Detecting an atmosphere in LHS 1140 b resolves a question that has been limiting the search for potentially habitable worlds: at least one rocky planet in the habitable zone of another star has managed to retain an atmosphere for billions of years. The result, published in Science on July 16, 2026, came from the detection of helium escaping from the upper layers of the planet.
This, however, does not equate to the discovery of life. The study found no organisms, biosignatures, oceans or an Earth-like atmosphere. He answered an earlier, more basic question: is there enough gas around this planet for us to talk about an atmosphere and start investigating it in more detail?
The authors' answer is yes, with an important caveat: the helium signal was detected in the 2024 observations, but did not reappear in 2025. The group interprets the difference as possible variation in atmospheric escape. External researchers also highlight that a new detection would be important to reinforce observational confirmation.
What was observed in LHS 1140 b
LHS 1140 b is about 49 light-years from the Sun and takes approximately 24.7 days to complete one orbit. The study calculates a mass of 5.60 ± 0.19 times that of Earth and a radius of 1.730 ± 0.025 Earth radius. The combination is compatible with a predominantly rocky interior accompanied by some less dense component, which may involve atmosphere and a significant amount of water.
On September 23, 2024, researchers followed the transit of the system with the WINERED spectrograph, installed on the Magellan Clay telescope, at the Las Campanas Observatory, in Chile. When LHS 1140 b passed in front of the star, absorption appeared close to the infrared lines characteristic of metastable helium, at around 10,833 angstroms.
The main absorption reached approximately 1.24%, and the apparent extent of the material responsible for the signal corresponded to approximately 1.52 times the radius of the planet. There was also absorption before the start of the transit, compatible with a gas tail located ahead of the planet in its orbit.
The group evaluated alternative explanations, including activity from the star and interference from Earth's atmosphere, and attributed the signal to a flow of gas leaving the planet, heated by the star's X-ray and extreme ultraviolet radiation.
There is also a useful contrast within the system itself. LHS 1140 c, a smaller planet and much more irradiated than LHS 1140 b, transited the same star just 39 minutes earlier that night. The researchers did not detect helium escaping from it. This result is compatible with the possibility that LHS 1140 c has lost a large part of its atmosphere, although the absence of helium alone does not allow us to reconstruct its entire atmospheric history.
Why finding helium means finding an atmosphere
The observed helium is not a static layer photographed around the planet. It is in the upper regions of the atmosphere and some of this gas is escaping into space.
This may seem contradictory: how can an atmosphere be discovered precisely because it is being lost?
Because the gas that escapes must come from some atmospheric reservoir. The study's models indicate that the upper atmosphere of LHS 1140 b is very rich in helium and poor in hydrogen. The current escape would be caused mainly by high-frequency energy received from the star.
The authors estimated atmospheric loss rates of the order of 2 × 10⁸ to 4 × 10⁸ grams per second, depending on the stellar spectrum adopted in the model. Although this may seem like a huge amount, it is low enough to be compatible with the survival of an atmosphere during the long history of the system, whose minimum estimated age is approximately 3.1 billion years.
The result has another important nuance: the detection of a helium-dominated upper atmosphere does not mean that the entire atmosphere of LHS 1140 b is composed mainly of helium.
The authors themselves argue that gases and heavier elements can remain trapped in the lower regions. At the inferred escape rate, elements such as oxygen, carbon, and nitrogen are too heavy to be efficiently entrained with the observed flow. The composition near the surface, therefore, can still be quite different from that seen in the upper layers.
Being in the habitable zone does not make LHS 1140 b habitable
LHS 1140 b receives approximately 42% of the stellar energy that the Earth receives from the Sun. Without considering atmospheric effects and adopting zero albedo, the study calculates an equilibrium temperature of 226 ± 4 kelvin, around -47 °C. These parameters place the planet within the so-called habitable zone of its star.
