The powerful vision of NASA's Hubble Space Telescope has allowed astronomers to study for the first time the layer-cake structure of the atmosphere of a planet orbiting another star. Hubble discovered a dense upper layer of hot hydrogen gas where the super-hot planet's atmosphere is bleeding off into space.
This is an artist's illustration of the extrasolar planet, designated HD 209458b, which is unlike any world in our solar system. It completes an orbit around its host star every 3.5 days. It is about the size of Jupiter. Unlike Jupiter, HD 290458b is so hot that its atmosphere is "puffed up." Starlight is heating the planet's atmosphere, causing hot gas to escape into space. Astronomers used Hubble to analyze the starlight that filtered through the planet's atmosphere. Imprinted on the starlight is information about the atmosphere's structure and chemical makeup.
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