These simulated views of the ultrahot Jupiter WASP-121b show what the planet might look like to the human eye from five different vantage points, illuminated to different degrees by its parent star. The images were created using a computer simulation being used to help scientists understand the atmospheres of these ultra-hot planets. (Credit: NASA/JPL-Caltech/Vivien Parmentier/Aix-Marseille University (AMU))
In a nutshell
- Scientists have mapped the three-dimensional structure of an exoplanet’s atmosphere for the first time, discovering three distinct layers of wind patterns on WASP-121b, including a powerful equatorial jet stream that accelerates to nearly 100,000 kilometers per hour
- The planet’s unique atmospheric structure shows winds flowing in different directions at different altitudes – with iron-rich gases moving from the hot dayside to the cold nightside in the deepest layer, while a massive jet stream circles the planet’s equator in the middle layer
- This discovery challenges current theoretical models of how planetary atmospheres work and provides crucial data for improving our understanding of weather patterns on worlds beyond our solar system
SANTIAGO, Chile — Forget hurricanes and heat waves—on WASP-121b, the weather is on another level. Astronomers have mapped, for the first time, the three-dimensional structure of an exoplanet’s atmosphere, revealing ferocious winds that accelerate to record-breaking speeds as they cross the planet’s scorching-hot dayside.
Located about 900 light-years away in the constellation Puppis, the planet WASP-121b (nicknamed Tylos) experiences weather patterns unlike anything seen before in our cosmic neighborhood. This massive gas giant orbits so close to its star that a year there lasts only about 30 Earth hours, creating extreme conditions that have fascinated astronomers.
Zooming in on WASP-121b’s atmosphere
The study, conducted with the European Southern Observatory’s (ESO) Very Large Telescope, uncovered an atmosphere so extreme that it challenges current models of planetary weather.
“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 lead author Julia Victoria Seidel, from the ESO in Chile, in a statement.
Published in Astronomy & Astrophysics, the study shows that WASP-121b’s atmospheric structure exists in distinct layers. In the deepest observable layer, iron-rich gases flow from the scorching hot dayside to the cooler nightside. Above this flows a powerful equatorial jet stream that accelerates as it crosses the dayside of the planet. The uppermost layer contains hydrogen gas influenced by both the jet stream below and the natural outward flow of the planet’s escaping atmosphere.
The jet stream’s behavior proved particularly dramatic. As gases in this atmospheric river cross from the planet’s morning side to its evening side, they heat up by nearly 1,000 degrees Celsius and almost double their speed from 13.7 to 26.8 kilometers per second. For comparison, Earth’s most powerful jet streams reach speeds of only about 100 meters per second. “Even the strongest hurricanes in the Solar System seem calm in comparison,” notes Seidel.
The international research team achieved this breakthrough by combining the light-gathering power of four large telescope units into a single signal using an instrument called ESPRESSO. This sophisticated setup allowed them to detect the signatures of multiple chemical elements as they moved through different layers of the planet’s atmosphere.
“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. “It’s the kind of observation that is very challenging to do with space telescopes, highlighting the importance of ground-based observations of exoplanets.”
ESO/M. Kornmesser)
A companion study published alongside this research revealed another surprise: the presence of titanium just below the jet stream. This discovery was particularly intriguing since previous observations had shown this element to be absent, suggesting it might be hidden deep in the atmosphere where it’s harder to detect.
‘Climate never seen before on any planet’
Ultra-hot Jupiters like WASP-121b serve as natural laboratories for studying extreme atmospheric conditions that don’t exist anywhere in our solar system. Unlike Earth’s relatively mild temperature variations, these planets experience such extreme temperature contrasts between their day and night sides that they create powerful atmospheric dynamics scientists are only beginning to understand.
The research team observed the planet during what’s known as a transit, which is when it passes between its star and Earth. This positioning allowed them to study how different chemicals in the atmosphere affected the starlight passing through it. By analyzing these effects at different heights in the atmosphere, they could map out the complex wind patterns and temperature variations.
Current theoretical models struggle to fully explain the observed circulation patterns on WASP-121b. While scientists have used computer simulations to model atmospheric circulation on ultra-hot Jupiters, none have fully captured the complex patterns observed in this study. This discovery highlights how much we still have to learn about the physics governing these extreme worlds.
“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,” Seidel explains.
Looking ahead, the European Southern Observatory is currently constructing the Extremely Large Telescope in Chile’s Atacama Desert, which will significantly advance our ability to study other worlds.
“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, who led the companion study. “The next generation of telescopes will be game-changers for studying these distant worlds. We’re on the verge of uncovering incredible things we can only dream about now.”
Paper Summary
Methodology
The research team used the ESPRESSO instrument on ESO’s Very Large Telescope, combining light from four 8.2-meter telescopes to achieve unprecedented sensitivity. They observed WASP-121b during two separate transit events in November 2018 and September 2023. By analyzing how different chemical elements in the planet’s atmosphere affected starlight passing through it, they could map wind patterns at various altitudes.
Results
The study revealed distinct wind patterns in three atmospheric layers, with winds flowing from day to night in the deepest layer at 6-10 km/s, an equatorial jet stream accelerating from 13.7 to 26.8 km/s, and complex interactions in the upper atmosphere. They also discovered significant temperature variations, with the jet stream heating up by about 950K as it crosses the planet’s dayside.
Limitations
The researchers could only observe the atmosphere during transit events, providing limited views of the morning and evening regions. They also couldn’t obtain absolute pressure values for different atmospheric layers, relying instead on relative measurements. The study was further limited to regions where their chosen chemical tracers were present.
Discussion and Takeaways
This groundbreaking research provides the first three-dimensional view of an exoplanet’s atmosphere, challenging current theoretical models and advancing our understanding of extreme planetary environments. The findings demonstrate how sophisticated ground-based telescopes can reveal detailed information about distant worlds.
Funding and Disclosures
The research involved multiple institutions and received support from the European Southern Observatory, French National Research Agency, Swiss National Science Foundation, and various European research organizations. The authors declared no competing interests.
Publication Information
The main study, “Vertical structure of an exoplanet’s atmospheric jet stream,” was published in Nature, with a companion paper on titanium detection published in Astronomy & Astrophysics. The research represents a collaborative effort involving multiple institutions across Europe and beyond.
