SR388... This is an unnamed frontier world that has yet to be examined by the Federation...

Old Bird

This is where the trouble began...

Chief Hardy

SR388 as designated by the Federation and Ili Agar Nalima by the Chozo,[note 1] was a planet that was explored by Samus Aran during Metroid II: Return of Samus and its remake, Metroid: Samus Returns. It was then briefly visited again in the opening of Metroid Fusion, before the rest of the game takes place on the Biologic Space Laboratories research station which orbits the planet.

The planet was of great significance due to the fact that it served as the homeworld of the Metroid species. As such, it was referenced numerous times throughout the series, including in the original Metroid's manual. It was later discovered that the X Parasites were native to the planet as well.

The planet's coordinates are given as 371° / 012° / 02° in the Samus Returns introduction, observable on Samus's Gunship monitor.


The surface of SR388.

The barren surface of SR388 was notable for its rough, rocky and dry terrain (possibly as a result of earthquakes), with a green-tinged atmosphere that was possibly toxic for humans, who were never seen without protective suits while exploring the planet. Severe storms were observed in the planet's sky, which made conditions even harsher for life.[1] A vast majority of SR388's local fauna thus made their homes in the vast maze of tunnels and caverns beneath the planet's surface, with occasionally coming to the surface in search of food.[2]

The Chozo and their machines exploring the interiors of SR388.

The interior of the planet is also home to a vast complex of buildings - all that remains of the ancient Chozo who once inhabited the planet, but abandoned it after their bio-engineered Metroids started evolving and turned on them. According to the 11th Chozo Memory, these same Chozo were later killed by others. Most of the Chozo colony's buildings have long since deteriorated into ruins, and range from crumbling temples to vast mining complexes. Many robots and drones left by the ancient civilization are still functioning during Samus' mission on the planet, but most of these synthetic beings had seemingly gone rogue since then and display high aggression against her. One of them is the Diggernaut, a rogue, gigantic robot originally used for mining operations. Incidentally, Chozo Statues and weaponry can be found amongst the ruins.

A unique quality to the planet is the presence of Aeion energy. While it is evident that Aeion is found within all native lifeforms of SR388 and can be collected from their deceased bodies, it is later implied that the energy is initially produced by the planet itself as a form of natural radiation; several Chozo Memories feature rays of golden light (matching those from Aeion) emanating from fissures on the ground deep below the surface of SR388. Aeion energy has several uses, the most notable being fuel for the gauge which powers four mysterious artifact abilities.

In Metroid II: Return of Samus, an odd liquid on SR388 blocked off many of the underground caverns and ruins. The planet was described in various sources as being unstable and prone to earthquakes. In the game, these frequent earthquakes occurred and when they did, it usually happened in conjunction with the liquid level decreasing, often-times exposing new areas of the planet to be explored. These earthquakes coincided with Samus exterminating a certain amount of Metroids; the reason behind this link is never explained and left up to interpretation.

In Metroid: Samus Returns, this liquid is now a purple hazardous one which would be lowered when Metroid DNA was inserted into the Chozo Seals. One of the Chozo Memories and the Official Guide state that the seal was built in order to somehow contain the Metroids within SR388 after the artificial lifeforms started rebelling against their creators. Much more traditional lava, as seen in Sector 1 (SRX) of the BSL, is still present in superheated areas of SR388.

SR388's solar system[]

Based on the cutscenes seen in Metroid Fusion and Metroid: Samus Returns, an asteroid belt appears to be in close proximity to SR388, possibly caught in its orbit. In the latter game, the planet's star which illuminates it can be seen in the distance, as well as what appears to be a black hole with a line of matter erupting from both sides. A neighboring planet unofficially designated as "SR387" is seen in a wire-framed map of this solar system.

After the Metroid species was rendered extinct on the planet by Samus Aran in Metroid II and its remake, the Galactic Federation constructed a massive space station out of an asteroid that orbited near SR388.

BSL Station[]

A large explosion engulfed the planet, but the neighboring SR387 was not destroyed.

This facility was used to observe, research and study animals from SR388 and various other planets. Specimens from the now-destroyed BOTTLE SHIP were also brought in; unlike the prior ship, the B.S.L. was allegedly intended for peaceful, scientific purposes. Within the station were six sectors; five of these were constructed to emulate specific climates and housed the organisms that best suited each of them. A single sector called SRX would be entirely dedicated to replicating SR388's environment and causing Metroids to evolve.

