Astronomers spot rare three-planet system in a tight binary, likely with planets transiting both stars

by Cezar Valentin Ionescu, Ph.D. student

31.10.2025

Credit: Mario Sucerquia (University of Grenoble Alpes)

On Oct 29, 2025 an international team reports three Earth-size worlds in TOI-2267, a compact pair (binary system) of cool dwarf stars separated that are about 190 light-years away from us. Space-based TESS data and ground telescopes (SPECULOOS/TRAPPIST) reveal two confirmed planets with 2.28-day and 3.49-day periods plus one possible candidate near 2.03 days period.

The binary system is separated by roughly eight astronomical units (comparable to the distance between the Sun and Saturn) making it a stringent environment in which to assemble and keep planets. The light curves show two secure, repeating transit signals with periods of 2.28 and 3.49 days, and a third candidate at about 2.03 days. Transits are slight, periodic dips in starlight when a planet crosses the face of its star, from the dip depth alone the team infers planet sizes around one Earth radius, with the exact radius ranges depending on which star each planet orbits.

A key complication is the fact that the light we observe comes from both stars, so attributing each transit to star A or star B is not straightforward. The authors therefore combine the photometry with a dynamical-stability analysis as such they concluded that if all three bodies circled the same star at those tight spacings, the system would not remain stable over long times. The most robust solution has two planets around one star (the 2.28- and 3.49-day pair) and the third body orbiting the companion star. If that architecture is correct, TOI-2267 becomes the first known binary where we see transiting planets against both stellar component so rare geometry that lets astronomers compare planet properties in nearly the same system but under two slightly different host stars.

Reference: DOI: 10.1051/0004-6361/202554419