Could Life Exist on This Nearby World? In a First, Astronomers Find an Atmosphere on an Earth-Like Exoplanet in the Habitable Zone
While the celestial body seems to host three features that could make a livable environment—an atmosphere, a rocky composition and a temperature that could allow liquid water to sit on the surface—researchers have not currently detected any residents
An artistic rendering of LHS 1140 b and its host star, with another smaller exoplanet orbiting nearby. Melissa Weiss / Center for Astrophysics | Harvard & Smithsonian An exoplanet just 49 light-years from Earth seems to have a characteristic that might help it host life: an atmosphere, researchers report in the journal Science on July 16. This gaseous envelope might protect it from cosmic radiation, regulate its climate and allow water to linger on its surface.
The relatively nearby world is also rocky, like our home planet, and orbits in its star’s habitable zone, meaning that the temperature might let water remain liquid on its exterior. All three features hint that the exoplanet could host livable environmental conditions—although currently, no one has found any evidence of organisms residing 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.
Cherubim and his colleagues found tantalizing evidence of the gaseous shield around an exoplanet called LHS 1140 b, which was discovered in 2017. It’s technically a super-Earth, meaning that it’s a rocky, or terrestrial, world larger than Earth and smaller than Neptune. Its radius is 1.7 times that of our home planet, and it’s about 5.6 times as massive.
LHS 1140 b takes only around 25 days to complete a trip around its host star, a red dwarf, which are believed to be the most common type of star in the universe.
Researchers estimate that up to 80 percent of all stars are red dwarfs. They are about 0.08 to 0.6 times the mass of the sun but have significantly longer lifespans, at billions to trillions of years. (For comparison, the sun is about halfway through its ten-billion-year lifespan)
“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.”
However, he notes, molecules like water and carbon dioxide, which could be life-related, are usually relatively close to a planet’s surface in the lower atmosphere, making them difficult to detect on another world. So, the team searched for signals that might be present in the upper atmosphere using an instrument on the Magellan Clay Telescope in Chile.
Analyses of 2024 observations revealed the light signature of excited helium atoms, hinting that the gas was escaping from an atmosphere into space. That’s probably caused by extreme heating from stellar X-rays and ultraviolet radiation, according to the researchers. However, observations collected the following year didn’t contain evidence of escaping helium, indicating that the phenomenon isn’t constant.
The team suspects that LHS 1140 b’s upper atmosphere contains lots of helium and little hydrogen, while other atoms and molecules, like water, might be hiding 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. Still, he urges caution about the findings, especially because of the inconsistent detections of helium, which can also be found in stars.
“I think we need more observations in the end to really know what is going on with this habitable-zone planet,” Cadieux says.
What’s more, the team looked at a smaller rocky exoplanet in the system. The data yielded no trace of an atmosphere on this body, dubbed LHS 1140 c, suggesting that the two observed planets sit on either side of what’s known as the “cosmic shoreline.” Worlds on one side can keep their atmospheres for billions of years, while those on the other quickly lose their atmospheric gases to space.
Does the discovery of LHS 1140 b’s atmosphere mean that the celestial body hosts otherworldly organisms? Not necessarily.
“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.”
Margherita Bassi is a freelance journalist and trilingual storyteller. Her work has appeared in publications including BBC Travel, Discover magazine, Live Science, Atlas Obscura and Hidden Compass.
