First planet from another galaxy 'discovered'

A team at Germany's Max Planck Institute for Astronomy has found the planet, called HIP 13044 b, around a star which seems to be an interloper from another galaxy - by the way its gravity caused its host star to wobble.

Curiously, the star also contains fewer heavy elements -- thought to be needed to build planets -- than any other planet-hosting star yet discovered, the 'New Scientist' reported.

The planet, which is 1.25 times as massive as Jupiter, lies 2300 light years from Earth and orbits a bloated, ageing star slightly less massive than the sun.The host star, called HIP 13044, is a member of a group of stars called the Helmi stream that have unusual, elongated orbits that bring them far above and below the disc of the galaxy where sun and most other Milky Way stars reside.

The Helmi stars are thought to be remnants of a small galaxy torn apart by the Milky Way some 6 billion to 9 billion years ago.

"This cosmic merger has brought an extragalactic planet within our reach," said team member Rainer Klemen

In addition to its unusual origins, the host star is puzzling because it has fewer elements heavier than hydrogen and helium than any other star known to host a planet. Its light spectrum suggests it has just 10 per cent as much iron as the previous record holder, and only 1 per cent as much as the sun, say the astronomers.

Planets are thought to form from discs of gas and dust left over from the formation of the parent star. In the prevailing theory of planet formation, called core accretion, dust grains stick together to form rocky worlds, and some of these rocky bodies then grow massive enough to attract surrounding gas, becoming gas giants like Jupiter.

Dust is made up of heavy elements, so stars depleted in these elements would have a hard time making planets in this scenario.

"This suggests the planet formed another way," said Alan Boss of the Carnegie Institution of Washington, DC, who was not a member of the team.

He added: "The fact that the star is also likely to have come from somewhere other than the disc of our galaxy makes it even more remarkable, and supports the suspicion that planetary systems are rife in the universe."

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