The exoplanets WASP-76 b and WASP-121 b are already known to be peculiar places, but a new discovery has raised even more questions about the composition of these celestial bodies. Astronomers studying the pair have discovered the heaviest element ever found in an exoplanet atmosphere, which is several times heavier than iron and suggests these ultra-hot Jupiter-like planets are even stranger than suspected.
The two exoplanets at the center of this study are no strangers to dramatic discoveries. Both orbit their host stars in tight proximity and are known to be incredibly hot, with extreme atmospheres reaching blistering temperatures in excess of 2,400° C (4,350° F), hot enough to vaporize metals like iron and vent them into space. One 2020 study even found that this could be transferred by atmospheric winds and fall to the surface as iron rain.
Scientists using the European Southern Observatory’s Very Large Telescope to study WASP-76 b and WASP-121 b have now made another perplexing discovery. The astronomers used the telescope to analyze the starlight filtering through the planets' atmospheres, enabling them to identify chemical elements hiding inside.
This revealed the presence of barium in the upper atmosphere, which is 2.5 times heavier than iron. The authors describe the discovery as “puzzling and counterintuitive,” with heavy elements like this not something you’d expect to find in the upper layers of an atmosphere.
“Given the high gravity of the planets, we would expect heavy elements like barium to quickly fall into the lower layers of the atmosphere,” explained co-author Olivier Demangeon.
Barium has not been spotted on any exoplanet before, and the researchers were therefore not looking for it specifically. The serendipitous discovery suggests this class of ultra-hot, Jupiter-like exoplanets are even stranger than we thought, and raises new questions about the makeup of their extreme atmospheres that scientists hope to answer with instruments like the European Extremely Large Telescope.
Source: European Southern Observatory