“Habitable zone”, however, describes an orbital range in which certain atmospheric conditions could allow liquid water. It is not a certification that this water exists, much less that a planet is suitable for life.
To know the real conditions of LHS 1140 b it would still be necessary to determine factors such as atmospheric pressure, greenhouse effect, chemical composition, heat circulation and presence or absence of water on the surface.
Previous observations with James Webb had already made the planet especially interesting. In 2024, JWST data ruled out extensive atmospheres dominated by hydrogen in the tested scenarios and found an indication, still of low statistical significance, compatible with an atmosphere of higher molecular weight, possibly rich in nitrogen. The same work highlighted that LHS 1140 b could still be a world with a lot of water.
New helium detection strengthens the case that an atmosphere exists. It does not, however, confirm the hypothesis of a nitrogen-rich atmosphere nor the presence of an ocean.
Why discovery matters for the search for life
The advance is less in what helium says about organisms and more in what it allows us to ask from now on.
- Shows that a temperate rocky planet can retain an atmosphere around a red dwarf. This was a critical point because stars of this type can emit high-energy radiation capable of removing planetary atmospheres, especially during more active phases of their evolution.
- It turns LHS 1140 b into a concrete atmospheric target. Instead of trying to characterize a planet without knowing whether it has an observable atmosphere, astronomers now have direct evidence of gas escaping from its upper layers.
- Demonstrates a technique applicable to other worlds. The signal was detected with high-resolution spectroscopy from the ground. Similar models could help choose which rocky planets deserve more expensive and contested observations with space telescopes.
- Allows you to compare two planets in the same system. The presence of helium escape in LHS 1140 b and its absence in LHS 1140 c are compatible with the idea of the “cosmic coastline”, a proposed boundary between worlds capable of preserving atmospheres and worlds that lose them.
It's an advance on potential habitability, not biology.
What the discovery didn't show
To avoid confusing categories of evidence, the result does not represent detection of:
- life;
- a biosignature;
- biologically produced oxygen;
- organisms or biological activity;
- liquid water on the surface;
- an ocean;
- climate similar to Earth;
- an Earth's atmosphere in composition or pressure.
Helium, in this case, functions as a physical marker of the presence and escape of the upper atmosphere. It is not presented by the study as a signature of life.
The signal of 2025 is the main caution
The observation supporting the discovery was made in September 2024. When LHS 1140 b was observed again in September 2025, the helium signal did not appear above the detection limit.
The authors reprocessed the datasets with an independent approach and maintained the difference. In their models, plausible changes in the star's ultraviolet and X-ray radiation or in the temperature of the upper atmosphere could cause the signal to fall below the sensitivity of the 2025 observation. Therefore, they interpret the behavior as variable atmospheric escape.
This does not automatically invalidate the 2024 detection, but it makes new observations particularly important. Laura Kreidberg, of the Max Planck Institute for Astronomy and not involved in the study, told Science News that another detection would help confirm that the atmosphere is indeed present.
It is an important distinction to follow the discovery without transforming a recent scientific result into greater certainty than the evidence itself allows.
The question has changed
For years, one of the difficulties of astrobiology was finding rocky planets in temperate regions and discovering whether they still had an atmosphere. LHS 1140 b offers the first clear observational answer in such a case: at least one of these worlds appears to have managed to maintain it.
Now the question is no longer just “is there an atmosphere?” and it becomes “what atmosphere is this?”.
Future observations will need to retest helium escape and investigate deeper regions of the atmosphere where heavier gases may be present. It is this work — identifying composition, pressure, climate and eventually water that will make it possible to assess whether LHS 1140 b is just a planet with an atmosphere or an environment truly compatible with habitability.
Life remains a much more distant hypothesis.
The discovery is important precisely because we do not need to call the planet inhabited to recognize the advance: before looking for biological signs on a temperate rocky world, it is necessary to demonstrate that there is an atmosphere where these signs could emerge and be observed. LHS 1140 b has just passed this stage.
