Ring World Planet

A new home for mankind, where people are born and raised... and die.

"This world. Looping. Repeating... forever. Is it a symbol of life or a cruel joke by the Forerunners?

— Escharum, Halo Infinite

One of the World Shapes more often found in Science Fiction than in Fantasy, a Ring World Planet is a world in the shape of a concave cylinder. The horizon curves up, not down, but only in one dimension, meaning that the ground in that direction would be "uphill"^note If gravity is generated by spinning the cylinder, it would only look like it was uphill. The surface would be "level" as far as walking, water flow, etc is concerned. unless the ring is large enough that the curve is impossible to notice over small distances. The sides of the cylinder will be walls, with or without a "ceiling." These can range in size from the equivalent of a true Dyson Sphere to a cylindrical space station in planetary orbit. These variants of worlds usually at least pay some lip service to the known laws of physics, since a spinning ring generates a centrifugal force that could be used instead of gravity. However to exist for real, particularly large ones over a few dozen kilometers would have to be made of Unobtainium.

Note that it would always be "day" in such a cylindrical world unless measures are taken to simulate day and night, either through sun shades, mirrors, or some combination of the above. Another alternative is choosing an orbit where the ring periodically gets shadowed by something. Orbits that use the Earth for this would produce night about every 90 minutes (ISS altitude) or a few minutes every few months (a typical geostationary orbit, about the same frequency as a lunar eclipse).

These rings fall into two broad types. The smallest are toroidal space stations, consisting of a fully enclosed circle around a central spindle or hub area, with the habitable area within the volume of the outer ring-shaped tube. These are usually referred to as Stanford toruses after a study at Stanford University that popularized them in 1975, but the concept of rotating space habitats of this sort has been explored since at least 1903 — a less common name, the "von Braun wheel", refers to a proposal by the aerospace engineer Wernher von Braun in 1952. These are usually the size of regular space stations, just large enough to hold a city's worth of people at most, and orbit larger celestial bodies such as planets.

Bigger hoop-shaped worlds are depicted as ribbon-like affairs, and are usually "roofless" due to rotating fast enough that centrifugal force keeps their air in. This version was popularize by Larry Niven, who thought it up as a mid-point between a Dyson Sphere and a planet, in his 1970 novel Ringworld, which depicts a version as wide around as the orbit of the Earth and with an absolutely massive habitable area. Colossal rings of this sort, with a star in their center, are still referred to as "Niven rings". Since something this big turns out to be impossible in real life, harder science fiction leans towards using smaller hoops, still large enough to host more than a world's worth of land but which orbit stars like regular planets do. These are usually called "Banks orbitals" or "Bishop rings".

Compare Planet Spaceship, and the super-trope Centrifugal Gravity.

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Examples

Anime and Manga

• Cowboy Bebop: Most space stations are ring-shaped.
• Futaba-kun Change!: The ending reveals that the Shimerus are Human Aliens from a ringworld made out of nano-engineered giant ivy.
• Gundam:
  • The franchise helped popularize the O'Neill Cylinder space colony (see below in "Literature"), as well as other designs.
  • Actual ring shaped colonies (known as the "Stanford Torus" or "Island 2" model) are only common in the Gundam Wing continuity, though one also shows up in Gundam Unicorn, which was apparently the first ever built in the UC-verse and promptly got blown up.
• Voices of a Distant Star: The Lysithea briefly docks at a ring-shaped space station built around a moon, which Words of Love/Across the Stars states is Europa.

Comic Books

• Supergirl: In the story arc Crucible, Supergirl is enrolled in Crucible Academy, a ring-shaped interplanetary school for superheroes.

