RTT Worldgen

The RktkT Complicated Star System Generator is a detailed, but not too detailed, random star system and world generation system for Mongoose Traveller. It attempts to walk that fine line between realistic (as based on current astronomical and planetological research) and easy to use. Drawn from a number of sources, including the core rules, GURPS Space (for 4th edition), GURPS Traveller: First In, various idea seeds on the Traveller Mailing List and Citizens of the Imperium fora, and the Arc Builder Planetary Classification List.

This is a "bottom up" system, where you start with the primary star and work through all the planetary orbits. However, a lot of the process has been greatly simplified and fudged, mainly so you don't have to go crazy calculating the molecular weight of the atmosphere and the effects of axial tilt, but also to make it easier to update the system when new scientific discoveries make it outdated. The end results are all in the conventional UPP format, with the addition of a single new rating, Biosphere, to describe the complexity of life on the world.

I've made the assumption that minor bodies aren't worth mentioning. Assume all systems have a Kuiper belt and Oort cloud, that most Jovians will have their Trojans and Greeks, and that pretty much any planet at all has a number of minor satellites, meteor clouds, etc. Space is big.

Playtesting Notes (Last updated 6 June 2008: The tables seem to turn out rather small planetary systems, especially for the ubiquitous red dwarfs, but I'm not sure that's a bug; if anything, it makes it easier to cope. And considering that we still don't know how common planets really are in the universe; under these rules, the Sol system is neither rare nor typical, which works for me. If you want more planets, try applying DM +1 to the three orbit rolls. Microscopic life is fairly common and macroscopic life less so, which seems a reasonable assumption for Traveller, and there look to be plenty of quiet lifeless worlds suitable for terraforming.

– Shadowjack (William)

To Do List

Populations and Terraforming, Special Features, internal links for dice tables, descriptive links for planetary and stellar classes

Basic Star Placement

Any hex has a 50% chance of having a brown dwarf (class L) somewhere.

Any hex has a 50% chance of having a star system somewhere.

A hex can contain both, drifting far apart from each other. For either kind of system, follow the procedure below.

Star System Generation

Number of Stars

Roll 3d6. DMs: Open Cluster +3. Don't roll for a lone brown dwarf; it's always solitary.

3-10 — Solitary star

11-15 — Binary system

16+ — Trinary system

Spectral Types

For the Primary, roll 2d6.

For each Companion, roll and add 1d6-1 to the Primary's number.

This generates a main sequence star; if the star later turns out to be a subgiant or giant, its spectral type will be changed. Don't roll for lone brown dwarfs.

2 — A-type or larger. (You may choose to place an O or B star, supergiant, etc.; max. 1 per sector.)

3 — F-type

4 — G-type

5 — K-type

6-13 — M-type

14+ — L-type

System Age & Luminosity Classes

System Age = 3d6-3 (in billions of years). Use this to determine the luminosity class and final spectral type of each star.

A-type

If Age ≤ 2: A-V

If Age = 3, roll 1d6:

1-2 — F-IV

3 — K-III

4-6 — D

If Age ≥ 4: D

F-type

If Age ≤ 5: F-V

If Age = 6, roll 1d6:

1-4 — G-IV

5-6 — M-III

If Age ≥ 7: D

G-type

If Age ≤ 11: G-V

If Age 12-13, roll 1d6:

1-3 — K-IV

4-6 — M-III

If Age ≥ 14: D

K-type

Automatically K-V.

M-type

Roll 2d6. DMs: Companion star +2.

2-9 — M-V

10-12 — M-Ve (flare star)

13+ — L

L-type

Automatically L.

Companion Orbits

For each Companion, roll 1d6:

1-2 — Tight orbit

3-4 — Close orbit

5 — Moderate orbit

6 — Distant orbit

Planetary System Generation

Each Primary and Distant Companion has its own planetary system, consisting of:

Epistellar orbits: 1d6-3, maximum 2. DMs: M-V star -1.

Type III, D, or L star: automatically 0.

Inner Zone orbits: 1d6-1. DMs: M-V star -1. If Close Companion present, automatically 0.

