Earth-like Exoplanet LHS 1140b Found With Water-Supporting Atmosphere

In a groundbreaking discovery for astrobiology, researchers have confirmed the existence of an atmosphere around the Earth-like exoplanet LHS 1140b, located approximately 49 light-years from our solar system. This significant finding suggests the planet could host liquid water on its surface, a key ingredient for life as we know it. The planet, first identified in 2017, orbits a small red dwarf star in the constellation Cetus.

The atmosphere's confirmation marks a pivotal moment, as it is the first such envelope directly observed around a rocky exoplanet situated within its star's habitable zone. While atmospheres have been detected on gas giants and sub-Neptunes, and even around some rocky worlds outside this life-friendly region, LHS 1140b represents a unique case. "This is the first actually observationally confirmed atmosphere on a rocky planet in the habitable zone outside of our solar system," stated Dr. Collin Cherubim, lead author of the study and formerly of Harvard University. This detection also represents the first direct identification of any atmospheric species for any rocky exoplanet, regardless of its location relative to the habitable zone.

LHS 1140b is a substantial world, boasting a mass 5.6 times that of Earth and a radius 70% larger. While it shares some similarities with our home planet, including its general composition and temperature range conducive to liquid water, it also presents distinct differences. Notably, the planet is tidally locked, meaning one side perpetually faces its star, and it may possess a significantly larger volume of water. "This is a really exciting discovery because I think it really puts LHS 1140b at the forefront as the best, most promising, exciting laboratory for studying astrobiology and habitability outside of our solar system," Dr. Cherubim added.

Atmospheric Escape and Star Activity

The research team utilized an infrared spectrograph on the Magellan Clay telescope in Chile to observe LHS 1140b as it transited its host star. Data collected in 2024 revealed the escape of helium from the planet into space, a signal that scientists meticulously analyzed to rule out terrestrial contamination or other false positives. Intriguingly, observations made in 2025 showed no helium detection, a puzzling result that prompted further re-evaluation. "Every false positive we could think of, we have confidently ruled out," Cherubim affirmed.

The red dwarf star LHS 1140, though dimmer than our Sun, emits a substantial amount of ionizing radiation. However, this particular star is noted for its relative quietness, with fewer stellar flares than many other red dwarfs. This characteristic is crucial, as intense stellar activity can strip atmospheres from orbiting planets, rendering them inhospitable. "So it’s a really exciting place to keep looking, especially to look for signs of life," Dr. Cherubim commented, highlighting the planet's potential habitability due to its atmosphere's role in retaining water and shielding the surface.

The study also examined LHS 1140c, another rocky planet orbiting the same star, but found no evidence of an atmosphere. The variability in the detected helium signal from LHS 1140b is particularly fascinating. Professor Jayne Birkby of the University of Oxford noted, "It’s fascinating that the signal varies too, it shows how the exoplanet’s atmosphere reacts to the high [extreme ultraviolet radiation] radiation of its host star, and may even tell us how this changes the planet’s surface conditions too." This atmospheric dynamism offers a unique window into planetary evolution around red dwarf stars, which are the most common type of star in the galaxy.

Dr. Yamila Miguel of Leiden Observatory acknowledged the significance of detecting atmospheric escape, especially from a small, rocky planet. "What makes this planet so interesting is that it is losing enough of its atmosphere that we can actually detect it from here, which is not easy for a small, rocky planet," she explained. However, Dr. Miguel cautioned that these observations primarily pertain to the planet's upper atmosphere, not the regions closer to the surface where life would likely emerge. "Therefore I do not think these results have any direct implications for detecting life on other planets," she stated, emphasizing the need for further research to understand the surface conditions.