Environment Tables For Your Sci-fi TTRPG

Edited by Paul G.

Mar 1, 2025

Your players are deep in space, orbiting a strange new planet, or traversing the surface of a small moon. Environments in your sci-fi TTRPG are a critical story-telling component; they add tension, obstacles, and excitement for your players. The following tables should help you create awesome and unique environments and solar systems to explore! Roll for a random environment or pick and choose for inspiration to concoct your own creations.

Use these environment tables to quickly generate solar systems—and the environments contained within—for your science fiction table top role playing game: Star Wars D6, Star Trek Adventures, or (my favorite) Index Card RPG's Warp Shell setting.

Overview

The systems presented here are designed to add fun in your TTPRG without sacrificing speed of play. By no means is the content here 100% scientifically accurate or strictly adhere to the known laws fo physics. In fact, this content is geared towards playing in an awesome 1950's sci-fi movie—not replicating the vast emptiness of space.

Adjust as needed for your game's system and setting.

Table	Summary
Systems	The number of stars in the system.
Stars	From blazing blue giants to dim brown dwarfs, stars are the primary source of energy in the universe.
Asteroid Belts	Miscellaneous fields of asteroids and space-junk orbiting a star. Rich in minerals and resources.
Planets & Moons	Gas and terrestrial planets and moons.
Rings	Whether a planetoid has a ring, and if so, what it's made of.
Gravity	Measurement of a celestial body's mass; relative to the arbitrary scale of Old Earth's gravity: 1g.
Atmosphere	Composition of gases in the environment; whether the biome supports common lifeforms or is hostile.
Pressure	The force exerted on characters, their ship, space station, or planetoid. Measured in atmospheres (atm).
Radiation	Ever present in the void of space, radiation can quickly go from easily ignored to life threatening. Measured by radiation category level.
Temperature	From the stark cold of the vacuum of space to the raging lava flows of the laval planet Morbix 12. Measured in degrees Celsius.
Biomes	The type of environment on a terresterial planet or moon; from deserts to jungles, and everything in between.
Civilizations	Who will you meet? From primitive communities to advanced civilizations.
Anomalies	Wormholes, black holes, space stations, and space anomalies.

Systems – d4

Roll a d4 to determine the number of stars in the system.

Roll	Stars
1	Uni (single star) system
2	Binary star system
3	Trinary star system
4	Nebula

Stars – d20

Roll a d20 for each each star in the system.

Roll	Star	Description
1	Red dwarf (M-Type)	Small, dim, long-lived stars that host many rocky worlds.
2	Yellow Main Sequence (G-Type)	Sun-like, stable, prime real estate for life.
3	Blue Giant (B-Type)	Massive, intensely bright stars with short lifespans.
4	White Dwarf	The husk of a dead star, extremely dense.
5	Neutron star	A collapsed stellar core, spinning rapidly and emitting deadly radiation.
6	Pulsar	A rotating neutron star emitting rhythmic bursts of electromagnetic radiation.
7	Black Hole	The collapsed remnant of a massive star, devouring anything nearby.
8	Brown dwarf	A failed star, barely emitting heat, often mistaken for a gas giant.
9	Quasi-Star	A hypothetical giant, pre-supernova state star.
10	Magnetar	An ultra-magnetic neutron star, capable of disrupting ship systems.
11	Supergiant (O-Type)	Enormous, luminous star on the brink of exploding.
12	Wolf-Rayet Star	A massive, highly unstable star shedding layers rapidly.
13	Hypernova Progenitor	A star doomed to explode in a system-ending blast.
14	Protostar	A young, still-forming star surrounded by a dense accretion disk.
15	Variable Star	A star with irregular light emissions, sometimes linked to exotic matter.
16	Eclipsing Binary	Two stars frequently blocking each other from view, affecting planetary climates.
17	T Tauri Star	A newborn star blasting away its surroundings with stellar winds.
18	Flare Star	A seemingly quiet star that randomly erupts into violent solar storms.
19	X-ray Binary	A stellar corpse siphoning matter from a companion, emitting high-energy radiation.
20	Binary System	Roll twice on this table. Two stars locked in gravitational dance, affecting orbits dramatically.

Asteroid Belts — d6

Roll a d6 to determine the number of asteroid belts in the system, then roll a d6 for each belt's attribute.

Roll	Asteroid Belt	Description
1	Carbonaceous	Carbon, water, and organic compounds.
2	Metallic	Rich in metals and minerals.
3	Rocky	Primarily silicate rocks and minerals.
4	Ice	Water, ammonia, and methane ice belt.
5	Space Junk	Debris from destroyed ships, stations, and lost civilizations.
6	Mixed	Roll again. The belt is a combination of each roll.

