Astronomers have observed an atmosphere on an exoplanet that is small and rocky like Earth and orbits its star at a distance suitable for life. While atmospheres have previously been detected on exoplanets that are much larger than Earth or extremely hot, this is the first time an atmosphere has been found on a planet with conditions suitable for life.
Harvard University Department of Earth and Planetary Sciences Professor Robin Wordsworth and researcher Collin Cherubim said on the 17th in the journal Science that they observed helium escaping from the atmosphere of the rocky exoplanet LHS 1140b, located about 48 light-years (a light-year is the distance light travels in one year, about 9.46 trillion km) from Earth.
LHS 1140b orbits LHS 1140, a small, cool star called an M dwarf. M dwarfs are stars with less mass than the sun and make up 76% of the stars near the solar system. Because their surface temperature is low and they appear red, they are also called red dwarfs.
The Harvard team detected a helium signal in the light spectrum of LHS 1140b observed in 2024 with the Magellan Clay Telescope at Las Campanas Observatory in Chile. They said there are several possible explanations, but given the shape and strength of the signal, they concluded that the helium originated from the planet itself.
The planet was first discovered in 2016 by Jason Dittmann of the University of Florida. Exoplanets outside the solar system are small and do not emit their own light, so they cannot be observed even with the most advanced telescopes.
Dittmann used the so-called transit phenomenon to find the planet. Just as a solar eclipse occurs when the moon passes between Earth and the sun and the sun loses light, a star outside the solar system also appears briefly dimmer from Earth when a planet orbiting in front of it passes by.
The Harvard team later observed in 2024 that both LHS 1140b, which orbits the red dwarf LHS 1140, and LHS 1140c, which is smaller and orbits closer in, passed in front of the star. When LHS 1140b crossed the star, the starlight dimmed at wavelengths absorbed by helium. No such signal was observed when LHS 1140c transited.
Atmospheric escape also occurs on Earth. Based on other observations, the team showed that this rocky planet is continually replenishing helium. Otherwise, the helium would already be depleted. They estimated the planet has maintained its atmosphere for 3 billion years.
Scientists have so far discovered about 6,300 exoplanets outside the solar system. Of these, 40% are rocky like Earth. That does not mean they all have environments where life can live. Some planets orbit too close to their stars and are too hot at the surface, while others orbit too far away and are too cold.
LHS 1140b lies in the so-called Goldilocks zone, where conditions are suitable for life. The term comes from the fairy tale Goldilocks and the Three Bears, which is used as a metaphor for an environment that is neither too hot nor too cold. It means the surface temperature is in a range where liquid water, essential for life, is likely to exist.
There are known to be 24 to 45 rocky exoplanets in the Goldilocks zone. None have had their atmospheres confirmed. Atmospheres are considered key to the presence of life because they protect planets from cosmic radiation and regulate climate cycles that can create a mild environment.
For now, all that is known is that the planet has an atmosphere that leaks helium; little is known about the size and composition of the atmosphere itself. Contrary to expectations, it could look entirely different from Earth. Earth and Venus are very similar in size and both have atmospheres, but Venus' surface temperature exceeds 460 degrees Celsius, making it uninhabitable.
However, Dittmann, who discovered LHS 1140b, said that considering the star type, the planet's temperature is likely similar to Earth's. The Harvard team said they plan to search for water in the planet's atmosphere with the James Webb Space Telescope over the next 4 to 5 years. If water is confirmed, it would indicate a stable atmosphere and raise the likelihood of life.
References
Science (2026), DOI: https://doi.org/10.1126/science.aea9708