Using the European Southern Observatory’s Very Large Telescope (ESO’s VLT), a team has discovered the heaviest element ever detected in an exoplanet’s atmosphere: barium. The surprise came from the discovery of barium at high altitudes in the atmospheres of the ultra-hot gas giants WASP-76 b and WASP-121 b, two exoplanets orbiting stars outside our Solar System. This unexpected discovery raises questions about what these exotic atmospheres can be like. In the words of Tomás Azevedo Silva, a PhD student at the University of Porto and the Institute of Astrophysics and Space Sciences (IA) in Portugal, who led the study published in the journal Astronomy & Astrophysics, “the puzzling and counterintuitive part is: why is there such a heavy element in the upper layers of these planets’ atmospheres?” WASP-76 b and WASP-121 b are no ordinary exoplanets. Both are within the class of ultra-hot Jupiters, as they are comparable in size to our gas giant, while having extremely high surface temperatures rising above 1000°C. This is due to their proximity to their host stars, which also means that an orbit around each star is completed in just one or two days. This gives these planets rather exotic characteristics; on WASP-76 b, for example, astronomers suspect that it rains iron. But even so, the scientific community was surprised to detect barium, which is 2.5 times heavier than iron, in the upper atmospheres of WASP-76 b and WASP-121 b. “Given the high gravity of planets, we would expect heavy elements like barium to quickly fall to the lower layers of the atmosphere,” explains co-author Olivier Demangeon, also a researcher at the University of Porto and the IA. “This was, in a way, an ‘accidental’ discovery,” says Azevedo Silva. “We weren’t expecting or looking for barium in particular, and we had to verify that it was indeed coming from the planet, as it had never been seen on any exoplanet before.” Even stranger planets than thought The fact that barium was detected in the atmospheres of these two planets suggests that this category of planets might be even stranger than previously thought. Although we occasionally see barium in our own skies, such as in the bright green color of fireworks, the question for the scientific community is what natural process could cause this heavy element to be at such high altitudes on these exoplanets. “At the moment, we are not sure what the mechanisms are,” explains Demangeon. In the study of exoplanet atmospheres, ultra-hot Jupiters are extremely useful. As Demangeon explains, “Being gaseous and hot, their atmospheres are very large and therefore easier to observe and study than those of smaller or cooler planets.” Determining the composition of an exoplanet’s atmosphere requires highly specialized equipment. The team used the ESPRESSO instrument, installed on ESO’s VLT in Chile, to analyze starlight that had been filtered through the atmospheres of WASP-76 b and WASP-121 b. This allowed them to clearly detect several elements, including barium. MORE INFORMATION news No Billionaire Dennis Tito, the first space tourist, will travel to the Moon with SpaceX news No Spanish researchers believe that many black holes could be ‘fake’ These new results show that we have only scratched the surface of the mysteries surrounding exoplanets. With future instruments such as ANDES (ArmazoNes high Dispersion Echelle Spectrograph), which will operate on ESO’s upcoming Extremely Large Telescope (ELT), the astronomical community will be able to study the atmospheres of large and small exoplanets, including those of rocky Earth-like planets, at much greater depth and gather more clues about the nature of these strange worlds.
