An international team led by astronomers from the University of Geneva (UNIGE) used the James Webb Space Telescope (JWST) to detect for the first time that the exoplanet WASP-107b is escaping a large amount of helium, forming a huge cloud and flowing away from the planet into space. The discovery, published in the journal Nature Astronomy, reveals how atmospheric outgassing processes shape planetary evolution over time.
WASP-107b is located more than 210 light-years from Earth, orbiting only one-seventh of the distance from Mercury to the Sun. Although it is close to Jupiter in size, its mass is only one-tenth of that. It belongs to the rare "super floating" exoplanet category. Its low-density atmosphere is easily affected by the strong radiation of the star and escapes. Through infrared observations, researchers captured helium flow in the outer "exoatmosphere" of the planet's atmosphere, both in front and behind, extending to nearly ten times the planet's radius, and began to block the star's light even before the planet transited.
Observations also confirmed that the planet's atmosphere contains water vapor, as well as chemical mixtures such as carbon monoxide, carbon dioxide and ammonia, but no methane was detected. This provides clues for reconstructing the formation history of WASP-107b: the planet initially formed in a distant region far from its current orbit and later moved closer to the star, causing the atmosphere to expand and accelerate gas loss. Yann Carteret, a doctoral student in the Department of Astronomy at the University of Geneva, said that atmospheric escape models confirmed the existence of these helium trails, which is crucial to understanding the dynamics of "super floating" planets.
This study highlights that atmospheric escape plays a key role in exoplanets. The Earth loses about 3 kilograms of atmosphere (mainly hydrogen) every year, but for planets close to stars, this process is more intense, which may explain why nearby Venus loses water resources and even erodes the atmospheres of some rocky exoplanets. Vincent Bourrier, a senior lecturer at the University of Geneva, pointed out that such observations can help explain the observational characteristics of exoplanet populations and provide a benchmark for future exploration.