THE STRANGE YELLOW SKIES OF WASP-79B

Astronomers will feel blue if they don’t discover why this hot-Jupiter exoplanet has an odd-coloured sky

- David Crookes

If you’re looking for an ideal holiday destination, one thing’s for sure: you are not going to be choosing WASP-79b. As curious as this huge, hot exoplanet has proven to be ever since its discovery by Dr. Barry Smalley of Keele University, UK, in 2012, anyone deciding to lay on their deckchair and look skywards is going to be in for something of a surprise.

Here on Earth, the sky is a glorious blue, and that’s because the white light from the Sun – which is made up of all the colors of the rainbow – enters the atmosphere, bounces off small particles, and causes the shorter blue and violet wavelengths to become separated from the longer red, yellow and green. As the violet light is mainly absorbed by the upper atmosphere, it leaves the blue waves to be dispersed.

“This is called Rayleigh scattering, and it’s the primary effect that makes Earth’s sky look blue,” says Kristin Showalter Sotzen of the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland. “If WASP-79b had Rayleigh scattering, its sky would also have more of these shorter, bluer wavelengths, and so it would appear to have a blue or blue-green hue, depending on what the particles are actually made of.” And yet it doesn’t. Instead, observations suggest that WASP-79b has a total absence of this effect, which means the blue light is able to join the others in making its way through the atmosphere without any obstruction.