Astronomers using an infrared camera onboard NASA’s Spitzer Space Telescope have identified clear signs of water on a planet that is 63 light-years (about 370.3 trillion miles) from the Earth. HD 189733b is a planet classified as a gas giant, sometimes also called a Hot Jupiter because of its similarity with the planet Jupiter.

Hot Jupiters are also similar to Saturn, Uranus and Neptune, which also reside in our own Solar System. They are a class of extrasolar planets (exoplanets) whose mass is equal to or more than Jupiter.

However, Hot Jupiters are normally within 0.05 astronomical units (AU, or about 4.6 million miles) of their parent star, unlike Jupiter, which is about 5 AU (or about 464.8 million miles) from the Sun.

By comparison, a Hot Jupiter would be about twenty times closer to the Sun than the Earth, which is about 93 million miles from the Sun, and about eight times as close as the planet Mercury (which is the closest planet to the Sun), which is about 36 million miles from the Sun

HD 189733b orbits a yellow dwarf star (HD 189733) that is about 63 light-years away from the Earth in the constellation Vulpecula (the Fox). The exoplanet is about 15% larger than Jupiter. It is so close to its parent star that it orbits its star once every two days. Earth, by contrast, orbits the Sun once every 365 days.

Research leader Giovanna Tinetti, of the Paris Institute of Astrophysics (Institute d’Astrophysique de Paris), in France, said that they observed the planet as it passed in front of its parent star. Most of the star’s light was blocked by the planet, but a little bit of it was able to pass through the outer atmosphere of the planet. When the atmosphere of a planet contains water, the starlight passing through the atmosphere absorbs (filters out) certain wavelengths of light when particular chemicals are present. Those wavelengths of light that indicate water is present was missing when the light was analyzed by the Spitzer Space Telescope.

Although scientists now know that HD 189733b contains water, Tinetti states that the planet has an average temperature of over 1,300 degrees Fahrenheit (700 degrees Celsius). Unlike the Earth, the temperature of HD 189733b does not change with elevation. Because of its extreme temperature, all of its water is in the form of superheated steam.

Although water is considered a critical component for life anywhere in the universe, it is unlikely that life will be found on HD 189733b because of its closeness to its parent star. However, the scientists are excited to be able to say that it is now more likely to find other types of extrasolar planets that also contain water. They are especially excited with the possibility of finding water on rocky planets, similar to the one we live on.

So far, over 200 exoplanets have been discovered. About 40% of them are in the class of Hot Jupiters, like HD 189733b.

The results of the Tinetti team, titled, “Water vapour in the atmosphere of a transiting extrasolar planet”, will appear in the July 12, 2007 issue of the scientific journal Nature. Other authors of the paper include Alfred Vidal-Madjar, Jean-Phillippe Beaulieu, David Sing and Nicole Allard of the Institute d’Astrophysique de Paris: Mao-Chang Liang of Caltech and the Academia Sinica, Taiwan; Yuk Yung of Caltech; Robert J. Barber and Jonathan Tennyson of University College London in England; Ignasi Ribas of the Institut de Ciències de l'Espai, Spain; Gilda E. Ballester of the University of Arizona, Tucson; and Franck Selsis of the Ecole Normale Supérieure, France.

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Astronomy  Jupiter  NASA  Research  Science  Solar system  Spitzer  Sun  William Atkins