Ocean world

Read off: Proposed water worlds (models and candidates)

Water from horizon to horizon, perhaps hundreds of kilometres deep, with no shore and no land to stand on. Astronomers have found planets whose size and mass fit such a world, but none is confirmed: what follows is what models allow. Deep down, the pressure would turn water into exotic ice before any seabed; up top, storms would have a whole planet to grow over. Everything that lives or lands here floats, swims or sinks.

In figures

Gravity
About 1.3 g for K2-18 b, a candidate (A candidate, not settled)
Day
Unknown; K2-18 b circles its star in 33 days (A candidate, not settled)
Air
K2-18 b: methane and carbon dioxide seen by JWST; read either as an ocean under hydrogen or as a gas-rich mini-Neptune with no surface (A candidate, not settled)
Mean temperature
Equilibrium about 6 °C for Kepler-22b without air; not a surface figure (A candidate, not settled)
Liquids
Models allow oceans 30 to 500 km deep, over high-pressure ice; no exoplanet ocean is confirmed (What models say, not a measurement)
Light
Lit
Going
Hard

Hear it

Hazards

  • No land anywhere. There is nowhere to land, to rest or to dig in: everything that stays must float. A lost raft is lost for good. D&D 5e: Over water more than 30 m (100 ft) deep, a creature without a Swim Speed makes a DC 10 Constitution save after each hour of swimming or gains 1 Exhaustion level.
  • World-ocean storm. With no continent to break them, storms may grow without end and circle the planet. A floating station rides them out or is torn apart. D&D 5e (House rule): Strong wind gives Disadvantage on ranged weapon attacks, puts out open flames and scatters fog; a flyer must land at the end of its turn or fall. House rule: in the heart of the storm, everyone on deck makes a DC 15 Strength saving throw each hour or goes overboard.
  • Crushing depth. Every ten metres down adds the weight of a whole atmosphere. A few hundred metres needs a hard suit, a few kilometres a hull, and far below, models say, the water itself turns to ice under the pressure. D&D 5e (House rule): House rule: below the depth its suit or hull is rated for, a creature takes 4d10 Bludgeoning damage at the start of each of its turns, doubled for each further step of the same depth.

What may happen

  1. A wall of cloud from one horizon to the other: a storm that has been circling the planet for weeks.
  2. A raft of something like weed, kilometres wide, drifts past, and things move under it.
  3. At night the wake glows: the water is full of tiny living lights.
  4. A long swell from a storm on the far side of the world lifts the station a few metres, slowly, for a whole day.
  5. The sonar sweeps down and finds no bottom within its range.
  6. Warm rain falls on a flat grey sea for hours, and the horizon disappears.
  7. A third heavier than home: by evening every back aches, and the medic hands out pills and stretching exercises.
  8. The base cannot anchor: no cable reaches a bottom this deep. It drifts, and the navigator logs its course every hour.
  9. The water maker runs all day long. Here it is the one thing nobody ever rations, and the showers are famous for it.
  10. The submersible sinks until the last blue light fades. Past that, the lamps show only specks drifting upward past the ports.
  11. At depth, the submersible’s hull creaks once, loudly. The pilot says it always does that. The pilot is lying, or new.
  12. The analyser cannot settle on the sea’s salt: its mix matches no ocean on record, and the chemist is delighted.
  13. A supply drone lands on the pad as the swell rolls the base. The crate slides toward the rail.
  14. Three days into the swell, half the newcomers are green, and the mess is very quiet at breakfast.
  15. A line of data buoys runs to the horizon, each one blinking in turn, the only road on this world.
  16. The colony’s culture rafts trail long ropes of grown algae, and a team in waders checks them by hand.
  17. On deck at night there is no light anywhere but the base’s own and the stars, and the long swell lifting everything.
  18. A wrench slips over the rail. Somewhere below it is still sinking, and will be for a long time.
  19. The wave radar flags a swell twice the height of the rest, coming out of the dark.
  20. The mail capsule splashes down beside the base. Letters from home, months old, are read aloud in the mess.
  21. Over dinner two oceanographers argue whether the floor far below is rock or a kind of ice no human has ever touched.
  22. A life raft from a broken float base drifts into view, four people aboard, sunburnt and very thirsty.
  23. The tiltrotor to the next base leaves at dawn: four hours over nothing but water, and the pilot hums the whole way.
  24. A ballast pump fails and the base takes on a slow list. Coffee cups creep across the tables.
  25. A corporate inspector arrives to audit the base’s licence. On this world, drifting into another company’s water is a crime.

