An international team of researchers has just revealed the existence of three Earth-sized planets in the binary stellar system TOI-2267 located about 190 light-years away. This discovery, published in Astronomy & Astrophysics, is remarkable as it sheds new light on the formation and stability of planets in double-star environments, which have long been considered hostile to the development of complex planetary systems.
"Our analysis shows a unique planetary arrangement: two planets are transiting one star, and the third is transiting its companion star," says Sebastián Zúñiga-Fernández, researcher and member of the ExoTIC group at the University of Liège (ULiège) and first author of the study. "This makes TOI-2267 the first binary system known to host transiting planets around both of its stars."
An unusual double-star system
TOI-2267 is a compact binary: two stars orbit each other in a tight configuration, creating a gravitationally unstable environment for planet formation. Yet, researchers have identified three Earth-sized planets in short orbits, a surprising result that challenges several classical models of planetary formation.
"Our discovery breaks several records, as it is the most compact and coldest pair of stars with planets known, and it is also the first in which planets have been recorded transiting around both components," explains Francisco J. Pozuelos, a former member of the ExoTIC group, currently researcher at the Instituto de Astrofísica de Andalucía (IAA-CSIC), and co-leader of the study.
An international, multidisciplinary effort
While NASA's TESS space telescope provided the data, the initial identification of two of the three planets was first achieved by ULiège and IAA-CSIC astronomers using their own detection software, SHERLOCK. This early discovery allowed the team to trigger ground-based follow-up observations well in advance. The subsequent confirmation of the planetary nature of these signals required an intensive campaign with several observatories. Among them, the SPECULOOS and TRAPPIST telescopes, led by ULiège (PI: Michaël Gillon), played a central role. These robotic facilities, optimized for studying small exoplanets around faint, cool stars, were crucial in confirming the planets and characterizing the system.
A natural laboratory for planet formation
"Discovering three Earth-sized planets in such a compact binary system is a unique opportunity," explains Sebastián Zúñiga-Fernández. "It allows us to test the limits of planet formation models in complex environments and to better understand the diversity of possible planetary architectures in our galaxy."
Francisco J. Pozuelos adds: "This system is a true natural laboratory for understanding how rocky planets can emerge and survive under extreme dynamical conditions, where we previously thought their stability would be compromised".
Opening the door to future research
This discovery raises many questions about planet formation in binary systems and paves the way for new observations, notably with the James Webb Space Telescope (JWST) and the next generation of giant ground-based telescopes. These instruments will enable precisely measuring the masses, densities, and perhaps even the atmospheric composition of these distant worlds.
Beyond its spectacular nature, this discovery highlights the power of combining space missions with specialized ground-based telescopes, such as SPECULOOS and TRAPPIST, to push the frontiers of exoplanetary science.
