Scientists find exoplanet with an atmosphere completely free of clouds

The exoplanet is similar to Saturn in mass and exceeds the size of Jupiter by 20 per cent

Scientists at the University of Exeter claim to have found an exoplanet with an atmosphere that is completely free of clouds.

Described as a "pivotal breakthrough" in the pursuit of better understanding of planets beyond our solar system, the discovery was uncovered by an international team of astronomers, led by the University's Dr Nikolay Nikolov.

Using the 8.2m Very Large Telescope in Chile, the team found it is cloud-free after studying the atmospheric composition of the 'hot Saturn' exoplanet, named "WASP-96b2, when it passed in front of its host-star..

Published in research journal Nature, the scientists' results indicate that the planet is a typical 1300K hot gas giant similar to Saturn in mass and exceeding the size of Jupiter by 20 per cent. It also periodically transits a sun-like star 980 light years away in the southern constellation Phoenix, halfway between the 'southern jewels' Fomalhaut and Achernar.

"Just like an individual's fingerprints are unique, atoms and molecules have a unique spectral characteristic that can be used to detect their presence in celestial objects. The spectrum of WASP-96b shows the complete fingerprint of sodium, which can only be observed for an atmosphere free of clouds," the researchers claimed.

They added that it has long been predicted that sodium exists in the atmospheres of hot gas-giant exoplanets and, in a cloud-free atmosphere, it would produce spectra that are similar in shape to the profile of a camping tent.

"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, making the planet a benchmark for characterisation," added Nikolo.

"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 and hazes are known to exist in some of the hottest and coldest solar system planets and exoplanets. The presence or absence of clouds and their ability to block light plays an important role in the overall energy budget of planetary atmospheres.

Professor Jonathan J. Fortney, the study's co-author, added: "It is difficult to predict which of these hot atmospheres will have thick clouds. By seeing the full range of possible atmospheres, from very cloudy to nearly cloud-free like WASP-96b, we'll gain a better understanding of what these clouds are made of."