Newly discovered planet victim of game of ‘planetary billiards’

August 13th, 2009 - 12:23 pm ICT by ANI  

London, August 13 (ANI): A team of scientists has found a new planet which appears to have been the victim of a game of planetary billiards, flung into its unusual orbit by a close encounter with a “big brother” planet.

The planet, named WASP-17, and orbiting a star 1000 light years away, was found by the UK’s WASP project in collaboration with Geneva Observatory.

Since planets form out of the same swirling gas cloud that creates a star, they are expected to orbit in the same direction that the star spins.

Graduate students David Anderson, of Keele University, and Amaury Triaud, of Geneva Observatory, were surprised to find that WASP-17 is orbiting the wrong way, making it the first planet known to have a “retrograde” orbit.

The likely explanation is that WASP-17 was involved in a near collision with another planet early in its history.

WASP-17 appears to have been the victim of a game of planetary billiards, flung into its unusual orbit by a close encounter with a “big brother” planet.

According to Professor Coel Hellier, of Keele University, “Shakespeare said that two planets could no more occupy the same orbit than two kings could rule England; WASP-17 shows that he was right.”

“A near collision during the early, violent stage of this planetary system could well have caused a gravitational slingshot, flinging WASP-17 into its backwards orbit,” Anderson said.

The first sign that WASP-17 was unusual was its large size. Though it is only half the mass of Jupiter it is bloated to nearly twice Jupiter’s size, making it the largest planet known.

Astronomers have long wondered why some extra-solar planets are far bigger than expected, and WASP-17 points to the explanation.

Scattered into a highly elliptical, retrograde orbit, it would have been subjected to intense tides.

Tidal compression and stretching would have heated the gas-giant planet to its current, hugely bloated extent.

“This planet is only as dense as expanded polystyrene, seventy times less dense than the planet we’re standing on,” said Professor Hellier.

According to Professor Keith Mason, Chief Executive of the Science and Technology Facilities Council, which funded the research, “This is a fascinating new find and another triumph for the WASP team. Not only are they locating these far flung and mysterious planets but revealing more about how planetary systems, such as our own Solar System, formed and evolved.” (ANI)

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