The newly-discovered planet orbits at an angle of 90 degrees around 2MASS J15104786-2818174 (hereafter 2M1510), an eclipsing binary composed of two equal-mass brown dwarfs.
This illustration shows an exoplanet orbiting around two brown dwarfs. Image credit: ESO / M. Kornmesser.
Circumbinary planets are extrasolar worlds that exist in star systems with two stars, also known as binary star systems.
These planets typically occupy orbits that roughly align with the plane in which their host stars orbit each other.
There have previously been hints that planets on perpendicular, or polar, orbits around binary stars could exist: in theory, these orbits are stable, and planet-forming discs on polar orbits around stellar pairs have been detected.
However, until now, astronomers lacked clear evidence that these polar planets do exist.
“I am particularly excited to be involved in detecting credible evidence that this configuration exists,” said Thomas Baycroft, a Ph.D. student at the University of Birmingham.
The newly-discovered exoplanet, 2M1510b, orbits a pair of young brown dwarfs.
The two brown dwarfs produce eclipses of one another as seen from Earth, making them part of what astronomers call an eclipsing binary.
This system is incredibly rare: it is only the second pair of eclipsing brown dwarfs known to date, and it contains the first exoplanet ever found on a path at right angles to the orbit of its two host stars.
An artist’s impression of 2M1510b’s unusual orbit around a pair of brown dwarfs. Image credit: ESO / L. Calçada.
“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,” said University of Birmingham’s Professor Amaury Triaud.
The astronomers found 2M1510b while refining the orbital and physical parameters of the two brown dwarfs by collecting observations with the Ultraviolet and Visual Echelle Spectrograph (UVES) instrument on ESO’s Very Large Telescope.
They observed the orbital path of the brown dwarfs in 2M1510 being pushed and pulled in unusual ways, leading them to infer the existence of an exoplanet with its strange orbital angle.
“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 said.
“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,” Professor Triaud said.
“Overall, I think this shows to us astronomers, but also to the public at large, what is possible in the fascinating Universe we inhabit.”
This image shows the triple system 2M1510. Image credit: Centre de Données astronomiques de Strasbourg / SIMBAD / PanSTARRS.
The discovery was made possible thanks to pioneering data analysis developed by University of Cambridge’s Dr. Lalitha Sairam.
“From variations in velocity of the two brown dwarfs, we can measure their physical and orbital parameters, however being faint, these measurements and therefore their parameters were uncertain,” Dr. Sairam said.
“Thanks to that improvement we noticed the orbits of the two brown dwarfs around one another were being delicately affected.”
The study was published in the journal Science Advances.
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Thomas A. Baycroft et al. 2025. Evidence for a polar circumbinary exoplanet orbiting a pair of eclipsing brown dwarfs. Science Advances 11 (16); doi: 10.1126/sciadv.adu0627
