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Scientists Detect Unexpected Element Around 2 Exotic Exoplanets

One planet rains liquid gems, and the other experiences flurries of iron. And now another surprise has shown up in their atmospheres.

A reddish landscape view of an alien world. Iron rain is seen to the left of the image and wispy clouds throughout the top.
An artists's illustration shows the night-side view of exoplanet WASP-76 b. The rain you see is made of iron droplets. To the left of the image, we see the evening border of the exoplanet, where it transitions from day to night.
M. Kornmesser/ESO

On Thursday, astronomers working with the European Southern Observatory's Very Large Telescope announced a perplexing discovery. Two exoplanets, both of which are already considered highly exotic, appear to be even weirder than we thought. 

Not only do these worlds exhibit strange sci-fi characteristics -- one likely holds metal clouds from which liquid gems descend, and the other seems to rain iron rather than water -- but they also have barium in their atmospheres. 

What's the big deal about barium, you ask?

Well, this may be a breakthrough finding for astronomy because, according to the team's new study, published in the journal Astronomy & Astrophysics, it marks the heaviest element ever detected in an exoplanet's atmosphere. 

"This was in a way an 'accidental' discovery," Tomás Azevedo Silva, an astronomer at the University of Porto in Portugal and lead author of the study, said in a statement. "We were not expecting or looking for barium in particular and had to cross-check that this was actually coming from the planet since it had never been seen in any exoplanet before."

Even on Earth, barium atoms are known as pretty hefty. They're typically combined with other elements to make things like drilling fluids for oil wells, glassmaking tools and paint. In fact, the name "barium" is derived from the Greek word barys, which means -- you guessed it -- heavy.

So identifying such a medium in an exoplanet's atmosphere, where lighter elements like oxygen, carbon and hydrogen tend to reside, is fascinating.

Ultrapuzzling, ultrahot Jupiters

The extraordinary orbs, WASP-76b and WASP-121b, are both categorized as ultrahot Jupiters. While they're comparable in size to Jupiter, a giant about 11 times wider than Earth, they exhibit surface temperatures higher than 1,000 degrees Celsius. That's because they're really (really) close to their host stars. But this closeness is key to their quirks. 

First of all, such proximity, scientists believe, is what gives these worlds their oddball characteristics, like how WASP-76 b is thought to experience showers of iron, an element we use to build heavy-duty machinery here on Earth. And second, it's what makes them a great target for atmospheric observations. 

"Being gaseous and hot, their atmospheres are very extended and are thus easier to observe and study than those of smaller or cooler planets," Oliver Demangeon, study co-author and fellow astronomer from the University of Porto, said in a statement.

A bright yellow sun is seen glowing in the center of the image. In the foreground, there's a reddish planet.

An artist's impression of an ultrahot Jupiter transiting its host star.

M. Kornmesser/ESO

The team used an instrument on ESO's VLT named Espresso, which analyzes starlight passing through an exoplanet's atmosphere. Based on the properties of the starlight, it's possible to basically reverse-calculate what kind of atmosphere it had to pass through before reaching the analyzer, and therefore decode what elements live in that atmosphere. From Espresso's results, the researchers confirmed the existence of expected atmospheric elements such as hydrogen, magnesium, sodium and lithium. 

Barium was the new addition -- and it's especially intriguing, according to the scientists, that atmospheric barium wasn't just located in these planets' shields. It was specifically seen in the upper layers of those shields. If anything, it'd be more understandable for the heavy element to exist in lower layers, potentially pulled down by its own weight. A 2019 study about WASP-121 b's initial identification by the Hubble Space Telescope, for instance, even notes how the planet houses a bunch of heavy metals in its lower atmosphere.

"The puzzling and counterintuitive part is: why is there such a heavy element in the upper layers of the atmosphere of these planets?" Azevedo Silva said.

The answer? We simply don't know yet. Or as Demangeon puts it, "at the moment, we are not sure what the mechanisms are."

We have yet another exoplanet mystery waiting to be solved. And perhaps I'm thinking wishfully, but this does sound awfully like a job for everyone's favorite new astronomy toy: NASA's James Webb Space Telescope. Only time will tell.