Harvard scientists detect atmosphere on distant ‘Earth-like’ planet

Harvard scientists have discovered an atmosphere on an Earth-like planet in the temperate “habitable zone” of a distant star system — an intriguing hint of another world that might be hospitable to life.

In a study published this week in Science, the team details the helium-dominated atmosphere of the planet LHS 1140 b, located about 48 light-years from Earth.

“Connecting astronomy to life is always exciting for the public,” said lead author Collin Cherubim, Ph.D. ’26, who conducted the research during his doctoral studies at the Harvard Kenneth C. Griffin Graduate School of Arts and Sciences. “People are generally interested in the big questions: Are we alone? Is there life beyond the Earth or beyond our solar system? To that end, this study reveals the first atmosphere discovered on a rocky, planet in the habitable zone of a star outside of our solar system.”

The discovery marks a major advance in the decades-long quest to identify exoplanets — ones situated outside our own solar system — that might be amenable to life. Most of these planets orbit other stars, just as the Earth and other planets in our solar system revolve around the sun. (A smaller number of free-floating “rogue” exoplanets are unconnected to any star.) The “habitable zone” refers to a circular region around a star where a planet could have liquid water on the surface — a so-called "Goldilocks zone” that is neither too hot nor too cold.

“It’s perfectly reasonable to imagine that there might be life on that planet,” said co-author David Charbonneau, Fred Kavli Professor of Astrophysics and chair of the Department of Astronomy and researcher at the Center for Astrophysics. “We have no evidence of that, but all the pieces that we think are essential for life are present — it’s rocky, the right temperature, and has an atmosphere. I can imagine scientists now really beginning to think about making detailed observations to learn more about this atmosphere. I expect that a lot of attention now will be galvanized on this particular world.”

‘That’s crazy’

In the search for habitable planets, one key factor is the presence of an atmosphere to shield the surface from ionizing radiation, regulate its climate, and potentially enable the presence of liquid water. Another is that the planet must be terrestrial, or rocky, and not a larger one composed of gas.

In 2001, Charbonneau and colleagues achieved a breakthrough with the first discovery of an exoplanet with an atmosphere — a Jupiter-sized gas giant that was highly irradiated by its host star. Since then, a series of gas giants with atmospheres have been discovered. But the detection of atmospheres on smaller and cooler “Earth-like” planets (ones similar to our planet in bulk composition and temperature) poses a more difficult challenge because they are obscured in size and brightness by their stars.

The new discovery came from a scientist who marched to a different beat.

As an undergraduate, Cherubim studied physical biochemistry at Carnegie Mellon University then spent a year playing drums in a band and trying to make a living as a professional musician (he also moonlighted as a waiter). Next, he spent four years as a high-school physics and chemistry teacher, became fascinated by planetary science, volunteered as research assistant, and eventually got accepted into the Harvard Ph.D. program in the Department of Earth and Planetary Sciences.

He studied under Robin Wordsworth, Gordon McKay Professor of Environmental Science and Engineering and Professor of Earth and Planetary Sciences, and a leading researcher in the evolution of the Earth and other planets. Cherubim investigated the chemical evolution of planets over billions of years (he was jointly advised by both Wordsworth and Charbonneau).

Planetary theorists suspect that many planets are born big with abundant hydrogen and helium, but over time shrink into solid “terrestrial” or “rocky” planets composed of mostly rocks and metals as much of the hydrogen escapes. More than a decade ago, other researchers suggested planets in transition would have helium-rich atmospheres, and Cherubim developed a new model based on that idea.

He examined all the known exoplanets with measured mass, radius, and temperature and predicted which ones would have helium-dominated atmospheres. He collaborated closely with Shreyas Vissapragada, then a postdoctoral fellow in the Center for Astrophysics and now a Distinguished Scholar at Carnegie Observatories and co-author of the new paper.

Initially, Charbonneau was skeptical about his advisee finding rocky planets with helium-rich atmospheres.

“My reaction was, that’s crazy, because there’s nothing like that in the solar system — that’s just the product of some mathematical calculation,” Charbonneau recalled with a chuckle. “I didn’t say don’t do it, but I’d like to imagine that even if I did, Collin would have ignored me.”

Passing in the night

At present, most searching for exoplanet atmospheres focuses on small stars called “M dwarfs” because their size facilitates the detection of planets in their orbits. Until now, most surveys of these small, rocky planets have found airless worlds without atmospheres; a small handful of very hot, rocky planets are claimed to have atmospheres, but the evidence remains under debate.

In a 2025 paper, Cherubim, Wordsworth, and colleagues presented a model for how larger gas-enveloped exoplanets might evolve into smaller rocky planets and predicted a large population of helium-rich worlds.

The paper listed 30 candidates and two prime targets orbited the red dwarf star LHS 1140 in the constellation of Cetus. One planet, LHS 1140 b — more than five times the mass of Earth — had already been studied extensively, but no other researchers had detected an atmosphere. Another rocky planet, LHS 1140 c, also orbits closer to the same star.

Cherubim and Vissapragada realized that the two planets would pass in front of their star on one night — an event that would not reoccur for at least another 50 years — and Cherubim seized the opportunity to test his predictions.

He secured telescope time at the Magellan/Clay telescope at Las Campanas Observatory in Chile. On Sept. 23, 2024, he conducted observations on a night when the egress of planet 1140 c and ingress of planet 1140 b were separated by only 39 minutes.

He relied on a spectrograph mounted on the telescope. Spectroscopy, a foundational technique in astrophysics, analyzes the light spectrum emitted by celestial bodies to reveal chemical composition, temperature, density, mass, distance, and more.

“First and foremost, helium just tells us that there’s an atmosphere, period,” Cherubim said. “It’s a binary, yes-no thing.”

As predicted, the analysis revealed that LHS 1140 b had a helium-dominated upper atmosphere. Researchers detected helium escaping from the atmosphere in 2024 but not in observations conducted the following year, suggesting a variable rate of escape. No evidence of an atmosphere was found in the other candidate, planet c.

Wordsworth credited Cherubim with confirming his predictions with convincing observations.

“Discovering an atmosphere on such a small planet in the habitable zone for the first time is a major milestone,” he said. “The questions that arise from it are multiple, and there’s going to be a lot more attention on this planet in the near future … We’re also starting to suspect that maybe Earth very, very early on went through a phase when it had one of these primordial atmospheres.”

Scientific breakthroughs often occur because of new technologies, but this one resulted from a theoretical prediction of precisely where to look. As Charbonneau explained, “People largely have not tried to do this for rocky planets because they don’t think that there would be anything to detect.”

Cherubim, who will continue his research at the University of Chicago as a NASA Hubble Fellow, plans to examine more exoplanets for atmospheres.

“This is a small sample; it’s one planet so far,” he said. “I’d like to keep testing the predictions and see just how common this phenomenon might be.”

This research received federal funding NASA and the National Science Foundation.