Fan Works

• Austraeoh: In Urohringr, part five of the series, it turns out that the world Equestria is in is one part of a great, shattered ringworld named Urohringr.
• A Crown of Stars: Several artificial worlds of the Empire of Avalon are built like this. Shinji and Asuka see several of them as soon as they step through the dimensional portal.
• Nobledark Imperium: In its heyday, Great and Bountiful Human Dominion created an immense ringworld, the Cthonian Ring, in the Regulus system. It's not entirely clear why they did it or why they picked that specific location, since Regulus is a four-star system and thus arguably one of the worst places to built a stellar megastructure in; some in-universe speculators figure that the Dominion, then at the height of its power, built just to prove to that they could. It was almost entirely destroyed during the Revolt of the Iron Men, when its star was induced to go nova and scoured its inner surface clean down to its neutronium foundations, and most of the construction on its outer side was destroyed by the rest of the weapons being thrown around. It has since remained a place of wonder for humanity; scavengers during the dark ages often braved journeys from nearby systems to pick through its ruins, and the modern Imperium has romanticized it as a symbol of what humanity once achieved and might achieve again; most Mechanicum facilities display sculptures of it on their premises, and art of the Emperor often depicts him with the Ring as a halo. There are plans to rebuild it someday, although the sheer scale of the project keeps them purely theoretical, and permanent population has established itself in the more intact portions to service the steady stream of scavengers, researchers, pilgrims, and just travelers and traders passing through.

Film

• Interstellar: By the end of the movie, humanity manages to leave Earth and starts inhabiting giant space stations that resemble a Stanford torus.
• Moonfall: In the projection shown to Brian, there's a ringworld habitat.
• Starship Troopers: In a change from the novel, the film has a spaceship docking ring surrounding the entire Earth linked to the surface by space elevators.

Literature

• Beyond Infinity: The protagonists spend a brief time trapped in a Tunnelworld after an encounter with some four-dimensional aliens. It's a closed loop, so traveling in any direction for a long enough time would return you to your point of origin.
• The Culture: The Culture builds Ringworld-style Orbitals (but smaller) as housing for many of its citizens. They have a few full size, fits-round-a-star Ringworlds too but they're much rarer, since you can get more useable area by using the same mass to build orbitals so most of the Culture regards them as tacky.
• For Your Safety: The Groupmind builds a Ring around Earth for the humans it had to overthrow in order to save, where they can live in peace under its watchful eye. Though construction time is estimated at 1500 years so the humans have to be put in stasis until then.
• Gaea Trilogy: The Titans are living ringworlds.
• Gerard O'Neill proposed a real world cylindrical space colony: Island Three. The page image is a representation of the "Stanford Torus", another design inspired by both O'Neill's work and the classic "wheel-and-hub" space stations.
• Illium: Earth is surrounded by two huge ever-moving rings. They are not fun places.
• Rendezvous with Rama: Rama is a massive cylindrical spacecraft.
• Ringworld is set on a world shaped like a vast ring with a sun at its center. It's made of Unobtanium called scrith and is so massive that its geographical features include 1:1-scale maps of several planets (including Earth). These maps are significantly less than 1% of the ring's surface area. Day and night is created by massive solar panels in spinning in orbit between the sun and the ringworld. Bussard ramjets on the rim of the ringworld keep it centered. The whole thing is reasonably Ragnarok Proof, which is good, as it's also quite Ragnarok-prone: once high-technology civilization there collapses, the absence of available metals means that it can never arise again without outside interference.
• Star Trek: Titan: The Neyel are a human Lost Colony named after the O'Neill habitats they originally settled in.
• Voidskipper: Most people live in these, albeit usually the planet-sized kind rather than the solar system-sized variety. They get around the lack of materials stronger than carbon nanotubes by having the rotating part supported by a static shell, connected by a magnetic bearing.
• The Way Series: Thistledown is a hollowed-out asteroid containing seven cylindrical chambers separated by bulkheads. The seventh chamber connects to a cylindrical pocket universe with several million miles of terraformed interior.

Live-Action TV

• The Book of Boba Fett: In the fifth episode, Din Djarin travels to an ecumenopolis version of these called Glavis to both collect on his bounty and reunite with his sect of Mandalorians. The day/night cycle is created by a series of bands rotating closer to the star, periodically eclipsing it from the ring's surface. As the ring is open-sided, lacks walls and has urban growth right up until its edge, it's possible for people to accidentally fall off its sides and into the void.

