Astronomers have detected helium escaping from LHS 1140 b, a planet orbiting in the habitable zone. The finding provides direct evidence that a rocky planet in such a region can retain an atmosphere. It gives scientists a new target for studying whether temperate worlds around small stars can support stable surface conditions.
LHS 1140 b is about 49 light-years from Earth. It orbits a red dwarf star every 25 days. The planet is 1.73 times Earth’s radius and about 5.6 times its mass.
The research was published in Science on July 16, 2026. Lead author Collin Cherubim and his colleagues used near-infrared transit spectroscopy to study light passing through gas around the planet. Their paper reports helium absorption during observations made in 2024.
The signal appeared as the planet passed in front of its star. Helium absorbed part of the star’s light before, during, and after the transit. That pattern indicated that helium was extending beyond the planet and escaping into space.
Nature reported that the result marks the first direct identification of an atmospheric species around a rocky exoplanet in a star’s habitable zone. The habitable zone is the region where temperatures may allow liquid water, provided the planet has suitable pressure and atmospheric conditions. It does not mean the planet is inhabited.
The discovery also does not prove that liquid water exists there.
The planet’s host is an M dwarf, the galaxy’s most common star type. These stars are smaller and cooler than the sun, but they can produce strong ultraviolet radiation and powerful flares. That radiation can strip atmospheres from nearby planets.
The Guardian reported that the LHS 1140 star is old and quiet, with few recorded flares. That calmer environment may have helped the planet retain gases for billions of years. Researchers estimate that its atmosphere may have survived for more than three billion years.
The team’s observations included another planet in the same system, LHS 1140 c. Both planets crossed their star during the same night as seen from Earth. Researchers detected no comparable helium absorption around planet c, which is smaller and receives more radiation.
The contrast gives researchers a useful comparison. One planet appears to have retained an atmosphere, while the other showed no helium signal. Their different sizes and exposure levels may help explain why some rocky worlds keep gases while others lose them.
Space.com reported that the researchers used the WINERED spectrograph with the Magellan Clay telescope at Las Campanas Observatory in Chile. The method has usually been used to examine larger gaseous planets. Cherubim applied it to a smaller rocky world after his atmospheric evolution model predicted a helium-rich upper atmosphere.
The prediction was unusual because light gases are expected to escape from rocky planets. Hydrogen is especially vulnerable, and helium can also leak into space. The study’s model suggests that hydrogen has become depleted while helium remains dominant in the upper atmosphere.
Heavier volatile compounds may remain trapped lower down.
The 2024 helium detection was not repeated during observations in 2025. ABC Science reported that the team rechecked the earlier data and considered possible false signals, including contamination from Earth’s atmosphere. The researchers said those alternatives did not account for the 2024 result.
The missing 2025 signal remains important. The original paper interprets the difference as evidence that atmospheric escape changes over time. Outside experts noted that variable helium signals are not unprecedented, but additional observations are needed.
Science News reported that LHS 1140 b is cooler than many larger planets previously observed losing helium. Its atmospheric loss rate is therefore expected to be lower. Models suggest it could retain an atmosphere for at least another billion years, even as its composition slowly changes.
The planet may eventually lose much of its helium. However, heavier gases such as nitrogen or carbon dioxide could remain. Those gases would matter more for conditions near the surface than helium detected high above the planet.
Scientists do not yet know the full atmospheric composition. Previous measurements have left two broad pictures of LHS 1140 b. It could have an Earthlike rocky interior beneath a substantial atmosphere, or it could contain much more water than Earth.
Some models favor a water-rich world with about 10 percent of its mass in water.
Phys.org reported that future observations will search for water and carbon dioxide. LHS 1140 b is included in a joint James Webb Space Telescope and Hubble Space Telescope program focused on rocky planets around dwarf stars. Researchers expect the program to test the atmospheric claim over several years.
Detecting water vapor would strengthen the case for a stable atmosphere. It could help scientists distinguish between a persistent atmospheric envelope and occasional gas released from the surface or interior. Carbon dioxide measurements would provide more information about possible surface temperatures and climate.
The current helium result comes from the upper atmosphere, far above any surface where life might exist. It does not reveal oceans, biology, or breathable air. It also does not show whether the lower atmosphere has the pressure or chemistry needed for habitability, and researchers have found no evidence of life.
The importance of the discovery is narrower but substantial. Scientists have long questioned whether rocky planets orbiting red dwarfs can hold atmospheres against intense radiation. LHS 1140 b now provides observational evidence that at least one such planet has retained gas for a large part of its history.
The finding also shows that ground-based telescopes can contribute to atmospheric studies of small planets. Escaping helium produces a larger detectable region than many gases held close to a planet. That makes it a practical marker for locating atmospheres that would otherwise be difficult to observe.
Further measurements must confirm whether the helium signal returns and determine how quickly it changes. Researchers also need to identify gases deeper in the atmosphere and improve models of the planet’s interior. Those steps will decide whether LHS 1140 b is a dry rocky world, a water-rich planet, or something unlike any world in our solar system.