Tuesday , July 27 2021

Too much UV light can turn gas planets into sad rocky nuclei

The atmosphere of a giant gas planet exoplanet located 163 light-years from Earth is being launched into space by its host star, forming a ghostly tail. Excessive ultraviolet radiation is responsible for the celestial phenomenon, according to a new study, a finding that could provide new insights into planetary formation.

The excellent WASP-69b is about the size of Jupiter, but unlike Jupiter, it is located only 6.43 million kilometers from its host star. One year on the WASP-69b lasts only 3.6 days. In a new article published in the journal Science, astronomers at the Canary Islands Institute of Astrophysics (IAC) in the Canary Islands describe how the star's ultraviolet radiation is blowing helium particles from the WASP-69b with such force that the planet's immense gravity can not contain them.

Unbelievably, the gases that emerge form a distinctly comet-like tail, which researchers have been able to detect.

Helium may be the second most abundant element in the universe, but it is notoriously difficult to detect in distant exoplanets. To sniff, a team of astronomers led by IAC's Lisa Nortmann used the CARMENES instrument, coupled with the 3.5m telescope at the Calar Alto Observatory in Spain. This tool detects nearby visible and near infrared wavelengths at high resolutions, allowing astronomers to identify specific chemical signatures such as helium and the speed at which they are moving.

Using CARMEN, astronomers observed the WASP-69b as it passed in front of its host star from our perspective on Earth, an astronomical technique known as the transit method.

"We see a stronger and longer-lasting darkening of starlight in a region of the spectrum where helium gas absorbs light," Nortmann said in a statement. "The longer duration of this absorption allows us to infer the presence of a tail."

Using the same technique, astronomers observed several other exoplanets in similar situations. None of the observed exoplanets, however, exhibited the same helium release effect, except for one – a hot Jupiter known as HD 189733b. But instead of presenting a tail, this planet was surrounded by a helium balloon, which flowed into space in multiple directions.

In a related article, also published in the journal Science, astronomers describe the exoplanet HAT-P-11b, which, like WASP-69b and HD 189733b, is also losing its helium.

So this is apparently something that happens with a select group of exoplanets. As for the reason some gaseous orbiting giants loosen their helium, while others are not known, the team resorted to a different instrument: the European Space Agency's (ESA XMM-Newton) Multiple Mirror X-ray Mission. As this telescope revealed, the smoking gun turned out to be extreme levels of ultraviolet radiation from the host stars of the planets.

In terms of the mechanism of action, the researchers theorize that the helium particles are getting super-energized by the large amount of UV radiation entering, causing the particles to leave the atmosphere into space. But this is just the theory in progress; other observations, especially with the CARMENES instrument, could shed light on this mysterious process.

This is all very cool, but this discovery can also speak to the processes of planetary formation. Eventually, the researchers speculate, gaseous giants could be completely stripped of their atmospheres. All that remained would be a compact rocky core with densities and perhaps even masses similar to Earth or Venus. It may represent a new and seemingly complicated way for rocky planets to emerge, but again, it's still just a theory.

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With that possibility in mind, astronomers must now look for rocky planets with super short orbital periods that may be the remnants of this process. Better yet, they could detect gaseous giants in the final stages of helium release, as this could be considered more convincing (for example, at cosmological distances, it might be difficult to distinguish rocky remnants of gaseous gasses evaporated from accreted rocky planets). ).

Fortunately, the next generation of telescopes, including the Transiting Exoplanet Survey Satellite (TESS) and the James Webb Space Telescope (JWST), yet to be released, may be powerful enough to do the job.


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