The James Webb Space Telescope has once again become the focus of the scientific community. This time, astronomers used its capabilities for extended observation of the exoplanet WASP-121b, which has long drawn attention for its unusual atmospheric phenomena. As a result, researchers not only detected the planet’s atmospheric escape, but also discovered two elongated helium structures stretching into space for dozens of planetary radii.
WASP-121b is what’s known as an ultrahot Jupiter, orbiting its star in just 1.275 days. Its mass is greater than Jupiter’s, and its radius is nearly twice as large. The surface temperature reaches up to 2,350 Kelvin, making the planet’s atmosphere extremely unstable and highly susceptible to the star’s powerful radiation. This is precisely what led to the formation of the unusual tails that scientists can now study in detail.
For nearly 37 hours, the telescope recorded changes in the spectrum related to helium absorption. Such an extended observation period allowed scientists to track the dynamics of atmospheric loss not only during the planet’s transit across its star, but also throughout other phases of its orbit. This marks a real breakthrough in the study of exoplanetary atmospheres.
Atmospheric flows
Data analysis has shown that WASP-121b generates two helium streams. The first, the leading stream, forms ahead of the planet and is marked by a rapid increase in density. Scientists suggest that some of this gas may even flow back toward the star, beginning accretion near the fourth Lagrange point. The second, the trailing stream, extends behind the exoplanet and gradually dissipates under the influence of the stellar wind.
Between these streams lies the planet itself, with a remarkably inflated thermosphere. The atmosphere is so expanded that it extends beyond the Roche lobe, indicating intense tidal interactions between WASP-121b and its star. Such phenomena were previously observed only in fragments, but now a complete picture has emerged.
The length of the helium tails is staggering—they stretch across 107 exoplanet radii, which is about 0.1 astronomical units. This distance is comparable to that from Earth to the Sun, highlighting the scale of these processes.
Hydrodynamic processes
The cause of such a powerful atmospheric escape is hydrodynamic dissipation triggered by extreme heating and tidal forces. These processes cause not only light elements, such as hydrogen and helium, but also heavier substances, including alkali metals, to escape the planet’s atmosphere and disperse into interstellar space.
Previously, WASP-121b had already been the subject of close study. Its atmosphere was found to contain a stratosphere, clouds of calcium titanate, and even silicon monoxide. However, such a detailed analysis of atmospheric structures became possible only thanks to the unique capabilities of the James Webb telescope and the extended duration of its observations.
The results obtained offer a fresh perspective on the evolution of exoplanets located close to their stars. They also help explain why some planets lose a significant portion of their atmosphere and develop unusual characteristics that set them apart from the gas giants we are familiar with.
New horizons
The discovery of a complex system of helium tails around WASP-121b is a major step forward in understanding the processes occurring on exoplanets under extreme conditions. Astronomers can now not only detect atmospheric escape but also analyze its structure, speed, and composition. This paves the way for new opportunities in searching for and studying other similar objects in our galaxy.
In the coming years, observations of WASP-121b and other ultra-hot Jupiters are expected to continue. Scientists hope new data will help clarify the mechanisms behind tail formation and their impact on the long-term fate of exoplanets. Moreover, such research could shed light on the origins of statistical anomalies in the distribution of exoplanet mass and radius.
Questions remain: how long can the planet retain even part of its atmosphere? What other elements might be found in its tails? Answers to these mysteries may emerge in the near future.
The Spanish contribution
It is worth noting that Spanish astronomers were among the international team of researchers working with James Webb data. Their contribution was significant for interpreting spectral data and modeling atmospheric flows. Spain continues to strengthen its position in space research by taking part in today’s most advanced projects.
In recent years, Spanish observatories and research centers have been actively collaborating with leading global agencies, allowing specialists from the country to stand at the forefront of astronomical discoveries. WASP-121b is just one example where Spanish scientists have co-authored high-profile publications.
Such achievements are driving scientific progress in Spain and attracting the attention of young professionals to astronomy and space technology. In the future, new discoveries can be expected, with Spanish researchers set to play a key role.
In case you didn’t know, the James Webb Space Telescope is the largest and most advanced infrared telescope, launched in 2021 by an international consortium that includes NASA, ESA, and the Canadian Space Agency. Its main mission is to study the early Universe, exoplanets, and the processes of star and galaxy formation. Thanks to its unique instruments, the James Webb can obtain data unavailable to other observatories, opening up new frontiers for astronomy. Spanish scientists regularly participate in projects involving this telescope and make a significant contribution to interpreting the collected results.
