|Discovery date||Prior to the Suimar's rule.|
|Distinct features||Asteroid Field|
RX 338 is a planet only shown in the Nintendo Comics System and the Captain N: The Game Master comic Breakout. The name was likely derived from SR388. RX 338 is also known as Prisonworld, because the whole planet is literally a giant prison (consisting of over 100 individual blocks) that is currently used by the Galactic Federation. Samus Aran, who was imprisoned in Cell Block 1 for Mother Brain's crimes by Ridley impersonating Judge Racklas, is the only person to successfully arrange an escape using her navigation skills in the ducts and mines.
"The maximum security prison on Planet RX 338 was originally built generations ago, by an evil emperor named Suimar, to imprison all rebels against his despotic rule. Years later, after Suimar was overthrown, the Galactic Federation began using the world to imprison the most dangerous villains."
"In Suimar's ancient times, prisoners were put to hard labor mining the world's rich mineral deposits. The old tunnels still exist, deep inside the planet. There are over 100 separate prison blocks, each designed to secure villains of every aptitude, from every world. A chain of orbiting Hunter Killer Satellites and Space Mines prevent anyone from getting on or off."
"The asteroid field around RX 338 is infested with deadly Starsharks. These creatures feed on anything, from starship hulls to living flesh."
The Federation Police currently manage the prisons and prisoners on the planet. Punishments on the planet include solitary confinement and illegal beatings by the officers.
|Planets in the Metroid Series|
|Note: Italicized locations were visited by Samus Aran.|
Underlined planets were destroyed.
|Bilium | Oormine II | Tallon IV | Twin Tabula | Zebes|
|Alinos | Arcterra|
|Aether | Dark Aether|
|Federation Solar System|
|Bryyo | Elysia | Norion|
|Unknown Solar System|
a.k.a. Planet SN-883 or Urtraghus ("large booty")
|SR388 | Unnamed planet|
|Earth | Jupiter|
|Charybdis | Inteira | Scylla|
| 2466 URSA | Bes III | Daiban | Degrade | Jamoru |
Jatsuk | Jigrad | K-2L | Kankeh | Liberty
Naishii | Nest | RX 338 | Solairon 12 | Vho