Planets & Moons – d12

Roll a d12 for the number of planets in the system, then roll a d12 for each plant to determine its type.

For each planet, roll a d12 for the number of moons orbiting it.

Once you have your celestial bodies, roll Rings, Gravity, Atmosphere, and/or Biome for each planet and moon.

Roll	Planet	Description
1—6	Gas	A gas planet or gas giant.
7—9	Terrestrial	An ice or rock planet.
10	Binary Gas	Two gas planets orbiting each other.
11	Binary Terrestrial	Two icy or rocky planets orbiting each other.
12	Artificial	An artificially constructed planet or moon.

Rings – d10

For each planetoid roll to see if it has any rings.

Roll	Rings	Description
1—6	None	No rings here!
7	Space Dust	A ring of tiny dust particles.
8	Water & Ice	A ring of water and ice chunks and particles.
9	Rocks	Rocks and boulders orbiting the planetoid.
10	Mixed	All manner and sizes of ice, rock, and space junk.

Gravity — d6

Roll a d6 to determine a planet or moon's gravity—which determines its size and density.

Roll	Gravity	G-force	Description
1	Microgravity	<0.1g	Extremely low gravity environment. Almost weightless, allowing flight-like jumping and gliding. Common on large asteroids or dense debris fields. Always remember to tether.
2	Low	0.3g	Low gravity environment. Jumping and moving is magnified by 3x. Common to very small moons.
3	Standard	1g	Feels about like Old Earth.
4	High	1.5g	Heavy gravity environment. Movement is halved and jumping is difficult. Remote vehicles and rovers advised. Common on massive and/or very dense planetoids.
5	Extreme	>2g	Extreme gravity environment. Movement is extremely difficult and jumping is impossible. Space launch requires special equipment. Common on super-dense planetoids.
6	Fluctuating	∞	Roll twice on this table. Gravity fluctuates between rolls. Roll a d20 for intervals in minutes or a d100 for intervals in seconds.

Atmosphere — d10

Roll a d10. On a roll of 1, the planetoid has an atmosphere. Cool!

Roll another d10 and consult the table below to determine the atmosphere's composition. This table can also be used for pressurized vessels, capsules, and space stations.

Roll	Atmosphere	Composition	Description
1	Breathable	20% O₂ 80% N₂	Required to support common life on planets, moons, vessels, and space stations.
2	Unbreathable	5% O₂ 5% CO₂ 90% N₂	Requires oxygen support or an all-environment suit. Breathable atmosphere may be harvestable given the right equipment.
3	Toxic	10% O₂ 90% CH₄	Requires oxygen support or an all-environment suit.
4	Volatile	10% O₂ 90% H₂	Dangerously flammable atmosphere featuring frequent explosions and fires.
5	Vapor	90% H₂O 5% Ar	Steamy atmosphere with frequent rain and fog. Breathable, assuming a bearable temperature.
6	Carbon	95% CO₂ 5% N₂	Deadly to most lifeforms. Requires oxygen support or an all-environment suit. Reminiscent of the atmosphere of Mars in the Sol system.
7	Gaseous	80% H₂ 10% He 5% CH₄ 5% NH₃	Unstable atmosphere with frequent storms and lightning.
8	Thin	5% O₂ 95% He	Requires oxygen support or an all-environment suit. Breathable atmosphere may be harvestable given the right equipment.
9	Sulfur	90% SO₂O 10% O₂	Deadly to most lifeforms. Requires oxygen support or an all-environment suit. Reminiscent of the atmosphere of Venus in the Sol system.
10	Vacuum	99% nothing	An empty vacuum. Barren planetary bodies and asteroids.

Pressure — d6

Atmospheric pressure of a ship, station, elevation, depth, or planetoid. For planetoids, only roll if the body has an atmosphere.

Roll	Pressure	Atmospheres	Description
1	Low	0.5 atm	Extremely thin air, approximately equivalent to 20,000 feet above sea level of Old Earth. Breathable after acclimation.
2	Standard	1 atm	Feels good, just like Old Earth.
3	Medium	2 atm	Medium pressure, like being 30 feet underwater.
4	High	5 atm	High pressure, like being 150 feet underwater.
5	Extreme	50 atm.	Crushes submersibles and most spacecraft, not to mention unprotected biological and artificial lifeforms.
6	None	0 atm	The vacuum of space.

Radiation — d6

Radiation check: is it safe?

