a warm cloudless Jupiter

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A team of astronomers say they have detected the first Jupiter-like planet shrouded in a cloudless atmosphere. The results of this study are published in Letters from the astrophysical journal.

WASP-62b is a gas giant first detected in 2012. Its atmosphere, however, had never been closely studied until now. As part of his thesis, doctoral student Munazza Alam, from the Harvard-Smithsonian Center for Astrophysics, worked on the characterization of exoplanets, focusing mainly on the composition of their atmosphere. WASP-62b, found at 575 light years from Earth, was one of his targets.

A surprisingly clear atmosphere for this hot Jupiter

WASP-62b is what is called a “hot Jupiter”. In other words, it is a planet similar to Jupiter, but orbiting very close to its star. Unlike “our” Jupiter, which completes one revolution of the Sun in about twelve years, this one rotates around its star in just four and a half days. This proximity to its host makes it extremely hot, hence the name “hot Jupiter”.

As part of this study, Alam relied on the Hubble telescope to perform spectroscopic analyzes (or the study of electromagnetic radiation) in order to probe the various chemical elements contained in its atmosphere. The researcher particularly focused on the presence of sodium and potassium.

Although there was no evidence of potassium in the data collected, the presence of sodium was remarkably clear (thanks to the absorption lines or “fingerprints” of the element). The presence of clouds or haze in the planet’s atmosphere would normally have obscured the full signature of sodium, and in general, astronomers can only distinguish small clues to its presence. So the fact that this item appears so clearly in the data indirectly testifies to the absence of a cloud in the atmosphere of hot Jupiter.

Artist’s impression of a hot Jupiter-type exoplanet orbiting its star. Credit: NASA / CALTECH

The JWT to probe the atmosphere of exoplanets

The find is interesting as these “cloudless planets” are extremely rare. Astronomers believe that less than 7% of exoplanets do not have it. WASP-96b, the first and only other known exoplanet with a clear atmosphere, was not discovered until 2018.

Naturally, studying these exoplanets could lead us to a better understanding of how they form. These atmospheres also facilitate the study of their chemical composition. Researchers are now hoping to be able to rely on the James Webb Telescope (JWT), which is still scheduled to launch next October for probe the atmosphere of WASP-62b more deeply.

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