Webb detected carbon dioxide in the exoplanet atmosphere

The James-Webb Space Telescope has delivered an exceptional first scientific result.


The James-Webb Space Telescope continues to amaze scientists. Recently, it has detected, for the first time, CO2 in the atmosphere of WASP-39b, a planet located outside the solar system.

Located almost 700 light-years from earth, the planet WASP-39b is a hot gas-giant orbiting a Sun-like star. The distance between the planet and its star is only about one-eighth the distance between the Sun and Mercury. It completes one revolution in just over four Earth days. Due to the intense insolation it receives, the planet heats up to around 900°C. 

Study co-author, an astronomy professor at the University of Geneva and NCCR PlanetS member Monika Lendl explains, “The heat causes the planet’s atmosphere to expand, making WASP-39b a third larger than Jupiter, the largest gas giant in our solar system.”

“When a planet passes directly in front of its host star, some of the star’s light passes through the planetary atmosphere before it reaches the telescope. The atmosphere filters out some colors of this light more efficiently than others, depending on factors such as its composition, thickness, and cloud content.”

series of light curves
A series of light curves from Webb’s Near-Infrared Spectrograph (NIRSpec) shows the change in brightness of three different wavelengths (colors) of light from the WASP-39 star system over time as the planet transited the star on July 10, 2022. A transit occurs when an orbiting planet moves between the star and the telescope, blocking some of the light from the star. © NASA, ESA, CSA, Leah Hustak (STScI), Joseph Olmsted (STScI)

“With the James Webb Telescope, researchers can break down light into its colors to identify characteristic “fingerprints” of different gases and determine the composition of the atmosphere.”

Thanks to Webb Telescope’s Near-Infrared Spectrograph (NIRSpec) instrument, scientists could detect the fingerprint of carbon dioxide in the light that passed through the atmosphere of WASP-39b.

Dominique Petit dit de la Roche, a researcher at the University of Geneva, co-author of the study, and NCCR PlanetS member, said, “From the first glance at the data, it was already clear that we were dealing with a spectacular discovery. For the first time, carbon dioxide has been detected on a planet outside the solar system.”

Natalie Batalha of the University of California at Santa Cruz, the leader of the international research team that carried out the observations, said, “Detecting such a clear signal of carbon dioxide on WASP-39b bodes well for the detection of atmospheres on smaller, terrestrial-sized planets as well as for measuring abundances of other gases like water and methane.”

transmission spectrum of the hot gas giant exoplanet WASP-39 b
A transmission spectrum of the hot gas giant exoplanet WASP-39 b captured by Webb’s Near-Infrared Spectrograph (NIRSpec) on July 10, 2022, reveals the first clear evidence for carbon dioxide in a planet outside the solar system. This is also the first detailed exoplanet transmission spectrum ever captured that covers wavelengths between 3 and 5.5 microns. © NASA, ESA, CSA, Leah Hustak (STScI), Joseph Olmsted (STScI)

Elspeth Lee, a co-author of the study, Ambizione fellow at the University of Bern, and member of the NCCR PlanetS, said“Understanding the composition of a planet’s atmosphere also allows insights into the origin of the planet and its evolution. Carbon dioxide molecules are sensitive tracers of the story of planet formation. The clear detection of carbon dioxide in WASP-39b gives us information about the inventory of carbon and oxygen molecules in the atmosphere. This gives us an idea of the diverse chemical processes in atmospheres under such extreme conditions and the possible rock and gas material that the planet may have picked up during its formation phases.”

Watch this Space Sparks episode to learn more about how the James Webb Space Telescope has found definitive evidence for carbon dioxide in the atmosphere of a gas giant planet orbiting a Sun-like star 700 light-years away. Credit: ESA

The NIRSpec observations of WASP-39b are only part of a larger investigation with the James Webb Telescope, which includes further comments of WASP-39b and the words of two other planets. The observations are part of the so-called Early Release Science program, which was developed to make scientific data from the James Webb Telescope available to the international research community as quickly as possible, thereby ensuring the best possible scientific use of the space telescope.

Journal Reference:

  1. JWST Transiting Exoplanet Community Early Release Science Team. Identification of carbon dioxide in an exoplanet atmosphere. Earth and Planetary Astrophysics. DOI: 10.48550/arXiv.2208.11692
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