Rare Exoplanet Orbits Two Stars at a Wild 90-Degree Angle

In 2018, astronomers discovered a pair of brown dwarf stars orbiting each other in a rare system known as an eclipsing binary. Further observations show that the binary, named 2M1510, is even more unique than previously believed. Researchers are reporting the discovery of an exoplanet, named 2M1510 (AB) b, orbiting its host star at an angle of 90 degrees—called a polar orbit—in relation to the brown dwarfs’ orbital plane.

The discovery, made with the European Southern Observatory’s (ESO) Very Large Telescope (VLT), is the first time scientists have documented strong evidence of a “polar planet” orbiting a stellar pair, as detailed in a study published Wednesday in the journal Science Advances. “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,” Amaury Triaud, a co-author of the study and an astronomer at the University of Birmingham in the UK, said in an ESO statement . As of now, astronomers have discovered 16 circumbinary planets, according to the study: exoplanets orbiting two stars.



However, these planets’ orbits are roughly on the same plane as the binary stars’ orbit around each other. Before the recent discovery, scientists had only theorized the existence of such a system with a circumbinary planet on a perpendicular orbit—also called a polar orbit—based on clues such as the detection of perpendicular planet-forming disks around pairs of stars. “I am particularly excited to be involved in detecting credible evidence that this configuration exists,” said Thomas Baycroft , a PhD student in astronomy and astrophysics at the University of Birmingham and lead author of the study.

In addition to the exoplanet’s polar orbit, the brown dwarf pair itself is extraordinarily rare. They form an eclipsing binary, meaning their orbital paths make them eclipse each other as we see them from Earth. 2M1510 consists of only the second pair of eclipsing brown dwarfs known to science.

While studying these two brown dwarfs, Triaud, Baycroft, and their colleagues noted that their orbital paths were being strangely “pushed and pulled.” This suggested the presence of an exoplanet on an unusual orbital plane, whose gravity the researchers presumably believed was messing with the binary pair, according to the statement. “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 added.

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

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