Dubbed 55 Cancri e, the rocky world is only twice the size of Earth but has eight times its mass—classifying it as a "super Earth," a new study says. First detected crossing in front of its parent star in 2011, the close-in planet orbits its star in only 18 hours. As a result, surface temperatures reach an uninhabitable 3,900 degrees Fahrenheit (2,150 degrees Celsius)—which, along with carbon, make perfect conditions for creating diamonds.
NASA's Spitzer Space Telescope collected data on the planet's orbital distance and mass, and resulting computer models created a picture of 55 Cancri e's chemical makeup.
"Science fiction has dreamed of diamond planets for many years, so it's amazing that we finally have evidence of its existence in the real universe," said study leader Nikku Madhusudhan, a postdoctoral researcher at Yale University.
"It's the first time we know of such an exotic planet that we think was born mostly of carbon—which really makes this a fundamental game-changer in our understanding of what's possible in planetary chemistry."
At only 40 light-years away, in the northern constellation Cancer, the gemlike planet sits relatively near Earth. In dark skies, 55 Cancri e's host star is clearly visible to the naked eye. (See gem pictures.)
Diamond Planet Has Odd Chemistry
The new models fit with previous studies that showed 55 Cancri e's parent star was abundant in carbon—much more so than our sun.
"If we make the assumption that the star and its surrounding planets are all born from the same primordial disk of material, then it makes sense that the entire planetary system would be carbon rich," said Madhusudhan, whose study will appear in an upcoming issue of the journal Astrophysical Journal Letters.
Princeton astronomer David Spergel believes the diamond-planet find probably represents the first discovery of a whole new class of planets whose chemistry has never been encountered. (Related: "'Diamond Planets' Hint at Dazzling Promise of Other Worlds.")
"Unlike our solar system, which is dominated by oxygen and silicates, this planetary system is filled with carbon," said Spergel, who was not involved in the new study.
"While it's still unknown exactly what implication this will have on our understanding of evolution of planetary systems," he said, "there's no doubt it is an important step towards understanding the full diversity of planets."