Escaping helium atmosphere identified on the rocky exoplanet LHS 1140b

Star system: LHS 1140 | Distance from the Sun: 48.8 light years

Spectroscopic observations have identified escaping helium from the atmosphere of LHS 1140b, a rocky exoplanet located within the habitable zone of its host star. While scientists have previously observed atmospheric loss on massive gas giants, such evidence for rocky, Earth-like worlds is rare. This finding provides significant insight into the evolution and composition of planetary atmospheres in systems orbiting low-mass stars.

The findings were based on near-infrared transit spectra, which analyze the light filtering through a planet's atmosphere as it passes in front of its host star. Data captured in 2024 showed clear absorption signatures of helium. However, these signatures were absent in 2025, suggesting that the rate of atmospheric escape is time-variable rather than a constant process.

The absence of hydrogen and the presence of helium indicate an upper atmosphere that has been stripped of lighter elements, leaving heavier gases behind. This process is consistent with atmospheric fractionation, where lighter gases escape more easily over time. Interestingly, no similar helium escape was detected on LHS 1140c, a smaller and more intensely irradiated neighbor in the same system.

Key findings
- Helium gas is escaping from the upper atmosphere of the rocky exoplanet LHS 1140b.
- Atmospheric escape from LHS 1140b shows significant time variability between 2024 and 2025.
- The upper atmosphere appears to be dominated by helium and depleted of hydrogen.
- No evidence of escaping helium was found for the companion planet LHS 1140c.
- Observations support atmospheric fractionation models for rocky planets near low-mass stars.

Scientific study

Helium escaping from the atmosphere of a nearby rocky exoplanet orbiting in a habitable zone (external link)