Overview
- Astronomers tracked WASP-121 b with JWST’s NIRISS for roughly 37 hours, spanning more than one full orbit and capturing pre- and post-transit helium absorption.
- The planet exhibits two distinct helium structures—a trailing tail pushed by radiation and stellar wind and a leading tail curved toward the star—extending beyond 100 times its diameter and persisting over more than half an orbit.
- The complex, long-lived outflow suggests atmospheric escape must be modeled in 3D with explicit star–planet interactions rather than as a simple, single-tail flow.
- The WASP-121 b results appear in Nature Communications from a team including Université de Montréal and the University of Geneva, with Geneva-developed models used to interpret the data.
- Separately, a UNIGE-led Nature Astronomy study reports JWST’s first helium detection on an exoplanet, WASP-107b, along with water, carbon monoxide, carbon dioxide and ammonia but no methane, hinting at formation farther out and possible links to population patterns such as the Neptune desert.