My players need this for the up and coming campaign, for some reason I didn't put it into the book in time!
All non-gas planets are classes by how inhabitable they are. The higher the letter, the more inhabitable they are.
A - Volatile tectonics, toxic atmosphere, hot (proximity to the star). Not possible to live under, on or above the surface.
B - Volatile tectonics, toxic atmosphere, cool (not close to the star). Possible to live above the surface on a giant grav platform.
C - Highly toxic atmosphere, hot. Comfortable to live under the surface. On surface possible but not recommended.
D - Highly toxic atmosphere, cool. Comfortable to live under the surface. On the surface possible.
E - Low toxicity atmosphere, not breathable but not dangerous to skin contact. On or below the surface equally comfortable.
F - Low toxicity atmosphere, barely breathable but not more than a day at a time. On or below the surface equally comfortable.
G - Low toxicity atmosphere. Long term breathing might lead to death but not immediately lethal. Candidate for atmosphere generation to turn into H or I class.
H - Earth-like stable atmosphere but only through constant atmosphere generation.
I - Earth-like world, does not require atmosphere generation (although may have needed it to get to this state)