NASA scientists have found the first planet beyond the solar system that contains methane.
The giant planet lies too close to its parent star for the greenhouse gas to signal life.
But it suggests astronomers will one day be able to search for organic molecules on Earth-like worlds.
Dr Mark Swain, of the California Institute of Technology, and colleagues used the Hubble Space Telescope to observe the planet known as HD 189733b, which is bigger than Jupiter and lies 63 light years away. They confirmed the presence of methane by studying the chemical signature of starlight wavelengths as they passed through its atmosphere.