Planets are categorized by internal temperature, class, and depth.
There are five different classes of planets: Ern, Sin, Ilt, Oln and Nir.
There are three temperature types: glacial, temperate, and volcanic. Any planetary body can be any temperature, but the resources vary according to the temperature. For example, gas and crystals are more common on glacial planets, while minerals and lava are more common on volcanic planets. Temperate planets have a decent mix of all the resources.