The heaviest element found in the atmosphere of an exoplanet

Using the European Southern Observatory’s Very Large Telescope (ESO’s VLT), astronomers have discovered the heaviest element ever found in an exoplanet’s atmosphere: barium. They were surprised to find barium at high altitudes in the atmospheres of the superhot gas giants WASP-76 b and WASP-121 b, two exoplanets, planets orbiting stars outside our solar system. This unexpected discovery raises questions about what these exotic atmospheres might be.

“The most surprising and unreasonable thing is: why such a heavy element is in the upper layers atmosphere of these planets?” says Tomás Azevedo Silva, a postdoctoral fellow at the University of Porto and the Spanish Institute of Astrophysics and Science (IA) in Portugal, who led the study, published today in Astronomy and astrophysics.

WASP-76 b and WASP-121 b are not ordinary exoplanets. Both are known as superhot Jupiters because they are comparable in size to Jupiter, but have extremely high surface temperatures of over 1000°C. It is related to them closeness to the host stars, which also means that each star only takes a day or two to orbit. This gives these planets rather exotic features; in WASP-76 b, for example, astronomers suspect iron rains.

But even so, scientists were surprised to find barium, which is 2.5 times heavier than iron, in the upper atmosphere of WASP-76 b and WASP-121 b. “Given the high gravity of the planets, we expect heavy elements like barium to quickly fall into the lower atmosphere,” explains co-author Olivier Demonjon, a researcher also from the University of Porto and IA.

“It was, in a way, an ‘accidental’ discovery,” says Azevedo Silva. “We weren’t expecting or looking for a specific barium and had to double-check that it was actually coming from a planet, because it had never been seen on any exoplanet before.”

The fact that barium was detected in the atmospheres of both of these superhot Jupiters suggests that this category of planets may be even stranger than previously thought. Although we occasionally see barium in our skies as a brilliant green color in fireworks, the question for scientists is what natural process could cause this heavy element to be in this state. great heights in these exoplanets. “At this point, we’re not sure what the mechanisms are,” Demonjon explains.

When studying the atmospheres of exoplanets, ultrahot Jupiters are extremely useful. As Demonjon explains, “being gaseous and hot, their atmospheres are very extended and therefore easier to observe and study than the atmospheres of smaller or colder planets.”

Determination of the composition of the an exoplanetThe atmosphere requires very special equipment. The team used the ESPRESSO instrument on ESO’s VLT in Chile to analyze the starlight that passed through the atmospheres of WASP-76 b and WASP-121 b. This made it possible to clearly identify several elements in them, including barium.

These new results show that we have only touched the mysteries of exoplanets. With future instruments such as the ArmazoNes High Dispersion Spectrograph (ANDES), which will operate on ESO’s Extremely Large Telescope (ELT), astronomers will be able to study the atmospheres of large and small exoplanets, including rocky planets. similar to Earth, in many ways greater depth and gather more clues as to the nature of these strange worlds.

This research was presented in the paper “Detection of Barium in the Atmospheres of the Superhot Gas Giants WASP-76b and WASP-121b,” forthcoming in Astronomy and astrophysics.