Astronomers using the Hubble Space Telescope have, for the first time, determined the true colour of a planet orbiting another star. If seen up close, this planet, known as HD 189733b, would be a deep azure, reminiscent of Earth’s colour as seen from space.
But that’s where the similarities end. This “deep blue dot” is a huge gas giant orbiting very close to its host star. The planet’s atmosphere is a scorching 1 000-plus degrees Celsius, and it rains glass, sideways, in howling 7 000 km/hour winds!
At a distance of 63 light-years from us, this turbulent alien world is one of the nearest exoplanets to Earth that can be seen crossing the face of its star. It has been intensively studied by Hubble and other telescopes, and its atmosphere has been found to be dramatically changeable and exotic, with hazes and violent flares.
In order to measure what this planet would look like to our eyes, the astronomers measured how much light was reflected off the surface of HD 189733b – a property known as albedo. The planet’s azure colour does not come from the reflection of a tropical ocean, but is due to a hazy, turbulent atmosphere thought to be laced with silicate particles, which scatter blue light.