Helium absorption seen during a September 2024 transit gave astronomers direct evidence that rocky exoplanet LHS 1140b is losing gas from its upper atmosphere.
WINERED observations from Chile also found helium ahead of the planet, pointing to a possible leading tail driven by high-energy radiation from its red-dwarf host star.
The 5.6-Earth-mass planet sits in the habitable zone, gets about 42% of Earth’s sunlight, and appears helium-rich but hydrogen-poor—matching predictions that lighter hydrogen escapes first over time.
No helium was detected in 2025 follow-up observations, suggesting the escape may vary or briefly drop below detection limits rather than disappear entirely.
A second planet in the system, LHS 1140c, showed no atmospheric helium, sharpening the contrast and helping scientists gauge which rocky worlds can preserve atmospheres for billions of years.