Astronomers have detected the first atmosphere on a rocky exoplanet located in its star’s habitable zone. Using the Magellan Clay telescope in Chile, researchers identified helium escaping from LHS 1140 b, a super-Earth roughly 48 light-years away, providing critical evidence that rocky worlds can retain the gases necessary to support life.
While thousands of exoplanets are known, confirming an atmosphere on a small, rocky world—rather than a gas giant—has remained one of the most difficult challenges in the field. For LHS 1140 b, the detection of a helium-rich upper atmosphere suggests a world that is not a barren rock, but one capable of regulating climate and shielding its surface from radiation.
The Helium Signal and the Magellan Clay Telescope
The research team, led by Collin Cherubim of Harvard University, utilized the Warm Infrared Echelle (WINERED) Spectrograph at the Magellan Observatory in Chile. The breakthrough occurred during a rare astronomical alignment in September 2024, when LHS 1140 b and another planet in the same system both crossed in front of their host star.
By employing transit spectroscopy—breaking starlight into component colors to see which wavelengths are absorbed—the team spotted a specific signature of metastable helium. This gas was leaking from the planet’s upper atmosphere, creating a stream that extended ahead of the planet and potentially trailing behind it.
The detection was not without skepticism. David Charbonneau, head of the Harvard Department of Astronomy and Cherubim’s joint advisor, initially doubted the plan because the signal was based on a mathematical prediction and had never been seen around a rocky planet. However, the resulting data proved statistically rock solid
, according to Charbonneau.
LHS 1140 b: A Super-Earth in the Goldilocks Zone
LHS 1140 b is categorized as a super-Earth, possessing roughly five times the mass of Earth. These dimensions suggest a rocky composition that may include a low-density component, such as a significant amount of water or a thick atmosphere. The planet orbits a red dwarf star—an M dwarf—which is roughly one-fifth the size of the Sun and less than 1% of its brightness.
| Feature | LHS 1140 b Specification |
|---|---|
| Distance from Earth | Approximately 48–50 light-years |
| Mass | 5 times Earth’s mass |
| Radius | ~1.7 times Earth’s radius |
| Stellar Radiation | 42 percent of what Earth receives |
| Equilibrium Temp | 226 kelvins |
The planet sits within the habitable zone, where temperatures could allow liquid water to persist on the surface. However, the environment is far from identical to Earth’s. It also faces the typical risks of red dwarf systems, which often blast planets with X-ray and ultraviolet radiation that can strip away atmospheres through a process called irradiation.
Despite these risks, evidence suggests the atmosphere of LHS 1140 b has endured for more than three billion years. This longevity is a critical find, as it proves a rocky planet can maintain a stable envelope of gas even when orbiting a volatile red dwarf.
The M-Dwarf Trap and Comparative Habitability
Future Search for Surface Oceans
While the current detection focuses on helium in the upper atmosphere, the researchers note that helium itself cannot sustain life. The real prize lies deeper. The study suggests that other potential gases, including water vapor, may be located in the lower atmosphere. Detecting these would be the next step in determining if the planet possesses surface oceans.
The success of the WINERED spectrograph also provides a new roadmap for ground-based observatories. Instead of struggling to detect faint signals of carbon dioxide or water near the surface, astronomers can now look for the “leak”—the escaping gases in the upper atmosphere—as a proxy to confirm a planet’s atmospheric status.
Cherubim, who will join the University of Chicago as a post-doctoral researcher in the fall, intends to use his validated model to search for additional rocky worlds. As he noted in a statement, an atmosphere is essential for a planet to support life as we know it,
and the confirmation of one on LHS 1140 b moves the search for a truly Earth-like twin from theoretical prediction to observational reality.
