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Hot jupiters kick up a storm
Posted: 08 Septemver 2010

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Intense heat from the nearby star of a hot Jupiter is creating turbulent storms that envelope the entire planet says Dr. Adam Showman of the University of Arizona, USA. Showman, who is at the forefront of research into weather on hot Jupiters, presented his models describing atmospheric circulation at the Exoclimes conference at the University of Exeter.

An artist’s impression of a hot jupiter orbiting its star. Image: ESA - C. Carreau.

One such exoplanet, which has a mass slightly greater than Jupiter and lies 60 light years from Earth, is HD 189733b. This gas giant has winds that rage across the surface at a velocity of 6,700 mph. But how do these winds originate? The planet is tidally-locked, just like our Moon, which means that one side of the exoplanet continually faces its star, causing heat to become concentrated on one region of its surface. This results in this region becoming hundreds of degrees warmer than the night side of the planet, making all of the hot air flow to the cooler hemisphere. This difference in temperature causes the planet’s impressive wind speeds.

The winds, which are part of a giant global weather system, follow the pattern of so-called Rossby waves. “Rossby waves are blobs of air at a particular latitude, which spin either up or down, developing a type of swirling motion which then spin back to the latitude that they started from,” says Showman. These Rossby waves are a natural consequence of the day side heating and the wind blowing the hot air to the night side where it cools.

An additional consequence of these winds is that they distort the temperature patterns of the planet’s atmosphere, so that the hottest point is not directly beneath its parent star, but slightly to the east of this position. “The motion of the hotspot is entirely due to the weather in the atmosphere, the interior of the planet is assumed to be tidally locked,” says Showman. Furthermore, differences in atmospheric composition and the amount of heat received from the hot jupiter nearby star could result in a diverse range of circulation patterns from planet to planet.