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Strange Winds Blow Through this Exoplanet’s Atmosphere
Some exoplanets have characteristics totally alien to our Solar System. Hot Jupiters are one such type. They can have orbital periods of less than 10 days and surface temperatures that can climb to well over 4,000 K (3,730 °C or 6,740 °F). Unlike any planets in our system, they’re usually tidally locked.
Astronomers probed the atmosphere of one hot Jupiter and found some strange winds blowing.
The planet is WASP-121 b, also known as Tylos. It is about 860 light-years away from Earth in the constellation Puppis. It has about 1.16 Jupiter masses and a radius about 1.75 times that of Jupiter. It’s extremely close to its main sequence star and completes an orbit every 1.27 days. Tylos is tidally locked to its star, and its dayside temperature is 3,000 Kelvin (2,730 °C or 4,940 °F), qualifying it as an ultra-hot Jupiter.
“It feels like something out of science fiction.”Julia Seidel, European Southern Observatory
Since its discovery in 2015, Tylos’ atmosphere has been studied many times. Researchers found water in its stratosphere and hints of titanium oxide and vanadium oxide. They’ve also detected iron and chromium, though some subsequent studies failed to replicate some of these findings.
In new research, scientists examined Tylos’ atmosphere in greater detail with the four telescopes that make up the VLT. With help from the VLT’s ESPRESSO instrument, the researchers found powerful winds blowing through the exoplanet’s atmosphere and confirmed the presence of iron and titanium. The results are in two new papers.
“Even the strongest hurricanes in the Solar System seem calm in comparison.”Julia Seidel, European Southern Observatory
The first paper, “Vertical structure of an exoplanet’s atmospheric jet stream,” was published in Nature. The lead author is Julia Seidel, a researcher at the European Southern Observatory (ESO).
The second is “Titanium chemistry of WASP-121 b with ESPRESSO in 4-UT mode,” which was published in the journal Astronomy and Astrophysics. The lead author is Bibiana Prinoth, a PhD student at Lund University, Sweden, who is also with the European Southern Observatory.
Some of the researchers involved are co-authors of both papers.
“Ultra-hot Jupiters, an extreme class of planets not found in our solar system, provide a unique window into atmospheric processes,” the authors of the Nature paper write. “The extreme temperature contrasts between their day- and night-sides pose a fundamental climate puzzle: how is energy distributed?”
An artist’s impression of Tylos, also known as WASP-121 b. Image Courtesy: NASA, ESA, Q. Changeat et al., M. Zamani (ESA/Hubble)
“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,” said Julia Seidel, the lead author of the study published in Nature.
With the power of the VLT and ESPRESSO, the researchers were able to study Tylos’ atmosphere in detail. No other exoplanet atmosphere has ever been studied in such detail and to such depth. The researchers created a 3D map of the atmosphere, revealing distinct layers and winds.
Tylos’ atmosphere is divided into three layers, with iron winds at the bottom, followed by a very fast jet stream of sodium, and finally, an upper layer of hydrogen winds. This kind of climate has never been seen before on any planet. Image Credit: ESO/M. Kornmesser
“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,” said Seidel. 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.
“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, Lund University and the European Southern Observatory
The VLT has an interesting design and is billed by the European Southern Observatory as “the world’s most advanced visible-light astronomical observatory.” It has four main units with 8.2-meter primary mirrors and four smaller, movable auxiliary ‘scopes with 1.8-meter primary mirrors. When working together with the ESPRESSO instrument, the VLT operates as a single, powerful telescope. This combined power meant that the VLT gathered ample data during a single transit of Tylos in front of its star.
“The VLT enabled us to probe three different layers of the exoplanet’s atmosphere in one fell swoop,” said study co-author Leonardo A. dos Santos, an assistant astronomer at the Space Telescope Science Institute. The researchers traced the movement of the winds by tracking the movements of different elements: iron, sodium, and hydrogen correspond to the deep, mid, and shallow layers of the atmosphere. “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.
This diagram shows the structure and motion of the atmosphere of the exoplanet Tylos (WASP-121b). The exoplanet is shown from above in this figure, looking at one of its poles. The planet rotates counter-clockwise in such a way that it always shows the same side to its parent star. One side is perpetual day, and the other is perpetual night. The transition between night and day is the “morning side,” while the “evening side” represents the transition between day and night; its morning side is to the right, and its evening side is to the left. Image Credit: ESO/M. Kornmesser
The observations revealed an exoplanet atmosphere with unusual complexity.
