Planet torn apart by its own tides

Posted by Emma Woollacott

Astrophysicists have for the first time got the opportunity to watch a planet being distorted and destroyed by its host star.

"This is the first time that astronomers are witnessing the ongoing disruption and death march of a planet," says UC Santa Cruz professor Douglas NC Lin.

WASP 12-b, discovered in 2008 orbits a star, in the constellation Auriga, roughly similar in mass to our Sun. Like most known extra-solar planets, it is large and gaseous, like Jupiter and Saturn.

But unlike these, or indeed or most other extra-solar planets, it orbits its parent star at extremely close range – 75 times closer than the Earth is to the Sun, or just over 1 million miles. It is also larger than astrophysical models would predict, with six times Jupiter’s volume.

The reason, says the team, is tidal forces, which pull the planet into the shape of a rugby or American football. They also create friction in the its interior, producing heat, which causes the planet to expand.

"This is the first time that there is direct evidence that internal heating (or 'tidal heating') is responsible for puffing up the planet to its current size," says Lin.

Now, WASP-12b has ballooned to such a point that it cannot retain its mass against the pull of its parent star’s gravity.

As lead author Shu-lin Li of the National Astronomical Observatories of China explains, "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. This may sound like a long time, but for astronomers it's nothing. This planet will live less than 500 times less than the current age of the Earth."

The findings are published in Nature.