James Webb gets most detailed look yet at an exoplanet’s atmosphere

One of the big advances promised by the James Webb Space Telescope is the ability to investigate exoplanets in greater detail than ever before. Webb has already imaged its first exoplanet and made the first detection of carbon dioxide in an exoplanet atmosphere, but now astronomers have used the telescope to get the most in-depth look yet at the atmosphere of planet WASP-39 b.

Webb uses instruments called spectrometers which break light down into different wavelengths to see which ones have been absorbed by various molecules in an atmosphere. This allows researchers to see spectra of the planet’s atmosphere, telling them what elements are present, which the researchers describe as a “game changer” for the study of exoplanets.

Artist's illustration of WASP-39b displays newly detected patches of clouds scattered across the planet.
New observations of WASP-39b with the JWST have provided a clearer picture of the exoplanet, showing the presence of sodium, potassium, water, carbon dioxide, carbon monoxide, and sulfur dioxide in the planet’s atmosphere. This artist’s illustration also displays newly detected patches of clouds scattered across the planet. Melissa Weiss/Center for Astrophysics | Harvard & Smithsonian

This planet is very hot, orbiting its host star every four days. In the atmosphere, researchers found water and confirmed the previous finding of carbon dioxide, but most importantly they found sulfur dioxide for the first time. This is created by light from the star interacting with the atmosphere and creating new molecules, and this is the first time that this photochemistry has been observed on an exoplanet.

Learning about an exoplanet’s atmosphere is important not only for understanding the planet as it is now but also for understanding how it formed in the past. ‘‘The moment I first saw the results of my analysis was probably the most exciting moment of my career to date,’’ said one of the researchers, Dominique Petit dit de la Roche, in a statement. ‘‘The chemical inventory of WASP-39b suggests that the planet was assembled by a succession of mergers with smaller bodies, and that its formation originally took place far from the central star.”

The research is early release, meaning it has not yet been published in an academic journal. It is presented in five papers, three of which are accepted and two of which are under review for the journal Nature.

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