Carbon planet

A hypothetical planet unusually rich in carbon relative to oxygen. Its interior could contain abundant carbides, graphite, or diamond instead of the silicate minerals common on Earth.

Carbon-to-oxygen ratio: The relative abundance of carbon and oxygen in a material or astronomical environment. A high ratio can favor carbon-bearing minerals over the silicates that dominate rocky planets.
Terrestrial planet: A planet composed primarily of rock or metal, with a solid surface or interior. Carbon planets are a proposed compositional subtype of rocky planets.
Exoplanet characterization: The measurement of an exoplanet's properties, including its atmosphere, composition, and internal structure. Characterization methods could test whether a planet has carbon-rich chemistry.
Silicate planet: A rocky planet whose mantle and crust are dominated by silicate minerals. It represents the oxygen-rich rocky composition against which carbon planets are defined.
Exoplanet atmosphere: The gaseous envelope surrounding a planet outside the Solar System. Atmospheric measurements may constrain elemental ratios, though they do not directly reveal the deep interior.
Planetary differentiation: The separation of a planet's materials into layers with different compositions and densities. Differentiation would sort dense carbides and metals from any graphite- or diamond-rich mantle.
Silicate minerals: Minerals built from silicon–oxygen tetrahedra, forming most of Earth's crust and mantle. Their abundance on Earth illustrates the oxygen-rich mineralogy carbon planets might lack.
Planetary mass-radius relationship: The relationship between a planet's mass and radius, used to constrain its bulk composition. Carbon-rich interiors may produce mass-radius predictions that differ from silicate planets.
Water world: A planet with a substantial fraction of its mass in water or other volatile-rich layers. Its bulk makeup differs from the refractory carbon and carbide materials proposed here.
WASP-12b atmospheric carbon-to-oxygen ratio: An inferred estimate of the relative carbon and oxygen abundance in WASP-12b's atmosphere. The estimate has been debated and does not by itself establish a carbon-rich interior.

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