We’ve discovered the heaviest element in an exoplanet’s atmosphere – it’s weird

Discovered less than 10 years ago, the two exoplanets WASP-76 b and WASP-121 b continue to amaze astronomers even today. This time it’s their atmosphere that holds an element that shouldn’t 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 and astrophysics. Unexpected, because the discovery by astronomers of 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 discovered an unusual element which is not supposed to be permanent in the highest layers of the atmosphere. This surprising substance is barium. They are found on Earth, also occasionally in the atmosphere. It is referred to 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. Finding her very high…” in the upper layers », the researchers note – is another. Barium is a heavy element, two and a half times heavier than iron. So it should fall back” quickly in the lower layers, especially considering the gravity of the exoplanets.

WASP-76b and WASP-121b are huge. They approach the size of Jupiter, the largest planet in the solar system, which is large enough to contain 1,300 times the size of planet Earth. Within Jupiter, gravity is approximately 2.5 times that of Earth. A person weighing 70 kg on Earth would reach a weight of about 175 kg there.

Gases like Jupiter, WASP-76b and WASP-121b have a surface temperature that this time has nothing to do. While Jupiter fluctuates between -161 and -108°C on Earth, which freezes, the two exoplanets are real ovens: more than 1,000°C. The reason is very simple: they are both very close to their star, to the point that an orbit lasts only one or two days.

Ultra-hot Jupiter near your region. Or hundreds of light years away. // Source: ESO

Do the properties of these exoplanets — which are categorized as “ultra-hot Jupiters” — play a role in keeping the barium high? Why were they only found there? For the European Southern Observatory, these recent findings are likely to make this class of exoplanets ” even stranger than we thought “. Strange, it is the case to say so: one supposes rain of iron on WASP-76 b. That is, 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 discovery, on the other hand, is in honor of the SuperWASP project (for Wide Angle Search for Planets). One was seen in the constellation Pisces, the other Canis Major, respectively in 2013 and 2015. So far we can only spot them in our galaxy.

The extreme distance of these planets – it must be remembered that the photons that make up light take hundreds of years to reach Earth, whereas they already travel at almost 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 large and small exoplanets, including the atmospheres of rocky Earth-like planets, much more thoroughly and collect more clues about the nature of these strange worlds “, enthused the astronomers. Because at the moment we don’t only scratch the surface of the mysteries of exoplanets “.


Exoplanets of the TRAPPIST-1 system.  // Source: NASA's Goddard Space Flight Center

All about this fascinating celestial object, the exoplanet

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