Class H: Uninhabitable desert world. Tau Cygna V is one such planet.

Class A: Small Rocky Planetoid - Similar to Pluto

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.

This is the main planet of occupation. Human Beings live here for the most part.

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