May 12, 2011

Hot Jupiters Spin Backwards

Scientists said on Wednesday the majority of the 500 planets detected around stars besides the Sun appear to spin the same way the star does.

However, astronomers found that some of these extrasolar planets spin in the opposite direction of the stars they orbit.

These backward-spinning planets usually are gassy giants called hot Jupiters.

The scientists said these big planets huddle close to their stars, unlike Jupiter, which is about 483 million miles from the Sun.

"That's really weird, and it's even weirder because the planet is so close to the star," Frederic Rasio of Northwestern University said in a statement.

"How can one be spinning one way and the other orbiting exactly the other way? It's crazy. It so obviously violates our most basic picture of planet and star formation."

Astronomers have believed for a while that big gas planets form further away from their stars, while Earth-like rocks are born closer in.

However, the scientists said just because Jupiter-like planets form in the planetary boondocks does not mean they stay there.

"We had thought our solar system was typical in the Universe, but from day one, everything has looked weird in the extrasolar planetary systems. That makes us the oddball really," Rasio said in a statement.

They found that when planetary systems contain more than one planet, each planet has its own gravitational force, which causes the planets to interact and pull the gas giants close to the star and even reverse its orbit.

This process is known as gravitational perturbation, or an exchange of angular momentum.

Astronomers have detected extrasolar planets since 1995, but have only seen a handful. 

"Right now, the notion that solar systems are like ours is completely falling apart," Swiss astronomer Didier Queloz, who did not take part in the new study, said in an interview with AFP.

"We are just one type of solar system among an enormous diversity of planetary orbits and possibilities."

The study was published by the science journal Nature.


Image Caption: A retrograde hot Jupiter: the transiting giant planet orbits very close to the star and in a direction opposite to the stellar rotation. This peculiar configuration results from gravitational perturbations by another much more distant planet (upper left). Credit: Lynette Cook


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