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In a significant breakthrough for exoplanet science, a team of astronomers has confirmed the existence of a new planet orbiting a star roughly 120 light-years from Earth. Designated TOI-1231 b, this world is roughly the size of Neptune and sits in the habitable zone of its parent star, a small red dwarf. The discovery, made using data from NASA’s Transiting Exoplanet Survey Satellite (TESS) and follow-up observations with ground-based telescopes, adds to the growing catalog of planets beyond our solar system.
How Was the New Planet Discovered?
TESS detected TOI-1231 b by the transit method. Over the course of several weeks, the satellite measured tiny dips in the brightness of the star TOI-1231, indicating a planet crossing in front of it. These dips recurred every 24 days, revealing the planet’s orbital period. Subsequent observations with the Planet Finder Spectrograph on the Magellan Telescope in Chile and the HARPS spectrograph on the 3.6-meter telescope at La Silla confirmed the planetary nature and helped measure its mass.
The Transit Method in Action
The transit method remains the most successful technique for finding new planets. When a planet passes between its star and Earth, it blocks a small fraction of the star’s light. By analyzing the light curve, astronomers can deduce the planet’s size. For TOI-1231 b, the transit depth indicated a radius about 3.5 times that of Earth, placing it in the sub-Neptune category.
Follow-Up Observations
Once TESS identified a candidate, ground-based telescopes performed radial velocity measurements. These detect the star’s slight wobble caused by the gravitational pull of the orbiting planet. The radial velocity data gave a mass estimate of roughly 15 Earth masses. Combining size and mass yields the planet’s density, which for TOI-1231 b is about 2.5 grams per cubic centimeter—less than Earth’s density, suggesting a substantial atmosphere.
Where Is This New Planet Located?
The star TOI-1231 is an M-dwarf, or red dwarf, about half the mass of our Sun and considerably cooler. It lies in the constellation Vela, visible from the Southern Hemisphere. At 120 light-years away, it’s relatively close in galactic terms, making it an excellent target for further study. The planet orbits well within the star’s habitable zone—the region where temperatures could allow liquid water to exist on a solid surface. However, because the star is dim, the planet receives about the same amount of energy as Earth gets from the Sun, making it a potentially temperate world.
What Might the Atmosphere Be Like?
One of the most exciting aspects of TOI-1231 b is the possibility of studying its atmosphere. Its relatively low density and temperate orbit suggest it could have a thick hydrogen-helium envelope, similar to Neptune. But there’s also a chance it could contain water vapor, methane, or other molecules that could hint at biological activity. Future observations with the James Webb Space Telescope (JWST) could probe the planet’s transmission spectrum—the fingerprints of gases in its atmosphere when starlight filters through it. If JWST detects significant water vapor or methane, that would be a major step toward understanding exoplanet atmospheres.
Potential for Clouds and Hazes
Many exoplanets of this size show featureless spectra due to high-altitude clouds or hazes that block deeper atmospheric signals. TOI-1231 b might be different. Its host star is quiet, with low levels of ultraviolet radiation that can break apart molecules and create haze. This could mean a clearer view of the lower atmosphere. Astronomers are eager to see whether JWST will reveal distinct spectral features.
Could This Planet Support Life?
While TOI-1231 b is in the habitable zone, being a sub-Neptune—likely a gaseous world with no solid surface—makes it an unlikely candidate for life as we know it. Organisms would need to float in the atmosphere or live on hypothetical moons. The planet’s mass and radius suggest it probably has a thick atmosphere, and the surface pressure would be immense. Still, the discovery is valuable because it demonstrates that temperate, small planets exist around red dwarfs, which are the most common stars in the galaxy. If life can arise on such worlds, the number of potential habitats skyrockets.
What Makes This Discovery Special?
- Bright star: TOI-1231 is one of the brightest M-dwarfs hosting a transiting temperate planet, making follow-up observations easier.
- Favorable orbit: The planet’s 24-day orbit is long enough to allow detailed atmospheric studies without being too close to its star.
- Accessible for JWST: The planet’s atmospheric signal is expected to be strong, and JWST can observe it within its first few years of operation.
- Comparison to other planets: TOI-1231 b fills a gap between smaller super-Earths and larger Neptunes, helping refine models of planet formation.
Future Observations and Next Steps
The research team has already been awarded time on the Hubble Space Telescope to observe TOI-1231 b in the near-infrared. Hubble will look for evidence of water absorption. Meanwhile, ground-based observatories will continue monitoring the system for additional planets. The radial velocity data hint at a possible second, more distant companion, though that remains unconfirmed. The ultimate goal is to characterize the atmosphere in detail and compare it to other exoplanets in similar orbits.
The Role of Citizen Science
Part of the discovery involved citizen scientists who helped vet TESS data through the Exoplanet Explorers project. Volunteers flagged the initial transit signals, which the professional team then confirmed. This collaborative approach accelerates the pace of discovery and engages the public in cutting-edge research.
What This Means for Exoplanet Research
Each new planet discovered adds a piece to the puzzle of how planetary systems form and evolve. TOI-1231 b is particularly valuable because its star is bright and its orbit is favorable for atmospheric characterization. With JWST now operational, the next few years will be transformative. We may soon have spectra of a dozen or more temperate exoplanets, revealing the diversity of atmospheres in the galaxy. The new planet discovered is another step toward answering the age-old question: Are we alone?
