![Models of mass-loss rate, outflow temperature, and H:He ratio for LHS 1140b in 2024. (A) Models of atmospheric mass-loss rate as a function of outflow temperature, ๐wind. Color indicates the normalized likelihood calculation, where zero corresponds to the maximum likelihood. Black contours indicate 1๐ and 3๐ derivations from the maximum likelihood. Data points with 1๐ error bars are the best-fitting values from the MCMC analysis of the 2024 spectrum of LHS 1140b, assuming an SED normalized to GJ 699 (black) or GJ 1132 (green). All models assumed the GJ 1132-normalized SED and fixed ๐ฃwind the best-fitting value from the MCMC analysis. The dashed gray line shows a theoretical upper limit on the escape rate (see text). The dashed red line shows the theoretical minimum escape rate required to drag atomic oxygen in the outflow. The dashed black and green lines show the energy-limited escape rates calculated with the SEDs normalized by GJ 699 and GJ 1132, respectively. (B) Same as panel A, but as a function of the H:He ratio. Data points with dotted error bars assumed 10 times higher stellar XUV flux. -- [astro-ph.EP]](https://i0.wp.com/astrobiology.com/wp-content/uploads/2026/07/Helium-escaping.png?fit=1200%2C665&ssl=1)
[astro-ph.EP] Observations of highly irradiated gas giant exoplanets have shown helium escaping from their atmospheres. There is limited evidence for atmospheres on rocky exoplanets, perhaps because they have already escaped.
We report spectroscopic observations of LHS 1140b, a rocky exoplanet that orbits in the habitable zone of a nearby low-mass star. The near-infrared transit spectra show absorption by helium escaping from the planet’s atmosphere. Helium absorption is detected in 2024 but not in 2025, indicating time-variable atmospheric escape.
We interpret these results as indicating an upper atmosphere dominated by helium and depleted in hydrogen, with other volatile species trapped at lower altitudes, consistent with atmospheric fractionation models. No helium absorption is detected for LHS 1140c, a smaller and more heavily irradiated exoplanet in the same system.
Collin Cherubim, Shreyas Vissapragada, Tim Cunningham, Annabella G. Meech, David Charbonneau, Robin Wordsworth, Aaron Householder, Johanna Teske, Leonardo A. Dos Santos, Nicole L. Wallack, William Misener, Zifan Lin, Andrew McWilliam, Michael Zhang, Jason A. Dittmann, Mercedes Lรณpez-Morales
Comments: Published in Science on July 16, 2026
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2607.14326 [astro-ph.EP] (or arXiv:2607.14326v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2607.14326
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Related DOI:
https://doi.org/10.1126/science.aea9708
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Submission history
From: Collin Cherubim
[v1] Wed, 15 Jul 2026 19:45:28 UTC (3,347 KB)
https://arxiv.org/abs/2607.14326
Astrobiology, exoplanet,
