Planetary Generation System

This random star system generation came from the DC Heroes Legion of Superheroes World Book.

Star Generation

Determine the number of stars in the stellar system. Roll 1D10 and consult the table below.

Table 1A

1D10 Number of Stars
1-7 system has a single star
8 system is binary (two stars)
9 system is trinary (three stars)
10 system is quarternary (four stars)

In systems with more than one star, the GM may follow the generation procedure for each sun or ignore the effects of all stars other than the first (the "primary," usually the hottest and largest sun present.)

Next, roll 1D10 and use Table 1B to determine spectral type. A direct consequence of spectral type (and color) is the number of worlds in the system, as well as the position of the habitable worlds. (For the purpose of this system, "habitable" is defined as sufficiently Earthlike to allow a normal human to exist without extensive life-support equipment.)

Table 1B: Spectral Type

1D10 Spectral Class # of planets* Die Roll # of habitable planets Location**
1-2 B (blue-white) 1D10+8 - 1
3-4 A (white) 1D10+6 - 1
5 F (yellow-white) 1D10+5 1-8; 9-10 1; 2 ;
6 G (yellow) 1D10+4 1-8; 9; 10 1; 2; 3 ; ;
7-8 K (orange) 1D10+3 1-8; 9-10 1; 2 ;
9-10 M (red) 1D10-3 - 1

* Any roll of less than "1" should be treated as "1." However, the GM may populate the system with any number of planets. These ranges are given as reasonable estimates of the habitable zone around each type of star.

** Locations of planets are from the central star.

Only the most common spectral classes are represented above. Although many other types exist, including extremely hot (spectral class O or W) and extremely cool (spectral classes R, N, and S) stars, it is highly unlikely that even a remotely habitable world could exist in orbit around it.

It is also worth noting that the spectral type of the star provides insight into its stage of stellar evolution. Bright blue and white stars (types B and A) are significantly younger than dimmer stars (types K and M).

Brighter stars also have greater mass (and therefore more planets). Bright stars have not existed long enough to produce complex, higher-order life forms through natural evolution. Any sophisticated, native life forms that exist on the planets that surround these bright stars are usually due to the direct intervention of advanced races, such as the Oans, Controllers, or Celestials.

Habitable World Generation

Table 1C: Gravity Rating & Atmosphere Types determines the gravity and atmosphere of habitable worlds. First, roll 2D10 for the planet's gravity rating. Second, roll 1D10 for the planet's atmosphere type.

Table 1C

2D10 Gravity Rating Trace Very Thin Thin Light Standard Rich Thick Dense
2 Low Grav (5/-2) 1-3 4-7 8-9 0 - - - -
3-5 Light Grav (4/-1) 1 2 3-4 5-7 8-9 0 - -
6-10 Terran Grav (0/0) 1 2 3 4 5-6 7-8 9 0
11-16 Heavy Grav (4/1) - - - 1 2-3 4-6 7-8 9-0
17-19 High Grav (5/2) - - - 1 2 3 4-7 8-0
20 Very High Grav (6/3) - - - - 1-2 3-4 5-6 7-0

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