Cold desert world

Cold desert world
Gale crater on Mars, its summit and cliffs, seen by the Curiosity rover · NASA/JPL-Caltech/LANL/CNES/CNRS/IRAP/IAS/LPG, Public domain, Wikimedia Commons

Read off: Mars

Rust-red plains under a butterscotch sky, scattered with dark stones and old riverbeds that have not seen water in billions of years. The air is too thin to breathe or even to keep a body's fluids from boiling, so every step outside is taken in a suit. Days are a little longer than on Earth, nights are bitterly cold, and fine dust gets into every seal and joint.

In figures

Gravity
0.38 g (Mars)
Day
24 h 40 min
Air pressure
0.006 bar, under 1% of Earth's
Air
95% carbon dioxide, a little nitrogen and argon, 0.16% oxygen
Mean temperature
−59 °C
Coldest
about −153 °C at the poles
Hottest
about 20 °C at noon on the equator
Radiation
0.64 mSv a day at the surface (Curiosity), about 100 times Earth's background
Liquids
None at the surface; water as ground ice, polar caps and frost
Weather
Dust storms, regional to planet-wide (2018 covered the whole planet); winds up to 17–30 m/s in storms
Light
Lit
Going
Slow

Hear it

Hazards

  • Unbreathable air. There is air, but not air a human can live on: too thin, no oxygen, or the wrong gases. A mask and an oxygen supply are enough where the pressure holds; a full suit where it does not. D&D 5e: A creature holds its breath for 1 + its Constitution modifier minutes (at least 30 seconds), then gains 1 Exhaustion level at the end of each of its turns until it can breathe; it then loses all the Exhaustion it gained this way. Starfinder 2e: Thin atmosphere (GM Core): a few hours make a creature that is not acclimated fatigued; in severely thin air it attempts a Fortitude save every hour or becomes drained 1. With no oxygen at all, use holding breath and suffocating (Player Core). Armour environmental protections cover both. Archives of Nethys
  • Low gravity. Everything weighs a fraction of what it does on Earth: a person bounds rather than walks, falls slowly, and finds that stopping, turning and carrying momentum is harder than lifting. D&D 5e (House rule): House rule: jump distances are tripled, falling damage is halved, and a creature can lift and carry twice its usual weight. A creature unused to it has Disadvantage on Dexterity (Acrobatics) checks for its first day. Starfinder 2e: Low gravity (GM Core): Bulk is halved, so a creature carries twice as much and jumps twice as high and far; physical ranged attacks reach the 12th range increment. A fall deals nothing for the first 3 m (10 ft), then bludgeoning damage equal to a quarter of the rest of the distance. Archives of Nethys
  • Surface radiation. No thick air and no magnetic field to stop the particles of the sun and the stars. A day outside is harmless; months add up to a real risk of cancer, and a solar storm can bring a dangerous dose in hours. Shelters are buried or walled in rock and water. D&D 5e (House rule): House rule: no effect at the table for a few days. After each month spent mostly outside without shelter, a creature makes a DC 10 Constitution saving throw; on a failure its Hit Point maximum drops by 1d4 until it spends a month under shelter. Starfinder 2e: Cosmic radiation (GM Core): on a world with no atmosphere, creatures are usually exposed all the time to mild to severe radiation, which brings radiation sickness (mild: disease 1, Fortitude DC 17). A radiation buffer armour upgrade gives resistance and a bonus to the save. Archives of Nethys
  • Dust storm. A storm of fine dust that can grow for weeks until it hides the sun across half the planet. The thin wind barely pushes a person, but the dust blinds, starves solar panels and grinds into every seal. D&D 5e (House rule): Inside the storm the area is Heavily Obscured: a creature trying to see something in it has the Blinded condition. House rule: solar power gives a tenth of its output, and each day a suit or vehicle exposed to it needs a DC 12 Intelligence check with tinker's or mechanic's tools or a seal fails.
  • Deep cold. Cold far below anything on Earth: steel turns brittle, rubber cracks and an unheated suit fails within hours. Heating and power are life. D&D 5e (House rule): House rule: a creature without heated protection makes a DC 15 Constitution saving throw at the end of each minute, taking 2d6 Cold damage and gaining 1 Exhaustion level on a failure. Cold resistance halves the damage but not the Exhaustion; Cold immunity passes automatically. Starfinder 2e: Incredible cold (GM Core, −62 °C / −80 °F or colder): fatigued after 2 hours of travel and moderate cold damage (4d6 to 6d6) every minute. A superior thermal capacitor protects against it. Archives of Nethys

