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Planets

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planet classObservedModel
Arid world
A rocky planet with a thin, cold atmosphere and no stable liquid water at the surface, only ice and the traces of ancient rivers. Mars is the Solar System's example.
planet classObservedModel
Barren rock world
A rocky planet with no real atmosphere, whose surface lies bare to starlight, cosmic rays and meteorites. Mercury is the Solar System's example, and JWST has found several around other stars.
planet classModelSim
Dry habitable world
A rocky planet with liquid water on its surface but only a little of it, in lakes, brines and polar seas rather than oceans. Climate models suggest such land planets can stay habitable over a wider range of distances than an Earth-like world.
planet classObservedModel
Greenhouse world
A rocky planet smothered by a thick carbon dioxide atmosphere whose greenhouse effect bakes the surface far above the boiling point of water. Venus is the Solar System's example, a near-twin of Earth in size.
planet classObservedModel
Ice world
A cold world whose surface is made of frozen water, nitrogen, methane and carbon monoxide, like Pluto and Triton, where ices behave like rock and even the atmosphere can freeze out.
planet classObservedModel
Lava world
A rocky planet so close to its star that its dayside rock is molten, often a magma ocean under a thin atmosphere of vaporised rock. Dozens are known, most on orbits shorter than a day.
planet classObservedModel
Mini-Neptune
A planet between about 1.7 and 4 times Earth's radius with a rocky or icy core wrapped in a thin envelope of hydrogen and helium. The most common kind of planet Kepler found, and one the Solar System lacks.
planet classObservedModel
Mixed world
A rocky planet with both continents and oceans, a temperate climate and liquid water at the surface. Earth is the only known example, and the model every search for habitable planets starts from.
planet classModelSim
Ocean world
A planet whose surface is almost entirely water, from Earth-like worlds with a few scattered islands to true water worlds with oceans hundreds of kilometres deep. None is confirmed, but several planets are strong candidates.
physics conceptObservedModel
Planet classification
How astronomers sort planets by size, mass, temperature and composition, and how Pax Abyssi files every world it generates under one of 37 coded types.
physics conceptObservedModel
Radius valley
A shortage of planets between about 1.5 and 2 Earth radii that splits small close-in planets into rocky super-Earths and gas-wrapped sub-Neptunes.
planet classObservedModel
Subsurface ocean world
A world with a global ocean of liquid water sealed beneath a shell of ice, kept from freezing by tidal flexing and radioactive heat. Europa and Enceladus are the best-studied examples.
planet classObservedModel
Super-Earth
A planet more massive than Earth but lighter than Neptune, usually rocky, with no counterpart in the Solar System. Super-Earths are among the most common planets found around other stars.
planet classObservedModel
Volcanic world
A rocky world whose surface is continually remade by eruptions, powered by internal heat far above Earth's. Jupiter's moon Io, heated by tides, is the most volcanic body known.

Pages in this category

Arid world

Barren rock world

Dry habitable world

Greenhouse world

Ice world

Lava world

Mini-Neptune

Mixed world

Ocean world

Planet classification

Radius valley

Subsurface ocean world

Super-Earth

Volcanic world