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> Artist's conception of HD 209458b transiting its star
Artist's conception of HD 209458b transiting its star
author: Nasa/ESA/Novapix
reference: a-exo99-00501
Image Size 300 DPI: 21 * 26 cm
This artist's impression shows the extrasolar planet HD 209458b in front of its star. Astronomers have observed the atmosphere of an extrasolar planet evaporating off into space (shown in blue in this illustration). The planet's outer atmosphere is extended and heated so much by the nearby star that it starts to escape the planet's gravity. Hydrogen boils off in the planet's upper atmosphere under the searing heat from the star. HD 209458b belongs to a type of extrasolar planet known as 'hot Jupiters'. These planets orbit precariously close to their stars. They are giant, gaseous planets that must have formed in the cold outer reaches of the star system and then spiralled into their close orbits.
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