The atmosphere of an exoplanet in unparalleled detail

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Atmosphere of an exoplanet in unparalleled detail

Artistic illustration of the atmosphere of the exoplanet WASP-39 b.

Atoms, molecules, signs of chemical reactions and clouds. Components present in the atmosphere of the exoplanet WASP-39 b have been identified by Canadian astronomers thanks to data collected in part by the Canadian instrument NIRISS (Near Infrared Slitless Imager and Spectrograph) attached to the space telescope James Webb.

The full set of data paints a picture of the molecular structure and chemical composition of the atmosphere of the planet 700 light-years from Earth, the Canadian Space Agency said in a statement.

Table showing the composition of the atmosphere of exoplanet WASP-39 b.

The team of astronomers from the University of Montreal led by Professor Björn Bennek notably detected for the first time sulfur dioxide, a molecule produced by chemical reactions triggered by ultraviolet radiation from its star.

This type of process, called photochemistry, has never before been observed outside the solar system. On Earth, the protective ozone layer in the upper atmosphere is created the same way, notes the statement released by the University of Montreal.

Others Elements were also detected in WASP-39b's atmosphere such as sodium, potassium and water vapor, confirming previous observations made with space and ground-based telescopes. Carbon monoxide was also detected.

Last August, the same team provided clear and precise evidence of the presence of carbon dioxide (CO2) in the atmosphere of this same planet.

Artistic representation showing what the exoplanet WASP-39 b could look like, according to current knowledge of the planet.

The planet WASP-39 b orbits a Sun-like star. The mass of this hot gas giant is about a quarter of that of Jupiter, and its diameter is 1.3 times greater.

Unlike the cooler, more compact gas giants that populate our solar system like Jupiter or Saturn, WASP-39 b orbits very close to its star, barely one-eighth of the distance between the Sun and Mercury. It completes the tour in just over four Earth days.

  • The planet was detected in 2011 using the transit technique which shows a subtle, periodic dimming of a star's light as the planet transits, or passes, in front of the star.
  • Sound atmosphere appears puffy compared to other planets, a phenomenon likely related to its high temperature of around 900°C.
  • Due to its puffy atmosphere and frequent transits, WASP-39b is a perfect target for transmission spectroscopy, which can pinpoint the composition of a planet's atmosphere through transit.
  • During a pass, some of the light from the star passes through the planet's atmosphere. This light is filtered by the atmosphere and allows its composition to be measured.
  • Thus, the signatures of different chemical elements are imprinted in the atmosphere.

The chemical inventory of WASP-39 b suggests that it was created from the collision and fusion of several smaller bodies referred to as planetesimals.

This work once again shows the great capacity of the instruments of the James Webb telescope to study exoplanets. In the coming months, the telescope will probe the atmosphere of rocky Earth-sized planets, such as those in the TRAPPIST-1 system.

Five articles dedicated to the exoplanet are published on the ArXiv website (in English).

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