'Astronomers have detected water vapour in the atmosphere of a planet that orbits a star far beyond our solar system.
Observations of the Neptune-sized planet, which lies 120 light years from Earth in the constellation of Cygnus, revealed that its atmosphere was mostly hydrogen with around 25% made up from water vapour.
Until now, researchers have been frustrated in their efforts to study the atmospheres of planets much smaller than Jupiter because their skies were thick with clouds. The problem was so persistent that astronomers had begun to think that all warm, small planets formed with substantial cloud cover.
But writing in the journal Nature, scientists in the US describe how they found a Neptune-sized planet with cloud-free skies, enabling them to make detailed measurements of a small planet's atmosphere for the first time.
The planet, named HAT-P-11b, is about four times the diameter of Earth. It orbits so close to its star that surface temperatures reach more than 600C and a year passes in five Earth days. Like our own Neptune, the planet lacks a rocky surface – it's a ball of gas – and is thought to be lifeless'