Lonely planet discovered

An international team of astronomers, including Tiffany Meshkat and Matthew Kenworthy from Leiden University, have discovered a gigantic exoplanet. The planet revolves around its star at nearly 650 times the distance between the earth and the sun, which makes this planet a record-holder. The researchers are publishing their discovery in the Astrophysical Journal Letters.

Record holder

The gigantic extrasolar planet was discovered at an enormous distance from the sun-like star HD 106906. The planet is 11 times as heavy as Jupiter and revolves around its star at nearly 650 times the distance between Earth and the sun. No other known planet revolves in such a wide orbit around its star, and it does not fit into any theory about the formation of planets or stars.

Artist's impression of a young planet in a distant orbit around its star.

Artist's impression of a young planet in a distant orbit around its star.

Giant planets

Planets form in a proto-planetary disc around a young star by the fusion of planetoid-like objects. However, this process proceeds slowly in giant planets that are a long way from their star. At a certain point another process probably takes over, whereby giant planets are formed by the rapid collapse of matter in the disc. However, these sorts of discs seldom contain enough matter at distances of hundreds of AUs (astronomical units), out of which a planet like HD 106906 b could have emerged.

Theories on how planets are formed

Multiple alternative scenarios have been suggested, such as the formation of star and planet as a binary star system or the emergence of the planet near the star, after which it was hurled to the furthest regions by some violent event. The remaining matter seems to form a ring far within the planet's orbit. “We take this to be a drawback in the scenario in which the planet was been flung out of its original orbit, because such a violent event would also disturb the disc of gas and dust,” says Vanessa Bailey (University of Arizona), who is first author of the article. HD 106906 b could have emerged as part of a binary star system, but it is too light for that. Theories on how planets are formed, in turn, cannot explain how the planet is so far away from its star.

Challenge

Co-author Matthew Kenworthy says, 'The real challenge is to determine how this giant planet ended up so far away from its star. An exciting possibility is that this planet might have been hurled out of a much smaller orbit by a second, as yet unknown, planet closer to the star. We hope to find more planetary systems like this one in the coming years.'

A variety of planetary systems

System HD 106906 is 13 million years old, which is why planet HD 106906 b is still giving off an afterglow from its birth. Because the planet is about 1500 Celsius, about 4500 degrees colder than its star, it radiates mainly in thermal infrared, rather than in visible light. Leiden PhD student Tiffany Meshkat, who is second author on the paper, concludes: 'Every new, directly detected planet advances our understanding of how and where planets emerge. This discovery is particularly exciting because the planet is so far away from its star. This leads to many intriguing questions about its formation and its composition. Discoveries like HD 106906 b give us a better understanding of the variety of planetary systems.'

(9 December 2013, NOVA)

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Last Modified: 12-12-2013