A planet 49 light-years from Earth may have one of the big things scientists look for in a potentially livable place: an atmosphere.
Researchers reported in Science on July 16 that they found evidence of a gaseous envelope around LHS 1140 b, a rocky exoplanet in its star’s habitable zone. That means temperatures there might allow liquid water to remain on the surface. The planet is also rocky, and scientists say those three features together point to conditions that could be livable.
No evidence of life has been found there.
“This is the first actually observationally confirmed atmosphere on a rocky planet in the habitable zone outside of our solar system,” study co-author Collin Cherubim, a planetary scientist who conducted the research at Harvard, tells the Guardian’s Nicola Davis.
LHS 1140 b was discovered in 2017. It is a super-Earth, a rocky planet larger than Earth and smaller than Neptune. Its radius is 1.7 times Earth’s, and it is about 5.6 times as massive.
The planet orbits a red dwarf star and takes about 25 days to complete one orbit. Researchers estimate that up to 80 percent of all stars are red dwarfs. They have about 0.08 to 0.6 times the sun’s mass and can last billions to trillions of years.
“Red dwarf stars present a good opportunity for this kind of search because they are small and cool,” says study co-author Shreyas Vissapragada, a planetary scientist at the Carnegie Observatories, in a statement. “So, habitable-zone planets orbiting these stars are relatively accessible using the transit method, where we detect tiny, periodic dips in the host star’s brightness every time the planet passes in front of it from our point of view.”
Vissapragada said molecules such as water and carbon dioxide are usually closer to a planet’s surface in the lower atmosphere, which makes them hard to detect on another planet. So the team searched instead for signals in the upper atmosphere using an instrument on the Magellan Clay Telescope in Chile.
Analyses of observations from 2024 found the light signature of excited helium atoms. The researchers said that suggests gas was escaping from the atmosphere into space, probably because of intense heating from stellar X-rays and ultraviolet radiation.
But observations gathered the next year did not show escaping helium, suggesting the process is not constant.
The team suspects the planet’s upper atmosphere contains a lot of helium and little hydrogen, while atoms and molecules including water may be in the lower atmosphere.
The helium detection is “beautiful,” says MIT astrophysicist Sara Seager, who was not involved in the study, to the New York Times’ Katrina Miller. “There’s no other explanation.”
“I was very surprised and very excited about this result,” Charles Cadieux, a planetary scientist at the University of Montreal in Canada who did not participate in the research, tells Sky & Telescope’s Arielle Frommer.
He also urged caution because helium can be found in stars and because the detections were inconsistent.
“I think we need more observations in the end to really know what is going on with this habitable-zone planet,” Cadieux says.
The researchers also studied a smaller rocky planet in the same system, LHS 1140 c. They found no trace of an atmosphere there, suggesting the two planets may sit on opposite sides of the “cosmic shoreline,” where some planets keep atmospheres for billions of years and others lose them to space.
“At this point, we have absolutely no evidence for life on the planet,” Cherubim, now at the University of Chicago, tells the Times. “But we think all of the really important, essential ingredients are there.”
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