Exoplanet 'kicked' away from its star?

Researchers have suggested that an exoplanet in a distant orbit around its star could have been expelled from its planetary system, and may provide evidence for a similar process occurring in our own early Solar System.

An image showing the dust and exoplanet surrounding the star.
(Credit:  Paul Kalas, UC Berkeley)

An exoplanet discovered at a vast distance from its host star may have been kicked out of its planetary system by violent, cosmic disturbances.

The star in question, HD 106906, contains a ‘lopsided’ comet belt, indicating the planetary system may have been disturbed via highly energetic interactions with other bodies, which could have expelled the exoplanet from its original location close to its star.

The discovery, if proven, would have implications for the history of our own Solar System and the idea that former planetary members may have been kicked out in its formative years.

The planet, HD 106906 b, was discovered sitting at a distance from its star 16 times farther than Pluto from our Sun in 2013 by Vanessa Bailey at the University of Arizona. Images from the Gemini Planet Imager and the Hubble Space Telescope were used to map the system and reveal its lopsided comet belt. The forces that pushed the comets closer to the star may have been the same ones that caused the exoplanet expulsion.

“We think that the planet itself could have captured material from the comet belt, and that the planet is surrounded by a large dust ring or dust shroud,” says Paul Kalas of UC Berkeley. “We conducted three tests and found tentative evidence for a dust cloud, but the jury is still out.

“Is this a picture of our solar system when it was 13 million years old? We know that our own belt of comets, the Kuiper belt, lost a large fraction of its mass as it evolved, but we don’t have a time machine to go back and see how it was decimated. One of the ways, though, is to study these violent episodes of gravitational disturbance around other young stars that kick out many objects, including planets.”

The ‘disturbance’ that could be to blame for the exoplanet’s now-distant location may have been caused by a passing star that disturbed the inner planets, or a second massive planet in the system.

The team will now make follow-up observations to check whether the planet is encircled by a disc of dusty material, which would suggest it had been kicked out of its orbit closer to the star and dragged cosmic debris with it.

Front image: Artist’s conception of a planet in distant orbit around its host star, with a ring of debris surrounding it.
Credit: NASA/JPL-Caltech
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