- For other uses, see Class O.
In planetary classification Class O or Pelagic planets are those with surfaces comprising 80% or more water. These planets may have some surface land (up to 19%), but it is not a majority feature. In all other regards, Class O planets are identical to Class M planets. A true example of a Class O planet is Argo, while the planet Earth falls just short of the surface water requirement to be considered Class O. (ST reference: Star Charts)