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Sodium In Hot Saturn WASP-96b Suggests Exoplanet Has Cloud-Free Atmosphere

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Astronomers have reported detecting atmosphere free of clouds in exoplanet WASP-96b, a hot gas giant similar to Saturn in mass.

Detecting Fingerprint Of Sodium In Hot Saturn WASP-96b

In a new study published in the journal Nature on May 7, Nikolay Nikolov, from the University of Exeter, and colleagues used the 8.2-meter Very Large Telescope in Chile to study the atmosphere of the hot Saturn when it passed in front of its parent star.

By measuring the decrease of starlight as the planet transits, the researchers were able to determine the composition of WASP-96b's atmosphere.

Just like human fingerprints that are unique, atoms and molecules have unique spectral characteristics. The spectrum of planet WASP-96b reveals a complete fingerprint of sodium, which happens to be only observable in cloud-free atmospheres.

"We report an optical transmission spectrum for the 'hot Saturn' exoplanet WASP-96b obtained with the Very Large Telescope, which exhibits the complete pressure-broadened profile of the sodium absorption feature," the researchers wrote in their study.

"The spectrum is in excellent agreement with cloud-free, solar-abundance models assuming chemical equilibrium."

Cloud-Free WASP-96b

Scientists have long predicted that sodium is present in the atmospheres of hot gas giant planets. Researchers said that WASP-96b, however, is so far the only exoplanet they found that appears completely free of clouds.

"We've been looking at more than twenty exoplanet transit spectra. WASP-96b is the only exoplanet that appears to be entirely cloud-free and shows such a clear sodium signature," Nikolov said.

"Until now, sodium was revealed either as a very narrow peak or found to be completely missing. This is because the characteristic 'tent-shaped' profile can only be produced deep in the atmosphere of the planet and for most planet clouds appear to get in the way."

Clouds In Atmospheres Of Planets

Researchers said that seeing the range of possible atmospheres from very cloudy to nearly cloud-free such as that seen in WASP-96b may shed more light on the composition of clouds believed to exist in the atmosphere of some of the coldest and hottest planets. It is currently difficult to predict which of the hot atmospheres have thick clouds.

Clouds and their capacity to block light have an important role in the total energy budget of planetary atmospheres.

The researchers hope that WASP-96b will offer more opportunity to determine the abundance of other molecules such as carbon monoxide, water, and carbon dioxide in future observations.

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