Scientists Detect Helium Atmosphere on LHS 1140 b
Astronomers have, for the first time, confirmed the presence of an atmosphere around LHS 1140 b, an Earth‑sized rocky world orbiting a cool red dwarf 48 light‑years from Earth. The detection, announced on 16 July 2026, shows the planet is wrapped in a thin, helium‑rich shroud (according to official data). "An atmosphere is essential for a planet to support life as we know it," said Collin Cherubim, lead author and recent Harvard Ph.D. graduate, during the press briefing. "But finding helium on a rocky world this small is unexpected; it challenges our current understanding of how planets lose their primordial gas."
The finding arrives just as the next generation of space telescopes, such as the James Webb successor, prepares to scan dozens of nearby worlds for biosignatures. LHS 1140 b has long been a target of interest due to its high density—roughly 6.6 times the mass of Earth and 1.7 times its radius—suggesting a composition dominated by rock and iron, much like our own planet. However, the presence of a gaseous envelope adds a layer of complexity to its classification. The helium component makes up roughly 70 % of the detected gases, with traces of hydrogen and heavier molecules. Spectroscopic data were collected over 12 nights in June 2026, totalling 36 hours of exposure, revealing an extended exosphere that reaches several planetary radii into space.
This discovery is not merely a cataloging of atmospheric components; it validates theoretical models that predict atmospheres can survive on low‑mass planets despite the harsh radiation environments often associated with M-dwarf stars. It also offers a tangible target for future studies of atmospheric chemistry beyond our solar system, shifting the focus from merely detecting atmospheres to understanding their longevity and composition. The detection of helium, specifically, suggests that the planet's atmosphere may be undergoing hydrodynamic escape, a process where light gases are blown away by stellar radiation, providing a unique laboratory for studying atmospheric erosion in real-time.
Harvard Team Uses Chilean Telescope to Unveil Atmosphere
The breakthrough came from a collaborative effort led by Harvard's Department of Earth and Planetary Sciences, employing the high‑resolution spectrograph mounted on the 8.2‑metre Very Large Telescope (VLT) at the Paranal Observatory in Chile's Atacama Desert. Over a fortnight in early June, the team recorded the minute dimming of the host star LHS 1140 as the planet transited, allowing them to isolate the spectral fingerprints of gases escaping the planet's limb. This technique, known as transmission spectroscopy, relies on the principle that a planet's atmosphere filters starlight, absorbing specific wavelengths that betray the chemical makeup of the gas.
By comparing the observed spectra with laboratory‑measured absorption lines, analysts identified a distinct helium signature at 1083 nm. This particular wavelength corresponds to a metastable state of helium that is excited by stellar radiation. Unlike hydrogen, which is best detected in ultraviolet wavelengths that are largely blocked by Earth's atmosphere, the helium line at 1083 nm sits in the near-infrared, a window accessible to ground‑based telescopes. "The VLT's stability and the dry Atacama air gave us the precision needed to tease out a signal that is less than one part in ten thousand," explained Dr Emily Lupu, senior researcher at the Carnegie Institution, who co‑authored the paper.
The team also cross‑checked the results with data from the Gemini South telescope, ensuring that instrumental artefacts or stellar variability could not masquerade as a planetary signal. The helium line was detected at a signal‑to‑noise ratio of 9.2, well above the 5‑sigma threshold for a robust discovery. The planet's orbital period of 24.7 days meant that transits occurred roughly every three and a half weeks, dictating a rigorous observing schedule that required precise coordination to maximize exposure time during the brief transit windows. This meticulous approach demonstrates how ground‑based facilities can still lead exoplanet science, complementing space‑based observatories by providing high-resolution data that can disentangle planetary signals from stellar activity.
The Host Star: A Quiet Anchor in a Turbulent Galaxy
Central to the survival of LHS 1140 b's atmosphere is the nature of its host star, LHS 1140. Classified as an M4.5 red dwarf, the star is significantly cooler and smaller than our Sun, emitting the bulk of its radiation in the infrared spectrum. Red dwarfs are notorious for their volatile youth, often subjecting orbiting planets to violent flares and torrents of high-energy ultraviolet (UV) and X-ray radiation that can strip away atmospheres in the first billion years. However, LHS 1140 is estimated to be over 5 billion years old (according to official data), a geriatric by cosmic standards that has settled into a period of relative magnetic quiescence.
This stellar quiescence is a critical factor in the planet's ability to retain an atmosphere. The host star emits relatively low ultraviolet radiation compared to younger M-dwarfs, a factor that helps retain light gases like helium. "If this planet were orbiting a young, active star like TRAPPIST-1, a helium envelope of this size would likely have been blown away eons ago," noted Dr. Julien de Wit, a planetary physicist at MIT. The star's low luminosity also places the planet firmly within the habitable zone—the region where temperatures could allow liquid water to exist on the surface—despite the planet orbiting much closer to its star than Mercury does to the Sun.
However, proximity to a red dwarf brings other challenges. LHS 1140 b is likely tidally locked, meaning one hemisphere perpetually faces the star while the other faces the cold void of space. This configuration creates extreme temperature gradients that drive powerful winds, potentially redistributing atmospheric heat and gases. The interaction between the helium exosphere and the stellar wind—the stream of charged particles emanating from the star—creates a bow shock effect, which may have contributed to the extended size of the detected gas envelope. Understanding this stellar-planet interaction is key to modeling the long-term climate stability of LHS 1140 b and assessing whether liquid water could persist on its surface.
Why Helium Dominance Matters for Habitability
Helium is the second‑lightest element in the universe and, unlike hydrogen, does not readily combine with other atoms to form complex molecules. Its prevalence in LHS 1140 b's envelope suggests the planet has either retained a primordial atmosphere from its formation or is actively outgassing from its interior. In either case, the presence of a stable gaseous layer shields the surface from harmful stellar wind particles, moderates temperature swings, and could enable a water cycle if sufficient volatiles exist. However, a helium‑rich atmosphere also implies a low mean molecular weight, which can drive rapid atmospheric escape, especially around active red dwarfs.
Researchers therefore focus on the balance between escape rates and replenishment mechanisms, such as volcanic outgassing or cometary delivery. "Helium tells us the planet has not been stripped bare, which is a prerequisite for any kind of surface habitability," noted Dr Sarah Seager, a planetary scientist at MIT, who was not involved in the study but reviewed the findings. The detection also refines climate models that predict surface temperatures based on stellar irradiation and atmospheric composition. With a stellar flux of about 0.5 times that received by Earth, LHS 1140 b could host temperate conditions if greenhouse gases like carbon dioxide or water vapour are present in sufficient quantities.
However, a helium-dominated atmosphere is not automatically conducive to life. Helium is a noble gas; it is inert and does not contribute to a greenhouse effect. If the atmosphere is composed almost entirely of helium, the surface temperature would be determined primarily by the planet's albedo and atmospheric pressure, potentially leading to a cold, arid world unless heavier greenhouse gases are trapped beneath the helium layer. Ongoing observations aim to search for these heavier molecules, which would provide a clearer picture of the planet's potential to sustain liquid water. The presence of helium acts as a tracer, indicating that heavier elements might be lurking beneath, protected from the ravages of stellar erosion.
Evolutionary Crossroads: Primordial Origins or Secondary Outgassing?
The discovery of helium on LHS 1140 b places it at a critical evolutionary crossroads, forcing astronomers to reconsider the dividing line between rocky Super-Earths and gaseous Mini-Neptunes. In planetary formation theory, the