Hellish conditions on blue planet

As Irish eyes focus skywards every morning to see whether the sun soaked summer is set to continue, a look further afield might temper any complaints about high temperatures, sun stroke or hosepipe bans.

A dazzling blue planet 63 light years away bears a striking resemblance to Earth, scientists have learned — but only in appearance.

Like the Earth, the alien world known as HD 189733b would be a brilliant cobalt blue if seen from a short distance away in space.

Unlike Earth, however, the planet has no blue oceans and the chances of any form of life surviving on its surface are remote.

Conditions on HD 189733b are hellish. Temperatures are a scorching 1000 celsius, winds howl at more than 4,000 mph, and it rains slivers of silicate glass.

The planet is a gas giant orbiting very close to its parent star.

Scientists were able to calculate its colour by measuring the light reflected from its surface.

It is the first time astronomers have determined the true colour of an exoplanet orbiting a star beyond the sun.

"This planet has been studied well in the past, both by ourselves and other teams," said Professor Frederic Pont, from the University of Exeter, who led the international Hubble Space Telescope team. "But measuring its colour is a real first — we can actually imagine what this planet would look like if we were able to look at it directly."

To isolate the planet’s light, the astronomers conducted observations before, during and after the orbiting planet passed behind its parent star.

As it slipped behind the star, light reflected from the planet was temporarily blocked out. The total amount of light coming from the star system fell slightly as a result. Identifying the wavelengths of the missing light revealed the planet’s likely colour.

The findings appear in the August issue of the journal Astrophysical Journal Letters.

Co-author Tom Evans, from Oxford University, said: "We saw the brightness of the whole system drop in the blue part of the spectrum when the planet passed behind its star. From this, we can gather that the planet is blue, because the signal remained constant at the other colours we measured."

The blue colour is thought to arise from light scattered by silicate particles in the planet’s turbulent atmosphere.

HD 189733b belongs to a class of exoplanets known as “hot Jupiters”. These are massive planets similar in size to gas giants in our own solar system, but lying very close to their parent stars. Their size and tight orbits make them especially easy to detect by planet hunters.

Although hot Jupiters are common throughout our galaxy, the Milky Way, there are none orbiting the sun.

Astronomers hope to learn more about them by studying planets such as HD 189733b.

“We are slowly painting a more complete picture of this exotic planet,” said Professor Pont.

PA