Deep cobalt colouring comes from drops of liquid gas raining horizontally in 7,000 km/h winds
We are not alone. Scientists have discovered a second blue planet in
the Universe, although this one is decidedly inhospitable and unlikely
to support life.
Planet HD 189733b lies some 63 light years beyond our Solar
System in the constellation Vulpecula is a deep cobalt blue according to
data gathered by the Hubble space telescope, but its azure hue is not
due to water but drops of liquid glass raining down horizontally in
7,000 kilometre-per-hour winds.
By measuring the
wavelengths of light that are lost when the orbiting planet slips behind
its star, scientists have been able to calculate the colour that the
planet as it would appear if seen by the naked eye.
It is
the first time that scientists have been able to calculate the visible
colour of an “exoplanet” beyond our own Solar System, said Frederic Pont
of the University of Exeter, one of the authors of the study.
“This
planet has been studied well in the past, both by ourselves and other
teams. 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,” Dr Pont said.
The planet is a gas giant,
similar to Jupiter, and orbits very close to its sun, meaning that its
temperatures are a scorching 1,000C or higher. Extreme winds pelt
silicate particles sideways, which scatter blue light.
It
was technically challenging to work out the colour of the planet
because the light from its nearby star swamped any reflected light from
the planet. However, by measuring the loss of light as the planet
disappeared by its sun, the scientists were able to assess the
wavelengths that are reflected by HD 189733b.
“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,” said Tom Evans of Oxford University, the lead
author of the study.
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