Class XIX planet

A class XIX planet is a planetary class mentioned once in Metroid Prime. Zebes is said to be a planet of this class, and is described as inhospitable to most bioforms. Whether any other planets are of this class is unknown.

Observatory
"Planet Zebes  Mass: 4.8 trillion teratons.  Profile: Planet's crust is primarily Urthic ore, making it ideal for subterranean construction. A class XIX planet, Zebes is inhospitable to most bioforms. The world was considered unremarkable until it became a base for Space Pirate forces."