Big discovery reveals planet in upright orbit around brown dwarf binary

Big discovery reveals planet in upright orbit around brown dwarf binary
by Erica Marchand
Paris, France (SPX) Apr 22, 2025

Astronomers using the European Southern Observatory's Very Large Telescope (VLT) have uncovered the first robust evidence of a planet following a polar orbit around a binary system-a configuration long theorized but never confirmed until now.

Named 2M1510 (AB) b, the exoplanet circles a pair of brown dwarfs at a dramatic 90-degree angle to their mutual orbital plane. This makes it the inaugural verified example of a "polar planet" around a double-star system. While previous studies hinted such orbits might be feasible, this marks the clearest observational proof to date.

Brown dwarfs, which are more massive than gas giants but fall short of the mass needed to sustain hydrogen fusion like true stars, are rarely found in eclipsing binaries. The host duo in this case is only the second known eclipsing brown dwarf pair-and the first to host an exoplanet.

Lead author Thomas Baycroft, a PhD researcher at the University of Birmingham, emphasized the significance of the find: "I am particularly excited to be involved in detecting credible evidence that this configuration exists."

The planet's odd trajectory was revealed during a detailed study of the brown dwarfs using ESO's Ultraviolet and Visual Echelle Spectrograph (UVES) at the Paranal Observatory in Chile. Originally discovered in 2018 via the SPECULOOS project, the 2M1510 system drew further attention when astronomers noticed irregular gravitational interactions affecting the stars' motion.

"We reviewed all possible scenarios, and the only one consistent with the data is if a planet is on a polar orbit about this binary," Baycroft explained.

The team had not set out to search for a planet with this orientation. As co-author Amaury Triaud, also of the University of Birmingham, noted: "The discovery was serendipitous, in the sense that our observations were not collected to seek such a planet, or orbital configuration. As such, it is a big surprise."

Triaud added: "A planet orbiting not just a binary, but a binary brown dwarf, as well as being on a polar orbit is rather incredible and exciting."

The finding broadens the known diversity of planetary systems and supports theoretical models suggesting that planet-forming discs around binaries can evolve into such extreme orbital arrangements. It also underscores how ongoing, high-precision observation programs can yield surprising insights into celestial mechanics.

"Overall, I think this shows to us astronomers, but also to the public at large, what is possible in the fascinating Universe we inhabit," Triaud said.

Research Report:Evidence for a polar circumbinary exoplanet orbiting a pair of eclipsing brown dwarfs