In a new study published in Astronomy & Astrophysics, astronomers have discovered the heaviest element ever found in the atmosphere of an exoplanet to date. Barium was discovered at high altitudes in the atmospheres of the ultra-hot gas giants WASP-76 b and WASP-121 b. This discovery has astronomers questioning the nature of these exotic atmospheres and how such a heavy element could end up in the upper atmospheres of these planets.
WASP-76 b and WASP-121 b are characterized as ultra-hot Jupiters; these exoplanets are similar in size to our Solar System’s planet Jupiter, but are extremely hot (almost 2,000 degrees Fahrenheit, whereas the average temperature of Jupiter is minus 234 degrees Fahrenheit). The extremely hot temperatures are due to the planet’s close proximity to their host stars; these planets orbit their host stars within 1-2 Earth days, whereas Jupiter orbits the Sun in 12 years or 4,333 Earth days. These extreme conditions allow the planets to have exotic features. For example, astronomers suspect it rains iron on WASP-76 b. Even still, astronomers were surprised to find barium in the atmospheres of these two exoplanets.
Additionally, barium is 2.5 times heavier than iron. Since this is such a heavy element, and the gravity on these exoplanets is so strong, the team of astronomers was surprised to see barium in such high levels of the atmosphere. Something so heavy should quickly fall down into the lower levels of the atmosphere. This must imply that barium is being readily produced in the atmosphere to maintain these abundances. The mechanisms responsible for this heavy element’s existence at such high altitudes remains a mystery thus far.
The detection of barium was not an easy observation to make. Astronomers need to observe an exoplanet when it about to pass in front of its host star to determine the composition of its atmosphere. When the exoplanet passes in front of the star, light from the star gets absorbed by elements and molecules in the outer layers of the exoplanet. This alters the starlight that is emitted from the star, leaving unique chemical fingerprints in the spectrum of the star. Sensitive instruments must be used to make these observations. This team used the ESPRESSO instrument (Echelle SPectrograph for Rocky Exoplanet and Stable Spectroscopic Observations) on the European Southern Observatory’s Very Large Telescope in Chile to analyze the starlight that had been filtered through the atmospheres of WASP-76 b and WASP-121 b.
Source: European Southern Observatory