Podcasts

• Jemjammer: Iolara is the hatchery for many spacefaring Lizardfolk and used to be a ringworld. However, at some point it was broken into multiple pieces, although they are still in orbit around the star.

Tabletop Games

• Cyberpunk 2020: As of 2025 there are five ESA-built orbital colonies located at the Lagrange points of Earth-Moon system:
  • The Crystal Palace at L1 is a cross between the classic rotating wheel space station and a Stanford torus. It consists of five rings, a central hub and two giant mirrors illuminating the transparent roofs of the two outermost rings.
  • Two O'Neill cylinders, O'Neill One and smaller O'Neill Two (Galileo Cylinder), are located at L5 and L3 respectively. Originally built and controlled by ESA, those two habitats later rebelled and declared independence.
  • The newest cylinder, O'Neill Three (Paradise Station) at L4^note In some places described as a joint Japanese-American project rather than an european one, is still run by ESA which maintains a martial law since the rebellions.
  • Finally, at L2 there's a much smaller testbed cylinder which currently serves as deep space craft construction facility.
• Dark Heresy: Port Lokhart is an Imperial Navy shipyard that is built into a large artificial ring of unknown origin, circled around a tiny planetoid in the Pallisada system. Despite nine thousand years of occupation, the Navy only inhabits a fraction of the ring's honeycomb-like interior, although they've covered the exterior in countless docking arms and gun turrets.
• Dungeons & Dragons:
  • Sigil from the Planescape setting is a small version of this, with the ring's inner surface completely covered by city, floating over the top of an infinitely tall spire in the center of the Outlands, itself the hub of the "Great Wheel" planar cosmology. It's also a sort of hub that connects to all the other planes of existence.
  • There's also Penumbra, the illithid homeworld, which is an Alderson disk - a megastructure in the shape of a giant CD thick enough to generate its own gravity, with a habitable surface on both of its sides, a star in the middle of its spindle hole, and a wall along its inner edge to prevent the atmosphere from escaping into the central sun. It may or may not exist yet.
• Eclipse Phase: Many people following the Fall live in space habitats, many of the bigger ones are toruses or O'Neill cylinders. However there's also a number of habitats that don't bother with spinning since basic biomods counter the degeneration from microgravity.

Video Games

• Axiom Verge 2: Kiengir, the primary setting, is one of these. This is most easily noticeable in Irikar, where you can see the cratered surface of the ring's opposite end.
• Blazing Star: One is seen in the background of level 2.
• EV Nova has several of these, mostly ring-around-a-planet style. Though one is (for all intents and purposes) the Ringworld. (The Polaris use that one for effectively infinite farmland.) For bonus Shout-Out points, that ringworld is named Tre'ar Helonis.
• Halo: The seven titular ringworlds, which resemble Banks's Orbitals, are superweapons designed to kill off all sapient life in the galaxy. The entirety of Halo: Combat Evolved takes place on one of these Halos (Installation 04), which is located at the Lagrange Point 1 ^note Lagrange Point 1 (there are 5, creatively numbered 1 to 5) is a special position where an object can sit in a semi-stable orbit that is closer in than its orbital period would naturally allow. The reason why objects at Lagrange Point 1 (L1) don't fall in is because a second, much larger object (a moon around a gas giant in this case) with sufficient gravity cancels out some of the central body's gravity, allowing an object, like a Halo to sit between a gas giant and its moon.of a gas giant and its moon. All six other Halo ringwords appear to have originally orbited gas giants as well, though Installation 03 eventually found itself somehow orbiting a rocky planet instead.
• Mass Effect:
  • The Citadel is one of these. In particular, the Presidium is a huge ring with its own biosphere and simulated sky at one end of the space station.
  • The Alliance's Arcturus Station is described as a Stanford torus.
• In the Outer Wilds: Echoes of the Eye DLC, you discover "the Stranger," a ringworld larger than some of the local planets, hidden beneath an Invisibility Cloak and capable of flying between star systems. The inner ring features an artificial river complete with houses on stilts, wooded hills, rocky rapids, and finally a dam. Over the course of your exploration of the Stranger, said dam cracks and eventually breaks, letting you watch the Giant Wall of Watery Doom as it travels the inside of the ring.
• Shores of Hazeron has ancient ringworlds which can be colonized. The ringworlds are almost exactly like those from the Ringworld novel, with mountains flanking the inner walls, and with shadow squares creating day/night cycles on the surface. Ringworlds have the advantage of being able to carry far more population than a planet, and having 7 different resource zones - if the ore is bad in one zone, it may be high quality in the next one over. Additionally, since the ringworlds are all centered around the sun, and wormholes are always near the sun, any defenses installations on the ringworld will immediately be able to concentrate their fire on anything entering the system via wormholes.

