planet classObservedMeasured or catalogued in the real sky, with its source cited.SpeculativePlausible but unproven; an extrapolation the science does not yet settle.
Exotic worlds
Four kinds of planet that physics allows but the Solar System lacks. Iron-rich super-Mercuries are observed; carbon planets, helium-atmosphere planets and chthonian planets (the stripped cores of giants) remain hypotheses with candidates but no confirmed member.