Barium, a chemical element with the symbol Ba and atomic number 56, is the heaviest element detected to date in any exoplanetary atmosphere.
Exoplanets hotter than about 2,000 K called ultrahot Jupiters are currently the most readily accessible laboratories for the study of exoplanet atmospheres. Their size and large atmospheric scale heights, combined with the proximity to the host stars, make them appealing targets for the study of light that is transmitted through planetary atmospheres. Two of the best examples are WASP-76b and WASP-121b. Both planets are inflated ultrahot Jupiters on orbits with periods shorter than two days and equilibrium temperatures close to 2,500 K. This gives these planets rather exotic features; in WASP-76b, for example, astronomers suspect it rains iron. Tomás Azevedo Silva, a Ph.D. student at the University of Porto and the Instituto de Astrofísica e Ciências do Espaço, and his colleagues were surprised to find barium, which is 2.5 times heavier than iron, in the upper…