The planet that is getting eaten up (WASP-12b)

WASP-12b is an extrasolar planet orbiting the star WASP-12, discovered by the SuperWASP planetary transit survey. Its discovery was announced on April 1, 2008. Due to its extremely close orbit to its star, it has one of the lowest densities for exoplanets (‘inflated’ by the flux of energy from the star). The planet takes only a little over a day to orbit the star, in contrast to 365 days for the Earth to orbit the Sun. Its distance from the star is only 1/44 (approximately 2,115,000 miles) the Earth’s distance from the Sun, with the eccentricity the same as Jupiter’s.


Size comparison of WASP-12b (right) with Jupiter.


The planet is so close to WASP-12 that the star’s tidal forces are distorting the planet into an egg shape and pulling away its atmosphere at a rate of about 10−7 MJ (about 189 quadrilliontonnes) per year. The so-called “tidal heating”, and the proximity of the planet to its star, combine to bring the surface temperature to more than 2,500 K (2,200 °C).

On May 20, 2010, the Hubble Space Telescope spotted WASP-12b being “consumed” by its star. Scientists had been aware that stars could consume planets; however, this was the first time such an event had been observed so clearly. NASA has estimated that the planet has 10 million years left of its life.

The Hubble Space Telescope observed the planet by using its Cosmic Origins Spectrograph(COS). The Hubble Telescope observations have confirmed predictions published in Nature in February 2009 by Peking University’s Shu-lin Li. The planet’s atmosphere has ballooned to be nearly three times the radius of Jupiter, while the planet itself has 40% more mass than Jupiter.


Carbon content

Recent evidence indicates that WASP-12b has an enhanced carbon-to-oxygen ratio, significantly higher than that of the Sun, indicating that it is a carbon-rich gas giant. The C/O ratio compatible with observations is about 1, while the solar value is 0.54. The C/O ratios suggest that carbon-rich planets may have formed in the star system. One of the researchers behind that study commented that “with more carbon than oxygen, you would get rocks of pure carbon, such as diamond or graphite”.

The published study states: “Although carbon-rich giant planets like WASP-12b have not been observed, theory predicts myriad compositions for carbon-dominated solid planets. Terrestrial-sized carbon planets, for instance, could be dominated by graphite or diamond interiors, as opposed to the silicate composition of Earth.” These remarks have led the media to pick on the story, some even calling WASP-12b a “diamond planet”.

The carbon content of the planet is located within its atmosphere, in the form of carbon monoxide and methane. The study appears in the journal Nature.

This artist's concept shows the searing-hot gas planet WASP-12b (orange orb) and its star.

Candidate satellite

Russian astronomers studying a curve of change of shine of the planet observed splashes of light indicative of an extrasolar moon orbiting the planet.

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