Detected less than 10 years ago, the two exoplanets WASP-76 b and WASP-121 b amaze astronomers even today. This time, it is their atmosphere that harbors an element that should not be there, especially at high altitude.
This is a discovery that is as unexpected as it is spectacular. It was announced on October 13, 2022, and published in the journal Astronomy & Astrophysics. Unexpected, because the finding of astronomers on two exoplanets (WASP-76 b and WASP-121 b) is a stroke of luck. Spectacular, because these two worlds are located 640 and 850 light years from Earth. They were scanned by the Very Large Telescope of the European Southern Observatory, based in Chile.
But, why is there barium there?
It was on this occasion that astronomers detected an unusual element, which is not supposed to be permanently in the highest layers of the atmosphere. This surprising substance is barium. They are found on Earth, including occasionally in the atmosphere. It is referenced in the periodic table of elements as an alkaline earth metal.
In this case, the detection of barium in the atmosphere of an exoplanet is one thing. To find her very high—” in the upper layers », note the scientists — is another. Barium is a heavy element, two and a half times heavier than iron. So it should fall back” rapidly in the lower layers, especially given the gravity of exoplanets.
WASP-76b and WASP-121b are huge. They approximate the size of Jupiter, the largest planet in the solar system, which is large enough to contain 1,300 times the planet Earth. On the surface of Jupiter, the gravity is approximately 2.5 times that of Earth. Someone weighing 70 kg on Earth would reach a weight of around 175 kg there.
Gases like Jupiter, WASP-76b and WASP-121b have a surface temperature which this time has nothing to do. While Jupiter fluctuates between -161 and -108°C on the ground, which is freezing, the two exoplanets are real furnaces: more than 1,000°C. The reason is very simple: they are both very close to their star, to the point that an orbit only lasts one or two days.
Do the characteristics of these exoplanets — which are categorized as “ultra-hot Jupiters” — play a role in keeping barium high? Why were they only found there? For the European Southern Observatory, these recent findings are likely to make this class of exoplanet ” even weirder than we thought “. Strange, it is the case to say it: one supposes rains of iron on WASP-76 b. That is to say the extreme conditions.
It is already the Very Large Telescope (or VLO, for Very Large Telescope) which was at work in 2020 to characterize these showers of metal. Their detection, on the other hand, is to the credit of the SuperWASP project (for Wide Angle Search for Planets). One was spotted in the constellation Pisces, the other Canis Major, respectively in 2013 and 2015. For now, we can only spot them in our galaxy.
The extreme distance from these planets – it must be remembered that the photons making up light take hundreds of years to reach the Earth, whereas they are already traveling at nearly 300,000 km/s in a vacuum, and that there is nothing faster — makes it difficult to observe these distant worlds. But, future instruments are planned.
” With future instruments, […] astronomers will be able to study the atmospheres of exoplanets large and small, including those of rocky Earth-like planets, much more thoroughly and gather more clues about the nature of these strange worlds », enthuse the astronomers. Because for the moment, we don’t only scratch the surface of the mysteries of exoplanets “.
