Posted by Astronomers may have detected an atmosphere around LHS 1140 b, a temperate rocky exoplanet about 48 light-years from Earth. But a follow-up observation has made the picture more complicated: the atmospheric signal appeared in 2024 and then was not detected again in 2025.
LHS 1140 b is a super-Earth about 70% larger in radius than our planet. It orbits a cool M-dwarf star within the star’s habitable zone, where liquid water could potentially exist under suitable atmospheric conditions. Its relatively low density also suggests that water, an atmosphere, or both may contribute to its composition. Researchers observed the planet using the WINERED near-infrared spectrograph on the 6.5-meter Magellan Clay Telescope in Chile. During a transit, some starlight passes through the planet’s atmosphere, allowing astronomers to search for absorption signatures from specific atoms.
In 2024, the team detected metastable helium at about 1.0833 micrometers. This form of helium can survive long enough in a planet’s upper atmosphere to create a detectable spectral signal. Because it is expected to occur high above the planet, the detection is consistent with gas escaping into space. The result is particularly interesting because rocky planets are generally expected to lose much of the hydrogen and helium acquired during their formation. Models suggest, however, that hydrogen may escape more efficiently than helium, gradually leaving behind a helium-enriched atmosphere.
A second observation in 2025 did not recover the helium signature. That does not necessarily mean the atmosphere disappeared – the signal may simply have weakened below the detection threshold. Variations in stellar ultraviolet and X-ray radiation, stellar wind, or the structure of the escaping atmosphere could all change how visible the helium is from Earth.
The findings do not show that LHS 1140 b is habitable or inhabited. Instead, they suggest that a small, temperate rocky planet may be able to retain an atmosphere for billions of years while still losing some gas to space. Repeated observations will now be essential. If the helium signal returns or changes again, astronomers may be able to track atmospheric escape in real time and better understand how rocky planets preserve the environments required for long-term habitability.
For more details, read the full article by SETI Institute.