Adventure hooks

  1. A floating city wants to sink its anchor cable to the deep ice, and the divers who tried it came back changed.
  2. A raft of weed kilometres wide is drifting toward the station, and something steers it.
  3. The storm that has circled the world for a year is coming round again, and the station's engines are dead.
  4. Astronomers back home still argue that this world has no ocean at all; someone wants proof filmed and sent.

Who and what is met

Each is an SRD stat block under another name, as game masters reskin them.

Other worlds

Cold desert world, Ice moon with a hidden ocean, Methane world, Hothouse world, Volcanic world, Airless world, Tidally locked world, Earthlike world, Acid world, Jungle world, Swamp world

Sources

This work includes material from the System Reference Document 5.2.1 ("SRD 5.2.1") by Wizards of the Coast LLC, available at https://www.dndbeyond.com/srd. The SRD 5.2.1 is licensed under the Creative Commons Attribution 4.0 International License, available at https://creativecommons.org/licenses/by/4.0/legalcode.

This product is licensed under the ORC License located at the Library of Congress at TX 9-307-067 and available online at various locations including paizo.com/orclicense, azoralaw.com/orclicense, and others. All warranties are disclaimed as set forth therein. Attribution: this rules layer is based on the following Licensed Material: Starfinder Player Core © 2025 Paizo Inc., Authors: Jessica Catalan, Thurston Hillman, Jenny Jarzabski, Mike Kimmel, and Dustin Knight; Starfinder GM Core © 2025 Paizo Inc., Authors: Jessica Catalan, Thurston Hillman, Jenny Jarzabski, Mike Kimmel, and Dustin Knight; Starfinder Alien Core © 2025 Paizo Inc. Authors: Kate Baker, Lau Bannenberg, Rigby Bendele, Vishesh Bhartiya, Joseph Blomquist, Jeremy Blum, Tineke Bolleman, Brent Bowser, Michael Bramnik, Patrick Brennan, Charlie Brooks, Jessica Catalan, Brite Cheney, Jeremy Corff, Caryn DiMarco, Anthony Dollinger, Steve Fidler, Kim Frandsen, Andrew D. Geels, Basheer Ghouse, Sen H.H.S., Katrina Hennessy, Thurston Hillman, Joan Hong, Jenny Jarzabski, Sara Jeffers, Mikko Kallio, Lysle Kapp, Mike Kimmel, Dustin Knight, Cole Kronewitter, Mahpiya, Letterio Mammoliti, Randal Meyer, Jacob W. Michaels, Matt Morris, Dennis Muldoon, Quinn Murphy, Elizabeth V Nold, Chesley Oxendine, Emily Parks, Glen Parnell, Randy Price, Kyle T. Raes, Jessica Redekop, Erin Roberts, James Rodehaver, David N. Ross, Pidj Sorensen, Joel Southall, Kendra Leigh Speedling, Drew Taylor, Sam W Tennyson, Jalen Todd, Ruvaid Virk, Viditya Voleti, Christopher Wasko, Nicholas Wasko, Jackson Wery, Shan Wolf, and Basil Wright. If you use our Licensed Material in your own published work, please credit us as follows: Biomes, Starfinder Second Edition rules layer © 2026 Michael Ghelfi. Reserved Material: the names of Biomes and its catalogues, its descriptions, sounds, art and code. Starfinder is a registered trademark of Paizo Inc.; this site is not published, endorsed, or specifically approved by Paizo Inc.

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