Astronomers stunned by three Earth-sized planets orbiting two suns

"Our analysis shows a unique planetary arrangement: two planets are transiting one star, and the third is transiting its companion star," explains Sebastián Zúñiga-Fernández, a researcher at the University of Liège (ULiège) and first author of the paper. "This makes TOI-2267 the first binary system known to host transiting planets around both of its stars."

A Compact and Unusual Double-Star System

TOI-2267 consists of two stars locked in a close orbital dance, forming what astronomers call a compact binary system. Such systems create gravitational forces that typically disrupt planet formation. Despite this, researchers have detected three Earth-sized planets in tight orbits, a surprising outcome that challenges long-held theories about where rocky worlds can exist.

"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," says Francisco J. Pozuelos, a co-leader of the study and researcher at the Instituto de Astrofísica de Andalucía (IAA-CSIC).

Combining Space and Ground Observations

NASA's TESS space telescope first provided the data leading to this discovery. Two of the planets were initially identified by astronomers at ULiège and IAA-CSIC using their custom software tool, SHERLOCK. This early detection prompted ground-based observations to confirm the findings.

The confirmation process required a major effort involving several observatories. Among the most important were the SPECULOOS and TRAPPIST telescopes operated by ULiège (PI: Michaël Gillon). Designed to detect small exoplanets around cool, dim stars, these robotic instruments were vital for verifying the planets and studying their characteristics in detail.

A Natural Testbed for Planet Formation

"Discovering three Earth-sized planets in such a compact binary system is a unique opportunity," says 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."

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."

Looking Ahead to Future Exploration

The discovery opens up new questions about how planets form and persist in binary systems. Upcoming observations with the James Webb Space Telescope (JWST) and next-generation ground-based observatories could reveal more details, such as the planets' masses, densities, and even their atmospheric compositions.

Beyond its scientific importance, the finding underscores the value of combining data from space-based observatories like TESS with precise ground-based instruments such as SPECULOOS and TRAPPIST. Together, they continue to expand our understanding of how planetary systems form and evolve across the galaxy.