WASP-96b is a hot Saturn with no clouds

Artist's representation of WASP-96b (Image courtesy Engine House. All rights reserved)
Artist’s representation of WASP-96b (Image courtesy Engine House. All rights reserved)

An article published in the journal “Nature” describes a research on the exoplanet WASP-96b. It’s a hot Saturn, meaning a gas giant with a Saturn-like mass and an orbit close to its star which has as a consequece a high temperature on its surface. A team of researchers led by Nikolay Nikolov of the British University of Exeter used the FORS2 spectrograph mounted on ESO’s VLT to study WASP-96b discovering strong traces of sodium, an observation possible only in the absence of clouds in its atmosphere.

About 980 light years away from Earth, the star WASP-96 is slightly larger and more massive than the Sun but is much older, with an estimated age of about 8 billion years. The exoplanet WASP-96b was discovered in 2013 using the transit method, meaning when observing its star from the Earth the planet passes in front of it.

The mass of the exoplanet WASP-96b is similar to that of Saturn but its orbit is very close to its star with the consequence that its year lasts about 3.4 days. It’s very hot, with a surface temperature estimated at about 1,300 Kelvin, so the gas it’s made of is very expanded compared to normal gas planets and its size is about 20% higher Jupiter’s.

Many gas giant exoplanets of that type have already been discovered over the years and cataloged in the hot Jupiter category. WASP-96 has a mass similar to Saturn’s so it’s been called a hot Saturn. The FORS2 (FOcal Reducer/low dispersion Spectrograph 2) instrument mounted on the Very Large Telescope (VLT) in Chile allowed to verify how the light of its star was filtered while passing through this planet’s atmosphere with very interesting results.

In particular, the surprise came from the complete trace of the presence of sodium, which is an abundant element but can be detected in that way only if the atmosphere is completely devoid of clouds. This is a very rare case, in fact Nikolay Nikolov stated that he and his team examined the spectra of more than 20 exoplanets and WASP-96b was the only one to show those characteristics.

Sodium is expected to be normally present in the atmosphere of gas giants but is rarely detectable in that way. A cloudless exoplanet such as WASP-96b doesn’t block the traces of other molecules in its atmosphere so the researchers intend to keep on studying it with various telescopes.

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