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Scientists have successfully mapped the three-dimensional structure of the atmosphere of an exoplanet for the first time.
The research, published on February 18, 2025 in the journal Nature, focuses on WASP-121b, a gaseous giant located 900 light years away from Earth in the constellation Puppis.
WASP-121b, discovered in 2016, is known for its extreme weather conditions, with powerful winds that carry chemical elements such as iron and titanium across the planet’s atmosphere. These winds contribute to the formation of intricate weather patterns, unlike anything seen before on any other planet.
The study revealed that the exoplanet’s lower atmospheric layer contains iron winds, followed by a fast jet stream of sodium, with an upper layer dominated by hydrogen winds. According to the researchers, this type of climate is unprecedented in planetary science.
“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,” Julia Victoria Seidel, a researcher at the European Southern Observatory (ESO) in Chile and lead author of the study, said in a statement.
WASP-121b is massive, approximately 1.157 times the mass of Jupiter. A year on the planet lasts just 1.3 Earth days and its upper atmosphere reaches scorching temperatures of 2,537 degrees Celsius. By comparison, the surface of Mercury can only reach up to 430°C.
Researchers used the European Southern Observatory’s Very Large Telescope (ESO’s VLT) to study the atmosphere of WASP-121b. The VLT enabled them to probe three different layers of the exoplanet’s atmosphere in one fell swoop, study co-author Leonardo A dos Santos, an assistant astronomer at the Space Telescope Science Institute in Baltimore, United States, said in a statement.
“It’s the kind of observation that is very challenging to do with space telescopes, highlighting the importance of ground-based observations of exoplanets,” Santos added.
The VLT’s instrument detected signatures of multiple chemical elements, allowing the scientists to examine the various layers of the atmosphere in greater detail.
The research also revealed the presence of violent weather systems on the exoplanet. The jet stream, which rotates material around the planet’s equator, causes turbulence at high altitudes, while a lower atmospheric flow transports gas from the hot side of the planet to the cooler side, Seidel explained. One hemisphere of WASP-121b is permanently facing its star and remains intensely hot, while the opposite side is much cooler.
“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 Côte d’Azur Observatory, in France.
The study also uncovered extreme atmospheric activity, with the jet stream violently churning the atmosphere as it crosses the hot side of the planet. Seidel noted, “Even the strongest hurricanes in the Solar System seem calm in comparison.”
“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,” 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, said in a statement.
