Free Astronomy Magazine July-August 2025

JULY-AUGUST 2025 T his illustration shows an exo- planet orbiting around two brown dwarfs –– objects bigger than gas-giant planets but too small to be proper stars. [ESO/M. Kornmesser] tronomers 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. “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,” says co-author Amaury Triaud, a professor at the University of Birmingham. The team found this planet while refining the or- bital and physical parameters of the two brown dwarfs by collecting ob- servations with the Ultraviolet and Visual Echelle S p e c t r o g r a p h (UVES) instrument on ESO’s VLT at Paranal Observa- U sing ESO’s Very Large Telescope (VLT), astronomers have found an exoplanet orbiting a pair of peculiar stars at an angle of 90 degrees. There have previously been hints that these so-called polar planets around two stars could exist, but we now have clear evidence that this is the case. This special system was found by observing the orbital path of the two stars being pushed and pulled in a way that could only be explained by the presence of a planet on a polar orbit. This video summarises the discov- ery, explaining the nature of these peculiar stars and the method astronomers used to find this odd planet. [ESO] tory, Chile. The pair of brown dwarfs, known as 2M1510, were first detected in 2018 by Triaud and others with the Search for habit- able Planets EClipsing ULtra-cOOl Stars (SPECULOOS), another Paranal facility. The astronomers observed the or- bital path of the two stars in 2M1510 being pushed and pulled in unusual ways, leading them to infer the existence of an exoplanet with its strange orbital angle. “We re- viewed all possible scenarios, and the only one consistent with the data is if a planet is on a polar orbit about this binary,” says Baycroft. “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,” says Triaud. “Overall, I think this shows to us as- tronomers, but also to the public at large, what is possible in the fasci- nating Universe we inhabit.” The unprecedented exoplanet, named 2M1510 (AB) b, orbits a pair of young brown dwarfs — objects bigger than gas-giant planets but too small to be proper stars. The two brown dwarfs produce eclipses of one another as seen from Earth, making them part of what as- !