Scientists have reported the first conclusive discovery of water vapor in the atmosphere of an exoplanet, or a planet beyond our Solar System.

This artist's impression 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, dimming the star's light by some three percent.