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Hubble Detects Layered Atmosphere of Exoplanet:
The Hubble Space Telescope continues to provide excellent scientific data on the study of exoplanets. In another Hubble first, atmospheric layers of an exoplanet has been detected for the first time. The most common exoplanet that has been detected is the "hot-Jupiter," coined because of the detection of Jupiter mass planets found orbiting the host star at distances closer than the orbit of Mercury.
The star, HD 209458, is a G type star like our Sun and is only 1.01 times the mass of our Sun. The planet, HD 209458b, is one of the most studied exoplanets because it transits the host star. This allows astronomers to use Hubble's STIS (Space Telescope Imaging Spectrograph) to determine the chemical make-up of its atmosphere. Spectroscopy is a powerful tool used by astronomers. This tool can tell us chemical composition, velocity, and in many cases energy processes. By subtracting the known spectra of the host star, astronomers can determine the chemical makeup of the exoplanet's atmosphere.
Because HD 209458b orbits so close to the host star - 10 times closer than Mercury is to our Sun - the heat from the host causes the atmosphere to swell. With such a swollen atmosphere, the Hubble is able to detect four layers: a (possible) cloud layer, a sodium layer, a transition zone and the hydrogen coma.
The ultraviolet radiation from the host heats the upper layer of the atmosphere to 25,000 degrees Fahrenheit (15,000 K) which is hotter than the Sun. The heat is such that the gas escapes the planet much like a comet - as much as 10,000 tons per second. Regardless of this vast amount of lost material, astronomers estimate the planet will exist for another 5 billion years.
It is suggested that if Jupiter were as close to our Sun, its atmosphere would behave in the same way.
Study of HD 209458b will give astronomers insight to the atmospheres of the other discovered "hot-Jupiters." For additional Hubble stories on atmosphere related studies, see: First Direct Measurement of Exoplanet Atmosphere, Hubble Discovers Evaporating Planet, and Oxygen and Carbon Detected in Exoplanet Atmosphere.
From the Extrasolar Planet Encyclopedia: HD 209458
Image Credit: HubbleSite
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