Astronomers have made a groundbreaking discovery using the James Webb Space Telescope (JWST), observing the exoplanet WASP-121b as it loses its atmosphere in real time. This unprecedented observation reveals two massive helium tails streaming from the planet, providing insights into atmospheric escape processes that can reshape distant worlds.
Researchers from the Université de Genève (UNIGE), the National Centre of Competence in Research PlanetS, and the Trottier Institute for Research on Exoplanets (IREx) conducted the study, published in Nature Communications. For nearly 37 hours, the team monitored WASP-121b as it completed one full orbit around its star, marking the most extensive continuous observation of atmospheric escape to date.
Understanding WASP-121b and Its Environment
WASP-121b belongs to a group of planets known as ultra-hot Jupiters. These gas giants orbit very close to their stars, causing their atmospheres to reach staggering temperatures of several thousand degrees. This extreme heat allows lightweight elements like hydrogen and helium to escape into space. WASP-121b completes its orbit in just 30 hours, making its atmospheric loss particularly rapid and significant.
The research team utilized the Near-Infrared Spectrograph (NIRISS) aboard the JWST to measure how helium absorbs infrared light. They discovered that the helium gas does not escape as a single stream but instead forms two distinct tails. One tail trails behind the planet while the other stretches ahead, likely influenced by the star’s gravitational pull. These gas flows extend more than 100 times the planet’s diameter, illustrating the dramatic scale of atmospheric loss.
Significance of Continuous Observation
Previous studies of atmospheric escape relied on short observations during planetary transits, which provided limited information. The continuous monitoring of WASP-121b allowed scientists to gather detailed data on the structure and dynamics of escaping gas. Lead author Romain Allart, a postdoctoral researcher at the University of Montreal, expressed surprise at the longevity of the helium escape, stating, “This discovery reveals the complexity of the physical processes that sculpt exoplanetary atmospheres.”
The findings challenge existing numerical models that describe atmospheric escape. Although these models have been successful in explaining simple comet-like gas tails, they struggle to account for the double-tailed structure observed around WASP-121b. Co-author Yann Carteret emphasized the need for new three-dimensional simulations to better understand the interplay of gravity and stellar winds in shaping these atmospheric flows.
The JWST’s sensitivity to helium makes it an invaluable tool in exoplanet research. Future observations will help determine whether the twin-tail structure is a common characteristic among hot exoplanets. Researchers aim to refine their theoretical models to explain how various forces interact to influence atmospheric escape.
As the study concludes, Vincent Bourrier, a lecturer and researcher at UNIGE, noted that new observations often highlight the limitations of current models and drive scientists to explore new physical mechanisms. The ongoing research into exoplanet atmospheres promises to deepen our understanding of these distant worlds and their potential for habitability.
