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This ultra-hot exoplanet has yellow skies and iron rain

Published May 12th, 2020 11:20PM EDT
space news
Image: NASA, ESA and L. Hustak (STScI)

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  • Exoplanet WASP-79b is a massive gas giant with incredibly hot atmospheric temperatures.
  • Its atmosphere isn’t capable of scattering like in the way that Earth’s atmosphere does, so the daytime skies would look yellow instead of blue.
  • Like other hot Jupiter exoplanets, it’s thought that WASP-19b has iron rain due to its heat.
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Exoplanets come in many different varieties. Some are frigid and icy, while others are rocky and warm, and some, like WASP-79b, are just plain weird. WASP-79b orbits a star that sits roughly 780 light-years from Earth. In space, that’s a relatively short distance, and our proximity to the planet and its host star has allowed scientists to get a pretty good idea of what the world has to offer.

There are a number of things that make WASP-79b special. For starters, it’s absolutely massive and ranks high on the list of the largest exoplanets we know about. It’s also insanely hot, orbiting so close to its star that its atmosphere is a steamy 3,000 degrees Fahrenheit. Oh, and did I mention the iron rain?

WASP-79b is the subject of a research paper published in The Astronomical Journal, and the scientists studying it have painted a vivid picture of a planet that is just plain wild. If you were to be able to stand on the planet — which you can’t, because it’s a “hot Jupiter” gas giant — you’d notice that the sky isn’t blue like it is on Earth.

For a reason that scientists don’t yet understand, the planet’s atmosphere isn’t capable of a phenomenon known as Rayleigh scattering, in which tiny particles capture certain wavelengths of sunlight and turn the skies blue on a clear day. On a planet like WASP-79b with an atmosphere that doesn’t scatter light in such a way, the skies would likely be yellow, according to the scientists.

“This is a strong indication of an unknown atmospheric process that we’re just not accounting for in our physical models,” Kristin Showalter Sotzen, first author of the study, said in a statement. “I’ve shown the WASP-79b spectrum to a number of colleagues, and their consensus is ‘that’s weird.'”

“Because this is the first time we’ve seen this, we’re really not sure what the cause is,” Sotzen adds. “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.”

Because of the planet’s size — twice the mass of Jupiter — and its close proximity to its star, its atmosphere has swollen like a balloon. Many hot Jupiter exoplanets are believed to produce a phenomenon where hot iron particles are lifted high into the atmosphere before falling back down as rain, which sounds rather painful.

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