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JWST Delivered The Most Detailed Analysis Yet Of An Exoplanet’s Atmosphere

New observations reveal clouds, chemical composition, and even the formation of a distant planet.


Dr. Alfredo Carpineti

Senior Staff Writer & Space Correspondent

clockNov 22 2022, 16:00 UTC
A sun-like star is shown on the left side illuminating a bluish planet. Clouds are visible in the sulight.
This artist impression shows what exoplanet WASP-39b could look like. Image credit: NASA, ESA, CSA, Joseph Olmsted (STScI)

JWST has shown its potential to study the atmospheres of exoplanets in full. Back in August, astronomers announced the first unequivocal detection of carbon dioxide in the atmosphere of WASP-39b. More observations have also revealed sulfur dioxide, the first time it has been seen on an exoplanet, and evidence of how that chemical is created via starlight, which is also a first. They also gained an understanding of the cloud coverage on the exoplanet and hints at how it formed.

If you think that’s a lot when it comes to an exoplanet located 700 light-years away, you’d be right. This is the best understanding of an atmosphere for a world beyond the Solar System that scientists have achieved. The observations were part of the “Transiting Exoplanet Community Early Release Science Program”, and they have delivered something truly incredible.


WSP-39b is a puffed-up version of Saturn, having roughly the same mass but orbiting much closer to its star, which in turn is slightly smaller than the Sun. It orbits in just four days, being about one-eighth of the distance between Mercury and the Sun away from its star.

By being so close, astronomers can study its atmosphere when the planet transits in front of the star. Some of the starlight is filtered through the atmosphere, and JWST can use this filtered light to work out the chemical composition of the air in this distant world.

“These early observations are a harbinger of more amazing science to come with JWST. We put the telescope through its paces to test the performance, and it was nearly flawless – even better than we hoped,” Max Planck Institute for Astronomy director Laura Kreidberg, who is a member of the Transiting Exoplanet Community Early Release Science Program, said in a statement.

“Data like these are a game changer,” echoes Natalia Batalha, of the University of California at Santa Cruz, who coordinated the program.


Back in August, the carbon dioxide observations revealed the presence of an unknown feature. Thanks to the new data, astronomers can tell that it is sulfur dioxide. Water molecules, abundant in the atmosphere of WASP-39b, can be split apart by starlight, and hydrogen atoms interact with hydrogen sulfide. This leads to the formation of first sulfur oxide and then sulfur dioxide. This whole process is a photochemical reaction, the first time this has been confirmed on an exoplanet.

The chemical composition of this planet’s atmosphere has also allowed researchers to work out something about the past of the planet. By looking at the relative proportion of carbon to oxygen, potassium to oxygen, and sulfur to hydrogen, the team believes that the planet formed due to the accretions of smaller bodies.

Also, given that there’s a lot more oxygen than carbon in the atmosphere, the team believes it formed much further away from the star and then migrated inwards. The team can also tell that the atmosphere has clouds made of sulfides and silicates; but, rather than a blanket of clouds, they are distributed in a more broken-up way.

The incredible findings are reported in a series of papers some accepted for publication in Nature and some under review.  

spaceSpace and PhysicsspaceAstronomy
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  • exoplanet,

  • JWST,

  • Astronomy,

  • exoplanet atmosphere,

  • WASP-39b