So far, astronomers have had few knowledge of the weather on foreign planets. But now it has been possible for the first time to map the gas cover of a hot gas giant three -dimensional. The EXOPLANET WASP-121B is around 900 light years away and is one of the hot Jupiders, close to their stars. Analyzes with the help of the very large telescope (VLT) of the European South Sternhewarte in Chile revealed that the atmosphere of this exoplanet includes three layers with very different dynamics: a jet stream that only flows over the day side, a deeper current that flows from the day side to the night side and one Very outside zone with radial hydrogen winds. Such a circulation pattern had never been observed on a planet, according to the astronomers.
Many exoplanets examined in more detail are among the so -called “hot Jupiter”. These are large gas planets that are very close to your star and heated up accordingly: the day side of this planet, which is usually bound in bound rotation, is up to several thousand degrees hot. The chemistry in the gas sleeves of these extrasolar gas giants is correspondingly exotic: the extreme heat turns into gaseous metals and even stable molecules. Even the night side of some hot Jupiter is so hot that it rains liquid iron there, snows titanium dioxide or form clouds from liquid minerals. At the same time, these exoplanets offer almost perfect prerequisites to examine their gas sleeves. Because she is often upgraded by her stars and her gas cover is often bloated, there is a lot of light of the star through her atmosphere when the planets are transit. Their spectrometric signatures can therefore detect and analyze astronomers relatively well. “Ultraheiss Jupiter therefore opens up a unique window in atmospheric processes,” explain Julia Seidel from the European South Sternhewarte (ESO) in Chile and her colleagues.
View into the gas cover of an ultra -shot Jupiter
In one of these ultraue exoplanets, Seidel and her team have now deciphered the three -dimensional structure of the atmosphere for the first time and analyzed their dynamics with an exoplanet. The planet is the approximately 900 light years away hot Jupiter Wasp-121b. This gas giant is around 1.6 Jupiter masses, but has around 75 percent larger diameter. “The planet is therefore heavily inflated and has a 2.5 times lower density than the Saturn,” explain the astronomers. With a circulation of only 30.6 hours, the planet circulates its star extremely close and always returns the same side. There are therefore temperatures of more than 2700 degrees on its day side, that’s enough to tear apart molecules and to evaporate metals. It is still around 1200 degrees hot on the night side. “Wasp-121b is therefore an archetypical ultra-hewn Jupiter who offers us unique chances of researching these extreme atmospheric conditions in detail,” write Seidel and her team.
For their study, the astronomers switched on the four telescopes of the very large Telescope (VLT) of the European South Sternhewarte in Chile in such a way that they work like a large telescope of 16 meters in diameter. This combined mode of the VLT collects four times as much light as a single telescopic unit and makes weaker details visible. The light captured in this mode in the transit of WASP-121B in front of its star then analyzed them using the high-resolution espresso spectrograph. With the help of these spectral data, Seidel and her colleagues were able to demonstrate the signatures of numerous elements and ions, including hydrogen, but also metals such as iron, vanadium, titanium, barium, nickel, sodium, potassium and calcium. Three of these elements – hydrogen, iron and sodium – then used the astronomers to track the atmospheric currents at different heights of the gas cover. “The VLT enabled us to examine three different layers of the atmosphere of the exoplanet in one fell swoop,” says co-author Leonardo dos Santos from Space Telescope Science Institute in Baltimore.
(Video: ESO)
Three zones with different winds
For the first time, the spectral analyzes allowed the team to reconstruct the WASP-121B planet at different heights and to map the three-dimensional structure of its atmosphere. “It is really amazing that we are able to examine details such as the chemical composition and the weather pattern of a planet at such a great distance,” says co-author Bibiana Prinoth from the University of Lund in Sweden. The evaluation showed an unexpected complexity for the gas cover of this hot Jupiter: “Our find was a surprise: a jet stream rolled material around the equator of the planet, while a separate current in the lower layers of the atmosphere of gas transported from the hot side to the cooler side” , reports Seidel. The jet stream of WASP-121B extends in the top layer of atmosphere on the day side of the planet. The speed of this windbound increases from around 13.7 kilometers per second in the morning to 26.8 kilometers per second in the evening, as the astronomers determined. This corresponds to a pace of almost 50,000 and almost 100,000 kilometers per hour. “Even the strongest hurricanes in the solar system seem calm in comparison,” says Seidel.
Another current runs below this daily side jet stream, which the astronomers could track based on the iron ions. While the jet stream runs from the morning side from the morning, this lower current transports gas from the day to the night side of the planet. There is also a third atmospheric zone above the jet stream, in which hydrogen radially flows away from the most distant point. “Such a climate has never been observed on a planet,” says Seidel. “The atmosphere of this planet is in a way that questions our understanding of the weather sequences – not only on earth, but on all planets. It feels like something from a science fiction film. ”
Source: Julia Seidel (European Southern Observatory (ESO), Chile) et al., Nature, DOI: 10.1038/S41586-025-08664-1