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.
"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."
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"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.
"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.
"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.