Barium, which is 2.5 times heavier than iron , has been located thanks to the Very Large Telescope of the European Southern Observatory, in ultrahot Jupiters named WASP-76 by WASP-121 b.
The exoplanet WASP-76b is similar to an inferno where iron vaporizes and also falls from the sky as rain. The planet is tidally locked and one side gets hot enough to vaporize iron. The other side is colder and the iron atoms turn into rain.
WASP-121 b, for its part, is not an ordinary exoplanet either. It is another ultra-hot Jupiter whose surface temperature is extremely high. It is likely to harbor iron clouds, rain titanium and have 17,702 km/h winds. It’s also tidally locked, nearly twice the size of Jupiter, and on its hot day side facing the star, metals and minerals in the air evaporate. But the cooler night side features metal clouds and “rain made of liquid gems.”
an accidental discovery
Astronomers used the telescope to analyze starlight filtering through the planets’ atmospheres, allowing them to identify the chemical elements hiding inside them. This revealed the presence of barium in the upper atmosphere .
The fact that barium was detected in the atmospheres of these two ultra-hot Jupiters suggests that this category of planets might be even stranger than previously thought, as it is somewhat puzzling. The 56th member of the periodic table is the heaviest element ever discovered in the atmosphere of an exoplanet. And we have already seen: in one of the worlds it rains iron and in the other it would fall liquid sapphires and rubies.
The two planets orbit very close to their host stars and are known to be incredibly hot, with extreme atmospheres reaching scorching temperatures in excess of 2,400°C.
“The puzzling and counterintuitive part is: why is there such a heavy element in the upper layers of the atmosphere of these planets?” , explained Tomás Azevedo Silva, from the University of Porto and the Institute of Astrophysics and Space Sciences of Portugal and leader of the work published in the journal Astronomy and Astrophysics. “Given the high gravity of the planets, we would expect heavy elements like barium to fall rapidly into the lower layers of the atmosphere,” added study co-author Olivier Demangeon, a researcher at the same institutions.
Barium had not been seen on any exoplanet before, and so the researchers weren’t specifically looking for it. Their serendipitous discovery suggests that this class of ultra-hot, Jupiter-like exoplanets are even more complex than previously thought, and raise new questions about the composition of their extreme atmospheres.
“This was in a way an ‘accidental’ discovery ,” added Azevedo Silva. “We weren’t expecting or looking for barium in particular and had to verify that it actually came from the planet, as it had never been seen on any exoplanet before.”
We hope that the Extremely Large Telescope in Chile (29 meters in diameter and which would be completed this year), will help to resolve these questions.
Referencia: T. Azevedo Silva et al. “Detection of Barium in the atmospheres of ultra-hot gas giants WASP-76b & WASP-121b”. Astronomy & Astrophysics, 2022.
