Astronomers searching for extraterrestrial life have now identified the most promising places to look. Out of more than 6,000 known exoplanets, researchers have narrowed the list to just under 50 rocky worlds that may be capable of supporting life.
The findings, published in Monthly Notices of the Royal Astronomical Society, echo the kind of mission imagined in the Hollywood film Project Hail Mary. In that story, Ryan Gosling’s character travels to a distant star system in search of a way to save Earth, encountering alien life along the way, including a being named Rocky and fictional microorganisms like Astrophage and Taumoeba.
Habitable Zone Planets and Liquid Water Potential
Professor Lisa Kaltenegger, director of the Carl Sagan Institute at Cornell University, led the research alongside a team of undergraduate students. They analyzed new data from the European Space Agency’s Gaia mission and the NASA Exoplanet Archive to identify planets located in the “habitable zone.”
This region around a star is not too hot and not too cold, making it more likely that liquid water could exist on a planet’s surface. Since water is essential for life as we know it, planets in this zone are considered the best candidates.
The study, titled ‘Probing the limits of habitability: a catalogue of rocky exoplanets in the habitable zone’, also highlights planets that receive levels of stellar energy similar to Earth.
“As Project Hail Mary so beautifully illustrates, life might be much more versatile than we currently imagine, so figuring out which of the 6,000 known exoplanets would be most likely to host extraterrestrials such as Astrophage and Taumoeba — or Rocky — could prove critical, and not just to Ryan Gosling,” Professor Kaltenegger said.
“Our paper reveals where you should travel to find life if we ever built a ‘Hail Mary’ spacecraft.”
45 Rocky Worlds Identified as Top Targets
The team identified 45 rocky planets within the habitable zone that could potentially support life. They also highlighted an additional 24 planets within a more restrictive 3D habitable zone, based on tighter assumptions about how much heat a planet can tolerate before becoming uninhabitable.
Among these are well-known exoplanets such as Proxima Centauri b, TRAPPIST-1f, and Kepler 186f, along with lesser-known candidates like TOI-715 b.
Some of the most intriguing targets include the TRAPPIST-1 system planets d, e, f, and g, located about 40 light-years from Earth, as well as LHS 1140 b, which lies 48 light-years away. Whether these worlds can sustain liquid water depends partly on their ability to maintain an atmosphere.
Earth-Like Energy and Promising Nearby Worlds
Several planets receive levels of starlight similar to what Earth gets from the Sun. These include the transiting planets TRAPPIST-1 e, TOI-715 b, Kepler-1652 b, Kepler-442 b, and Kepler-1544 b, along with planets such as Proxima Centauri b, GJ 1061 d, GJ 1002 b, and Wolf 1069 b, which are detected through the motion they induce in their host stars.
Researchers also selected planets located near the inner and outer edges of the habitable zone to better understand where the limits of habitability lie. While the concept of the habitable zone has been studied since the 1970s, new observations could refine or even reshape current theories, Professor Kaltenegger explained.
Testing the Limits of Planetary Habitability
Some exoplanets follow highly elliptical orbits, meaning the amount of heat they receive from their star changes significantly over time. Studying these worlds could reveal whether a planet must remain continuously within the habitable zone or if it can move in and out while still maintaining conditions suitable for life.
Planets such as K2-239 d, TOI-700e, and K2-3d, along with Wolf 1061c and GJ 1061c, can help scientists study the inner boundary of habitability. Meanwhile, TRAPPIST-1g, Kepler-441b, and GJ 102 offer insight into the colder outer edge of the habitable zone.
“While it’s hard to say what makes something more likely to have life, identifying where to look is the first key step — so the goal of our project was to say ‘here are the best targets for observation’,” said Gillis Lowry, now a graduate student at San Francisco State University.
Fellow researcher Lucas Lawrence, now a graduate student at the University of Padua in Italy, said: “We wanted to create something that will enable other scientists to search effectively and we kept discovering new things about these worlds we wanted to investigate further.”
Using Telescopes to Search for Alien Atmospheres
Co-author Abigail Bohl, of Cornell University, emphasized that Earth, Venus, and Mars provide useful benchmarks for understanding habitability.
“We know Earth is habitable, while Venus and Mars are not. We can use our Solar System as a reference to search for exoplanets that receive stellar energy between what Venus and Mars get.
“Observing these planets can help us understand when habitability is lost, how much energy is too much, and which planets remain habitable — or maybe never were.
“The same idea applies to eccentric planets: how much orbital eccentricity can a planet have while still holding onto its surface water and habitable conditions?
“We identified planets at the inner and outer edges of the habitable zone, as well as those with the highest eccentricities, to test our understanding of what it takes for a planet to be and remain habitable. We also identified the targets that are most observable with the James Webb Space Telescope (JWST) and other telescopes.”
The team also matched different planets with observation methods to improve the chances of detecting signs of life.
Future Telescopes and the Search for Life
This curated list will guide astronomers using current and future observatories, including JWST, the Nancy Grace Roman Space Telescope (set to launch in 2027), the Extremely Large Telescope (set to see first light in 2029), the Habitable Worlds Observatory (expected to launch in the 2040s), and the proposed Large Interferometer For Exoplanets (LIFE) project.
According to Lowry, observing these small planets is essential to determine whether they have atmospheres and to refine models of habitability.
She noted that early analysis of the 10 planets receiving Earth-like radiation has already identified two strong candidates for near-term study: TRAPPIST-1 e and TOI-715 b.
The TRAPPIST-1 system is a major focus for JWST observations, led by Cornell astronomer Nikole Lewis. Both TRAPPIST-1 and TOI-715 b orbit small red stars, making it easier to detect and study their Earth-sized planets.
Full List of 45 Potentially Habitable Exoplanets Identified in the Paper
- GJ 1002 b
- GJ 1002 c
- GJ 1061 c
- GJ 1061 d
- GJ 251 c
- GJ 273 b
- GJ 3323 b
- GJ 667 C c
- GJ 667 C e
- GJ 667 C f
- GJ 682 b
- K2-239 d
- K2-288 B b
- K2-3 d
- K2-72 e
- Kepler-1229 b
- Kepler-1410 b
- Kepler-1544 b
- Kepler-1606 b
- Kepler-1649 c
- Kepler-1652 b
- Kepler-186 f
- Kepler-296 e
- Kepler-296 f
- Kepler-441 b
- Kepler-442 b
- Kepler-452 b
- Kepler-62 e
- Kepler-62 f
- L 98-59 f
- LHS 1140 b
- LP 890-9 c
- Proxima Centauri b
- Ross 508 b
- TOI-1266 d
- TOI-700 d
- TOI-700 e
- TOI-715 b
- TRAPPIST-1 d
- TRAPPIST-1 e
- TRAPPIST-1 f
- TRAPPIST-1 g
- Teegarden’s Star c
- Wolf 1061 c
- Wolf 1069 b