When Tylos crosses in front of its host star, known as a transit, atoms in the planet’s atmosphere absorb specific wavelengths of starlight, which was measured with the VLT’s ESPRESSO instrument. With that data, astronomers reconstructed the composition and velocity of different layers in the atmosphere. An iron wind blows in the deepest layer, away from the point of the planet where the star is directly overhead. Above the iron layer is a very fast jet of sodium that moves faster than the planet rotates. The sodium jet accelerates as it moves from the planet’s morning side to its evening side. The upper layer is made of hydrogen, where the wind blows outwards. The hydrogen layer overlaps with the sodium jet below it.
The authors explain that this unusual planet is more than just an oddity. Its unusual characteristics make it a great testbed for Global Circulation Models. “By resolving the vertical structure of atmospheric dynamics, we move beyond integrated global snapshots of the atmosphere, enabling more accurate identification of flow patterns and allowing for a more nuanced comparison to models,” the authors explain.
The study published in Astronomy and Astrophysics is also based on data from the VLT and ESPRESSO. It uncovered more details of Tylos’ atmosphere, including its chemistry. “The transmission spectrum of WASP-121 b has been extensively studied using the cross-correlation technique, resulting in detections and confirmations for various atoms and ions, including H I, Mg I, Ca I, V I, Cr I, Fe I, Ni I, Fe II, Ca II, and K I, Ba II,” the authors write. “We confirm all these detections and additionally report detections for Ti I, Mn I, Co I Sr I, and Sr II.”
“This experience makes me feel like we’re on the verge of uncovering incredible things we can only dream about now.”Bibiana Prinoth, Lund University and the European Southern Observatory
The researchers found titanium just below the jet stream. This finding is interesting because previous research detected titanium and subsequent research refuted that. “We attribute the capability of detecting Ti I to the superior photon-collecting power enabled by using ESPRESSO in 4-UT mode compared to a single 1-UT transit and to improvements in the application of the cross-correlation technique,” the authors explain.
The cross-correlation technique is a powerful method for studying exoplanet atmospheres. Light from the atmosphere is much fainter than light from the star and can be obscured by the much stronger starlight. The cross-correlation technique helps overcome this by comparing the observed spectrum with the known “template” spectrum of specific molecules and atoms expected to be present in the atmosphere.
This figure shows the two-dimensional cross-correlation function of H I, Li I, Na I, Mg I, K I, Ca I, Ti I, V I, Cr I, Mn I, Fe I, Fe II, Co I, Ni I, Ba II, Sr I and Sr II. The last panel shows the cross-correlation function for the entire atmospheric model. Image Credit: Prinoth et al. 2025.
“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,” said Bibiana Prinoth, lead author of the Astronomy and Astrophysics paper.
“The 4-UT mode of ESPRESSO, with its effective photon collecting area equivalent to that of a 16-meter class telescope, serves as a valuable test-bed for pushing the limits of S/N on relatively faint targets,” the authors write in their conclusion.
The study of exoplanet atmosphere with ground-based telescopes will soon get a big boost. In 2028, the long-awaited Extremely Large Telescope should begin operations. It will have a 39.3-metre-diameter primary mirror, giving it 250 times more light-gathering area than the Hubble. It will also feature powerful instruments to probe exoplanet atmospheres.
“The present analysis also allows us to anticipate the observational capabilities of the soon-to-be-commissioned ELT, particularly with regard to time-resolved studies of exoplanet atmospheres,” the authors write.
Who knows what further strangeness is waiting to be discovered in exoplanet atmospheres?
“The ELT will be a game-changer for studying exoplanet atmospheres,” said Prinoth. “This experience makes me feel like we’re on the verge of uncovering incredible things we can only dream about now.”
Press Release: First 3D observations of an exoplanet’s atmosphere
Research: Vertical structure of an exoplanet’s atmospheric jet stream
Research: Titanium chemistry of WASP-121 b with ESPRESSO in 4-UT mode
The post Strange Winds Blow Through this Exoplanet’s Atmosphere appeared first on Universe Today.
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