Type L star: instead roll 1d3-1.

Outer Zone orbits: 1d6-1. DMs: M-V star -1. If Moderate Companion present, automatically 0.

Orbit Contents

For each planetary orbit, roll 1d6. DMs: L star -1.

1 — Asteroid Belt

2 — Dwarf Planet

3 — Terrestrial Planet

4 — Helian Planet

5-6 — Jovian Planet

Then determine if the planets have any major satellites. (Small satellites are not counted.)

Asteroid Belt

Roll 1d6.

1-4 — All members are Small Bodies.

5-6 — Most members are Small Bodies, but there is also one Dwarf Planet.

Dwarf Planet

Roll 1d6.

1-5 — No major satellites.

6 — One Dwarf Planet as binary companion.

Terrestrial Planet

Roll 1d6.

1-4 — No major satellites.

5-6 — One Dwarf Planet as satellite.

Helian Planet

Satellites: 1d6-3. If there are any satellites at all, roll 1d6.

1-5 — All satellites are Dwarf Planets.

6 — One of the satellites is a Terrestrial Planet, and the others are Dwarf Planets.

Jovian Planet

Satellites: 1d6. Then, roll 1d6 again.

1-5 — All satellites are Dwarf Planets.

6 — Roll 1d6 again.

1-5 — One of the satellites is a Terrestrial Planet, and the others are Dwarf Planets.

6 — One of the satellites is a Helian Planet, and the others are Dwarf Planets.

Rings: Roll 1d6.

1-4 — Minor ring system only.

5-6 — Complex ring system.

World Types

Then for each planet, look up its zone and type on the tables below to find out which world generation type to use.

If the star is type III or D, the first 1d6 orbits (counting outward) were directly affected by the star's expansion. Any planets in those orbits are automatically of a particular type:

All Dwarf Planets become Stygian.

All Terrestrial Planets become Acheronian.

All Helian Planets become Asphodelian.

All Jovian Planets become Chthonian.

Dwarf Planets

Epistellar

Roll 1d6. DMs: Asteroid Belt member -2.

1-3 — Rockball

4-5 — Meltball

6 — Roll 1d6:

1-4 — Hebean

5-6 — Promethean

Inner Zone

Roll 1d6. DMs: Asteroid Belt member -2, Helian satellite +1, Jovian satellite +2.

1-4 — Rockball

5-6 — Arean

7 — Meltball

8 — Roll 1d6:

1-4 — Hebean

5-6 — Promethean

Outer Zone

Roll 1d6. DMs: Asteroid Belt member -1, Helian satellite +1, Jovian satellite +2.

0 — Rockball

1-3 — Snowball

4-5 — Rockball

6 — Arean

7 — Meltball

8 — Roll 1d6:

1-4 — Hebean

5-6 — Promethean

Terrestrial Planets

Epistellar

Roll 1d6.

1-4 — JaniLithic

5 — Vesperian

6 — Telluric

Inner Zone

Roll 2d6.

2-4 — Telluric

5-6 — Arid

7 — Tectonic

8-9 — Oceanic

10 — Tectonic

11-12 — Telluric

Outer Zone

Roll 1d6. DMs: Satellite +2.

1-4 — Arid

5-6 — Tectonic

7-8 — Oceanic

Helian Planets

Epistellar

Roll 1d6.

1-5 — Helian

6 — Asphodelian

Inner Zone

Roll 1d6.

1-4 — Helian

5-6 — Panthalassic

Outer Zone

Automatically Helian.

Jovian Planets

Epistellar

Roll 1d6.

1-5 — Jovian

6 — Chthonian

Inner Zone

Automatically Jovian.

Outer Zone

Automatically Jovian.

World Generation

World Generation Tables

Acheronian

Terrestrial Group, Telluric Class, Acheronian Type.
Worlds that were directly affected by their primary's movement from the main sequence.

Size: 1d6+4.

Atmosphere: 1.

Hydrosphere: 0.

Biosphere: 0.

