Why is this star killing its own planet?

Two million years ago, a planet was born in the constellation Orion. Today, astronomers say it could be in danger of death... at the hands of its own sun. 

Courtesy of A. Passwaters/Rice University
An artist’s impression of likely new giant planet PTFO8-8695b, which is believed to orbit a star in the constellation Orion every 11 hours. Gravity from the young star appears to be pulling away the outer layers of the Jupiter-like planet.

Brand new exoplanet PTFO8-8695b is in trouble. Just 2 million years old, its star is swiftly stripping its gaseous atmosphere, dooming it to rapid oblivion.

It takes just eleven hours for this baby exoplanet to orbit around its sun. The tightness of this orbit means that the planet’s outer layers are being rapidly stripped away by the sun’s gravity.

“A handful of known planets are in similarly small orbits,” said astronomer Christopher Johns-Krull in a Rice University press release, “but because this star is only 2 million years old this is one of the most extreme examples.”

While two million years may seem like forever to a human, it is a very short time in the life of most planets. Earth is about 2,300 times older than PTFO8-8695b.

Astronomers discovered newborn exoplanet several years ago, when astronomers noticed that the brightness of the sun it orbits was occasionally dimmed.

In order to determine whether the dimness was caused by a planet passing in front of it, astronomers analyzed light emitted by highly energized hydrogen atoms, or H alpha atoms.

After analysis, scientists found that there were two sources of H alpha atoms: the star, and a moving H alpha source that they concluded was a planet.

“When a planet transits a star, you can determine the orbital period of the planet and how fast it is moving toward you or away from you as it orbits,” explained astronomer Lisa Prato of the Lowell Observatory. “And it turned out that the velocity of the planet was exactly where this extra bit of H-alpha emission was moving back and forth.”

While astronomers are not yet sure of its mass, they remain confident that this is a planet.

“We compared our evidence against every other scenario we could imagine,” said Dr. Johns-Krull, “and the weight of the evidence suggests this is one of the youngest planets yet observed.”

PTFO8-8695b is located about 1,100 light years away from Earth. It is about twice the size of Jupiter, and is a member of a class of planets called “hot Jupiters,” gaseous planets that are similar to Jupiter but closer to their suns.

This particular “hot Jupiter” is located in the constellation Orion, one of the night sky's most recognizable constellations.

Scientists say that the planet likely formed farther away from its sun, and has slowly gotten closer. Other exoplanets have very tight orbits, but Johns-Krull says that those tend to be located near middle-aged stars.

PTFO8-8695, on the other hand, is very bright. And PTFO8-8695b, its planet, is even more impressive. Although it is just three to four percent of the size of its sun, it shines nearly as brightly.

According to Johns-Krull, in order to shine that brightly, the exoplanet’s gas must fill an exceptionally large space. A gas cloud that large is vulnerable to being pulled away from its own planet by another planet’s (or sun’s) gravity, meaning that little PTFO8-8695b could be in danger.

"We don't know the ultimate fate of this planet," Johns-Krull said. "We'll keep looking."

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