First 3D observations of an exoplanet’s atmosphere reveal a unique climate

By UdeMnouvelles Feb 18th, 2025

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In 5 seconds The first three-dimensional observations of the atmosphere of the exoplanet Tylos, in which astronomers from IREx participated, have revealed its unique climate.

Artist’s rendering of the exoplanet WASP-121b. It shows only a portion of the exoplanet, showcasing instead the three layers of its atmosphere with more detail.
Photo : ESO/M. Kornmesser

Joost Wardenier and Romain Allart, both IREx postdoctoral reseachers who contributed to the study.
Photo : Courtesy

An international team of astronomers, including Trottier Institute of Research on Exoplanets (IREx) and Université de Montréal members Joost Wardenier and Romain Allart, have peered through the atmosphere of a planet beyond the Solar System, mapping its 3D structure for the first time. By combining all four telescope units of the European Southern Observatory’s Very Large Telescope (ESO’s VLT), they found powerful winds carrying chemical elements like iron and titanium, creating intricate weather patterns across the planet’s atmosphere. The discovery opens the door for detailed studies of the chemical makeup and weather of other alien worlds.

“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, a researcher at the European Southern Observatory (ESO) in Chile and lead author of the study, published today in Nature.

The planet, WASP-121b (also known as Tylos), is some 900 light-years away in the constellation Puppis. It’s an ultra-hot Jupiter, a gas giant orbiting its host star so closely that a year there lasts only about 30 Earth hours. Moreover, one side of the planet is scorching, as it is always facing the star, while the other side is much cooler.

The team has now probed deep inside Tylos’s atmosphere and revealed distinct winds in separate layers, forming a map of the atmosphere’s 3D structure. It’s the first time astronomers have been able to study the atmosphere of a planet outside our Solar System in such depth and detail.

A climate never before observed on any other planet

“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 Seidel, who is also a researcher at the Lagrange Laboratory, part of the Observatoire de la Côte d’Azur, in France. The observed jet stream spans half of the planet, gaining speed and violently churning the atmosphere high up in the sky as it crosses the hot side of Tylos. “Even the strongest hurricanes in the Solar System seem calm in comparison,” she adds.

Joost Wardenier, a postdoctoral researcher at IREx (Université de Montréal) who contributed to the interpretation of the data with 3D atmospheric models of the planet, adds “The most powerful instrument of its kind, ESPRESSO on VLT, has provided us with a unique glimpse of the three-dimensional wind profile of WASP-121b. It is a spectacular observation that gives us key insights into the extreme climate of ultra-hot gas giants.”

To uncover the 3D structure of the exoplanet’s atmosphere, the team had to combine the light of the four large telescope units of ESO’s VLT into a single signal. This combined mode of the VLT collects four times as much light as an individual telescope unit, revealing fainter details. By observing the planet for one full transit in front of its host star, ESPRESSO was able to detect signatures of multiple chemical elements, probing different layers of the atmosphere as a result.

“The VLT enabled us to probe three different layers of the exoplanet’s atmosphere in one fell swoop,” says study co-author Leonardo A. dos Santos, an assistant astronomer at the Space Telescope Science Institute in Baltimore, United States. The team tracked the movements of iron, sodium and hydrogen, which allowed them to trace winds in the deep, mid and shallow layers of the planet’s atmosphere, respectively. “It’s the kind of observation that is very challenging to do with space telescopes, highlighting the importance of ground-based observations of exoplanets,” he adds.

Well-hidden titanium

Interestingly, the observations also revealed the presence of titanium just below the jet stream, as highlighted in a companion study published in Astronomy and Astrophysics. This was another surprise since previous observations of the planet had shown this element to be absent, possibly because it’s hidden deep in the atmosphere.

“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.

To uncover the atmosphere of smaller, Earth-like planets, though, larger telescopes will be needed. They will include ESO’s Extremely Large Telescope (ELT), which is currently under construction in Chile’s Atacama Desert.

IREx researcher Romain Allart, who contributed to securing, analysing and interpreting the data, concludes:

“The level of detail we achieved on the dynamic of Tylos is mind-blowing but only possible due to ESPRESSO’s unique capability to collect photons from the largest optical telescope. Yet, it is only a glimpse of what we will be able to do with ELT in the next decade. What an exciting time for astronomy!”