Barium, the heaviest element detected to date in the atmosphere of exoplanets

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Barium, the heaviest element detected to date in the atmosphere of exoplanets

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Artistic impression showing an ultrahot exoplanet as it is about to transit in front of its host star.

The upper atmospheres of two ultrahot gas giants contain barium, the element the heaviest ever detected in the atmosphere of exoplanets.

This accidental detection was carried out by Portuguese astrophysicists thanks to the instruments of the Very Large Telescope (TGT) of the European Southern Observatory (ESO) installed in Chile.

Artistic impression of exoplanet WASP-121 b.

This unexpected discovery raises questions about the nature of the exotic atmospheres of exoplanets WASP-76 b and WASP-121 b, note in a press release the authors of this work published in the journal Astronomy & Astrophysics.

“How could such a heavy element end up in the layers? upper atmospheres of these planets?

— Tomás Azevedo Silva, PhD student at the University of Porto

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WASP-76b and WASP-121b are among the most studied exoplanets. They are classified in the group of ultrahot Jupiters, and their orbits are so close to their host stars that the temperature on their surface exceeds 1000°C.

  • No less than 5178 exoplanets have been officially detected in more than 3874 planetary systems.
  • More than 8956 additional exoplanets are currently awaiting confirmation.

Astrophysicists already estimated that WASP-76b was raining iron, but they were surprised to detect barium, which is 2.5 times heavier than iron, in the upper layers of its atmosphere.


Illustration representing the night side of the exoplanet WASP-76 b.

“Given the strong gravity of the planets, we would expect heavy elements like barium to quickly fall to the lower layers of the atmosphere. »

— Olivier Demangeon, University of Porto

On Earth, barium can occasionally be found in the sky, as it is used to create the green color of fireworks , but the natural process that leads to the presence of this heavy element at high altitudes in these exoplanets remains to be explained.

Artistic representation of the exoplanet WASP-121b.

To determine the composition of the atmosphere exoplanets, the Portuguese team used the ESPRESSO instrument installed on the TGT. Barium was detected using the transit spectroscopy technique. As the planet passes in front of its star, the light from the star is filtered by the elements and molecules that make up the gaseous layer of the planet, which changes the starlight observed from Earth. It is thus possible to establish the chemical fingerprint of the atmosphere from the observed spectrum.

In an increasingly near future, the European Giant Telescope (which must be inaugurated in 2025) will continue to scrutinize exoplanets with its instruments, such as the ANDES spectrograph, which will analyze the atmospheres of exoplanets large and small, including those of rocky Earth-like planets.

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