Main article: Sector 1 (SRX)

The sector would be home to not only the animals captured on SR388 by the Biologic's research team, but also the Metroids created within the station's Restricted Laboratory. Interesting to note is the presence of nest-like structures from which Hornoads, a species native to SR388, continuously spawn from. Although these structures are never seen by Samus on the planet itself, they can be assumed to be a natural occurrence due to SRX being a replica of the SR388's environment.

Metroid Fusion[]

SR388. A vile planet, former home of the Metroids. After so many years, the remaining creatures on this planet still seemed to be trying to recreate a natural hierarchy, one without Metroids at the top.

—Samus Aran

The events of Metroid Fusion mainly take place on the previously mentioned Biologic Space Laboratories research station orbiting the planet. SR388 is only briefly visited by Samus in the game's cutscene introduction when she accompanies the Biologic's research team to protect them from hostile lifeforms as they collect samples and specimens.

It is during this visit that Samus becomes infected with an X Parasite (more specifically, a Hornoad-X after being shot with a Missile), leading to the events of Metroid Fusion where an outbreak would spread out in the B.S.L. station. Samus was ultimately forced to change the station's orbit and crash it into SR388 in order to eradicate the X on both the station and their native world.[3] Thus, the former home of both the Metroids and the X Parasites was destroyed in a giant explosion.

Lifeforms and robots[]

There are a variety of animals on the planet, the most well-known being Metroids who are at the top of the food chain. Originally, the X Parasite was the most prolific of SR388's fauna and had reached a point where they endangered all other life on the planet. The Chozo of the Thoha tribe that colonized the planet were attacked by the X when the latter were discovered; becoming fully aware of their potential threat outside of SR388, they genetically engineered the Metroids to be the perfect predator of the X Parasites. However, when the Metroids began molting into larger, more powerful forms that could no longer be controlled by their creators, the Chozo flooded their own cities with an extremely hazardous liquid. When this was not enough, they made plans to destroy the planet but were betrayed by the Mawkin tribe before they had the opportunity to carry them out.

Despite this, the Metroids seemingly kept acting out their primary function of hunting down X Parasites, reducing the latter's numbers to an extreme scarcity. This helped SR388's other native life and flora to expand, though they would come under occasional attacks from Metroids.

Living among the planet's wildlife is also a large amount of active mechanical constructs and hostile robots left behind by the Chozo. The reason for their overall violent behavior is unknown.

Native inhabitants[]

Internally-named inhabitants[]

Unofficially-named inhabitants[]


Metroid species (bio-engineered)[]

Chozo robots[]

Internally-named robots[]


Additional flora[]


Map of SR388, Metroid II instruction manual

Note: This article lists locations by their names in Samus Returns. These areas use a different naming scheme in official walkthroughs of Return of Samus in Nintendo Power, which lists them as Phase 1 through Phase 9. Note that Phase 5 and Phase 6 were combined into Area 4, and Phase 8 was divided into Area 6 and Area 7.


The Surface area of SR388, distinct for its rocky terrain and modest plantlife. This is where Samus's Gunship lands, and the first Alpha Metroid is fought. The Samus Returns-exclusive final boss Proteus Ridley is also fought here at the end of the game.

Area 1[]

Area 1 is a Chozo settlement that contains 4 Alpha Metroids.

Area 2[]

Area 2 is a hydroelectric power station located above volcanic caverns that contains 6 Alpha Metroids and 2 Gamma Metroids in Return of Samus; 7 Alpha Metroids and 1 Gamma Metroid in Samus Returns; and the boss Arachnus in both games.

Area 3[]

Area 3 is a robot-operated mining facility that contains 2 Alpha Metroids and 8 Gamma Metroids in Return of Samus; 3 Alpha Metroids and 7 Gamma Metroids in Samus Returns. In Samus Returns, the Diggernaut is first encountered here.

Area 4[]

Area 4 is a series of crystal-filled caverns that contains 1 Alpha Metroid and 2 Gamma Metroids in Return of Samus; 1 Alpha Metroid, 2 Gamma Metroids, and 1 Zeta Metroid in Samus Returns. This is also the area where Samus gets chased by the Diggernaut in Metroid: Samus Returns.

