Astronomers Confirm an Atmosphere on a Rocky Planet in the Habitable Zone

A missing piece in the search for habitable worlds

A rocky planet can orbit at the right distance from its star and still be a dead, airless world. Without an atmosphere, surface water can escape, temperatures can swing violently, and harmful radiation can reach the ground. That is why astronomers have spent years asking whether nearby rocky exoplanets can hold on to air at all.

A study published in Science now provides the clearest answer yet. Researchers detected helium escaping from LHS 1140 b, a rocky planet about 48 light-years away that circles a small red dwarf every 24.7 days. It is the first observationally confirmed atmosphere around a rocky exoplanet located in its star's habitable zone.

How the atmosphere was detected

The team watched LHS 1140 b pass in front of its star using a near-infrared spectrograph on the Magellan Clay telescope in Chile. During a transit, a tiny fraction of starlight filters through the planet's upper atmosphere. Different atoms absorb specific wavelengths, leaving chemical fingerprints in the light.

Observations taken in 2024 showed a helium signature extending away from the planet. The researchers tested alternative explanations, including contamination from Earth's atmosphere and activity on the host star, and reported that those possibilities could not explain the signal.

A second observing campaign in 2025 did not recover the same helium signature. Rather than hiding that inconsistency, the study treats it as an important clue. The escaping atmosphere may change with the star's ultraviolet output, or the plume may vary over time. The authors argue that extensive checks still support the original detection.

Why LHS 1140 b is unusual

LHS 1140 b is not an Earth twin. It has about 5.6 times Earth's mass and roughly 1.7 times its radius. It is probably tidally locked, meaning one side always faces the star. Models also allow for a world with much more water than Earth and a very different atmosphere.

What makes it compelling is the combination of rock, moderate stellar heating, relative proximity and retained air. Red dwarfs often emit intense ultraviolet and X-ray radiation capable of stripping atmospheres from nearby planets. Detecting helium loss shows that LHS 1140 b has an atmosphere to lose, even after billions of years around such a star.

This is not a detection of life

The helium comes from the thin upper reaches of the atmosphere, far above any surface where biology might exist. It does not reveal whether the lower atmosphere contains nitrogen, carbon dioxide, water vapour or gases associated with life.

The term "habitable zone" also describes orbital temperature, not actual habitability. Liquid water might be possible under the right atmospheric pressure and composition, but neither surface water nor life has been observed. Strong stellar radiation, tidal locking and atmospheric escape could still make the planet hostile.

What happens next

LHS 1140 b now becomes one of the most valuable nearby laboratories for studying how rocky planets retain and lose atmospheres. More transits can test whether the helium signal varies predictably, while future observations can search for molecules deeper in the atmosphere.

The milestone is important because it moves the field beyond finding planets of the right size and temperature. Astronomers can now begin asking the harder question: what kind of environment actually exists around one of the nearest promising rocky worlds?