Stunningly heavy in the distance

It is more than twice as heavy as iron and yet barium can apparently float in exotic atmospheres: astronomers have discovered the heaviest known element in the atmospheres of exoplanets in the gas shells of two planets from “Hell”. This surprising discovery now makes guesswork: It remains unclear how heavyweights can reach such great heights. It is clear that there are previously poorly understood dynamics in the atmospheres of exoplanets of the class of superhot gas giants.

Now that thousands of exoplanets have been discovered and some of them are fundamentally distinguished, astronomers are increasingly focusing on the properties of the atmospheres of distant worlds. Using transit spectroscopy, they are trying to see literally the features of gas envelopes: the formation can be recognized by spectroscopic analyzes of the light that shines through the atmosphere when the exoplanets pass in front of their host star. The signatures of radiation received by telescopes allow conclusions to be drawn about the occurrence of certain substances.

Infernal realms on the horizon

In the present case, the two exoplanets WASP-76 b and WASP-121 b were the focus of a team of astronomers led by Tomas Azevedo Silva of the University of Porto. These are called superhot Jupiters. This is what they are called celestial bodies, their size corresponds to the size of the giants of our solar system, but extremely high temperatures of more than 1000 ° C in some cases. This is because they circle their host stars so closely – they often only take a day or two to do so. These conditions lead to strange traits, as previous research has shown. In the case of WASP-76 b, astronomers have already found evidence that iron vapor seeps into the atmosphere and eventually condenses again there, forming iron rain. WASP-121 b also showed traces of strange air operations.

Now Azevedo Silva and his colleagues have once again taken a closer look at the atmospheres of the two hells. To analyze the flash of starlight through the atmosphere, the team used the ESPRESSO instrument at the Very Large Telescope at the European Southern Observatory (ESO) in Chile. In addition to the known material signatures, they were amazed to find the imprint of a special item. “We weren’t expecting or looking for barium. Then we had to make sure that it really came from the planet, because it hadn’t been detected on an exoplanet before,” says Azevedo Silva. But it was confirmed: barium is found in the upper atmospheres of WASP-76 b and WASP-121 b.

Mysterious heavyweight

Surprisingly enough, barium is 2.5 times heavier than iron. It is the heaviest element ever found in the atmosphere of an exoplanet. “It seems puzzling and paradoxical: How could such an element be found in the upper layers of the atmosphere of these planets?” says Azevedo Silva. Barium enters the earthly sky only through bombardment: it is responsible for the effects of the bright green color of fireworks. But researchers are now wondering what natural process could cause the barium to rise on these exoplanets. “Given the high gravity of the planets, we would expect heavy elements such as barium to sink rapidly,” explains co-author Olivier Demangeon of the University of Porto.

“The presence of this heavy element is indicative of unexpected atmospheric dynamics,” the scientists wrote. “At the moment, we are not yet clear about the mechanisms,” Dimanjohn says. He and his colleagues hope that atmospheric models will shed light on this phenomenon. In any case, the new results now show that the superheated Jupiter’s class of planets is even stranger than previously thought.

Source: European Southern Observatory, technical article: Astronomy and Astrophysics, doi: 10.1051/0004-6361/ 202244489

© wissenschaft.de – Martin Vieweg