Class B: Small Rocky Planetoid - Similar to Venus

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 S: Largest designation for gas giant. Ultra giant, not suitable for Iffens.