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Monday, March 1, 2010

Massive planet will die young

Among the hundreds of extrasolar planets found in the past few years is WASP-12b, discovered in 2008. This planet has been studied by Shu-lin Li of the National Astronomical Observatories of China and others from the Kavli Institute for Astronomy and Astrophysics (KIAA) at Peking University.

Although WASP-12b orbits a star similar in size to our sun, the similarities end there. WASP-12b is six times the volume of Jupiter (the largest planet in our planetary system) and orbits its star at a distance of just over one million miles. To put that in perspective, the Earth is 93 million miles from our sun, and even Mercury is 36 million miles from the sun. Our first gas giant, Jupiter, is almost 500 million miles from the sun.

Because WASP-12b is so close to its star, the tidal forces on the planet are tremendous. So much so, that the planet is actually distorted into an American football shape. These tides create so much internal friction that the resultant heat is responsible for expanding the planet to its giant size. It’s that giant size that spells doom for the planet.

According to Li:

WASP-12b is losing its mass to the host star at a tremendous rate of six billion metric tons each second. At this rate, the planet will be completely destroyed by its host star in about ten million years.

Once again, it is instructive to compare with the Earth, which has already existed for over four and a half billion years, and is only halfway through its expected lifetime.

Artist's rendition of the WASP-12 system. The massive gas giant WASP-12b is shown in purple with the transparent region representing its atmosphere. Mass from the gas giant's atmosphere is pulled off and forms a disk around the star, shown in red. (Courtesy: KIAA/Graphic: Neil Miller)