ONE/4 Planetary Orbits

STEP ONE: Determine the number of potential orbits by rolling on table 1.4.1.

STEP TWO: Determine the mean distance of the orbits by consulting the formulae under 1.4.2.

STEP THREE: Remove all impossible orbits. This includes any orbit which would put a planet within a star's radius or so close as to vaporize it, and any orbit which is unstable in a binary system (between the binary's closest separation / 3 and the furthest separation x 3 distance). Worlds may orbit both stars in a binary, if the more massive companion has any orbits generated beyond the furthest separation distance x 3. Only consider such orbits for the more massive companion. For white dwarves, remove all orbits within the limit provided by table 1.4.3.

STEP FOUR: Remove all orbits where a planet would be vaporized, according to the formulae in 1.4.4. Also, determine the limit of the original inner system. Note this limit, it will be used in the next section.

Table 1.4.1 Number Of Orbits

-1:  1d10 + 10
2-5:  1d10 + 5
6-7:  1d10
8-9:  1d5 (1d10 / 2)
10+:  None

Modifications to initial roll:
+1 if star is K5v to K9v
+2 if star is M0v to M4v
+3 if star is M5v to M9v
+5 if star is Brown Dwarf
Subtract Abundance Modifier

Table 1.4.2 Orbit Sizes

The first orbit has a distance in AU of:

D = M2 x 0.05 x 1d10

... where M is the mass of the star

Subsequent orbits have a distance in AU of:

D = P x [1.1 + (1d10 x 0.1)] + 0.1

... where P is the distance of the previous orbit

Table 1.4.3 White Dwarf Removed Orbits

1-4:  Remove all orbits within 2 AU
5-8:  Remove all orbits within 4 AU
9-11:  Remove all orbits within 6 AU
12+:  Remove all orbits within 10 AU

+1 if the mass of the white dwarf is 0.6-0.9
+4 if the mass of the white dwarf is over 0.9

Table 1.4.4 Untenable Orbits and the Inner System Zone

Planets cannot survive if hotter than about 2000°K. Thus, remove orbits within:

D = L0.5 x 0.025

... where L is the luminosity of the star

The system's Inner Zone is within:

D = L0.5 x 4

... where L is the luminosity of the star

To be exacting: For main sequence stars use the luminosity of a mid-age star of the same spectral class, for subgiants and giants use the luminosity of a main sequence star of the same mass, and for white dwarves consider any surviving worlds to be outside the Inner Zone.


The area of the stellar system where the early system is too hot to allow icy planetoids. Inner system objects thus have higher density and mostly consist of silicates and metals, while the area outside is more dominated by frozen water and gasses.


There may be some other objects around these stars, typically either a few icy chunks in distant random orbits (1d10 x 1d10 AU) or more rarely a captured planetoid. Captured planetoids have eccentric orbits (1D10 AU) and may be of any general planet type. Some planetless stars have very sparse "rings" of chunks of debris:

1-3  Icy chunks
4  Captured body
5-7  Rings
8+  Nothing


If any orbits where removed by the binary effects, the system is likely to have a fair deal of stray asteroids and debris.