Cape Town - Scientists have confirmed that a planet discovered in 2005 is a beautiful cobalt blue – not unlike the view of Earth from space.
But this blue doesn’t signal life-giving oceans like it does on our home planet. On the contrary, HD 189733b is an extremely inhospitable exoplanet (a planet outside our solar system) with an atmosphere that pushes the mercury over 1 000ºC and where it rains glass that is driven sideways by winds reaching 7 000km/h.
The remarkable new discovery has come from a group of astronomers using the Hubble Space Telescope, a joint project of Nasa (the US National Aeronautics and Space Agency) and the European Space Agency.
Their findings will be reported in the August 1 issue of the journal Astrophysical Journal Letters.
HD 189733b, a huge gas giant, has been well studied by astronomers using Hubble and other telescopes. In 2007, Nasa’s Spitzer Space Telescope measured the infrared light, or heat, from this planet – one of the first temperature maps of an exoplanet. This map showed that the “day side” and “night side” temperatures of the planet differed by about 260ºC, creating fierce winds.
Now, the first measurement of an exoplanet’s visible colour has been done.
The research team used Hubble’s imaging spectrograph to measure light in the system before, during and after the planet passed behind its host star as it orbited. As it slipped behind its star, the light reflected from the planet was temporarily blocked from view, and the amount of light observed from the system dropped. But this technique also shows how the light changed in other ways – including its colour.
“We saw the brightness of the whole system drop in the blue part of the spectrum when the planet passed behind its star,” explained Tom Evans of Oxford University, lead author of the paper. “From this, we can gather that the planet is blue, because the signal remained constant at the other colours we measured.”
The cobalt or azure blue colour probably derives from the exoplanet’s hazy, turbulent atmosphere. This is thought to be laced with silicate particles that, when condensing in the heat, could form very small drops of glass that scatter blue light more than red light.
“It’s difficult to know exactly what causes the colour of a planet’s atmosphere,” said Professor Frédéric Pont of the University of Exeter in Britain.
“But these new observations add another piece to the puzzle over the nature and atmosphere of HD 189733b. We are slowly painting a more complete picture of this exotic planet.” – Cape Argus