Scientists have made the first conclusive discovery of water vapor in
the atmosphere of a planet beyond our solar system, or exoplanet.
This artist’s rendering shows a gas-giant exoplanet transiting across
the face of its star. Infrared analysis by NASA’s Spitzer Space
Telescope of this type of system provided the breakthrough. The
planet, HD 189733b, lies 63 light-years away in the constellation
Vulpecula. It was discovered in 2005 as it transited its parent star. (source)