For the first time the colour of a planet outside of our solar system has been measured, and its blue! HD 189733 b is a planet 63 light years away, orbiting the star HD 189733. The planet is Jupiter sized and similarly is a giant ball of gas. The colour of the planet was discerned using a spectrograph onboard the Hubble space telescope. During an eclipse of the planet light reflected off the atmosphere was found to be blue however as the planet is a gas giant that blue colour is unlikely to be due water.
It is thought the blue colour may come from silicon clouds in the atmosphere. Another possibility is light scattering caused by hydrogen in the atmosphere.
Blue planet HD 189733b around its host star (artist’s impression) from HubbleESA on Vimeo.