Hubble Probes Layer-Cake Structure of Alien World's Atmosphere

Puffed-Up Atmosphere of a Star-Hugging Gas Giant Planet - This artist's illustration shows an extrasolar planet orbiting very close to its host star. The planet, designated HD 209458b, is about the size of Jupiter. Unlike Jupiter, the planet is so hot that its atmosphere is 'puffed up.' Starlight is heating the planet's atmosphere, causing hot got to escape into space like stream rising from a boiler. HD 209458b completes an orbit every 3.5 days. The Hubble Space Telescope could not image the planet directly because it is too close to the star. 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. (Credit: NASA, ESA and G. Bacon of StScI)