A Scorching Planet Grew Two Tails ⚡ экспресс
Atmospheric outflow from short-orbit planets is studied using the metastable helium triplet. Only a few cases have shown absorption outside of transit, indicating hydrodynamic outflow, but its scale remained unknown due to fragmentary observations. For the first time, continuous monitoring of the full helium phase curve was conducted for the ultra-hot Jupiter WASP-121b using JWST/NIRISS. Absorption was detected over ~60% of the orbit at >3σ, revealing powerful outflow with leading and trailing tails. From Doppler shifts and persistent absorption at large distances, it was found that the gas remains in a collisional regime: the leading tail is denser and moves toward the star, while the trailing tail moves away, with a blueshift due to radiation pressure. The structure qualitatively matches theory, but self-consistent models do not yet reproduce it, limiting the accuracy of mass-loss estimates. For detailed dynamics, ground-based observations of the triplet are needed, supplemented by continuous JWST curves for absolute calibration.
Planet WASP-121b orbits so near its star that the fierce heat boils its atmosphere away, streaming like a comet's tails. With the James Webb Space Telescope, astronomers continuously watched this process for the first time. They found that helium from the atmosphere is pulled into two enormous plumes, stretching across 60% of the orbit—hundreds of millions of kilometers. One tail, pushed by stellar radiation, surges ahead of the planet and falls onto the star. The other trails behind and escapes into space. The planet is morphing into a comet-like body, shedding its gaseous envelope. Such twin tails had never been seen in their full extent before. This helps us understand how swiftly gas worlds perish under alien suns. The observations relied on a special glow from helium, allowing light analysis to detect even the thinnest layers of the atmosphere—like peering deep into space weather.
🎯 The unique glow of helium lets us peek into the uppermost, bloated layers of exoplanet atmospheres—regions where ordinary light can't reach.