Heaviest element ever discovered in exoplanet atmospheres is a puzzle

By Georgina Torbet October 15, 2022

When it comes to finding habitable exoplanets, the next big challenge is not just spotting exoplanets or looking at their orbits, but getting a better understanding of what conditions there might be like by analyzing their atmospheres. New tools like the James Webb Space Telescope will allow us to peer into the atmospheres of exoplanets and see what they are composed of, which can affect the planet’s surface temperature, pressure, and weather systems.

Now, astronomers using the European Southern Observatory’s Very Large Telescope (ESO’s VLT), a ground-based telescope located in Chile, have discovered the heaviest element ever in an exoplanet atmosphere. Looking at two ultra-hot gas giants called WASP-76 b and WASP-121 b, the researchers identified the element barium in their atmospheres.

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Artist’s impression of an ultra-hot exoplanet as it is about to transit in front of its host star. — This artist’s impression shows an ultra-hot exoplanet, a planet beyond our Solar System, as it is about to transit in front of its host star. Using the ESPRESSO instrument of ESO’s Very Large Telescope, astronomers have found the heaviest element yet in an exoplanet’s atmosphere, barium, in the two ultra-hot Jupiters WASP-76 b and WASP-121 b. ESO/M. Kornmesser

These two planets orbit extremely close to their respective stars and thus have extremely high surface temperatures which can go over 1,000 degrees Celsius. On one of the planets, WASP-76 b, it gets so got that iron falls from the sky as rain. But the researchers were surprised to find barium high in the atmospheres of these planets because it is so heavy.

“The puzzling and counterintuitive part is: why is there such a heavy element in the upper layers of the atmosphere of these planets?” said lead author Tomás Azevedo Silva of the Instituto de Astrofísica e Ciências do Espaço (IA) in Portugal, in a statement.

“Given the high gravity of the planets, we would expect heavy elements like barium to quickly fall into the lower layers of the atmosphere,” said co-author Olivier Demangeon.

The researchers still aren’t sure what is causing this very heavy element to appear in the exoplanet atmospheres, but the fact it has been identified in not one but two different hot Jupiter atmospheres is interesting. Further research will be needed to discover where this barium came from and how it stays so high in the atmosphere.

The research is published in the journal Astronomy & Astrophysics.

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