Posted
AstrophysicsA heavy discovery in the atmosphere of two planets
The ESPRESSO spectrograph has detected barium around two exoplanets, at an altitude where this heavy element should not be found.
This artist’s impression shows an ultra-hot exoplanet about to transit in front of its host star. As starlight passes through the planet’s atmosphere, it is filtered by the chemical elements and molecules in the gaseous layer. With sensitive instruments, the signatures of these elements and molecules can be observed from Earth.
ESO/M. Grain fairs
An international team comprising scientists from the University of Geneva (UNIGE) and the National Research Center (PRN) PlanetS has detected the heaviest element ever found in the atmosphere of an exoplanet: barium. This feat was made possible thanks to ESPRESSO, a spectrograph developed largely by UNIGE and installed on the Very Large Telescope of the European Southern Observatory (ESO’s VLT).
Scientists were surprised to discover such an element at high altitude in the atmosphere of the ultrahot gaseous giants WASP-76 b and WASP-121 b, their strong gravity having indeed (in theory) driving it towards their deep layers. This study, to be discovered in the journal «Astronomy & Astrophysics»raises questions about the nature of these exotic atmospheres.
Geneva know-how
“This discovery once again demonstrates the effectiveness of Geneva’s know-how in the field of high-precision spectroscopy”, comments Francesco Pepe, full professor in the UNIGE Department of Astronomy, co-author of this research and main initiator of the ESPRESSO instrument. “This instrument allows us both to accurately detect new exoplanets using the radial velocity method, but also to characterize in detail the composition of the atmosphere of exoplanets, as this study demonstrates”.
WASP-76 b and WASP-121 b are not ordinary exoplanets. They are both known as ultra-hot Jupiters because they are comparable in size to Jupiter, but their surface temperatures are extremely high, exceeding 1000°C. This is explained by the proximity of these planets to their host star. Their orbit around it lasts only one to two days, which gives them rather exotic characteristics: on WASP-76 b, for example, astronomers suspect that it is raining iron.
An accidental discovery
The detection of barium is “sort of an ‘accidental’ discovery,” says Tomás Azevedo Silva, a doctoral student at the University of Porto and the Instituto de Astrofísica e Ciências do Espaço (IA) in Portugal, who led the ‘study. We weren’t expecting or looking for barium in particular and had to cross-check that it was from the planet, as the presence of this metal had never been identified on an exoplanet before.”
So, scientists were surprised to find barium, which is 2.5 times heavier than iron, in the upper layers of the atmospheres of both planets. “There must therefore be a physical mechanism that we do not know and which brings Barium into the upper layers of the atmosphere of these hot Jupiters”, explains David Ehrenreich, associate professor in the UNIGE Department of Astronomy. and co-author of the study.
very strange worlds
The fact that barium has been detected in the atmosphere of these suggests that this category of planets could be even stranger than previously thought. The question for scientists now is to determine the natural process that could cause the presence of this heavy element at such high altitudes on these exoplanets. With future instruments, such as the ArmazoNes High Dispersion Scale Spectrograph (ANDES), which will operate on ESO’s forthcoming Extremely Large Telescope (ELT), astronomers at UNIGE, PlanetS and around the world will be able to study the atmospheres of exoplanets, large and small. These instruments will also make it possible to analyze those of the rocky planets similar to the Earth, in a much more thorough way and to collect more indices on the nature of these strange worlds.