thousands of light years but only link to one other relay, its "partner". Secondary relays can link to any other relay over shorter distances, only a few hundred light years. After the Rachni Wars, space faring species won't open a primary relay without knowing where it links to, in case they run into another powerful and hostile species like the rachni. This caused a rift when the turians found human pioneers, ignorant of this Citadel Council prohibition, trying to open any mass relay they could find while exploring the relay network, eventually leading to the First Contact War.

Many mass relays are currently dormant for unknown reasons, though they can be easily reactivated. A Prothean data cache found on Mars led humans to a mass relay encased in ice and orbiting Pluto, previously thought to be a moon called Charon, which the Charon Relay was eventually named after.

A piece of Prothean artwork depicting a mass relay, the Relay Monument, can be found on the Citadel Presidium. It has been interpreted as either a symbol of Prothean vanity, expressing the relays as their means to build a galaxy-wide empire, or possibly as a symbol of galactic unity, which the relay network also embodies. Tali'Zorah nar Rayya claims that after their long voyage through the galaxy, the quarians have also come to appreciate the aesthetic value of the mass relays.

An asari matriarch once suggested that the asari should build new mass relays of their own, but it is unknown if modern galactic civilization actually has the capacity to do so.

Origins

The mass relays, despite common belief, were created not by the Protheans but by the Reapers. As stated by Sovereign, the Protheans were merely one of many alien races to find the relays and the Citadel and take advantage of them. When the Reapers wiped out the Protheans, the asari were the next race to find the relays thousands of years later. According to Sovereign, by using the relays, galactic civilizations evolve along the paths the Reapers desire. In addition, the relays serve to accelerate the rate at which those civilizations advance, shortening the time between Reaper harvests.

However, the Protheans did have a keen interest in the relays, and managed to crack the secret behind their operation. This enabled them to build the Conduit before they were destroyed by the Reapers.

Commander Shepard also discovers that the Citadel itself is an enormous, inactive mass relay leading to dark space, as well as the control center for all the relays, enabling the Reapers to sever travel between clusters. Its reactivation is, fittingly, more complex than that of an ordinary mass relay, requiring either a coordinated effort by the keepers or manual intervention by a Reaper.

Alpha Relay

Mass relays are believed to be indestructible by galactic society, but no known attempts have been made to actually damage or destroy a relay because they are the only means of long distance space travel and thus too vital to risk. Prior to the events of Arrival, however, Dr. Amanda Kenson and her research team calculated that if a large enough mass impacts a relay with enough force, the relay should not be able to withstand it. The consequences of destroying a mass relay are immense: as a huge mass effect engine manipulating massive quantities of energy, a relay could produce an explosion of supernova proportions. This proves true when during Arrival, a large asteroid is purposely steered into the Bahak system's Alpha Relay. The resulting impact tears apart the relay, causing an explosion which annihilates the Bahak system and kills its more than 300,000 inhabitants.

The Crucible

During the battle to retake Earth from the Reapers, the superweapon known as the Crucible is activated. When Commander Shepard interacts with the Catalyst, the AI that controls the Reapers, the Commander is given the option to destroy the Reapers, control the Reapers, or merge organic and synthetic life together. In all cases, the energy reaction required to achieve those options is transmitted through the mass relay network from the Citadel. If the control option is chosen, the Citadel survives intact, but the relays are severely damaged and the Reapers rebuild them. If the destroy or synthesis options are chosen, the Citadel and the relays are severely damaged, but eventually are rebuilt.

