Hothouse world

Hothouse world
The cloud deck of Venus, by Mariner 10, newly processed · NASA/JPL-Caltech, Public domain, Wikimedia Commons

Read off: Venus

A runaway greenhouse: an ocean of carbon dioxide presses on the ground as hard as the sea a kilometre down, and the surface is hot enough to melt lead, day and night, pole and equator alike. Clouds of sulphuric acid hide the sun in a yellow-orange glow. Nothing unprotected lasts more than hours; the longest-lived probe ever landed there lasted barely two. High above, in the clouds, the temperature and pressure are almost earthly, and that is where stations float.

In figures

Gravity
0.90 g (Venus)
Day
About 117 Earth days from sunrise to sunrise
Air pressure
92 bar, like nearly a kilometre under the sea
Air
96.5% carbon dioxide, 3.5% nitrogen, traces of sulphur dioxide
Mean temperature
464 °C, day and night alike
Coldest
about 377 °C on the highest mountains
Hottest
about 477 °C in the deepest lowlands
Weather
Sulphuric acid clouds 45 to 70 km up, circling the planet in about 4 days; barely a breeze at the ground
Light
Dim
Going
Hard

Hear it

Hazards

  • Crushing atmosphere. The air presses on the ground about ninety times as hard as on Earth, the weight of a kilometre of sea. Only a hull built like a submarine's survives the surface. D&D 5e (House rule): House rule: a creature without a pressure hull takes 6d10 Bludgeoning damage at the start of each of its turns. Moving through the dense air costs 1 extra foot of movement for each foot moved, as in water. Starfinder 2e: Thick atmosphere (GM Core): a creature breathing it attempts a Fortitude save every hour or is sickened 1 until it breathes normal air. Starfinder's rules stop there; a pressure ninety times Earth's, with this heat, is beyond them. Archives of Nethys
  • Searing heat. Hot enough to melt lead. Electronics fail within hours, and only active cooling, at a great cost in power, keeps anyone alive. D&D 5e (House rule): House rule: a creature or device without cooled protection takes 10d10 Fire damage at the start of each of its turns. A cooled suit protects for as many hours as its power lasts; Fire immunity protects the wearer, not the suit's electronics. Starfinder 2e: Incredible heat (GM Core, 60 °C / 140 °F or hotter): fatigued after 2 hours of travel and moderate fire damage (4d6 to 6d6) every minute. Starfinder has no band beyond this one; a superior thermal capacitor is the least a visitor needs. Archives of Nethys
  • Acid clouds. Droplets of sulphuric acid fill the cloud decks. Floating stations live among them; every hull, seal and lens is slowly eaten away. D&D 5e (House rule): House rule: a creature in the clouds without an acid-proof suit takes 2d6 Acid damage at the end of each minute. Each day, exposed gear needs a DC 12 Intelligence check with tinker's tools or a piece of it is ruined. Starfinder 2e: Corrosive atmosphere (GM Core): minor to moderate acid damage (1d6 to 2d6, up to 4d6 to 6d6) every minute to creatures and objects. Armour environmental protections do not stop it. Archives of Nethys

What may happen

  1. Droplets of acid bead on the viewports and run in slow yellow streaks; the hull crew goes out to scrub them before they etch the glass.
  2. A floating station rises out of the yellow haze, its envelope full of breathable air: on this world, air is a lifting gas.
  3. On the surface, the scorched shell of a lander that lasted about two hours before the heat won.
  4. The sun has hardly moved since the last shift: here a day lasts months, and the clouds race round the world far faster than the ground turns.
  5. Radar shows a plain of old lava flows, cracked into tiles the size of fields.
  6. The station drifts with the wind; by tonight it will be over the night side, and by next week back again.
  7. After months in orbit, the cloud station’s weight feels almost like home: nine-tenths of a g, and nobody floats anymore.
  8. Outside at this height a worker needs no pressure suit, only an acid-proof coverall and an air mask. Today the envelope needs a patch.
  9. The armoured lander drops through the cloud deck. Lower down the haze clears and the ground appears, dim and orange, far below.
  10. On the ground the light is a dull orange, like a stormy evening at home, and the shadows are soft.
  11. Through the lander’s thick quartz port: flat slabs of dark rock, like broken paving, as far as the camera reaches.
  12. The lander’s clock counts down the minutes its cooling can hold. The geologist works faster with every reading.
  13. At the surface the air barely moves, yet in air this dense even a breeze leans on the lander like a river current.
  14. Radar shows the highest peaks capped with something bright: a metal frost, the scientists think, settled where it is coolest.
  15. Radar maps a flat-topped dome of old lava, round as a pancake and wider than a city.
  16. Below the station, streaks of acid rain fall from the cloud deck and vanish long before they come near the ground.
  17. A cloud chemist swears her sampler found a trace gas that life might make. Nobody else’s instrument agrees.
  18. On the upper gallery the sun pours through the thinning cloud, and the station’s greenhouse drinks it in.
  19. The station vents a little lifting gas and sinks a few hundred metres to ride beneath a band of thicker acid haze.
  20. A weather balloon on a long tether is reeled in, its skin pitted and yellowed by a single week in the clouds.
  21. The station almanac reminds newcomers that this world turns backwards: from its ground, the sun would rise in the west.
  22. Teodora, an engineer who harvests sulphuric acid from the clouds for the station’s factories, complains about nothing else all evening.
  23. On the night side, the infrared cameras show the upper air glowing faintly with a light of its own.
  24. The shuttle from orbit docks with the floating station, its paint pitted by the climb down through the cloud.
  25. A routine check finds acid creeping under a gasket on the airlock. A week more and it would have eaten through.

Adventure hooks

  1. A floating city is losing lift, and the only spare envelope is on a rival station.
  2. Someone wants a probe dropped to the surface to retrieve a black box from the first lander, before it melts entirely.
  3. Microbes have been found in the cloud deck, and a cult says they are the planet's soul.
  4. The station's acid scrubbers were bought cheap, and the hull crew has found the first etched rivet.

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, Volcanic world, Airless world, Ocean 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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