This article provides a list of all known planet classifications.
- Gas giant: A massive planet composed primarily of hydrogen and helium.
- Gas dwarf: A low-mass planet composed primarily of hydrogen and helium.
- Helium planet: A type of planet that may form via mass loss from a low-mass white dwarf. Helium planets are predicted to have roughly the same diameter as hydrogen–helium planets of the same mass.
- Ice giant: A giant planet composed mainly of 'ices'—volatile substances heavier than hydrogen and helium, such as water, methane, and ammonia—as opposed to 'gas' (hydrogen and helium).
- Ice planet: A type of planet with an icy surface. Ice planets consist of a global cryosphere. Ice planets are bigger versions of icy moons such as Neptune's moon Triton, Pluto, and many other icy celestial bodies.
- Ocean planet: An ocean planet (also termed a waterworld) is a type of planet which has a substantial fraction of its mass made of water.
- Terrestrial planet: A terrestrial planet, telluric planet or rocky planet is a planet that is composed primarily of carbonaceous or silicate rocks or metals.
- Carbon "diamond" planet: A type of incredibly rare terrestrial planet composed of an an almost entirely carbon atmosphere and carbon surface. Such surfaces are often covered in a layer of carbon in the form of graphite, possibly with a kilometers-thick substratum of diamond if there is sufficient pressure. During volcanic eruptions, it is possible that diamonds from the interior could come up to the surface, resulting in mountains of diamonds and silicon carbides. Such planets are well sought after for their incredible mining and economical potential.
- Coreless planet: A type of terrestrial planet that has undergone planetary differentiation but has no metallic core.
- Desert planet: A type of terrestrial planet with very little water.
- Ecumenopolis: A terrestrial planet that has been turned into one massive city.
- Iron planet: A type of terrestrial planet that consists primarily of an iron-rich core with little or no mantle.
- Lava planet: A type of terrestrial planet, with a surface mostly or entirely covered by molten lava. Situations where such planets could exist include a young terrestrial planet just after its formation, a planet that has recently suffered a large collision event, or a planet orbiting very close to its star, causing intense irradiation and tidal forces.
- Silicate planet: A terrestrial planet that is composed primarily of silicate rocks.