Exoplanet given three-million-year death sentence

Exoplanet given three-million-year death sentence
Artist's concept of WASP-12b spiraling into its sun
Artist's concept of WASP-12b spiraling into its sun
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Artist's concept of WASP-12b spiraling into its sun
Artist's concept of WASP-12b spiraling into its sun

A team of astrophysicists led by Princeton University has found an exoplanet that is within three million years of destruction. Situated 14,000 light-years away from Earth in the constellation Auriga, WASP-12b is spiraling toward its sun and will eventually be destroyed by tidal forces.

WASP-12b is already unusual even by exoplanet standards. Discovered in 2008, it's a "hot Jupiter" that orbits its parent star every 26 hours at a distance of two million miles (3.6 million km). Not only does the tidally-locked planet have a dayside temperature of 4,600° F (2,600° C), it's also exceptionally rich in carbon and has an albedo of 0.064, which means that it reflects light like a lump of asphalt and is one of the darkest planetary objects ever identified.

Another thing that's odd about WASP-12b is that it is so close to its star that both bodies exert tidal forces on one another that heat WASP-12b and set up distorting tidal waves in the star. These waves eventually die down from friction, converting WASP-12b's orbital momentum into heat within the star. The friction also exerts gravitational torque on the planet, causing it to spiral in toward its sun.

When it comes close enough, the planet will reach what is called the Roche limit, where the tidal forces become strong enough to rip it apart, though, in the short term, it could be converted into a rocky super-Earth or mini-Neptune as its atmosphere is stripped away.

Aside from the drama of a planet facing a premature doom, this phenomenon teaches astrophysicists more about exoplanet orbit mechanics and the interior dynamics of stars. Though the tidal destruction of hot Jupiters like WASP-12b had been predicted, this is the first time that one has been seen in the wild, providing scientists with first-hand data.

"Ever since the discovery of the first ‘hot Jupiter’ in 1995 – a discovery that was recognized with this year’s Nobel Prize in Physics – we have wondered how long such planets can survive," says Joshua Winn, a professor of astrophysical sciences at Princeton. "We were pretty sure they could not last forever. The strong gravitational interactions between the planet and the star should cause the planet to spiral inward and be destroyed, but nobody could predict how long this takes. It might be millions of years, it might be billions or trillions. Now that we have measured the rate, for at least one system – it’s millions of years – we have a new clue about the behavior of stars as fluid bodies."

The study was published in Astrophysical Journal Letters.

Source: Princeton University

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