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This baby planet is probably being torn apart by its own sun

An artist's impression of likely new giant planet PTFO 8-8695 b, which is believed to orbit a star in the constellation Orion every 11 hours. Gravity from the newborn star appears to be pulling away the outer layers of the Jupiter-like planet. (A. Passwaters/Rice University)
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Sometime in the past 2 million years, from the swirling gas and rubble surrounding a star in the constellation Orion, scientists believe a planet was born.

If this newborn world exists, it's a massive, boiling place — twice as big as Jupiter, cloaked in a cloud of gas and so close to its star that a year there lasts just 11 Earth hours. It's also incredibly rare: Before it was discovered in 2012, scientists didn't think that gas giants could exist around stars as young as its host.

But the planet, dubbed PTFO 8-8695 b, is already falling apart, says Rice University astronomer Christopher John-Krull. Like Icarus, it got too close to the sun. Now it's slowly being stripped of its mass by the inexorable pull of the star's gravity.

John-Krull released his findings, which will be published in the Astrophysical Journal later this year, on the academic paper sharing website arXiv this week. The findings suggest that PTFO 8-8695 b really is a planet, even though "it kind of defies all of our obvious explanations" for how planets form, he said. 

And they leave him and his team wanting to know more.

"We don't know the ultimate fate of this planet," he said. "We'll keep looking at this star."

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PTFO 8-8695 b was first identified several years ago, when another team of researchers began noticing regular dips in the brightness of the star it orbits. This suggested that a planet was crossing in front of the star, briefly blocking some of its light from Earth's view.

But the star was young — just about 2 million to 3 million years old — and young stars are often covered in sun spots that make then gutter and flare unpredictably. So there was some skepticism that a planet had really been found.

That's when John-Krull and his team decided to take a closer look. It was a relatively easy thing to do — at least, as far as stargazing goes — since PTFO 8-8695 b completes an orbit once every 11 hours. The astronomers could get an entire year's worth of data in just a single night.

Using spectroscopic analysis, which divides light up into its component parts, they identified two separate sources of a type of light emitted by highly energized hydrogen atoms, called H alpha. One set of H alpha emissions was clearly coming from the star, since it carried signatures of the type of magnetic activity that happens on stars. But the other source seemed to move back and forth across the star — at exactly the pace you would expect to see from a planet like PTFO 8-8695 b, based on previous observations of its transit.

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That find helped boost the belief that a planet had really been spotted (though John-Krull noted that better measures of its mass would be needed before he can be certain). But there was also something odd about it.

"The H alpha emission is very strong, almost as strong as what's coming from the star, even though the planet is only 3 percent of the size of the star," John-Krull said.

Gas confined to the planet's surface couldn't produce that effect, he knew. So the planet must be swathed in a vast cloud whose outer layers were being stripped away as the pull of the sun's gravity overpowered the planet's. 

There are a few explanations for this behavior, he said. It's possible that PTFO 8-8695 b formed farther out in the solar system and somehow got knocked or pulled closer to its sun — which could explain how such a large planet exists so close to a star. That phenomenon has been observed elsewhere in the galaxy and seems to result in smaller, Neptune-sized planets that orbit in tight circles around their suns.

"We may be seeing that in action right now," John-Krull said. "But then the question is: Where does it stop? Does it eventually stop losing mass, or does it keep going until it falls into the star?"

He and his team will keep observing this star, and other ones like it, in hope of finding the answer.

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