Shopping for Diamonds—in Space

Astrophysicists are hypothesizing that a previously discovered planet could have a diamond interior.

This planet, called 55 Cancri e, is an exoplanet (a planet outside the solar system) that orbits a star called 55 Cancri. Its was the one of the first ‘Super-earths’ to be discovered—its mass is greater than that of earth (around 7.8 times), yet much smaller than the masses of Uranus and Neptune. Estimates of its interior composition and atmosphere had already been made from previous studies observing its transits across the star (similar to the much talked-about Venus transit earlier this year). It was estimated that this planet had a core of iron and silicates, and an envelope of supercritical water (i.e., water in a blurred state between liquid and gas).

However, these estimates were based on the assumption that the planet had an oxygen-rich interior, similar to earth. This assumption is now being challenged in a new model proposed by researchers at Yale University. The star around which the planet orbits itself has a carbon-rich interior, and 55 Cancri e is the closest planet to the star. This led to a new model that the planet could have an interior of carbon instead of oxygen, which could also lead to the observed properties of the planet.

An illustration of the planet 55 Cancri e’s interior. A molten iron core at its center, an outer layer of graphite, and an interior of diamond. [Image Credit: and Haven Giguerre]

However, based on the known temperature and pressure of 55 Cancri e, any carbon in its interior would have to exist in the form of diamond. “This is the 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,” said Nikku Madhusudhan, who was the first author on this paper.

If this proves to be true, the phrase ‘like a diamond in the sky’, may turn out to be more than a simile. You can read about this research here and here.

Published by

Shweta Ramdas

Beginning life as a grad student studying human genetics.