Astronomers have mapped the atmosphere of a planet orbiting a star beyond our Solar System in 3D for the first time.
This unprecedented study has revealed fierce winds carrying chemical elements, and intricate weather patterns.
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“This planet’s atmosphere behaves in ways that challenge our understanding of how weather works — not just on Earth, but on all planets.
"It feels like something out of science fiction," says Julia Victoria Seidel, researcher at the European Southern Observatory (ESO) in Chile and lead author of the study.
About the planet
WASP-121b (also known as Tylos), is an 'exoplanet', a planet orbiting a star beyond our Solar System.
Since the first one was confirmed in the 1990s, nearly 6,000 exoplanets have now been discovered, and each one that's studied reveals more about the sort of planets we can expect to find in other star systems.
WASP-121b is located 900 lightyears away around a star in the constellation Puppis. That's a relative stone's throw in cosmic terms.
The exoplanet is a so-called ultra-hot Jupiter, meaning it's a gas giant (like Jupiter our Solar System) that orbits its host star scorchingly close.
In fact, a year on WASP-121b lasts just 30 Earth hours.
It's also tidally locked, meaning one side is always facing the star. The star-facing side is always scorching, while the side facing away from the star is much cooler.
Peering beyond WASP-121b's atmosphere
The study marks the first time astronomers have created a map of an exoplanet's 3D structure, and they did so by peering through its atmosphere.
The team used all four telescope units of the European Southern Observatory’s Very Large Telescope (ESO’s VLT) and found powerful winds carrying chemical elements like iron and titanium, generating intricate weather patterns across the atmosphere.
The team found distinct winds in separate layers, enabling them to produce a map of the atmosphere’s 3D structure.
"What we found was surprising: a jet stream rotates material around the planet’s equator, while a separate flow at lower levels of the atmosphere moves gas from the hot side to the cooler side.
"This kind of climate has never been seen before on any planet," says Julia Seidel, who is also a researcher at the Lagrange Laboratory, part of the Observatoire de la Côte d'Azur, in France.
The jet stream stretches across half of the planet, reaching high speeds and churning up the atmosphere at high altitudes as it crosses the hot, star-facing side.
“Even the strongest hurricanes in the Solar System seem calm in comparison,” says Seidel.
How they did it
The team used the ESPRESSO instrument to combine the power of all four of the Very Large Telescope's units, making it effectively four times as powerful as a single telescope unit.
This technique enabled the team to see fainter details within the structure of the exoplanet's atmosphere.
They observed the exoplanet passing in front of its star – known as a 'transit' – and, studying the starlight that had passed through the planet's atmosphere, the ESPRESSO instrument detected signatures of multiple chemical elements and different layers of the atmosphere.
The team tracked the movements of iron, sodium and hydrogen, allowing them to trace winds in the deep, mid and shallow layers of the atmosphere, respectively.
They also found a surprise hidden deep within.
Previous observations of the exoplanet had found titanium to be absent, but peering deeper into the atmosphere revealed titanium just below the jet stream.
This discovery was presented in a companion paper published in Astronomy and Astrophysics.
"It’s truly mind-blowing that we’re able to study details like the chemical makeup and weather patterns of a planet at such a vast distance," says Bibiana Prinoth, a PhD student at Lund University, Sweden, and ESO, who led the companion study and is a co-author of the Nature paper.
Now, all eyes are on ESO’s Extremely Large Telescope (ELT), currently under construction in Chile’s Atacama Desert, and its ANDES instrument.
"The ELT will be a game-changer for studying exoplanet atmospheres," says Prinoth.
"This experience makes me feel like we’re on the verge of uncovering incredible things we can only dream about now."
Read both papers at Nature and Astronomy and Astrophysics.