Arean

Dwarf Group, GeoCyclic Class, Arean / Utgardian / Titanian Types.
Worlds with semi-active geology but little liquid, leading them to cycle through a slow build-up of activity, a short period where the surface is wet and clement, and a long decline.

Size: 1d6-1.

Atmosphere: Roll 1d6. DMs: D star -2.

1-3 — 1.

4-6 — A.

Hydrosphere: 2d6+Size-7. DMs: Atmos 1 -4.

Biosphere:

Chemistry: Roll 1d6. DMs: L star +2; Outer Zone +2.

1-4 — Water (Age modifier +0) [Arean]

5-6 — Ammonia (Age modifier +1) [Utgardian]

7-8 — Methane (Age modifier +3) [Titanian]

If Age ≥ 1d3 + modifier, and Atmos 1: 1d6-4.

If Age ≥ 1d3 + modifier, and Atmos A: 1d3.

If Age ≥ 4 + modifier, and Atmos A: 1d6+Size-2.

Otherwise: 0.

Arid

Terrestrial Group, Arid Class, Darwinian / Saganian / Asimovian Types.
Worlds with a limited hydrological cycle, that maintain equilibrium with the help of their geoactivity and/or biosphere.

Size: 1d6+4.

Biosphere:

Chemistry: Roll 1d6. DMs: K-V star +2; M-V star +4; L star +5; Outer Zone +2.

1-6 — Water (Age modifier +0) [Darwinian]

7-8 — Ammonia (Age modifier +1) [Saganian]

9-10 — Methane (Age modifier +3) [Asimovian]

If Age ≥ 1d3 + modifier: 1d3.

If Age ≥ 4 + modifier: 2d6. DMs: D star -3.

Otherwise: 0.

Atmosphere:

If Biosphere 3+ and Water Chemistry: 2d6-7+Size, minimum 2, maximum 9.

Otherwise: A.

Hydrosphere: 1d3.

Asphodelian

Helian Group, GeoHelian Class, Asphodelian Type.
Worlds that were directly affected by their primary's movement from the main sequence.

Size: 1d6+9.

Atmosphere: 1.

Hydrosphere: 0.

Biosphere: 0.

Chthonian

Jovian Group, Chthonian Class.
Worlds that were directly affected by their primary's movement from the main sequence, or that have spent too long in a tight epistellar orbit.

Size: G.

Atmosphere: 1.

Hydrosphere: 0.

Biosphere: 0.

Hebean

Classification: GeoTidal Class; Hebean Type (water chemistry), or Idunnian Type (ammonia chemistry).

Size: 1d6-1.

Atmosphere: 1d6+Size-6.

If 2+: change to A.

Hydrosphere: 2d6+Size-11.

Biosphere: 0.

Helian

Classification: GeoHelion Class or Nebulous Class.

Size: 1d6+9.

Atmosphere: D.

Hydrosphere: Roll 1d6.

1-2 — 0.

3-4 — 2d6-1.

5-6 — F.

Biosphere: 0.

JaniLithic

Classification: Epistellar Class, JaniLithic Type.

Size: 1d6+4.

Atmosphere: Roll 1d6.

1-3 — 1

4-6 — A

Hydrosphere: 0.

Biosphere: 0.

Jovian

Classification: Jovian Group; if life, is probably DwarfJovian Class, Brammian Type (water chemistry) or Khonsonian Type (ammonia chemistry).

Size: G.

Atmosphere: G.

Hydrosphere: G.

Biosphere: Roll 1d6. DMs: Inner Zone +2.

1-5 — 0

6 — Life is possible.

If Age ≥ 1d6: 1d3.

If Age ≥ 7: 2d6. DMs: D star -3.

Chemistry: Roll 1d6. DMs: L star +1; Epistellar -2; Outer Zone +2.

1-3 — Water

4-6 — Ammonia

Otherwise: 0.

Meltball

Classification: GeoThermic Class, Phaethonic, Apollonian, or Sethian Type; GeoTidal Class, Hephaestian or Lokian Type.

Size: 1d6-1.

Atmosphere: 1.

Hydrosphere: F.

