Hubble Witnesses a Slow Exoplanet Murder


Nobody said the universe was a peaceful place, especially for exoplanets orbiting a tad too close to their host stars. And in a violent new Hubble observation announced today, a gas giant about 40 percent more massive than Jupiter is slowly being eaten alive, its outer layers ripped away through extreme tidal forces, stretching its body into the shape of a football.

This is an unprecedented discovery. Never has this kind of planetary torture been seen before.

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WASP-12b is orbiting a sun-like yellow dwarf star 600 light-years away and it has such a tight orbit (of only 1.1 days) that it is being roasted to nearly 2,800 degrees Fahrenheit. This superheated state has caused the doomed exoplanet to puff up to nearly twice the size of Jupiter.

Using Hubble’s new Cosmic Origins Spectrograph (COS), astronomers have been able to study WASP-12b with amazing detail, revealing that exoplanet gas giants can suffer the same fate as smaller binary stars pulled too close to their more massive partners. In both cases, material from the smaller body is sucked away and devoured by the larger gravitational bully.

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

Wide Angle: The Age of the Exoplanet

Although this is the first example of an exoplanet dying in such a way, the event was predicted by a theoretical paper that appeared in the journal Nature in 2009. Shu-lin Li of the Department of Astronomy at the Peking University, Beijing, showed that a tightly orbiting exoplanet would distort under the pressure the star’s gravity, while the extreme tidal forces would cause internal heating, making the exoplanet expand.

This exoplanet was first revealed by the U.K.’s Wide Area Search for Planets (WASP) in 2008. By looking for the slight dimming of stars, transiting exoplanets can be discovered, blocking a fraction of starlight reaching Earth.

Using Hubble to zoom in on WASP-12b as it transited the star revealed elements such as aluminum, tin and manganese. Once the exoplanet had completed its transit, passing behind the star, these elements could still be seen, but in smaller quantities. This was a sure sign that the material that was once on the exoplanet was spilling into the star’s outer layers.

Astronomers don’t expect WASP-12b to live much longer, but estimate the tortuous orbits to last for another 10 million years before the exoplanet is completely consumed.

Although this might be bad news for the unlucky exoplanet, witnessing a gas giant bigger than Jupiter getting ripped to shreds by a star must make for an awesome sight. Sadly, we can’t see the event up-close, but fortunately we have Hubble’s excellent vision to understand what that view must look like.

Image: An artist’s impression of the Hubble observation of WASP-12b being eaten alive (NASA/ESA/G. Bacon)


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