Planet reveals stunning true colours

Astronomers say they have found another blue planet a long, long way from Earth - no water world, but a scorching, hostile place where it rains glass sideways.

Using the Hubble Space Telescope, scientists from NASA and its European counterpart, ESA, have for the first time determined the true colour of an exoplanet, a celestial body that orbits a star other than our own Sun.

They concluded that HD 189733b, a gas giant 63 light-years from Earth, was a deep cobalt blue, "reminiscent of Earth's colour as seen from space".

"But that's where the similarities end," a statement said.

This planet orbits very close to its host star and its atmosphere is heated to more than 1000 degrees Celsius.

"It rains glass, sideways, in howling 7000 kilometre-per-hour winds," the statement said.

The planet is one of the nearest exoplanets to Earth that can be seen crossing the face of its star, and has been intensively studied by Hubble and other telescopes.

Frederic Pont of the University of Exeter, who co-wrote the paper in Astrophysical Journal Letters, said measuring the colour was "a real first".

The blue comes not from the reflection of a tropical ocean, as in Earth's case, but a hazy, turbulent atmosphere believed to be laced with silicate particles - the stuff of which glass is made - which scatter blue light.

"It's difficult to know exactly what causes the colour of a planet's atmosphere, even for planets in the Solar System," Pont said.

"But these new observations add another piece of the puzzle over the nature and atmosphere of HD 189733b. We are slowly painting a more complete picture of this exotic planet."

- AAP