Defying expectations that binary systems are unlikely areas for planet formation, an international team of researchers has now identified a trio of Earth-sized exoplanets 190 light-years away in the TOI-2267 system.
How these planets could form and maintain their stability in such an environment is a significant question for astronomers. The stars within this system are only separated by eight astronomical units (AU), far closer than the tens to hundreds of AU theoretically demonstrated to provide a stable planet-forming environment in earlier work.
A Strange System
“Our analysis shows a unique planetary arrangement: two planets are transiting one star, and the third is transiting its companion star,” said co-lead author Sebastián Zúñiga-Fernández, researcher and member of the ExoTIC group at the University of Liège (ULiège). “This makes TOI-2267 the first binary system known to host transiting planets around both of its stars.”
The system in question is unusual not just for its planets but also for the extremely tight orbit of the binary pair. That closeness should only exacerbate the gravitational instability of binary systems, adding further confusion to the situation.
Researchers say that this observation runs counter to multiple commonly accepted models of planet formation. Despite those expectations, recent observations made by the Atacama Large Millimeter/submillimeter Array (ALMA) and the Very Large Telescope (VLT) have revealed planet-forming disks around binary stars. Still, none were observed under conditions quite this close.
“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,” explained study co-lead author Francisco J. Pozuelos, a former member of the ExoTIC group, who is currently a researcher at the Instituto de Astrofísica de Andalucía (IAA-CSIC).
Discovering the Binary Star Exoplanets
The astronomers from ULiège and IAA-CSIC behind the discovery used their self-developed software, SHERLOCK, in the research, which was fed by data collected by NASA’s TESS space telescope. Following their initial discovery, the team conducted subsequent observations that confirmed their findings for two of the three planets, with the third remaining likely but unconfirmed. Intriguingly, dynamical analyses suggest that the planets must be split between the two binaries rather than orbiting a single star
These confirmations were performed using ground-based telescopes such as SPECULOOS and TRAPPIST. Most known exoplanets surround the most common type of star in the universe, the M-class Dwarf. The features of M Dwarfs include cool temperatures, low masses, and small sizes, making them particularly easy to observe exoplanets around. The team selected these telescopes for their ability to observe small exoplanets around faint, cool stars, which are typically difficult to detect.
“Discovering three Earth-sized planets in such a compact binary system is a unique opportunity,” explains co-lead author 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.”
Continued Exploration
“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,” Pozuelos said.
From this discovery, future researchers will have a new target for testing new telescope systems. Today, the James Webb Space Telescope is joined by a new generation of ground-based systems capable of collecting data to aid in measurements of the masses and densities of celestial objects, as well as collecting spectrographic data about their compositions over tremendous distances.
Determining the habitable zone for this system will be exceptionally challenging, however, as both stars and their interactions must be accounted for.
Perhaps most excitingly, spectroscopy is now allowing scientists to characterize the atmospheres of such distant planets, looking for habitable atmospheres or even biosignatures. The study demonstrates how collating data from these various space and ground-based observation platforms can drive exoplanetary science.
The paper, “Two Warm Earth-sized Exoplanets and an Earth-sized Candidate in the M5V-M6V Binary System TOI-2267,” appeared in Astronomy and Astrophysics on October 24, 2025.
Ryan Whalen covers science and technology for The Debrief. He holds an MA in History and a Master of Library and Information Science with a certificate in Data Science. He can be contacted at ryan@thedebrief.org, and follow him on Twitter @mdntwvlf.