Identified Mass Relays

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Cluster	System	Common Name(s)	Notes
Aethon Cluster	Aru	Unknown	Links the rest of the galaxy to the volus homeworld Irune and the turian colony Oma Ker
Annos Basin	Pranas	Unknown	Links the rest of the galaxy to the salarian homeworld Sur'Kesh
Apien Crest	Trebia	Unknown	Links the rest of the galaxy to the turian homeworld Palaven and the turian colony Digeris
Arcturus Stream	Arcturus	Unknown	Links the rest of the galaxy to Arcturus Station, the capital of the human Systems Alliance and the human colony Benning
Argos Rho	Hydra	Unknown	Connects the rest of the galaxy to Intai'sei and Pinnacle Station
Armstrong Nebula	Unknown	Unknown	Unknown
Artemis Tau	Unknown	Unknown	Connects the rest of the galaxy to Therum
Athena Nebula	Parnitha	Unknown	Links the rest of the galaxy to the asari homeworld Thessia and the asari colonies Lusia and Niacal
Attican Beta	Hercules	Unknown	Connects the rest of the galaxy to the human colony Feros
Caleston Rift	Balor	Unknown	Connects the rest of the galaxy to the human colonies of Arvuna and Caleston
Crescent Nebula	Tasale	Tasale Relay	Connects the rest of the galaxy to the asari colony Illium
Eagle Nebula	Imir	Unknown	Links the rest of the galaxy to Korlus, the vorcha/krogan colony Wrill, the human-batarian world Anhur, and Jarrahe Station
Exodus Cluster	Utopia	Unknown	Links the galaxy to several of humanity's colonies, including Eden Prime and Terra Nova
Far Rim	Dholen	Unknown	Links the rest of the galaxy with the former quarian colony Haestrom
Gemini Sigma	Han	Unknown
Hades Gamma	Antaeus	Unknown
Hades Nexus	Hekate	Unknown	Links the rest of the galaxy with the human colony Trident
Hawking Eta	Chandrasekhar	Unknown
Hawking Eta	Century	Unknown	Mentioned in the codex entry for Corang. Evidently, not the relay often used for travel to and from the Hawking Eta cluster; instead the relay in the Chandrasekhar is more often used.
Hawking Eta	Unknown	Mu Relay	Displaced by a supernova 4,000 years ago and enveloped in a cloud of hot gas and dust, making it impossible to detect and seemingly lost forever. It links to several other relays and is the only relay that links to the remote Pangaea Expanse cluster and to the former Prothean colony Ilos.
Horse Head Nebula	Pax	Unknown	Connects the rest of the galaxy to the human colony Noveria
Hourglass Nebula	Osun	Unknown
Ismar Frontier	Aquila	Unknown
Kepler Verge	Newton	Unknown	Connects the rest of the galaxy to the human colony Ontarom
Kite's Nest	Harsa	Harsa Relay	Links the galaxy to the batarian homeworld Khar'shan and the batarian colonies Adek, Camala, and Erszbat
Krogan DMZ	Aralakh	Unknown	Connects the rest of the galaxy with the krogan homeworld Tuchanka
Local Cluster	Sol	Charon Relay	Links the galaxy to the humans' home system. Encased in ice until it was discovered by humanity in 2149 CE.
Local Cluster	Sol	Conduit	Located on Earth in London. Used by the Reapers to ferry humans to the Citadel for processing. Later used by Commander Shepard to get aboard the Citadel in order to activate the Crucible.
Maroon Sea	Unknown	Unknown
Minos Wasteland	Fortis	Unknown	Links the galaxy to the turian colonies Gellix and Invictus
Nimbus Cluster	Pelion	Pelion Relay	Connects the rest of the galaxy to the asari colony Lesuss
Ninmah Cluster	Maskim Xul	Rachni Relay	Links the rest of the galaxy to the former rachni homeworld Suen
Nubian Expanse	Dakka	Unknown	Links the rest of the galaxy to the colony Yamm
Omega Nebula	Sahrabarik	Omega 2 Relay	The relay typically used for interstellar travel to and from the Omega Nebula. Links to the rest of the galaxy to Omega, the batarian colony Lorek, and the elcor colony Thunawanuro.
Omega Nebula	Sahrabarik	Omega 4 Relay	A mysterious seemingly navigable only by the Collectors; no non-Collector vessel has ever returned from doing so. Leads to the Galactic Core and the Tartarus Debris Field and the Collector Base. Unlike other relays, which are silver emit blue light, the Omega 4 Relay is brown and glows red.
Pangaea Expanse	Refuge	Conduit	A Prothean-built prototype relay on Ilos. Connects to the Relay Monument on the Citadel, but the trip is only one way.
