Nearby super-Earth likely a diamond planet

A rocky planet twice Earth’s size orbiting a nearby star might be a diamond planet.

New research led by Yale University scientists suggests that a rocky planet twice Earth’s size orbiting a nearby star is a diamond planet.

Lead researcher Nikku Madhusudhan said:

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

Star map showing the planet-hosting star 55 Cancri in the constellation of Cancer. The star is visible to the naked eye, though better through binoculars. (Image by Nikku Madhusudhan; created using Sky Map Online)

The planet — called 55 Cancri e — has a radius twice Earth’s, and a mass eight times greater, making it a “super-Earth.” It is one of five planets orbiting a sun-like star, 55 Cancri, that is located 40 light years from Earth yet visible to the naked eye in the constellation of Cancer.

The planet orbits at hyper speed — its year lasts just 18 hours, in contrast to Earth’s 365 days. It is also blazingly hot, with a temperature of about 3,900 degrees Fahrenheit, researchers said, a far cry from a habitable world.

Illustration of the interior of 55 Cancri e — an extremely hot planet with a surface of mostly graphite surrounding a thick layer of diamond, below which is a layer of silicon-based minerals and a molten iron core at the center. Image by Haven Giguere

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, allowed Madhusudhan and colleagues to infer its chemical composition using models of its interior and by computing all possible combinations of elements and compounds that would yield those specific characteristics.

Astronomers had previously reported that the host star has more carbon than oxygen, and Madhusudhan and colleagues confirmed that substantial amounts of carbon and silicon carbide, and a negligible amount of water ice, were available during the planet’s formation.

Astronomers also 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, Madhusudhan said. But the new research suggests the planet has no water at all, and appears to be composed primarily of carbon (as graphite and diamond), iron, silicon carbide, and, possibly, some silicates. The study estimates that at least a third of the planet’s mass — the equivalent of about three Earth masses — could be diamond.

The paper reporting the findings has been accepted for publication in the journal Astrophysical Journal Letters.

Bottom line: Research results, released in October, 2012 led by Yale University scientists, suggests that a rocky planet twice Earth’s size orbiting a nearby star is a diamond planet.

Read more from Yale University

EarthSky

MORE ARTICLES