Biosphere: 0.

Oceanic

Classification: Oceanic Class, Pelagic (water chemistry), Nunnic (ammonia chemistry), or Teathic (methane chemistry) Type; Tectonic Class, BathyAmunian (water chemistry), BathyNunnic (ammonia chemistry), or BathyTartarian (methane chemistry) Type.

Size: 1d6+4.

Biosphere:

Chemistry: Roll 1d6. DMs: K-V star +2; M-V star +4; L star +5; Outer Zone +2.

1-6 — Water (Age modifier +0)

7-8 — Ammonia (Age modifier +1)

9-10 — Methane (Age modifier +3)

If Age ≥ 1d3 + modifier: 1d3.

If Age ≥ 4 + modifier: 2d6. DMs: D star -3.

Otherwise: 0.

Atmosphere:

If Water Chemistry: 2d6+Size-6, minimum 1, maximum C. DMs: K-V star -1; M-V star -2; L star -3; any IV star -1.

Otherwise: Roll 1d6.

1 — 1

2-4 — A

5-6 — C

Hydrosphere: B.

Panthalassic

Classification: Panthalassic Class.

Size: 1d6+9.

Atmosphere: 1d6+8, maximum D.

Hydrosphere: B.

Biosphere:

Chemistry: Roll 1d6. DMs: K-V star +2; M-V star +4; L star +5.

1-6 — Roll 2d6.

2-8 — Water (Age modifier +0)

9-11 — Sulfur (Age modifier +0)

12 — Chlorine (Age modifier +0)

7-8 — Methane (Age modifier +1)

9-10 — Methane (Age modifier +3)

If Age ≥ 1d3 + modifier: 1d3.

If Age ≥ 4 + modifier: 2d6.

Otherwise: 0.

Promethean

Classification: GeoTidal Class, Promethean (water chemistry), Burian (ammonia chemistry), or Atlan (methane chemistry) Type.

Size: 1d6-1.

Biosphere:

Chemistry: Roll 1d6. DMs: L star +2; Epistellar -2; Outer Zone +2.

1-4 — Water (Age modifier +0)

5-6 — Ammonia (Age modifier +1)

7-8 — Methane (Age modifier +3)

If Age ≥ 1d3 + modifier: 1d3.

If Age ≥ 4 + modifier: 2d6. DMs: D star -3.

Otherwise: 0.

Atmosphere:

If Biosphere 3+ and Water Chemistry: 2d6+Size-7, minimum 2, maximum 9.

Otherwise: A.

Hydrosphere: 2d6-2.

Rockball

Classification: GeoPassive Class, Ferrinian, Lithic, or Carbonian Type.

Size: 1d6-1.

Atmosphere: 0.

Hydrosphere: 2d6+Size-11. DMs: L star +1; Epistellar -2, Outer Zone +2.

Biosphere: 0.

Small Body

Classification: Small Body Group.

Size: 0.

Atmosphere: 0.

Hydrosphere: 0.

Biosphere: 0.

Snowball

Classification: GeoPassive Class, Gelidian Type; GeoThermic Class, Erisian Type; GeoTidal Class, Plutonian Type.

Size: 1d6-1.

Atmosphere: Roll 1d6.

1-4 — 0

5-6 — 1

Hydrosphere: Roll 1d6.

1-3 — A (entirely frozen)

4-6 — 2d6-2 (represents subsurface oceans)

Biosphere:

Chemistry: Roll 1d6. DMs: L star +2; Outer Zone +2.

1-4 — Water (Age modifier +0)

5-6 — Ammonia (Age modifier +1)

7-8 — Methane (Age modifier +3)

If subsurface oceans, and Age ≥ 1d6: 1d6-3.

If subsurface oceans, and Age ≥ 6 + modifier: 1d6+Size-2.

Otherwise: 0.

Stygian

Classification: GeoPassive Class, Stygian Type.

Size: 1d6-1.

Atmosphere: 0.

Hydrosphere: 0.

Biosphere: 0.

Tectonic

Classification: Tectonic Class, Gaian (water chemistry), Amunian (ammonia chemistry), or Tartarian (methane chemistry) Type.

