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 about 63 light years beyond our Solar System in the constellation Vulpecula and is a deep cobalt blue, according to data from the Hubble space telescope. But its azure hue is not because of water but drops of liquid glass raining down horizontally in 7000km/h winds.
By measuring the wavelengths of light lost when the orbiting planet slips behind its star, scientists have been able to calculate its colour as it would appear to the naked eye.
It is the first time scientists have been able to pinpoint 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," he said.
The planet is a gas giant, similar to Jupiter, and orbits very close to its sun, meaning that its temperatures are a scorching 1000C or higher. Extreme winds pelt silicate particles sideways, which scatter blue light.
It was 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 behind its sun, scientists were able to assess the wavelengths 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.