What may happen

  1. A dust devil a kilometre tall crosses the plain, scrubbing a dark track behind it across the red ground.
  2. The sun sets blue: the fine dust scatters its light so that a cold blue glow rings it while the rest of the sky goes brown.
  3. At dawn a thin frost covers the stones and is gone into the air an hour later without ever melting.
  4. Two small moons cross the night sky, one fast enough to watch it move.
  5. Half buried in a dune, an old lander from the first exploration, its panels dusted over and its antenna still pointing home.
  6. A suit alarm: a slow leak at a glove seal, fine dust in the joint. Nothing urgent if someone notices now.
  7. Every sol runs forty minutes longer than a day at home. The crew who still keep Earth time find their breakfast sliding into the night by the end of the month.
  8. A supply crate weighs barely a third of what it would at home, but it swings with all its mass and knocks the geologist off her feet.
  9. Overnight a gust has swept the solar panels clean of dust, and the base wakes to more power than it has had in weeks.
  10. Fine red dust clings to the suit legs with static and follows everyone through the airlock, however hard the brushes work.
  11. A trench dug for a cable shows bright ice a hand’s depth down. A few sols later the exposed chips have vanished into the thin air without melting.
  12. The weather satellite reports a regional dust storm two sols away. The base starts charging every battery it owns.
  13. The ground rises so gently that it seems flat, yet the survey says this is the flank of a volcano wider than many countries at home.
  14. A canyon wall shows hundreds of thin layers, banded like the pages of a book. The geologist reads old lakes into them.
  15. Small grey spheres of iron mineral lie scattered on the ground like spilt shot. The old hands call them blueberries.
  16. The base greenhouse harvests its first lettuce, grown in red soil washed three times of its perchlorate salts. Everyone gets one leaf.
  17. A miner has coughed for a week. The medic blames the dust tracked into the habitat and the perchlorate salts it carries.
  18. Low in the dusk, a bright blue-white star: Earth, with the Moon a faint speck beside it for those who know where to look.
  19. A message home takes many minutes each way. The young technician talks into the recorder as if her mother could answer, and waits.
  20. The rover’s rear wheel breaks through a thin crust into soft sand and spins in place, digging itself deeper.
  21. After sunset the cold comes fast. The thin air holds no heat, and the ground gives up in hours what the sun gave it all day.
  22. An ice hauler named Okafor sells real Earth chocolate out of her rover’s tool locker, one square at a time, at a price that makes the crew wince.
  23. A corporate surveyor in a spotless suit plants claim markers across the ice field the colony has quarried for years.
  24. High, thin clouds of water ice streak the butterscotch sky, pale and faintly blue.
  25. A dark, smooth boulder sits alone on the plain, pitted and polished by the wind: an iron meteorite.

Adventure hooks

  1. A rover crew went silent in a dust storm three days ago; their last message was coordinates and the word "door".
  2. Someone is buying ice-claim deeds at the poles for far more than the ice is worth.
  3. An old riverbed holds fossils that should not exist, and the survey company wants them gone before the inspectors land.
  4. The dome's water recycler is failing, and the spare part is on a lander that crashed two hundred kilometres away.

Who and what is met

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

Other worlds

Ice moon with a hidden ocean, Methane world, Hothouse 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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