Astronomers scanning the galaxy for alien worlds are very interested in finding blue planets, in the hopes that they will be very similar to Earth. Recently, they found a planet that is blue, but this amazing world apparently doesn't get its colour from water, but instead from molten glass rain whipping about in its atmosphere.
HD 189733b is a roughly Jupiter-sized planet that orbits a star smaller and cooler than our Sun, located about 63 light years away in the northern constellation of Vulpecula, 'the little fox'. Astronomers first discovered this planet in 2005, when they saw the light from its star dim as it passed in front of it (the transit method), and they were able to confirm it by watching as it caused its star to wobble. Since the planet is already remarkable for being a 'hot Jupiter' that makes a full orbit of its star in just over 53 hours, astronomers have been keeping an eye on it, and more recent observations have shown that its more amazing than we first thought.
In drawings of other planets we've discovered, the colour has been left up to the artist's imagination. However, HD 189733b is the first where astronomers were actually able to tell what the real colour of the planet is, by watching for a change in the colour of light from the system as the planet ducked behind the star. With the planet's atmosphere reaching temperatures far above anything we see here in our solar system (between roughly 1,000-1,300°C), the blue colour likely comes from tiny molten particles of silicate glass that are whipping around in the atmosphere at over 7,000 km/h. The molten glass scatters blue light easier than it does any other colour of light (the molecules in Earth's atmosphere do the same thing, which gives us our blue sky during the day), so makes the planet look like a deep blue marble.
Not only that, this planet is the first one that astronomers saw 'transit' using two space-based X-ray telescopes (NASA's Chandra X-ray Observatory and the ESA's XMM-Newton). Their observations showed that the planet's atmosphere is much bigger than they expected, and that its star is stripping that atmosphere from it at a rate of between 100 million to 600 million kilograms per second.
We still can't directly see HD 189733b, because it's just too close to its star for us to pick out with existing telescopes. This video, by the Hubble-ESA team, gives an artists impression of a flyby of the planet, though:
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Science fiction has offered us incredible ideas of what kinds of planets we may find out in the galaxy, but discoveries like the 'diamond planet', planets that orbit their star in mere hours, and the new findings about HD 189733b are just a hint of the real wonders that await us.
As always, truth is stranger than fiction.
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