Pencils and engagement rings

Nearby Exoplanet Could Be Covered With Diamond
Using information about 55 Cancri e’s size, mass and orbital velocity, as well as the composition of its parent star 55 Cancri (located 40 light years away in the constellation Cancer) a research team led by scientists from Yale University created computer models to determine what the planet is most likely made of. They determined that 55 Cancri e is composed primarily of carbon (as graphite and diamond), iron, silicon carbide, and possibly some silicates. The researchers estimate that at least a third of the planet’s mass — the equivalent of about three Earth masses — could be diamond…“On this planet there would basically be a thin layer below the surface which will have both graphite and diamond,” Madhusudhan told Universe Today in an email.

55 Cancri e's host star is a mere 40.2 light years from Earth.