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Physical Chemistry

Steam detected on extrasolar planet

by Sarah Everts
July 16, 2007 | A version of this story appeared in Volume 85, Issue 29

Credit: ESA/C. Carreau
Credit: ESA/C. Carreau

The toasty atmosphere around the planet HD 189733b boasts some very hot water, the first convincing evidence of this much-sought substance on a planet outside our own solar system (Nature, DOI: 10.1038/nature06002).

HD 189733b, shown in the foreground in this artist's rendition, is just over 60 light years from Earth, but it is so close to its parent star in the constellation of Vulpeca the Fox that atmospheric temperatures on the planet can reach a sweltering 1,200 K. This means the water is present as a vapor but is unlikely to form clouds.

An international team of researchers led by Giovanna Tinetti at the European Space Agency detected the steamy water by making use of some convenient astrogeometry.

With every revolution, HD 189733b passes directly in front of its star in a planetary eclipse, as viewed from Earth. The researchers were able to use NASA's Spitzer Space Telescope to detect water absorption from starlight that is transmitted through the planet's atmosphere during the eclipse.


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