Astronomers have detected an atmosphere around a rocky exoplanet in the habitable zone of a nearby star. The finding marks a first. It challenges long-held assumptions about whether such worlds can hold onto their gaseous envelopes despite fierce radiation from their host stars.
The planet, LHS 1140b, sits 48 light-years from Earth. It orbits a cool, dim M dwarf star. Previous observations hinted at its potential. Yet direct proof of an atmosphere remained elusive. Until now.
Using the Magellan Clay telescope in Chile, researchers spotted excess helium gas absorbing starlight just before and after the planet transited its star. That signature points to helium escaping from the planet’s atmosphere. Confirmation comes in a paper published yesterday in Science.
“Really, the most exciting thing here is that the planet has an atmosphere at all,” said lead author Collin Cherubim of the Harvard-Smithsonian Center for Astrophysics. The discovery boosts optimism for habitable conditions elsewhere.
LHS 1140b measures 1.73 times Earth’s radius and 5.6 times its mass. Those stats fit a rocky composition wrapped in gas. Or a world covered in a global ocean. Its orbit places it where surface temperatures could allow liquid water. But M dwarfs like its host star bombard planets with flares and radiation. Many scientists wondered if atmospheres could survive.
“The open question is, can rocky exoplanets even keep their atmospheres around M dwarfs?” Cherubim asked. The answer appears yes. At least for this one.
Implications stretch beyond this single world.
The helium detection doesn’t reveal the full atmospheric mix. Follow-up with the James Webb Space Telescope could identify other molecules. It might confirm the signal. And it could show whether the air holds nitrogen, carbon dioxide or water vapor. Earlier JWST data already ruled out a thick hydrogen envelope. It favored a denser, higher-mean-molecular-weight atmosphere.
Laura Kreidberg of the Max Planck Institute for Astronomy called the planet an “exotic weirdo.” Its atmosphere seems thicker than typical for rocky bodies yet thinner than gas giants. “This is a kind of planet that we’ve never seen before,” she told Science News. The finding makes her “more optimistic now about the chances of habitable environments beyond the solar system.”
Helium escape doesn’t doom the planet. LHS 1140b loses mass slowly. It has retained its atmosphere for more than 3 billion years. Models suggest it could hold on for a billion more. Even after that, heavier gases might remain. The world isn’t evaporating into nothing like some hotter mini-Neptunes.
Those larger planets have shown helium outflow before. But they lose gas faster. LHS 1140b runs cooler. Its escape rate stays modest. So the atmosphere persists on astronomical timescales. That’s good news for habitability prospects.
But questions linger. Does the planet have a surface ocean? Or a thick ice layer with occasional liquid? Prior hints from JWST pointed to possible nitrogen and a water world scenario. One analysis even described it as an “eyeball” planet, with open ocean at the substellar point and ice elsewhere.
The new helium data fits secondary atmospheres. These form from volcanic outgassing or impacts rather than captured primordial gas. Such envelopes could support stable climates. They might even allow for life-friendly chemistry.
Experts reacted quickly to the announcement. Reports poured in across outlets. Phys.org highlighted how the result provides the strongest evidence yet for an atmosphere on this world. Carnegie Science noted it as a milestone toward understanding potentially habitable rocky planets.
Discovery of LHS 1140b dates back nearly a decade. Astronomers have studied it intensely. Hubble once suggested water vapor, though at low confidence. JWST observations in 2024 tightened constraints. They excluded hydrogen-dominated air. The latest ground-based work adds the helium piece.
And the star itself helps. LHS 1140 shows low activity for an M dwarf. Fewer flares mean less atmospheric stripping. That factor likely explains why this planet kept its envelope while others didn’t.
Still, the helium-rich profile stands out. Helium dominates the upper atmosphere in this detection. What lies below? Models predict possible CO2 or N2. Absorption features at 4.2 microns could appear in future spectra. Signal strength around 20 parts per million might be detectable.
Business implications remain distant. Yet the find sharpens focus for missions targeting biosignatures. Space agencies prioritize such targets. LHS 1140b now ranks high. Its proximity helps. Light from the system reaches us quickly enough for detailed study.
Critics caution against overinterpretation. One detection doesn’t prove habitability. The planet might still prove barren. Stellar history could have baked it dry early on. Or intense early flares might have left it with a thin, inhospitable shell.
But the data tilts positive. Kreidberg and others see reason for hope. Rocky worlds around M dwarfs can hold atmospheres. This one does. Others might too.
Observations continue. Teams plan more transits. They will probe deeper wavelengths. They seek additional species. Confirmation could come soon. So could surprises.
The result arrives amid a wave of exoplanet advances. JWST has transformed the field. Ground telescopes like Magellan still deliver key finds. Together they build a clearer picture of distant worlds.
LHS 1140b won’t host visitors anytime soon. Forty-eight light-years separates us. Yet it offers a proxy. A laboratory for understanding how planets evolve around common stars. And whether conditions for life arise often or rarely.
Cherubim’s team calculated long-term stability. Billions of years matter for biology. Time enough for complex chemistry to emerge. For evolution to take hold. The planet’s past, present and future all look promising.
So does the broader search. This “exotic weirdo” expands the possibilities. It shows atmospheres survive where skeptics doubted. Optimism grows. Telescopes sharpen. The hunt accelerates.
One planet. One detection. A shift in perspective. Astronomers now eye similar targets with fresh eyes. The galaxy may hold more such worlds. Some could even harbor life. We just need to look.
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