An impression of a possible carbon (or diamond or carbide) planet. According to theory, a planet such as this might form in a protoplantetary disc which is rich in carbon but poor in oxygen. A carbon planet would have an iron core, much like an ordinary terrestrial planet, but this would be encased in layers of liquid silicon carbide and titanium carbide. The crust would be made of graphite, several kilometres thick, or even solid diamond under the right conditions.