• Star Ruler: You can build these, admittedly as a lategame option. They are Capital-H Huge, larger than some planetary orbits.
• Startopia has you turn several of these into profitable space stations. Apparently, all known races use the same exact design for their space stations, right down to the color scheme. They were originally built by a galactic empire that has since fallen, and a big part of your job is getting them into a usable state.
• Stellaris:
  • The Ancient Caretakers Fallen Empire has ring worlds built in its star systems that formerly served as a shelter for biological sapients trying to escape from some unknown threat.
  • Empires with the "Shattered Ring" origin will enter the game on one of the ring world's sections, with others being damaged.
  • With the Utopia DLC installed, it's possible to build ring worlds late in the game in planet-rich (though not necessarily inhabitable) star systems, dismantling the planets in the process.
  • With a probability of 4% to 20%, depending on the size of the galaxy, the Sanctuary system can be generated, inside which the ring world is located. The highlight of this ring world is that it once served as a preserve for rare species from across the galaxy. Over time, its architects had disappeared for unknown reasons, and primitive civilizations arose on the sections of the ring. However, it is not easy to get to them, as the automated defense platforms near the ring world are enough to scare off anyone who comes.

• X:
  • X3: Terran Confict: The Torus Aeternal is a massive space station ringing Earth's equator. It serves as a docking ring, shipyard, and orbital defense station. In X3: Albion Prelude, it gets blown up.
  • X: Rebirth: The Teladi Union's space station has a centrifugal habitation ring that is over a dozen kilometers wide. The ring has an artificial atmosphere contained by energy shields, and alternates between manufacturing sectors and park-like habitation sectors.

Web Original

• The Journal Entries of Kennet Shardik: The world of Pendor is Niven's Ringworld with the Serial Numbers Filed Off, because Niven had threatened to sue Elf Sternberg over writing gay BDSM Known Space fanfic.
• Orion's Arm: Rotating space habitats are very common, and numerous variations exist.
  • Stanford tori are the smallest and most common kind, consisting of a donut-shaped space station with a transparent inner roof that allows light to be reflected onto the inhabited surface.
  • Bishop rings are larger, enough so as to be able to rely entirely on spin and walls to retain their atmospheres without requiring roofs. They're much too large to be built of mundane materials — steel alloys would tear apart under their rotational speeds — and as such are built out of carbon nanotube weaves instead. They can be up to 2000 kilometers in diameter, but most are smaller, and are lit by a large sun-lamps in their centers.
  • Banks orbitals, named in honor of Iain Banks in-universe, are much larger. They can be a good couple million kilometers in diameter, with walls hundreds of kilometers high to hold in their atmospheres, and rotate once per day to simulate Earth gravity; the immense rotational stresses that this produces are too much for even carbon nanotubes — constructing one requires the use of exotic matter types that only transapients can create. On the other hand, once one of these is built, it can be home to truly absurd amounts of people.
  • Star-encompassing ringworlds are also found in some systems, usually but not exclusively around small stars like white dwarfs. They are innately unstable and will eventually collide with their parent stars if left to themselves, and so require repeated small adjustments to keep them in their orbits.
  • There are also variations such as diskworlds (complete disks rather than rings, a shape which gives a lot more living space for the same diameter) and topopolises (essentially O'Neill cylinders extended all the way around a star so the two ends meet, resulting in something similar to Niven-style ringworlds but without needing extremely strong materials).

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