Astronomers mapped out the three-dimensional structure of an exoplanet's atmosphere for the first time ever and found it to consist of three distinct layers in a wedding cake structure. The discovery was made on a super-hot gas planet located far away called WASP-121b, or Tylos for short. 

It is an "ultra-hot Jupiter," meaning it is a massive gas planet that orbits very close to its star. This star is much larger and hotter than our Sun. Because of its extreme proximity to the star—about 2.5% of the distance between Earth and the Sun—the planet experiences scorching temperatures.  But what is more interesting is its weird atmosphere, never before seen.

How did scientists study this alien atmosphere?

To analyze WASP-121b's atmosphere, researchers employed the European Southern Observatory's Very Large Telescope in Chile. By uniting all four telescope units, they could observe how various chemicals were distributed in its atmosphere. Previously, astronomers were only able to determine what gases were present in an exoplanet's atmosphere, but not how the gases were distributed in layers. This new research alters that!

What are the three layers composed of?

The atmosphere of the planet is predominantly hydrogen and helium, similar to Jupiter. Yet, it also consists of special layers that consist of various elements:

Bottom layer: Researchers discovered iron here! Due to the fact that WASP-121b is extremely hot, iron is a gas rather than solid metal, similar to Earth. Strong winds drive this gas from the hot side of the planet to the cool side.

Middle layer: The middle layer consists of sodium, another element discovered in the upper atmosphere of our planet. It is really rough weather down here – mighty jet streams rage about the world at almost 70,000 km an hour (43,500 miles an hour) – infinitely quicker than all our wind has to offer!

Upper layer: The outermost layer consists primarily of hydrogen. Some of that even is escaping into space. Researchers also discovered gaseous titanium, something unheard of on our planet as metals such as iron and titanium are typically solid here because of our cold temperatures.

Why is this discovery so exciting?

Astronomers had never observed an atmosphere like this before. In fact, the findings challenge existing theories on how atmospheres should behave. “This structure has never been observed before and defies current predictions as to how atmospheres should behave,” said Julia Victoria Seidel, the lead author of the study.

Meet WASP-121b – A planet unlike any other

WASP-121b is an "ultra-hot Jupiter," an exoplanet similar in mass to Jupiter but double its size, hence appearing fluffier. Found 900 light-years from our planet in the constellation Puppis, it is tidally locked, which means one side perpetually faces its star and the other stays in the dark.

Hot side: This side has a scorching 2,700°C (4,900°F).

Cooler side: Still incredibly hot at approximately 1,250°C (2,200°F).

Orbit: WASP-121b orbits its star in only 1.3 days! That's a lot closer than Mercury is to the sun.

Its host star, WASP-121, is roughly 1.5 times larger and hotter than our sun, contributing to the extreme environment on this planet.

Knowing the layers of an exoplanet's atmosphere is a major leap. This information may aid astronomers in looking for smaller, Earth-like worlds with perhaps life-friendlier conditions. "In the future, we will probably be able to give similar observations for cooler and smaller planets and therefore more Earth-like," stated co-author Bibiana Prinoth.

"This research informs us about the variety of planetary atmospheres and whether the climate of Earth is really exceptional," said Seidel. "There is much greater variety out there than we have at home."

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