Size: 1d6+4.

Biosphere:

Chemistry: Roll 1d6. DMs: K-V star +2; M-V star +4; L star +5; Outer Zone +2.

1-6 — Roll 2d6.

2-8 — Water (Age modifier +0)

9-11 — Sulfur (Age modifier +0)

12 — Chlorine (Age modifier +0)

7-8 — Ammonia (Age modifier +1)

9-10 — Methane (Age modifier +3)

If Age ≥ 1d3 + modifier: 1d3.

If Age ≥ 4 + modifier: 2d6. DMs: D star -3.

Otherwise: 0.

Atmosphere:

If Biology 3+ and Water Chemistry: 2d6+Size-7, minimum 2, maximum 9.

If Biology 3+ and Sulfur or Chlorine Chemistry: B.

Otherwise: A.

Hydrosphere: 2d6-2.

Telluric

Classification: Telluric Class, Phosphorian or Cytherean Type.

Size: 1d6+4.

Atmosphere: C.

Hydrosphere: Roll 1d6.

1-4 — 0.

5-6 — F.

Biosphere: 0.

Vesperian

Classification: Epistellar Class, Vesperian Type.

Size: 1d6+4.

Biosphere:

Chemistry: Roll 2d6.

2-11 — Water

12 — Chlorine

If Age ≥ 1d3: 1d3.

If Age ≥ 4: 2d6.

Otherwise: 0.

Atmosphere:

If Biosphere 3+ and Water Chemistry: 2d6+Size-7, minimum 2, maximum 9.

If Biosphere 3+ and Chlorine: B.

Otherwise: A.

Hydrosphere: 2d6-2.

Revised Planetary Profile Codes

Size

0 — ≤800 km, neg. gravity

1 — 1,600 km, 0.05 G

2 — 3,200 km, 0.15 G (Triton, Luna, Europa)

3 — 4,800 km, 0.25 G (Mercury, Ganymede)

4 — 6,400 km, 0.35 G (Mars)

5 — 8,000 km, 0.45 G

6 — 9,600 km, 0.70 G

7 — 11,200 km, 0.9 G

8 — 12,800 km, 1.0 G (Terra)

9 — 14,400 km, 1.25 G

A — ≥16,000 km, ≥1.4 G

B-E — Helian sizes

G — Jovian sizes

Atmosphere

0 — Vacuum

1 — Trace

2 — Very Thin Tainted

3 — Very Thin Breathable

4 — Thin Tainted

5 — Thin Breathable

6 — Standard Breathable

7 — Standard Tainted

8 — Dense Breathable

9 — Dense Tainted

A — Exotic

B — Corrosive

C — Insidious

D — Super-High Density

G — Gas Giant Envelope

Hydrosphere

0 — ≤5% (Trace)

1 — ≤15% (Dry / tiny ice caps)

2 — ≤25% (Small seas / ice caps)

3 — ≤35% (Small oceans / large ice caps)

4 — ≤45% (Wet)

5 — ≤55% (Large oceans)

6 — ≤65%

7 — ≤75% (Terra)

8 — ≤85% (Water world)

9 — ≤95% (No continents)

A — ≤100% (Total coverage)

B — Superdense (incredibly deep world oceans)

F — Intense Volcanism (molten surface)

G — Gas Giant Core

Biosphere

0 — Sterile

1 — Building Blocks (amino acids, or equivalent)

2 — Single-celled organisms

3 — Producers (atmosphere begins to transform)

4 — Multi-cellular organisms

5 — Complex single-celled life (nucleic cells, or equivalent)

6 — Complex multi-cellular life (microscopic animals)

7 — Small macroscopic life

8 — Large macroscopic life

9 — Simple global ecology (life goes out of the oceans and onto land or into the air, etc.)

A — Complex global ecology

B — Proto-sapience

C — Full sapience

D — Trans-sapience (able to deliberately alter their own evolution, minimum Tech Level C)

If Biosphere C or more, this is a Homeworld; proceed to the Population tables.

