For the first time, scientists have detected barium in the atmosphere of two exoplanets. Never had such a heavy element been identified at high altitude in the sky of a distant world. This unexpected discovery was made by ESPRESSO, the spectrograph developed by UNIGE.
The worlds that populate the Universe beyond the Solar System can be particularly exotic. Two years ago, David Ehrenreich, professor at the Observatory of the University of Geneva, conducted research on the giant and ultra-hot exoplanet WASP-76 b on which, in the evening, it’s raining iron. Yes, metallic rain.
>> An ESO video presenting the strangest exoplanets (possibility to choose French subtitles):
>> Consult a NASA gallery on the same theme: Strange New Worlds
And this time, the same instrument developed by Switzerland which operates on the Very Large Telescope, ESPRESSOdetected in the atmosphere of this same planet and another ultra-hot gas giant barium, an element two and a half times heavier than iron, reveals a study with participation from Geneva and the National Research Center PlanetS published in Astronomy & Astrophysics.
A piece of pure barium in a protective atmosphere of argon gas. [Curnen/Public Domain – Wikimedia]It is the heaviest element ever detected in the sky of an exoplanet – atomic number 56. Its Greek root, βαρύς, means exactly that: “heavy”.
The high altitude, a surprise
“It is in a way an accidental discovery”, explains in a UNIGE press release Tomás Azevedo Silva, doctoral student at the University of Porto and the Instituto de Astrofísica e Ciências do Espaço (IA) in Portugal, who conducted 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.”
Finding this element so high in the atmosphere is “curious and counter-intuitive”, according to him. This suggests that this category of exoterres is even stranger than previously thought.
WASP-76 b and WASP-121 b are among the ultra-hot Jupiter-like planets (read box) the best studied: many chemical elements have already been identified by spectroscopy – ESPRESSO’s specialty – as signatures of their atmospheric dynamics. Both of these worlds possess strong gravity, and therefore it should in theory pull barium into the deep layers of the heavens or blast it to the ground.
Extreme weather
Barium was brought to high altitudes through mechanisms that scientists do not yet understand: “Their atmospheres are almost stellar,” notes David Ehrenreich, who also participated in this research. “We also found cobalt and strontium. All the natural elements, or almost, of the periodic table can be there, as in the atmosphere of our Sun”.
And to specify that this similarity with a star only exists on the day side of these worlds which radiate strongly: “On the night side, everything remains very hot. But we don’t really know if the barium sinks, condenses, or if it rains, as is the case with iron … It will depend on the conditions prevailing at night and the properties of the vapors of these metals. It is an extreme and unknown meteorology”, he summarizes on the phone , joined by RTSinfo.
Who knows…millions of years from us, the ultra-hot gas giants WASP-76 b and WASP-121 b may have permanent fireworks in their skies. [Ken Thomas – Public Domain/Wikimedia]If iron is present in the evening, but not in the morning on WASP-76 b and WASP-121 b, astronomers have not been able to determine whether this is also the case for barium, the instruments not having the precision needed for the time.
Permanent fireworks?
On Earth, pyrotechnic specialists use barium for green explosions and iron for gold.
Millions of light-years from our blue planet, with these two metals in their atmospheres, these mysterious burning exoplanets may have permanent polychrome fireworks in their skies…
Stephanie Jaquet
