Mercury has a layer of diamond 10 miles thick, NASA spacecraft finds

On the left a blue and silver sphere on the right a large spherical diamond.

The solar system's tiniest planet may be hiding a big secret. Using data from NASA's MESSENGER spacecraft, scientists have determined that a 10-mile-thick diamond mantle may lie beneath the crust of Mercury, the closest planet to the sun. 

Mercury has long puzzled scientists as it possesses many qualities that aren't common to other solar system planets. These include its very dark surface, remarkably dense core, and the premature end of Mercury's volcanic era.