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and the effects of axial tilt, but also to make it easier to update the system when new scientific discoveries make it outdated.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.

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:

2-7 — M-V

8-10 — M-Ve (flare star)

11-12 — L

L-type

Automatically L.

Companion Orbits

For each Companion, roll 1d6:

1 — Tight orbit

2-3 — Close orbit

4-5 — Moderate orbit

6 — Distant orbit

Planetary System Generation

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

Epistellar orbits: 1d6-4. 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.

1-5 — All members are Small Bodies.

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 satellite or binary companion. It cannot be of larger Size; reroll Size if this occurs.

Terrestrial Planet

Roll 1d6.

1-4 — No major satellites.

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.

In addition, if the star is type D, no world may have a Biosphere greater than 2.

Asteroid Belt

Roll 1d6.

1-5 — All members are Small Bodies.

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

Dwarf Planets

Epistellar

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

1-3 — Rockball

4-5 — Meltball

6 — Roll 1d6:

1-3 — Hebean

4-6 — Promethean

Inner Zone

Roll 1d6. DMs: Asteroid Belt member -2, Terrestrial satellite +1, Helian satellite +2, Jovian satellite +3.

1-4 — Rockball

5-6 — Arean

7 — Hebean

8 — Promethean

9 — Meltball

Outer Zone

Roll 1d6. DMs: Asteroid Belt member -1, Terrestrial satellite +1, Helian satellite +2, Jovian satellite +3.

1-2 — Rockball

3-4 — Snowball

5-6 — Arean

7 — Hebean

8 — Promethean

9 — Meltball

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

Classification: Acheronian Class.

Size: 1d6+4.

Atmosphere: 1.

Hydrosphere: 0.

Biosphere: 0.

Arean

Classification: GeoCyclic Class, Arean (water chemistry), Utgardian (ammonia chemistry), or Titanian Type (methane chemistry).

Size: 1d6-1.

Atmosphere: Roll 1d6.

1-3 — 1.

4-6 — A.

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

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

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

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

Otherwise: 0.

Arid

Classification: Arid Class, Darwinian (water chemistry), Saganian (ammonia chemistry), or Asimovian (methane chemistry).

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:

If Age ≥ 4 + modifier: 2d6.

Otherwise: 0.

Atmosphere:

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

Otherwise: A.

Hydrosphere: 1d3.

Asphodelian

Classification: Asphodelian Class.

Size: 1d6+9.

Atmosphere: 1.

Hydrosphere: 0.

Biosphere: 0.

Chthonian

Classification: Jovian Group, Chthonian Class.

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: 1d6-6+Size.

If 2+: change to A.

Hydrosphere: 2d6-11+Size.

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:

If in Inner Zone, roll 1d6:

1-3 — 0

4-6 — Life is possible.

If Age ≥ 1d6: 1d3.

If Age ≥ 7: 2d6.

Chemistry: Roll 1d6. DMs: L star +1.

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: F.

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.

Otherwise: 0.

Atmosphere:

If Water Chemistry: 2d6-6+Size, 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: A.

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.

Otherwise: 0.

Atmosphere:

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

Otherwise: A.

Hydrosphere: 2d6-2.

Rockball

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

Size: 1d6-1.

Atmosphere: 0.

Hydrosphere: 2d6-11+Size. 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

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

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

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

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.

Otherwise: 0.

Atmosphere:

If Biology 3+ and Water Chemistry: 2d6-7+Size, 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: 0.

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: 2d6-7+Size, 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

Size 0 is Micro Gravity.
Size 6- are Low Gravity.
Size 9+ are High Gravity.
Size D+ are Extreme Gravity, not normally survivable by humans.

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 — High Density

F — Intense Volcanism

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 — Deep and Dense

F — 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.