It's confirmed: a planet located only 49 light-years away does indeed have an atmosphere. Named LHS 1140 b, it orbits within the habitable zone of a small red dwarf star.
LHS 1140 b is what is known as a super-Earth: its radius is about 1.7 times that of our planet and its mass is nearly 5.6 times greater. Available data indicate a rocky composition, possibly accompanied by a significant amount of water.
Size comparison of two planets of LHS 1140, including LHS 1140 b (artist's concept) with Earth.
Illustration Wikimedia
To detect its atmosphere, astronomers observed the planet as it passed in front of its star. A portion of the starlight then passes through the gases. Each chemical element absorbs certain wavelengths, leaving a measurable signature in the light spectrum.
The researchers thus detected helium escaping from the upper atmosphere of LHS 1140 b. The signal was recorded in 2024 using the Magellan Clay telescope, located in Chile.
A new campaign conducted the following year did not find this signal; this difference could stem from variable atmospheric escape. Nevertheless, the authors consider the initial observations to be a solid detection. The helium would form the upper part of a denser gas envelope.
This discovery does not yet formally prove the presence of liquid water, although evidence is increasingly consistent. The composition of the lower atmospheric layers remains unknown: they could contain nitrogen, carbon dioxide, oxygen, or water vapor, among others.
The very existence of this atmosphere, however, represents important information. LHS 1140 is a red dwarf, a category of stars that can produce intense ultraviolet radiation. This can progressively strip away the gases surrounding nearby planets, especially during the early phases of their evolution.
LHS 1140 b shows that a rocky planet located in this region can retain a gas envelope for several billion years. Future observations will now need to clarify its composition and pressure. This planet thus becomes a priority target for studying the conditions necessary for liquid water outside the Solar System.