World Codes

• Alternative Biochemistry:

Ammonia: NH3

Chlorine: Cl

Methane: CH4

Sulfur: SO2

• Asteroid (As): Size 0, Atmos 0, and Hydro 0.
• Desert (De): Atmos 2-C, and Hydro 0.
• Dry (Dr): Atmos 0-3 or A, and Hydro 0-3.
• Extreme (Ex): Size D+, Atmos C-G, or Hydro F.
• Fluid Oceans (Fl): Atmos A-C, and Hydro 1-B.
• Habitable (Ha): Size 1-A, Atmos 2-9, and Hydro 0-B.
• High Gravity (Hg): Size A-F.
• Garden (Ga): Size 5-A, Atmos 4-9, and Hydro 4-8.
• Ice-Capped (Ic): Atmos 0-1, and Hydro 1+.
• Low Gravity (Lg): Size 1-6.
• Poor (Po): Atmos 2-6 and Hydro 0-3.
• Prime (Pr): Atmos 6 or 8.
• Vacuum (Va): Atmos 0.
• Water World (Wa): Atmos 1-D, and Hydro A-B.
• Zero Gravity (Zg): Size 0.
• Zoosphere (Zo): Bio 7+.

Desirability

For each world, add up all the world codes and other factors that apply:

• Desert and Poor: +1
• Desert or Poor, and not Extreme: +2
• Dry: -1
• Extreme: -2
• Garden: +5
• Habitable, but not Dry, Desert, Garden, Poor, or Water World: +4
• High Gravity, but not Extreme: -1
• Prime: +1
• Water World, but not Fluid Oceans: +3
• Zero Gravity, but not an Asteroid Belt: -1
• Inner Zone orbit, M-V, D, or L star: +1
• Inner Zone orbit, other star: +2

To this total, add 1d3-1d3, to reflect differences in climate, availability of resources, and other random factors. The final result is the desirability of the world for colonization.

Asteroid belts, being sparse but easy to make use of, instead add 1d6-1d3.

Habitation

If the world has Biosphere C+, it has a native population. For normal carbon-and-water based life, Population will be equal to the Desirability score, +1d3, -1d3.

If the world has Desirability 3+, and is within the sphere of influence of a starfaring culture (TL9+), it will automatically be colonized. The initial Population equals TL-10+1d3-1d3; add +1 per century of habitation and immigration. Maximum Population is equal to the Desirability, modified by the local Industrial Base:

Stone Age: -1

Primitive: 0

Industrial or Pre-Stellar: +1

Stellar: +2

If you get a too-high Population score, note it down; after you calculate the world's TL score, if the Pop. is still too high, reduce it.

If the world is habitable (Size 1-B, Atmos 2-9, no life or carbon-water life), your colonists will bring along other life, raising the local Biosphere to 1d6+5.

If the world has Desirability 2-, and is within the sphere of influence of a starfaring culture (TL9+), it may have an outpost. Roll 1d6+Desirability; if this is equal to or less than (TL-9), the planet has Population = 1d3. This can exceed the world's Desirability.

Terraforming

This is the intentional (or unintentional) alteration of a world's Desirability.

If a homeworld or colony's Population is higher than its Desirability, the world becomes polluted due to overpopulation.

Atmos 3 becomes Atmos 2.

Atmos 5 becomes Atmos 4.

Atmos 6 becomes Atmos 7.

Atmos 8 becomes Atmos 9.

You may attempt to terraform any world with Size 1-B, Atmos 1-D, and Pop 1+. Roll 1d6: If you roll equal to or less than (TL-10), you successfully terraform. You may roll 1d6 again for every century of habitation.

For each success, you receive 1d3 points, which you may add to or subtract from the world's Atmosphere, Hydrosphere, or Biosphere codes. If the world has non-carbon/water-based life, it must be exterminated (reduced to Bio 0) before you may add carbon/water life. You can do this to reduce the effects of overpopulation, but you have to do it every century or the changes swing back.

If a world is left alone for thousands of years, it slowly loses the effects of terraforming, and returns to its normal type.