Massive diamond planet discovered by astronomers

New research led by Yale University scientists suggests that a rocky planet twice Earth's size is composed partially of diamond.

55 Cancri e has a radius twice as big as Earth's

A NASA artist's rendition shows 55 Cancri e orbiting its sun in the constellation of Cancer. (NASA/Reuters)

A large, rocky planet composed partially of diamonds has been discovered by astronomers at Yale University.

The planet, called 55 Cancri e, has a radius twice as big as Earth’s and a mass eight times greater. It is one of five planets that orbit a star 40 light years from Earth.

"This is our first glimpse of a world with a fundamentally different chemistry from Earth," said lead researcher Nikku Madhusudhan, a Yale postdoctoral researcher in physics and astronomy.

"The surface of this planet is likely covered in graphite and diamond rather than water and granite."

The planet orbits exceedingly quickly. Its year lasts just 18 hours, in contrast to Earth’s 365 days. Researchers say it is also blazingly hot, with a temperature of about 2,149 C — a far cry from a habitable world. 


The planet was first observed transiting its star last year, allowing astronomers to measure its radius for the first time. This new information, combined with the most recent estimate of its mass, enabled Madhusudhan's team to infer its chemical composition using models of its interior.

"It's close in astronomical standards," Madhusudhan says. "But if you're thinking of getting there, it's not possible."

The discovery of a carbon-rich "super-Earth" means that distant rocky planets can no longer be assumed to have chemical constituents, interiors, atmospheres or biologies similar to those of Earth, Madhusudhan said.

Astronomers initially thought 55 Cancri e contained a substantial amount of super-heated water, based on the assumption that its chemical makeup was similar to Earth’s. But the new research suggests the planet has no water at all, and appears to be composed primarily of carbon, iron, silicon carbide, and, possibly, some silicates. 

'That's scientific discovery. You don't know what's out there.'—Nikku Madhusudhan

It is estimated that at least one-third of the planet's mass — the equivalent of about three Earth masses — could be diamond.

"That's scientific discovery. You don’t know what's out there. And you sometimes find something completely different from what you expect," Madhusudhan said. "It can uplift your spirits as a scientist."

David Spergel, a professor of astronomy and chair of astrophysical sciences at Princeton University, who is not a co-author of the study, said: "This diamond-rich super-Earth is likely just one example of the rich sets of discoveries that await us as we begin to explore planets around nearby stars."

Madhusudhan's research will be published in the journal Astrophysical Journal Letters.


Shenaz Kermalli is a freelance writer and journalism instructor at Humber College in Toronto. Her work has been published in The Globe and Mail, the Toronto Star, the Ottawa Citizen, CTV News, The Guardian, Al Jazeera English, and Foreign Policy among others.