Pasadena, CA—A Harvard-led team has reported the strongest evidence yet that a nearby rocky exoplanet, LHS 1140 b, retains an atmosphere despite orbiting within its star’s habitable zone. The work, published in Science, marks a crucial step toward identifying which worlds can persist with the atmospheric ingredients thought to enable surface water and long-term climate stability.
The search for atmospheres on rocky planets has been notoriously difficult. While gas giants often show clear spectral fingerprints, habitable-zone super-Earths produce extremely subtle signals. Even with powerful observatories such as NASA’s James Webb Space Telescope, previous observations frequently suggested airless or weakly buffered worlds, leaving open the key question of whether they can hold onto atmospheres long enough to be habitable.
Red dwarf stars offer a practical advantage: their small size makes planetary transits more detectable. By measuring periodic dips in starlight as a planet passes in front of its host star, researchers can perform transmission spectroscopy—splitting the starlight into a spectrum and reading which atmospheric constituents absorb particular wavelengths. In this study, the team targeted a more accessible atmospheric layer by searching for helium in the upper atmosphere.
LHS 1140 b orbits an older, cool red dwarf every 24.7 days. With a mass about 5.6 times Earth’s and a radius roughly 1.7 Earth radii, the planet is consistent with a rocky composition. It receives about 42% of the radiation Earth gets from the Sun, placing it in a temperature range where liquid water could exist, though the presence of an Earth-like surface remains unknown.
Using the WINERED spectrograph on the Magellan Clay telescope at Las Campanas Observatory in Chile, the researchers observed the planet in 2024 and detected spectral evidence of helium escaping from its atmosphere. The result indicates an active gaseous envelope, challenging assumptions that many rocky habitable-zone planets rapidly lose volatiles.
The data show that heating from stellar X-rays and extreme ultraviolet radiation likely drives the escape. In 2025, however, the team found no escaping helium, implying the atmospheric outflow is variable rather than constant. This short-timescale change provides rare real-time evidence that an exoplanet’s atmosphere can evolve quickly under changing stellar forcing.
By combining the observations with models of exoplanet evolution, the team interpreted the atmosphere as highly layered: a helium-dominated, hydrogen-poor upper region, with heavier species such as water trapped at lower altitudes nearer the surface. Such stratification helps explain both the detectability of helium and the lack of signals from deeper atmospheric layers.
The group also examined a second planet in the same system, LHS 1140 c, which is smaller and more strongly irradiated. No atmospheric evidence was found there, suggesting the planets may lie on opposite sides of the “cosmic shoreline,” where some worlds retain atmospheres for billions of years while others lose them quickly.
The study was conducted by scientists across Harvard and Carnegie, including Shreyas Vissapragada, Collin Cherubim, and multiple Carnegie co-authors, and involved prior observations and advanced interpretation. Together, these results strengthen the case that at least some rocky habitable-zone exoplanets can maintain atmospheres—and that helium escape spectroscopy can reveal them.
Subject of Research:
Not applicable
Article Title:
Helium escaping from the atmosphere of a nearby rocky exoplanet orbiting in a habitable zone
News Publication Date:
16-Jul-2026
Web References:
http://dx.doi.org/10.1126/science.aea9708
References:
10.1126/science.aea9708
Image Credits:
Melissa Weiss/Center for Astrophysics | Harvard & Smithsonian
Keywords
exoplanets; rocky worlds; habitable zone; atmospheric escape; helium; transmission spectroscopy; red dwarf stars; LHS 1140 b; WINERED; James Webb Space Telescope
