Astronomers find sun-like star eating Jupiter-sized planet

Scientists in the UK believe that the hottest known planet in our solar system became superheated while being “eaten” by its parent star. Shades of Saturn devouring his children! The planet – called WASP-12b – might have only another 10 million years left before it is completely devoured.

“We see a huge cloud of material around the planet which is escaping and will be captured by the star,” said Carole Haswell of The Open University in Great Britain. “We have identified chemical elements never before seen on planets outside our own solar system.”

Haswell and her science team paint the grisly scene in the following way. The planet, WASP-12b, is similar to our solar system’s largest world, Jupiter, but it is thought to be about 40 percent more massive than Jupiter and exceedingly close to its star – a star similar to our sun, by the way. In fact, the planet is thought to be so close that it has become superheated to nearly 2,800 degrees Fahrenheit and stretched into a football shape by enormous gravitational forces being exerted on it by its star. All of this nearness and stretching has caused the atmosphere of WASP-12b to balloon to nearly three times Jupiter’s radius. Material from WASP-12b is thought, in fact, onto the star: the star is “eating” the planet.

Astronomers have seen effects similar to this for decades, but always between two stars. This is the first time it has been seen so clearly for a planet.

WASP-12 is a yellow dwarf star – visible through telescopes – located approximately 600 light-years away in the constellation Auriga the Charioteer (whose brightest star is golden Capella). The hot planet – romantically named WASP-12b by astronomers – is so close to the star it completes an orbit in 1.1 days.

The unprecedented ultraviolet (UV) sensitivity of COS enabled measurements of the dimming of the parent star’s light as the planet passed in front of the star. These UV spectral observations showed that absorption lines from aluminum, tin, manganese, among other elements became more pronounced as the planet transited the star, meaning that these elements exist in the planet’s atmosphere as well as the star’s. The fact the COS could detect these features on a planet offers strong evidence that the planet’s atmosphere is greatly extended because it is so hot.

The UV spectroscopy was also used to calculate a light curve to show precisely how much of the star’s light is blocked out during transit. The depth of the light curve allowed the COS team to calculate the planet’s radius. They found that the UV-absorbing exosphere is much more extended than that of a normal planet that is 1.4 times Jupiter’s mass. It is so extended that the planet’s radius exceeds its Roche lobe, the gravitational boundary beyond which material would be lost forever from the planet’s atmosphere.

Haswell and her science team published their ideas about WASP-12b in the May 10, 2010, issue of The Astrophysical Journal Letters. The concept is based on observations made by a new instrument on NASA’s Hubble Space Telescope, called the Cosmic Origins Spectrograph (COS).

A theoretical paper published in the science journal Nature last February by Shu-lin Li of the Department of Astronomy at the Peking University, Beijing, first predicted that the planet’s surface would be distorted by the star’s gravity, and that gravitational tidal forces make the interior so hot that it greatly expands the planet’s outer atmosphere. Now Hubble has confirmed this idea, leaving us on Earth to contemplate a planet-eating star.

May 20, 2010

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