Diamond 'Super-Earth' may not be as precious as believed

An alien world 40 light years from our solar system, believed to be the first-ever discovered planet to consist largely of diamond, may in fact be of less exquisite nature, according to a new research.
Researchers led by the University of Arizona astronomy graduate student Johanna Teske analysed public data from previous telescope observations.
They concluded that carbon - the chemical element diamonds are made of - appears to be less abundant in relation to oxygen in the planet's host star - and by extension, perhaps the planet - than was suggested by a study of the host star published in 2010.

"The 2010 paper found that '55 Cancri,' a star that hosts five planets, has a carbon-to-oxygen ratio greater than one," Teske said.
"This observation helped motivate a paper last year about the innermost planet of the system, the 'super-Earth' 55 Cancri e.
"Using observations of the planet's mass and radius to create models of its interior that assumed the same carbon-to-oxygen ratio of the star, the 2012 paper suggested the planet contains more carbon than oxygen."

"However, our analysis makes this seem less likely because the host star doesn't appear as carbon-rich as previously thought," Teske said.
Based on previous results, it was suggested that the "diamond planet" is a rocky world with a surface of graphite surrounding a thick layer of diamond instead of water and granite like Earth.

The new research, to be published in the Astrophysical Journal, found that the planet's host star contains almost 25 per cent more oxygen than carbon.
"In theory, 55 Cancri e could still have a high carbon to oxygen ratio and be a diamond planet, but the host star does not have such a high ratio," Teske said.
"So in terms of the two building blocks of information used for the initial 'diamond-planet' proposal - the measurements of the exoplanet and measurements of the star - no longer verify that," she said.
Teske said the 'diamond planet' results hinge on the presumption that a star's composition bears some relation to the composition of its planets.

"The compositions of planets and stars don't always match," she said, explaining that in a swirling disk of dust and gas giving birth to a star and planets, "you can have pockets where there is a lot of water, meaning an enhancement of oxygen. Or places where water has frozen out, leaving behind carbon species as the dominant gas molecules.
"So the planets that are accreting gas at those locations in the disk could be more carbon-rich instead of oxygen-rich.
"Depending on where 55 Cancri e formed in the protoplanetary disk, its carbon-to-oxygen ratio could differ from that of the host star," Teske said.

"It could be higher or lower. But based on what we know at this point, 55 Cancri e is more of a 'diamond in the rough," Teske said.