Carbon planet

A carbon planet is a theoretical type of planet that contains more carbon than oxygen.

Marc Kuchner and Sara Seager coined the term "carbon planet" in 2005 and investigated such planets following the suggestion of Katharina Lodders that Jupiter formed from a carbon-rich core. Prior investigations of planets with high carbon-to-oxygen ratios include Fegley & Cameron 1987. Carbon planets could form if protoplanetary discs are carbon-rich and oxygen-poor. They would develop differently from Earth, Mars, and Venus, which are composed mostly of silicon–oxygen compounds. The theory is now built on reasonable scientific ideas and has gained support. Different planetary systems have different carbon-to-oxygen ratios, with the Solar System's terrestrial planets closer to being "oxygen planets". The exoplanet PSR J1719-1438 b, discovered on August 25, 2011, as well as the planet 55 Cancri e, are likely examples of carbon planets.

Such a planet would probably have an iron- or steel-rich core like the known terrestrial planets. Surrounding that would be molten silicon carbide and titanium carbide. Above that, 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. The surface would contain frozen or liquid hydrocarbons (e.g. tar and methane) and carbon monoxide. A weather cycle is theoretically possible on carbon planets with an atmosphere, provided that the average surface temperature is below 77 °C.

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