WASP-76 b and WASP-121 b are not run-of-the-mill exoplanets. Both are known as ultrahot Jupiters, as they are comparable in size to the largest planet in the solar system, and have extremely high surface temperatures that exceed 1000°C.
This is due to their close proximity to their host stars, which also means that an orbit around each star takes only a day or two. This gives these planets quite exotic features; in WASP-76 b, for example, astronomers suspect that it rains iron .
And that’s not all, since recently a group of astronomers, using the Very Large Telescope (VLT) of the European Southern Observatory, a telescope located in Cerro Paranal, Antofagasta (Chile), discovered in both exoplanets the heaviest element ever found in the atmosphere of an exoplanet: barium, which is 2.5 times heavier than iron. The surprise was also great, due to the height in the atmospheres of the ultra-hot gas giants.
“Given the high gravity of the planets, we would expect heavy elements like barium to fall rapidly into the lower layers of the atmosphere,” explains Olivier Demangeon, co-author of the research published today in Astronomy & Astrophysics, and academic at the University of Porto. and the Institute of Astrophysics and Sciences of Space (IA) in Portugal.
“This was somewhat of an accidental discovery. We were not expecting or looking for barium in particular and we had to verify that it actually came from the planet, since it had never been seen on any exoplanet before,” adds Tomás Azevedo Silva, a doctoral student at the same university and institute as Demangeon.
The fact that barium has been detected in the atmospheres of these two ultra-hot Jupiters suggests that this category of planets might be even stranger than previously thought. Although we occasionally see barium in our own skies, like the bright green color in fireworks, the question for scientists is what natural process could cause this heavy element to be found such high altitudes on these exoplanets. “At the moment, we’re not sure what the mechanisms are,” explains Demangeon.
In the study of the atmospheres of exoplanets, ultra-hot Jupiters are extremely useful, explains the latter. “Being gaseous and hot, their atmospheres are very extensive and therefore easier to observe and study than those of smaller or cooler planets.”
The puzzling and counterintuitive part is: “why is there such a heavy element in the upper layers of the atmosphere of these planets? “, states Azevedo Silva,
The science team used the instrument ESPRESSO at ESO’s VLT in Chile to analyze starlight that had filtered through the atmospheres of WASP-76 b and WASP-121 b. This made it possible to clearly detect various elements in them, including barium.
With future instruments such as the Echelle High Dispersion Spectrograph High Resolution Frames (ANDES), which will operate on the upcoming Extremely Large Telescope (ELT) of ESO, astronomers will be able to study the atmospheres of large and small exoplanets, including those of rocky planets. similar to Earth, with much greater depth and thus be able to collect more clues about the nature of these strange worlds.