WASHINGTON, Oct. 8 (Xinhua) -- An alien world reported to be the first known planet to consist largely of diamond appears less likely to be of such precious nature, U.S. researchers said Tuesday.
Researchers from the University of Arizona examined previous observations of the so-called "diamond planet", 55 Cancri e, which is 40 light years from our solar system, and found that there is less carbon, the chemical element diamonds are made of, than oxygen in the planet's star, and perhaps the planet itself.
Previous studies have suggested that the planet contains more carbon than oxygen and 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," University of Arizona astronomy graduate student Johanna Teske, who led the study, said in a statement.
"So in terms of the two building blocks of information used for the initial 'diamond-planet' proposal -- the measurements of the exoplanet and the measurements of the star -- the measurements of the star no longer verify that," Teske said.
Since astronomers can't probe the makeups of stars and planets directly, they rely on indirect observational methods such as absorption spectra. Each chemical element absorbs light at different wavelengths in a characteristic pattern that can be used as a fingerprint of that element.
By analyzing the absorption spectra of starlight passing through a star's atmosphere, it is possible to deduce what elements are present in the star's atmosphere.
"Instead of using the same absorption lines in the spectrum of the host star as the previous study of 55 Cancri, we looked at more lines of carbon and more lines of oxygen," Teske said. "We find that because this particular host star is cooler than our sun and more metal-rich, the single oxygen line analyzed in the previous study to determine the star's oxygen abundance is more prone to error."
Teske instead relied on several different indicators of the oxygen abundance that were not considered previously. "Averaging all of these measurements together gives us a more complete picture of the oxygen abundance in the star," she said.
The findings were published online in the Astrophysical Journal.