Could there be a planet made of diamond?

The answer

The exoplanet 55 Cancri e, about 40 light-years away, may have a carbon-rich interior where extreme pressures and temperatures have compressed carbon into a massive diamond layer. At about twice Earth's diameter and eight times its mass, this super-Earth orbits so close to its star that one hemisphere is a molten lava ocean at over 2,000°C. Studies published in the Astrophysical Journal suggest that up to one-third of the planet's mass could be diamond - worth approximately 26.9 nonillion dollars at Earth's market prices.