Astronomers have detected escaping helium gas around LHS 1140 b, a rocky super-Earth orbiting in the habitable zone of a nearby cool star, making it the first rocky world in such an orbit to show direct evidence of an atmosphere. The signal appeared during near-infrared transit observations in 2024 but was absent in follow-up observations in 2025, raising immediate questions about what drives the variability. The finding, produced using the WINERED spectrograph on the Magellan Telescope at Las Campanas Observatory, shifts the search for habitable worlds from theory into direct measurement and places LHS 1140 b at the center of the emerging science of atmospheric escape on temperate rocky planets.
Why escaping helium on LHS 1140 b changes the search for habitable worlds
For years, astronomers have tried and failed to confirm that rocky planets in temperate orbits can hold onto gaseous envelopes. Earlier attempts to probe LHS 1140 b’s atmosphere using Hubble’s WFC3 instrument produced only upper limits, setting no firm detection. The new result breaks that pattern. Near-infrared transit spectroscopy captured absorption consistent with metastable helium, a specific excited state of the element that traces gas streaming away from a planet’s upper atmosphere, according to the peer-reviewed helium analysis.
The detection matters because it demonstrates that a rocky planet receiving moderate starlight can still possess a gaseous layer, even as that layer actively escapes into space. If atmospheres can persist on worlds like LHS 1140 b despite ongoing loss, the pool of potentially habitable targets grows substantially. The planet orbits within the star’s nominal habitable zone, where surface temperatures could, in principle, allow liquid water if pressure and composition cooperate. A stable atmosphere is a prerequisite for that scenario, and metastable helium is one of the few tracers that can be detected with current instruments from light-years away.
Yet the disappearance of the helium signal in 2025 complicates the picture. One working explanation is that stellar activity cycles on the host star, rather than changes in the planet’s own atmospheric loss rate, control whether the helium signature is visible during any given transit. When the star emits more high-energy radiation, it can pump more helium atoms into the excited state that produces the observed spectral line, temporarily boosting the signal without fundamentally changing how much gas the planet is losing. Testing that idea would require simultaneous X-ray and helium monitoring across multiple transits to separate the star’s influence from the planet’s behavior, a level of coordination that has not yet been achieved.
More broadly, the LHS 1140 b result underscores that habitability is not a binary property but a moving target shaped by time-variable processes. A planet might cycle between phases of stronger and weaker atmospheric escape, or between periods when its upper atmosphere is more or less visible at particular wavelengths. The 2024 detection shows that the system can enter a configuration where helium is clearly detectable; the 2025 non-detection shows that such configurations are not guaranteed. For upcoming surveys that will prioritize targets for detailed atmospheric follow-up, this kind of variability will have to be folded into observing strategies.
WINERED, Magellan, and the data trail behind the detection
The observations were carried out at Las Campanas Observatory in Chile using the WINERED spectrograph mounted on the Magellan Telescope. During 2024 transit events, the instrument recorded absorption at wavelengths matching metastable helium, a signature that appears when high-energy radiation from the host star excites helium atoms escaping a planet’s atmosphere. The technical preprint on WINERED data reports that a subsequent 2025 observation showed no helium absorption at all, confirming clear variability between epochs and ruling out simple instrumental artifacts as the cause.
LHS 1140 b was first identified in 2016 by University of Florida astronomer Jason Dittmann, and the discovery was formally published the following year as a temperate rocky super-Earth transiting a nearby cool star. The planet’s relatively large size compared with Earth, combined with its short orbital period and the small radius of its red dwarf host, produces deep, frequent transits that are ideal for atmospheric characterization. Those same attributes made it a high-priority target once helium-sensitive instruments like WINERED came online.
The Harvard-Smithsonian Center for Astrophysics noted that a rare same-night transit alignment of LHS 1140 b and its sibling planet LHS 1140 c provided additional observational leverage during the campaign. Having two planets cross the stellar disk in close temporal proximity allows astronomers to compare how each world imprints itself on the star’s light under nearly identical stellar conditions. In practice, this means that differences in detected spectral features can be more confidently attributed to the planets themselves rather than to changing behavior of the host star over longer timescales.
