A new paper reports spectroscopic evidence that the rocky exoplanet LHS 1140b is losing helium from its upper atmosphere. Using near-infrared transit observations, the researchers detect helium absorption consistent with an escaping atmospheric component. The helium signal appears in data collected in 2024, but it is not seen in 2025, suggesting the escape rate or atmospheric conditions vary over time. The authors interpret the observations as an upper atmosphere dominated by helium and depleted in hydrogen, while other volatile species are thought to remain at lower altitudes, in line with atmospheric fractionation models.
The study focuses on LHS 1140b, which orbits within the habitable zone of a nearby low-mass star. It also examines another planet in the same system, LHS 1140c, which is smaller and more strongly irradiated. For LHS 1140c, the authors report no helium absorption in the available transit spectra. The findings aim to address earlier uncertainty about whether rocky exoplanets retain atmospheres and whether such atmospheres may already have been depleted by escape processes.
