spaceSpace and Physics

Astronomers' Weather Forecast For Hellish Exoplanet: "Yellow Skies With A Chance Of Iron Showers"


Dr. Alfredo Carpineti

Senior Staff Writer & Space Correspondent

clockMay 1 2020, 13:25 UTC

Artist's illustration of the super-hot hellish exoplanet WASP-79b. NASA, ESA, and L. Hustak (STScI)

WASP-79b also known as Pollera, is one of the largest exoplanets known orbiting a star hotter and brighter than our Sun. It orbits the star every 3.6 days, so close that the atmosphere of this gas giant is absolutely hellish. Now, new research published in The Astronomical Journal has shown that it looks hellish too: to a human observer, the planet's skies are yellow.

The characteristic blue of Earth’s sky – praised by poets, artists, and singers – is due to an effect called Rayleigh scattering. Blue light is scattered more efficiently than other wavelengths in our atmosphere and for this reason, the sky appears blue. In a similar way, due to its dust, on Mars, the sky appears a peculiar butterscotch color.


But it’s not like that for WASP-79b, which is located 780 light-years from Earth in the constellation Eridanus. Using the Hubble Space Telescope and Magellan II Telescope in Chile to analyze this planet's atmosphere, researchers found that the planet doesn’t have any Rayleigh scattering present, which would make its sky yellow. The lack of this phenomenon is very perplexing.

"This is a strong indication of an unknown atmospheric process that we're just not accounting for in our physical models. I've shown the WASP-79b spectrum to a number of colleagues, and their consensus is 'that's weird,'" lead author Kristin Showalter Sotzen of the Johns Hopkins University Applied Physics Laboratory, said in a statement.

"Because this is the first time we've seen this, we're really not sure what the cause is," Sotzen added. "We need to keep an eye out for other planets like this because it could be indicative of unknown atmospheric processes that we don't currently understand. Because we only have one planet as an example, we don't know if it's an atmospheric phenomenon linked to the evolution of the planet."


The findings may give clues to other similar planet's history, and climates. The planet itself is a bit of a mystery as worlds like this, known as hot Jupiters, are believed to migrate inwards in the orbit of their star. WASP-79b's orbit is almost a polar orbit, which goes against how scientists think these planets should form.

Some hot Jupiters have hazy or cloudy atmospheres, while others appear clear. The team believes that WASP-79b is a hot steamy world, sizzling around 1,648°C (3,000°F), with scattered clouds and the occasional rain shower. But it’s not water falling down from the clouds, it's molten iron. Hellish indeed.

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