Astronomers have detected helium escaping from LHS 1140 b, a rocky super-Earth orbiting 49 light-years away in the habitable zone.
When astronomers search the cosmos for signs of extraterrestrial life, they generally look for three distinct ingredients: a rocky composition, a temperature range that permits liquid water, and a protective layer of gas. Until recently, finding all three on a single world beyond our solar system remained out of reach. That landscape changed with new observations of a distant exoplanet known as LHS 1140 b.
Detecting an Atmosphere on LHS 1140 b
Located roughly 49 light-years from Earth in the constellation Cetus, LHS 1140 b has a mass about five times that of our planet, placing it firmly in the category of a super-Earth
. Its density measurements suggest it features an iron core and a silicate mantle alongside a low-density component that includes water and an atmosphere. The discovery stems from a computer model developed by Collin Cherubim during his doctoral studies at Harvard University.
To test the model, researchers waited for a rare transit event where LHS 1140 b and another planet crossed in front of their host star on the same night. Using the Warm Infrared Echelle Spectrograph on the Magellan Clay Telescope at Las Campanas Observatory in Chile in September 2024, the team detected helium escaping from the outer envelope of LHS 1140 b.
Cherubim explained that many planets form with hydrogen-and-helium-dominated atmospheres. As rocky bodies evolve, they often shed their lighter hydrogen while holding onto heavier helium. We believe LHS 1140 b is in that sweet spot, where it lost its hydrogen and it kept its helium, which is now slowly escaping,
he noted.
Navigating the Red Dwarf Trap
The host star of LHS 1140 b is a red dwarf, which is an M dwarf roughly one-fifth the size of our Sun and less than one percent of its brightness. Because red dwarfs are small and dim, a transiting rocky planet blocks a much larger share of light, making atmospheric measurements easier to capture than they would be around a bright, Sun-like star.
However, red dwarfs present a severe obstacle for habitability. They frequently blast intense X-rays and ultraviolet radiation toward their orbiting planets, which can heat and strip away planetary atmospheres entirely.
“They’re really feisty, ferocious stars that emit lots of X-rays and ultraviolet radiation, which are really bad for atmospheres because they heat them up, expand them and blow them off into space.”
Collin Cherubim, NASA Sagan Fellow at the University of Chicago
Robin Wordsworth, Gordon McKay Professor of Environmental Science and Engineering and Professor of Earth and Planetary Sciences at Harvard, noted that while researchers previously confirmed terrestrial planets are common, proving they could retain an atmosphere remained a major hurdle.
Twenty years ago we wondered whether other terrestrial-type planets even existed,
Wordsworth said. Then we learned they’re common, and found some in the habitable zone. The next question was whether any of them had managed to keep an atmosphere. Now we know at least one has.
Future Observations and Unresolved Mysteries
Despite the milestone, scientists emphasize that the discovery requires further confirmation.
Researchers intend to utilize additional facilities to study the exoplanet in greater detail.
Future investigations aim to determine whether heavier molecules, such as oxygen or water vapor, accompany the helium in the atmosphere of LHS 1140 b, providing clearer clues in the ongoing search for life beyond the solar system.
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