Area 5[]

Area 5 is a jungle-like area that contains 4 Gamma Metroids and the only 3 Zeta Metroids in Return of Samus; 1 Alpha Metroid, 4 Gamma Metroids, and 2 Zeta Metroids in Samus Returns.

Area 6[]

One of the most desolate areas in SR388, Area 6 contains 1 Alpha Metroid replaced by a Zeta Metroid in Metroid: Samus Returns and 1 Omega Metroid, as well as the Diggernaut boss battle exclusive to Samus Returns.

Area 7[]

Area 7 is the laboratory where the very first Metroids in existence were bio-engineered by the Chozo. It contains 3 Omega Metroids.

Area 8[]

Area 8 is the main hive of the Metroids and final area of SR388, containing 8 (Return of Samus) or 10 (Samus Returns) Metroid larvae, the Queen Metroid and the baby, which Samus brings back to Ceres Space Colony.

Official data[]

Development Room[]

MetroidFusion Fan.gif
Warning: Fan Translation(s) Ahead

This article, section, or file contains text that is unofficially translated by Metroid Database. Some information (such as proper English names of characters or items) may not be accurate. If an official translation becomes available, the fan translation(s) may be replaced.

Indo: "In the "Metroid" manga, it describes that "The Chozo developed the Metroids in order to exterminate the X living on SR-388", but I think it was previously established that "there is a high probability that the Metroid destroyed the civilization on SR-388." I think it was the X that really destroyed SR-388."

Yoshio Sakamoto: "I think SR-388's civilization was destroyed and the Chozo left for Zebes after the Metroids were released into the wild (became feral). The Galactic Federation, not knowing the reason why the Metroids were developed, requested Samus to clean them up ("Metroid II"). The result of Samus exterminating the Metroids was that the propagation of the X could permit the SR-388 ecosystem to be destroyed ("Metroid Fusion")."[4] (Samus Returns)[]

"This desolate landscape looks empty at first glance, but there is a dark and dangerous world waiting for you just below the surface."
A lost world
"The underground labyrinth of SR388 is filled with peril at each turn. From vicious flora to killer creatures, each step you take may be your last. As you explore the dark tunnels, you may notice the remains of an ancient civilization. Could this long-lost culture be connected to the Metroids that now infest its ruins?"
"The deadly Metroids that inhabit SR388 are rapidly growing in number. Worse yet, they are evolving, becoming increasingly more powerful by the minute. This vicious species must be wiped out before they destroy the entire galaxy."
DANGER IN THE DARKNESS — [Blinking light]
"Countless explorers have been lost in the twisted underground tunnels of SR388. Luckily, you will be equipped with enhanced tools to help you safely navigate the treacherous caverns."
ANCIENT ARTIFACTS — [Blinking light]
"Besides the equipment you start with, there are many strange items you can find throughout SR388 to assist you."


Metroid II Commercial.

  • SR388 is the fourth of five planets to be destroyed, even if unintentionally, by Samus Aran, the others being Dark Aether, Phaaze, Zebes, and ZDR. It, Dark Aether and ZDR are also the three planets that she deliberately destroyed.
  • As mentioned before, artificial beings created by the Chozo can be found among the latter's ruins on SR388, many of which have weapons installed on them and attack on sight. It is possible the Chozo created them to keep the native wildlife at bay or more specifically, to use against the even more dangerous X Parasites and X infected creatures.
  • Ever since the discovery of the Metroids and Chozo ruins on SR388, it was believed that the life-sucking organisms were responsible for the supposed annihilation of the Chozo inhabitants of the planet. However, when the existence of the X Parasites was uncovered, the initial theory had been put into doubt and the X were equally considered to be the main culprit. The Chozo Memories in Samus Returns eventually confirmed it was the Metroids combined with the treachery of the Mawkin.
  • During Metroid II and Samus Returns, SR388 seemed to have a relatively low population of wildlife. The X Parasites were seemingly responsible for this, as stated by Yoshio Sakamoto and the Metroid manga. This would also explain why, in Metroid Fusion, the BSL Station's SRX (a sector that perfectly replicates the planet) contained very few of SR388's wildlife seen in the earlier games; after the extinction of Metroids, the X undoubtedly resurfaced in large numbers and steadily reduced the fauna on the planet even further (if not completely), making Galactic Federation researchers' task of collecting varied specimens that aren't X mimics a difficult one.
  • The planet's name is pronounced differently between games. Fusion renders the last two numbers as an "88" (eighty-eight) while Other M and Metroid and Me (by Samus Aran) make them distinct digits as "8-8" (eight-eight). During the countdown sequence in Fusion, the computer voice pronounces it as "SR-three-eighty-eight". The narrators in the Overview Trailer for Metroid: Samus Returns and SR388 Data File also pronounce it as "Eighty-eight".

