Class C: Small Rocky Planetoid - Similar to Gothos

Class D: Planetoid, moon or asteroid. Examples include Regula and Rura Penthe.

Class N: Extremely high surface temperature, and an atmosphere inhospitable to most life.

Class M: Earth-like both in its size, core, and age as well as in the advancement of the native creatures. Class M worlds are frequently the home of sapient races capable of traveling in space.

Class K: Planet that is barren and has no native life, but could be hospitable with terraforming or if buildings were constructed inside habitable domes. Mars is considered a Class K world.

Class T: Gas giant. Second smallest designation of gas giant, one size larger than Class J. Typically, Iffens occur here