Carbon planet

Carbon planets are a class of planets hypothesized to form around stars with a higher carbon-to-oxygen ratio than the Sun. Unlike the terrestrial planets of our solar system, carbon planets would have an unusual geology comprised of carbide compounds, graphite, and even diamond in their deep mantles rather than oxygen-rich silicate rock.

While low levels of oxygen should leave water a rarity on carbon planets, they may have hydrocarbon compounds on their surfaces in the form of tar-like substances or bodies of liquid.