🪐 Helium Leak on Exoplanet WASP-107b

An international team has observed gigantic clouds of helium escaping from the exoplanet WASP-107b. Obtained with the James Webb Space Telescope, these observations could be modelled thanks to tools developed at UNIGE. Their analysis, published in the journal Nature Astronomy, provides valuable clues for understanding this atmospheric escape phenomenon, which influences the evolution of exoplanets and shapes some of their characteristics.

Sometimes a planet's atmosphere escapes into space. This is the case for Earth, which loses, irrevocably, a little more than 3 kg (about 6.6 pounds) of matter every second (primarily hydrogen). This process, called "atmospheric escape," is of particular interest to astronomers studying exoplanets located very close to their star. Heated to extreme temperatures, they are precisely subjected to this phenomenon, which plays a major role in their evolution.


These are valuable clues for tracing the history of WASP-107b's formation and migration.

Thanks to the James Webb Space Telescope, an international team - including scientists from UNIGE as well as McGill, Chicago, and Montreal universities - was able to observe immense flows of helium gas escaping from the planet WASP-107b. This exoplanet is located more than 210 light-years from our solar system. This is the first time this chemical element has been identified by JWST on an exoplanet, allowing for a detailed description of the phenomenon.

A "Cotton Candy" Planet

Discovered in 2017, WASP-107b is seven times closer to its star than Mercury, the closest planet to our Sun. Its density is very low because it is the size of Jupiter but possesses only one-tenth of its mass. These planets are sometimes nicknamed "cotton candy planets," their low density reminiscent of the candy.

The vast helium flow was detected in the continuation of its atmosphere, called the "exosphere." This cloud partially blocks the star's light even before the planet passes in front of it. "Our atmospheric escape models confirm the presence of helium flows, at the front and back of the planet, extending in the direction of orbital motion over nearly ten times the planet's radius," explains Yann Carteret, a PhD student at the Department of Astronomy of the Faculty of Science at UNIGE and co-author of the study.

Valuable Clues

In addition to helium, astronomers were able to confirm the presence of water and traces of chemical mixtures (carbon monoxide, carbon dioxide, ammonia notably) in the planet's atmosphere while noting the absence of methane, which JWST is capable of detecting. These are valuable clues for tracing the history of the formation and migration of WASP-107b: the planet formed far from its current orbit, then moved closer to its star, which would explain its bloated atmosphere and gas loss.

This study serves as a reference for better understanding the evolution and dynamics of these distant worlds. "Observing and modeling atmospheric escape is a major area of research in the Department of Astronomy at UNIGE, as it is thought to be responsible for some characteristics observed in the exoplanet population," specifies Vincent Bourrier, a senior lecturer and researcher in the Department of Astronomy of the Faculty of Science at UNIGE and co-author of the study.

"On Earth, atmospheric escape is too weak to drastically influence our planet. But it is thought to be responsible for the absence of water on our close neighbor, Venus. It is therefore crucial to understand well the mechanisms at work in this phenomenon, which could erode the atmosphere of some rocky exoplanets," he concludes.