Astronomers have found a planet orbiting a pair of stars at a 90° angle.
Known as a 'polar planet' because it orbits above and below the poles of its host star, this is the first time astronomers have found evidence of such a planet orbiting two stars at once.
The discovery was made using the European Southern Observatory’s Very Large Telescope (VLT).
Polar planets around binary stars
Binary stars – two stars that orbit one another – are common across the Galaxy, and some even have planets orbiting them.
Astronomers often refer to a planet orbiting a binary star pair as a 'Tatooine-like' world, in reference to the fictional planet in Star Wars in which two moons can be seen in the sky.
However, planets orbiting distant binary stars usually orbit in the same plane as the stars' orbits.
While there had been previous hints that polar planets – planets orbiting perpendicular to their star's orbital plane – exist around binary stars, this is the first strong evidence of such an alignment.
The study was led by Thomas Baycroft, a PhD student at the University of Birmingham, UK, and published in Science Advances.
About the polar planet
The exoplanet is named named 2M1510 (AB) b, and orbits a pair of young brown dwarfs.
Brown dwarfs are celestial objects bigger than gas giant planets, but still too small to be stars.
The two brown dwarfs in question are an 'eclipsing binary', which means that, from our view on Earth, they appear to pass in front of one another as they orbit.
This is only the second pair of eclipsing brown dwarfs known to date, and they also host the first polar planet ever found around a binary star system.
The brown dwarf pair is known as 2M1510 and was detected in 2018 by Triaud and others with the Search for habitable Planets EClipsing ULtra-cOOl Stars (SPECULOOS), another Paranal facility.
The team found 2M1510 (AB) b while taking a closer look at the two brown dwarfs using the Very Large Telescope.
While observing the stars, the team noticed they were wobbling in strange ways, which is one key indicator of a planet in orbit around a star.
But not just any old planet.
"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,” 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 Amaury Triaud, a professor at the University of Birmingham and co-author of the study.
"Overall, I think this shows to us astronomers, but also to the public at large, what is possible in the fascinating Universe we inhabit."
Read the full paper at www.science.org/doi/10.1126/sciadv.adu0627