Pangaea Expanse	Refuge	Unknown	Connects the rest of the galaxy to Ilos. Connects only with the Mu Relay.
Perseus Veil	Tikkun	Unknown	Links the rest of the galaxy to the quarian/geth homeworld Rannoch
Petra Nebula	Vetus	Unknown	Connects the rest of the galaxy with the human colony Elysium and the space station Grissom Academy
Pylos Nebula	Nariph	Unknown
Rosetta Nebula	Enoch	Unknown	At some point, it was on the list of forbidden relays due to its leading to uncharted space.
Sentry Omega	Hoc	Unknown	Connects the rest of the galaxy to Virmire
Serpent Nebula	Widow	Citadel	A large space station that serves as the seat of the galactic government. Unbeknownst to its occupants, it is also an enormous mass relay that the connects directly to dark space, allowing the Reapers to decapitate each cycle's power base quickly.
Serpent Nebula	Widow	Relay Monument	Located on the the Citadel. Mistakenly believed to be a work of art, it as actually a miniature, prototype relay built by the Protheans. Serves as the destination terminus for the Conduit on Ilos, but a return trip is not possible.
Serpent Nebula	Widow	Widow Relay	Connects the Citadel and the human colony Bekenstein to the rest of the galaxy.
Shadow Sea	Iera	Unknown	Connects the rest of the galaxy with the human colony Horizon
Sigurd's Cradle	Skepsis	Unknown	Connects the rest of the galaxy with the human colonies Sanctum and Watson and the Leviathan colony 2181 Despoina.
Silean Nebula	Kypladon	Unknown	Links the galaxy with the elcor homeworld Dekuuna and the asari colonies Cyone and Nevos
Styx Theta	Unknown	Unknown
The Phoenix Massing	Tassrah	Unknown	Links the rest of the galaxy with the elcor colony Ekuna, the human colony Aite, and the Heretic Station
The Shrike Abyssal	Xe Cha	Unknown	Connects the rest of the galaxy with the vorcha homeworld Heshtok and the volus colony Talis Fia
Titan Nebula	Haskins	Unknown
Valhallan Threshold	Raheel-Leyya	Unknown	Connects the rest of the galaxy with the krogan colony Garvug
Voyager Cluster	Unknown	Unknown
Viper Nebula	Bahak	Alpha Relay	A mass relay with unique properties that enable it to connect to numerous relays over long distances. The Reapers attempt to use it as their "Plan B" when they are rendered unable to enter the galaxy through the Citadel. Destroyed, along with the Bahak System, by the Systems Alliance in 2185 in an effort to slow down the Reapers' invasion. Connected the rest of the galaxy to the batarian colony Aratoht.
Unknown	Turix	Unknown	A relay located about 18,000 light years from Earth. Located in a system that orbits a neutron star. Connects to the Kappa Iota Relay. Destination of the TR-15 Letus probe.
Unknown	Unknown	Arcturus Prime Relay	Connects to the relay in the Exodus Cluster
Unknown	Unknown	Kappa Iota Relay	A charted but rarely-used relay predating the Rachni Wars. Previously abandoned due to the highly lethal radiation of Turix, the neutron star on the other side. The controversial TR-15 Letus probe was deployed through this relay.
Unknown	Unknown	Lowas Relay	Two researchers were arrested for landing on and attempting to tamper with the Lowas Relay without authorization in March of 2186.
Unknown	Mactare	Mactare Relay	Connects the rest of the galaxy to the turian colony of Taetrus.
Unknown	Unknown	Relay 314	Unauthorized activation by humanity led to turian retaliation, starting the First Contact War.
Unknown	Unknown	Seinhand Relay	Said to have seen a 43% decrease in a relay traffic report intercepted by the Shadow Broker.
Unknown	Unknown	Shanxi-Theta Relay	A key relay in the First Contact War. Near the human colony Shanxi.
Unknown	Unknown	Sol Relay	Close to the Sol System. One of the relays used by allied forces during for the Battle of Earth.

See Also

• Cerberus Daily News
  • "TR-15 Letus Probe" storyline
  • "Origin of Mass Relays Questioned" storyline
  • "Heightened Security at Mass Relays" storyline

Trivia

• The mass relays were originally known as "phase gates"; a relic of this can be seen in the Codex under Systems Alliance: Military Doctrine.
• The mass relays evolved from more monolithic designs to their final "tuning fork" shape (as described in The Art of Mass Effect).