Metroid: Samus Returns

  • A Galactic Federation Ripper specimen was known as "SR-478", a planet in the Nintendo Comics System was called RX 338, and the Pirate Homeworld is also identified in unused Logbook entries as "SN-883", all with very similar names to SR388. Several GF Database files identified in scans have similar names, such as BY-550.
  • Despite the Space Pirates being absent in the original Metroid II, the Space Pirates are known to be aware of SR388's significance, as well as having visited the planet; a scanned tank in the Metroid Processing room in Metroid Prime 3: Corruption states a specimen from SR388 had been moved. In addition, the presence of Metroid Eggs (matching those seen on SR388) within their facilities in Metroid Prime 3: Corruption and Metroid Prime: Federation Force heavily insinuates that they acquired these from the Metroid homeworld. In the remake Metroid: Samus Returns, Proteus Ridley arrives on SR388 to acquire the last Metroid, making it the first observable instance of Pirates setting foot on the planet; the same game's intro also states that they deliberately timed their attack on the Research Vessel Marina to coincide with their discovery of the Metroid in order to steal it, indicating they knew about the species' existence on the planet.
  • In the 2014 strategy game Planetary Annihilation, the name "SR-388" was included as one of the possible names a generated planet could have in the System Editor mode.
  • An interview with several of the staff from the original Metroid state that SR388 came from a Yamaha motorcycle engine, the SR400: " those days, while it was called 400cc, you didn't have any choice but 388cc, but it was written like that for the time being, and that's how it came out!"[5]

The atmospheric limit.

  • In Return of Samus, Samus can attempt to ascend into a high altitude on the planet's surface via her Space Jump or Spider Ball, but she will take heavy damage upon reaching a certain limit. This limit is denoted by a line, above which is greyed-out, clouded space. On her return to her Star Ship, the harmful atmosphere appears much higher than it initially did, which allows Samus to climb over a cliff to reach her Star Ship. The atmosphere is blocked off by clouds in Samus Returns, observable if Samus attempts to leave the Surface without using the Gunship.
  • The Fusion website data states that SR388 was Samus' first mission. This is not true, her Zero Mission on Zebes was. However, it is more likely the data is talking about her first mission pertaining to SR388.
  • Metroid Fusion: The Official Nintendo Player's Guide states that SR388 was the site of Samus Aran's early battles against Space Pirates,[6] although this claim is not supported by the canonical storyline. The only Space Pirate that Samus has battled on SR388 is Proteus Ridley, which is a retcon made by Samus Returns fifteen years after the release of Fusion.
  • Although Samus canonically destroyed SR388 by sending the BSL research station on a collision course with the planet, such an event would be very difficult to achieve in reality with an asteroid of the BSL's size. Even with the most powerful explosives known today, the maximum damage done from such a collision would have simply made the planet uninhabitable for life without destroying it completely. SR388 is stated to have a much thicker crust than Zebes,[citation needed] a planet that itself weighs 4.8 trillion teratons.[7]



  1. ^ This is an approximate transcription; the Chozo name for SR388 is spoken aloud, but never appears in writing.


  1. ^ Metroid: Samus Returns - Proteus Ridley Battle
  2. ^ Metroid: Samus Returns - Post-Credits Cutscene
  3. ^ Question 31 of the "Metroid FAQ," Metroid Zero Mission Official Site
  4. ^ Metroid Zero Mission Official Site Development Room, as translated by Metroid Database
  5. ^ Kiyotake, Hiroji (August 6, 2004). Nintendo Dream. Mainichi Communications Inc. pp. 96–103.
  6. ^ Metroid Fusion: The Official Nintendo Player's Guide pg. 26
  7. ^ Observatory scan

External links[]