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

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

Class C: Small Rocky Planetoid - Similar to Gothos

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

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