Astronomers are perplexed: how does barium enter the exoplanet’s atmosphere?

Updated 10/17/2022 12:09

  • WASP-76b and WASP-121b are two exoplanets that belong to the gas planets and are located hundreds of light years from Earth.
  • Astronomers are basically good at studying their atmospheres.
  • Now they have discovered a heavy element they weren’t expecting at all – and that really shouldn’t even exist.

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The two exoplanets WASP-76b and WASP-121b contain the heavy element barium in their upper atmosphere. This is demonstrated by the high resolution spectra obtained with the Very Large Telescope of the European Southern Observatory ESO in Chile. It is the heaviest element so far detected in the atmosphere of the planets around other stars.

And it poses a problem for astronomers: with the strong gravitational pull of the two planets, there shouldn’t be such heavy substances in the atmosphere, the discoverers write in the journal “Astronomy & Astrophysics”.

Experts don’t know which mechanism transports barium to altitude

“The barium should fall from the upper atmosphere very quickly,” explains Olivier Demangeon of the University of Porto in Portugal. “At this moment we have no idea which mechanism carries this element upward.” The two planets, 640 and 860 light-years from Earth, are “hot Jupiters” – gas planets similar in size and mass to Jupiter in our solar system.

However, they orbit their central star in a very narrow orbit with an orbital period of less than two days. Due to the star’s proximity, the temperature of the atmosphere is around 2,000 degrees Celsius.

Such planets are particularly useful observation objects for astronomers. “Because they are mostly gaseous and very hot, they have extended atmospheres,” says Demangeon, “so we can observe and study their atmospheres much more easily than those of smaller, colder planets.” The position of the planetary orbits also helps sky researchers in these observations: they are oriented in such a way that the planets regularly pass in front of their central star when viewed from Earth.

The atmosphere leaves a kind of fingerprint in part of the starlight

During these “transits”, the planets obscure part of the star, dimming its light – and these regular eclipses help discover the planets. Crucial to studies such as that of Demangeon and his colleagues is that a small portion of starlight shines through each planet’s atmosphere.

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In this part of the starlight, the atmosphere leaves a sort of fingerprint: the materials that make up the atmosphere absorb the light of the stars at characteristic wavelengths.

Researchers can then use these “spectral lines” to identify the substances that make up the planet’s atmosphere. However, the whole process is long and complicated. First, the researchers need a high-resolution spectrograph, a special add-on device on the telescope that breaks down the radiation into its wavelengths. And then astronomers have to eliminate all influences from the star and even from the Earth’s atmosphere from the data.

Experts did not expect barium

Demangeon and his colleagues were initially able to confirm a large number of substances that had already been indicated by previous observations. The researchers also discovered new cobalt and strontium. And then they came across spectral lines of barium and initially doubted that they actually came from exoplanets.

“We didn’t look for barium,” says Azevedo Silva of the University of Porto, “because we didn’t expect barium there.” Only after further checks did the scientists become convinced of their surprising discovery.

According to the researchers, the detection of barium in the atmospheres of two hot Jupiters indicates that such heavy elements can often be found in the atmospheres of extremely hot juveniles. There must be previously unknown atmospheric currents carrying these substances into the upper atmosphere. (ff / dpa)

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Mars, Jupiter, Saturn: For decades, probes have been sending impressive images of the planets of our solar system and their moons to Earth. Note: This image gallery is constantly updated.

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