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HD 189733

This yellow star is orbited by a planet with 1.15 times the mass of Jupiter and 1.26 its diameter in only 2.219 days and in a distance of 0.0313 AU. This is one of the closest planet-star systems known. So the planet is very hot and its orbit is synchronous. It is transiting its star and thereby decreases the star's luminosity for 3%, which is very much. The planet's surface temperature is 920 kelvin on the poles and 1220 kelvin on the bright side. To keep this relatively moderate temperature difference, strong winds have to rake up the whole atmosphere. This is also implied by the fact, that the hottest spot isn't directly opposit to the star, but about 30° east of it.

In February 2007 for the first time molecules have been discovered in exoplanets for HD 189733b and HD 209458b (with the Spitzer telescope). In July of the same year water vapor has been discovered in the atmosphere of HD 189733b. HD 209458b even contains silicates, in the form of sand grains. This is a great step to the discovery of alien life, even though these two planets aren't suitable for this.

Constellation: Vulpecula
Distance: 62.8 light-years
Spectral class: G5
Visual magnitude: 7.50
Luminosity: 0.32 * Sun

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    HD 189733
HD 189733 and M27, the Dumbbell Nebula.
Photo: Daniel Jaroschik
HD 189733b
Temperature distribution of the planet, grid spacing 30°.
Image: Heather Knutson (Harvard-Smithsonian CfA) et al., NASA / JPL-Caltech

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