Astronomers confirm first atmosphere on a rocky planet in the habitable zone

Astronomers have for the first time confirmed an atmosphere around a rocky, temperate planet beyond our solar system, a discovery that marks a turning point in the decades-long search for potentially habitable worlds.

The planet, LHS 1140b, orbits a dim red dwarf star roughly 49 light-years from Earth in the constellation Cetus. A team led by Collin Cherubim, who completed his Ph.D. at Harvard University and is now at the University of Chicago, used NASA's James Webb Space Telescope to detect helium escaping from the planet's atmosphere — evidence that LHS 1140b has maintained a substantial gaseous envelope billions of years after its formation. The findings were published on Wednesday in the journal Science.science+2

A Planet That Checks the Boxes

LHS 1140b is about 1.73 times Earth's diameter and 5.6 times its mass, placing it in the category of "super-Earths". It sits squarely in its star's habitable zone — the orbital region where temperatures could allow liquid water to exist on a planet's surface.news.umich+3

"An atmosphere is essential for a planet to support life as we know it," Cherubim said. He described LHS 1140b as the foremost candidate for studying astrobiology and the possibility of life beyond our solar system.cfa.harvard+1

Previous JWST observations in 2024 had already ruled out the possibility that LHS 1140b was a mini-Neptune — a small gas giant — and suggested it might possess a nitrogen-rich atmosphere with water vapor. The new study goes further by directly detecting atmospheric gas escaping from the planet, confirming the atmosphere's existence rather than merely inferring it.exoplanetes.umontreal+3

What Comes Next

The detection of escaping helium implies LHS 1140b is losing atmospheric mass, but at a rate low enough that it has held onto its atmosphere over its multi-billion-year lifetime. Earlier analyses estimated that 10 to 20 percent of the planet's mass could be water, raising the possibility that it harbors a liquid ocean beneath an icy surface at the point permanently facing its star.sciencenews+3

The discovery stands in contrast to recent findings from the TRAPPIST-1 system, where several rocky planets in the habitable zone appear to have been stripped of their atmospheres entirely. LHS 1140b now becomes the primary target for follow-up observations aimed at characterizing what its atmosphere contains and whether conditions on its surface could support life as we know it.skyandtelescope