In a major breakthrough, researchers using the Hubble Space Telescope have seen the true color of a planet outside our solar system. HD 189733b, as the gas giant is called, is blue. A deep, vibrant, cobalt blue. And just wait til you hear why it's that color.
An international team of researchers led by Oxford astrophysicist Tom Evans deduced the planet's hue by measuring the light it reflects, a property known as albedo. To do so, the team measured fluctuations in light as it passed in front of and behind its parent star.
An artist's impression of HD 189733b transiting its parent star | ESA/NASA/Frédéric Pont (Geneva University Observatory)
"We saw the brightness of the whole system drop in the blue part of the spectrum when the planet passed behind its star," said Evans in a statement. "From this, we can gather that the planet is blue, because the signal remained constant at the other colors we measured."
From space, HD 189773b looks a lot like our own pale blue dot. Previous research even suggests that sunsets on the planet may look a lot like those seen from here on Earth, its atmosphere tinted a hazy rouge by the last light of a sun dipping over the horizon. But unlike Earth, HD 189773b's azure hue is thought to result not from the reflection of a tropical ocean, but its alien atmosphere.
Evans and his team hypothesize that atmosphere contains a layer of sodium that selectively absorbs red light. But here's the real kicker: While temperatures on the planet come in at over 1,000 degrees Celsius on average, that number swings by as much as 260 degrees between day and night. It is thought that these dramatic fluctuations in temperature lead to 4,500-mile-per-hour, planet-sweeping winds. Weirder still: those temperatures are such that silicates in its atmosphere are converted to small droplets of glass, and those droplets scatter blue light. The result, the researchers write, is a planet that would appear to the naked eye "a deep blue color at visible wavelengths."
A gas giant with 4,500 mph winds is cool. A gas giant with 4,500 mph glass-winds is freaking awesome. And it's blue! Previous artist's renderings of HD 189773b depicted it as brown, or red. Now we know better, and with more certainty than any exoplanet that's come before. That's just incredible.
"This planet has been studied well in the past, both by ourselves and other teams," said Frédéric Pont of the University of Exeter, co-author of the study and leader of the Hubble observing program. "But measuring its color is a real first."
The researchers' findings will appear in the August 1 issue of the journal Astrophysical Journal Letters. In the meantime, you can access the paper here.