Yale/Haven Giguere

A team of astrophysicists has estimated that an exoplanet twice the size of Earth is mainly made up of diamond.

The planet, 55 Cancri e, is located around 40 light years from Earth and has a mass eight times that of our planet's. With that knowledge in mind, now picture a third of that mass being made up of graphite and diamond. Or just look at the artist's impression above, created by the team at Yale University and Institut de Recherche en Astrophysique et Planetologie in Toulouse, which represents the ratio of diamond to, well, everything else. Earth, by comparison, has "less than a part in thousand by mass".

"On this planet there would basically be a thin layer below the surface which will have both graphite and diamond," lead author on the paper Nikku Madhusudhan told Universe Today. "But, below that there will be a thick layer (a third of the radius) with mostly diamond. For a large part the diamond will be like the diamond on Earth, except really, really pure. But at greater depths the diamond could also be in liquid form." So once we've nailed warp drive and can hop over to the planet, expect the cost of diamonds to plummet significantly.

"This is our first glimpse of a rocky world with a fundamentally different chemistry from Earth," said Madhusudhan. "The surface of this planet is likely covered in graphite and diamond rather than water and granite."

The planet, part of the constellation of Cancer that's clearly visible from Earth sans-binoculars, is the first exoplanet to display these unique properties -- in 2011 a "diamond planet" was spotted in the constellation of Serpens, but that planet did not orbit a star similar to our Sun and was not studied in such detail. The two do share certain characteristics, however, For instance, a year on the fast-orbiting 55 Cancri e lasts just 18 hours, while the Milky Way planet's orbit lasts around two hours.

The team presumably used radio telescope data to determine the mass, diameter and orbit of the 1,648 C-hot 55 Cancri e (the method and results are yet to be published in Astrophysical Journal Letters), which in turn was used to estimate the make-up of the planet. We do know that the team used computer models to estimate possible planetary compositions from the data, with updated information on its mass being key. The most likely explanation for this planet's formation, the models concluded, is a water-light recipe of carbon -- in the form of graphite and diamond -- and silicon carbide, which is a combination of silicon and carbon. There will also be smaller amounts of iron. 

The find, though providing us with a wonderful mental image, means that in our hunt for Earth-like exoplanets orbiting Sun-like stars, we can expect to find plenty more disappointingly uninhabitable sites, such as the water planet GJ 1214b (another great and satisfying mental image, however). 


  1. Constructed by the team at Magrathea perhaps?  

    Oct 12th 2012

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