Roll	Level	Description
1	Category 1	Natural background radiation, ever present with no critical effects.
2	Category 2	Elevated but still safe.
3	Category 3	Avoid extended periods of exposure.
4	Category 4	Extreme radiation. Expect radiation sickness and possible death. Take necessary precautions.
5	Category 5	A lethal radiation level. Evacuate immediately and seek medial attention.
6	Fluctuating	Roll twice on this table. Radiation fluctuates between rolls. Roll a d20 for intervals in minutes or a d100 for intervals in seconds.

Temperature — d6

Roll a d6 to determine the temperature of a planet, moon, space station, abandoned ship, etc.

Roll	Temperature	Celsius	Description
1	Freezing	–270.4°C	The dire cold of the vacuum of space.
2	Freezing	-20°C and below	Extreme cold. Frostbite and hypothermia are immediate threats.
3	Cold	-20—0°C	Chilly. Snow and ice are common.
4	Temperate	0—30°C	Usually comfortable. Not too hot, not too cold.
5	Warm	30—50°C	Uncomfortably hot for most lifeforms. Frequent hydration and a level 5 sunblock advised.
6	Extreme	50°C and up	Deadly hot. Heatstroke, heat exhaustion, dehydration, and death are immediate threats.

Biomes — d12

Roll a d12 for a Biome. For multiple biomes on one planetoid, roll several times and note each area or continent.

Roll	Planetoid	Description
1	Archipelago	An ocean world dotted with small island groups, shallow reefs, and atolls.
2	Arctic	A frozen wasteland planetoid of ice, snow, and glaciers. May contain geothermal activity.
3	Desert	Sunbaked barren sphere of dunes, rocks, and canyons.
4	Forest	A lush, green forest planetoid, thriving with biological plant and/or animal life.
5	Ice	A frozen ocean world. Rich in H₂O and other rare molecules.
6	Jungle	A dense, tropical, biome teeming with life.
7	Mountain	A rough rocky planetoid featuring jagged peeks, deep ravines, and savage weather systems.
8	Ocean	A water world containing abundant aquatic plant and/or animal activity.
9	Rocky	A relatively flat, rocky, barren, and cold world. Rich in mineral ore though!
10	Swamp	A planetoid of misty swamp forests, hazy bayous, and shallow oceans checkered with mangroves.
11	Terraformed	A planetoid artificially altered to support life.
12	Volcanic	Volcanic mountains, steaming oceans, and active lava flows covering a geologically unstable celestial body.

Civilizations & Life — d12

Does it support life? It does in our game if we want it to!

Roll	Civilization	Description
1	Plant life only	A planetoid with no animal life.
2	Insect	A planetoid rich with plant and insect life.
3	Prehistoric	A planetoid supporting prehistoric lifeforms.
4	Primitive	Stone age technology, tribal societies, and hunter-gatherer cultures.
5	Classical	Ancient civilizations, city-states, and empires.
6	Medieval	Feudal societies, castle-like fortifications, and shady political systems.
7	Industrial	Factories, steam engines, and early electricity.
8	Technological	Advanced technology, space travel, and cybernetics.
9	Artificial & Cybernetic	Artificial intelligence, cyborgs, sentient robots, synthetic lifeforms, and bio-enhanced beings.
10	Transcendent	Post-singularity civilizations, god-like beings, and incomprehensible technology.
11	Apocalyptic	A once advanced civilization on the brink of extinction. Ruins, wastelands, and desperate survivors.
12	Clashing	Roll twice on this table, this planet has two drastically clashing levels of evolution.

Anomalies – d12

Roll one anomaly for your system, or a whole bunch! I don't care!

Roll	Anomaly	Description
1	Asteroid Field	The entire system is a chaotic sprawl of colliding asteroids and debris. Extreme caution advised.
2	Asteroid Mining Colony	A space colony built into an asteroid.
3	Black Hole	Gravitational singularity with an event horizon. Approach with caution.
4	Distress Signal	Signal from a stranded vessel or colony. May be a trap or a genuine call for help.
5	Dyson Sphere	Megastructure surrounding a star to maximize solar energy harvest. Might be inhabited by artificial, biological, or transcendent life, or may be abandoned and dormant.
6	Floating Colony	Self sustaining colony floating in space. Possibly abandoned.
7	Space Station	Orbital station around a planet, moon, or asteroid.
8	Supernova	The entire system is bombarded with energy from a star which has undergone a catastrophic explosion, ejecting most of its mass into an asymmetrical field of energy.
9	Wormhole	Space-time tunnel connecting two points in space. Hopefully stable.
10	Quantum Anomaly	Unexplained phenomena defying the laws of physics.
11	Artifacts	Remnants and clues of an ancient civilization.
12	Multiple	Roll twice on this table. The system contains two anomalies.