Dittmann, a co-author on the new study, has pointed out that the presence of helium on an older planetary system is itself surprising. Helium is light enough to escape relatively quickly from a rocky world’s gravity, so detecting it implies an active replenishment process or a reservoir large enough to sustain losses over billions of years. The University of Florida’s account of the research frames this as evidence supporting a genuine atmosphere rather than a transient outgassing event. In that view, LHS 1140 b is not merely shedding the remnants of a primordial envelope but may be maintaining a long-lived gaseous layer that interacts continuously with the host star’s radiation and wind.
From an observational standpoint, WINERED’s role is central. The instrument’s high resolution in the near-infrared allows it to isolate the narrow helium feature against the bright continuum of the host star. By comparing in-transit spectra, when the planet is in front of the star, with out-of-transit spectra, when the planet is elsewhere in its orbit, the team can measure minute differences that correspond to absorption by the planet’s extended atmosphere. The 2024 data showed a statistically significant excess at the helium wavelength, while the 2025 data, reduced with the same pipeline, did not.
Stellar variability, missing spectra, and the limits of a single detection
The most pressing open question is why the helium signal vanished between observing seasons. Two broad explanations compete. The first is that the planet’s atmospheric escape rate itself fluctuates, perhaps driven by changes in the stellar wind or ultraviolet output from the host star. Under this scenario, the upper atmosphere of LHS 1140 b might puff up or contract in response to varying energy input, sometimes presenting a large, easily detectable cross-section and sometimes shrinking below current detection thresholds.
The second explanation is that the star’s activity, such as flares or changes in its X-ray luminosity, altered the population of metastable helium atoms visible during transit without any real change in the escape rate. Because the observed helium line depends on both how much gas is escaping and how many atoms occupy the excited state, even a steady flow of material could appear or disappear from view as the star’s high-energy output varies. Distinguishing between these scenarios requires coordinated multi-wavelength monitoring that has not yet been reported, ideally combining X-ray, ultraviolet, and near-infrared observations over many transits.
Several gaps in the public record limit how far conclusions can be drawn. No raw transit spectra or data reduction pipelines from the 2024 Magellan runs have been released alongside the primary publications, making it difficult for independent teams to test alternative reduction methods or search for subtle systematics. Detailed statements from the full author team about the 2025 non-detection remain confined to institutional summaries rather than extended interviews or open data releases. And the orbital and atmospheric models built from the original 2017 discovery paper have not been publicly updated with parameters informed by the new helium data, leaving a disconnect between early characterizations and the latest observations.
The long-term stability of LHS 1140 b’s atmosphere is the central unresolved tension. If helium is escaping at a rate high enough to detect from Earth, the atmosphere could be thinning on timescales relevant to habitability, potentially transitioning from a thick, insulating envelope to a thinner, more Earth-like shell or even to a bare rocky surface. Alternatively, if the escape is modest and the variability is stellar in origin, the planet may retain a substantial gaseous envelope for billions of years, preserving surface conditions that could support liquid water if other factors align.
Future observations with the James Webb Space Telescope or ground-based extremely large telescopes could measure additional atmospheric species, such as water vapor or carbon dioxide, and test whether the helium-traced outflow is part of a broader, multi-component atmosphere. Repeated helium measurements, spread over many years and paired with high-energy monitoring of the host star, will be essential to determine whether LHS 1140 b is gradually losing its air or simply presenting a changing face to our telescopes. Until then, the planet stands as both a milestone-the first rocky world in a habitable-zone orbit with a directly detected atmosphere-and a reminder that atmospheric habitability is a dynamic, time-variable state rather than a fixed label.
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*This article was researched with the help of AI, with human editors creating the final content.
