An atmosphere has been discovered on a potentially habitable planet
For the first time, astronomers have obtained conclusive evidence of the existence of an atmosphere around a rocky planet orbiting within the habitable zone of another star. The planet in question is the super-Earth LHS 1140 b, located approximately 48 light-years away from us.
The atmosphere was revealed by helium escaping from the planet into space. The gas was detected when LHS 1140 b passed in front of its star and some of the star’s light shone through its outer atmosphere.
This discovery makes LHS 1140 b one of the most interesting targets for the search for conditions suitable for life. However, scientists have not detected any signs of life, liquid water or oxygen. Being within the habitable zone merely means that, given a suitable atmosphere, liquid water could theoretically exist on the planet’s surface.
Details
LHS 1140 b orbits a cool red dwarf – a small and relatively dim star. As a result, the planet does not receive a great deal of heat, even though it is considerably closer to its star than Earth is to the Sun. It completes one orbit in approximately 25 Earth days.
This world is markedly different from Earth. Its radius is approximately 1.7 times that of Earth’s, and its mass is about 5.6 times greater. Such objects are known as super-Earths: they are more massive than our planet, but considerably smaller than ice giants and gas giants.
To detect the atmosphere, the researchers used the WINERED spectrograph, mounted on the Magellan Clay telescope at the Las Campanas Observatory in Chile. The spectrograph breaks down the star’s light into individual spectral lines, allowing the researchers to detect characteristic signatures of chemical elements.
In September 2024, astronomers observed a rare event: first, the neighbouring planet LHS 1140 c passed in front of the star, and less than an hour later, LHS 1140 b began its transit. No traces of an atmosphere were found around the first planet. However, the instrument detected helium around LHS 1140 b.
The signal extended far beyond the visible edge of the planet. According to the authors, this is helium from the upper layers of the atmosphere, which is gradually escaping into space under the influence of the star’s radiation. Simulations have shown that the upper atmosphere of LHS 1140 b may be rich in helium and almost devoid of the lighter hydrogen.
The composition of the lower, denser layers remains unknown. These may contain heavier gases, which the planet is capable of retaining for much longer. However, the presence of water vapour, carbon dioxide, nitrogen or oxygen has yet to be confirmed.
The study has one important limitation. During follow-up observations in 2025, the helium signal could not be detected. The authors acknowledge that the rate of gas leakage may vary over time; however, further observations will be required to definitively confirm the presence of an atmosphere.
Why this is important
Astronomers have already detected atmospheres around many exoplanets, but most of these are large, hot gas giants. Their massive atmospheres are relatively easy to spot against the backdrop of their host star.
With small rocky planets, things are much more complicated. It is particularly difficult to study cool worlds located in the habitable zone: their atmospheres are thinner, and the signals available for observation are significantly weaker.
LHS 1140 b shows that some rocky planets orbiting red dwarfs can still retain a gaseous envelope for billions of years. This is important because young red dwarfs often emit intense radiation capable of stripping nearby planets of their atmospheres.
The presence of an atmosphere does not in itself make a planet habitable. However, without a gaseous envelope, it is difficult to maintain a stable temperature and liquid water on the surface. This discovery therefore leads us to the next question: what is the atmosphere of LHS 1140 b made of, and can it support a climate suitable for water?
Background
The planet LHS 1140 b was discovered in 2017. Since then, it has been regarded as one of the most promising nearby worlds for studying its atmosphere. It transits in front of its star as seen from Earth, allowing telescopes to analyse the light that has passed through the gases surrounding it.
Previous measurements of its mass and size have suggested that the planet could be either a massive rocky world or a world with a large amount of water. Some models allow for the existence of a global ocean or an ice-covered surface with a patch of open water on the permanently sunlit side.
The new study does not confirm this scenario, but it makes testing it more meaningful. If the planet has indeed retained a dense atmosphere, future observations will be able to search for water, carbon dioxide and other substances within it.
Of particular interest is the comparison of the two planets in the same system. No atmosphere has yet been detected on LHS 1140 c, which is closer to the star, whilst the more massive and cooler LHS 1140 b, judging by the helium signal, has managed to retain its atmosphere. This may help scientists understand why some rocky worlds lose their gaseous envelope, whilst others retain it for billions of years.
Source
The study by Collin Cherubim and his colleagues, ‘Helium escaping from the atmosphere of a nearby rocky exoplanet orbiting in a habitable zone’, was published in the journal *Science* in 2026.