Generate a planet's orbit period using the table below, dependent on the spectral type of its sun. If there are two Earthlike or marginal planets orbiting the same star, generate two periods and assign them in the correct order (the inner planet, obviously, gets the shorter period). If the outer period is less than 25% more than the inner one, generate both of them again.

To find the planet's rotation period, roll D100, add 10 for each moon, and refer to the following table. Note that the orbit periods (above) are given in Earth days, not local days.

Roll (D6+6)/2 (keep fractions, don't round) for the planet's density in grams per cubic centimetre. Multiply diameter by density and divide by 70,000 to calculate the surface gravity in Earth gravities (round to the nearest 0.1).

Roll 2D6-4 for Earthlike planets, or D10+D6-6 for marginal planets, and multiply by 5 to find the average surface temperature in degrees Celsius (of course negative numbers should be retained here, not counted as zero). If a star has two planets in zone B and both of them are Earthlike or marginal, make sure the temperatures are in the right order; the outer planet should have a temperature no higher than the inner one (greenhouse effects and similar phenomena can affect a planet's temperature, of course, but not by all that much on a planet with an approximately Earthlike atmosphere). If the outer planet's temperature comes out higher, generate both temperatures again.

Roll 2D6-2 and multiply by 10 to find the percentage of the planet's surface covered with liquid water. Subtract 20 if the temperature is zero; subtract 40 if the temperature is below zero.

A planet's mineral resources are measured on an arbitrary scale, running from 1 (worst) to 10 (best). The Earth is rated 8, fairly high, because of its high density (implying a relatively high ratio of metal to rock), and its active volcanic and tectonic processes (which carry minerals from deep in the interior to the surface). A planet's mineral resources rating is generated by the formula:

Minerals = Density + (Diameter/10,000) + D6 - 4