Planet Found Orbiting Sideways Around Twin Stars

In a finding that challenges conventional understanding of planetary systems, astronomers have discovered a planet orbiting perpendicular to its host stars. Using the European Southern Observatory’s Very Large Telescope (VLT), researchers identified this unique configuration around a pair of brown dwarfs—objects larger than gas giants but too small to be proper stars.

The discovery marks the first strong evidence of a planet orbiting at a 90-degree angle to the orbital plane of its binary star system, a configuration astronomers have theorized but never before confirmed.

“I am particularly excited to be involved in detecting credible evidence that this configuration exists,” said Thomas Baycroft, a PhD student at the University of Birmingham who led the study published in Science Advances.

The planet, named 2M1510 (AB) b, orbits around two brown dwarfs that eclipse each other when viewed from Earth. This system represents a remarkable rarity in astronomy—only the second known pair of eclipsing brown dwarfs, and now the first with a confirmed “polar” orbiting planet.

Brown dwarfs occupy a curious middle ground in cosmic classification—too massive to be considered planets but lacking sufficient mass to sustain the nuclear fusion that powers stars. They’re sometimes called “failed stars” for this reason.

The research team wasn’t originally hunting for planets. They were refining measurements of the brown dwarfs using the Ultraviolet and Visual Echelle Spectrograph (UVES) on the VLT in Chile when they noticed something unusual.

“The discovery was serendipitous, in the sense that our observations were not collected to seek such a planet, or orbital configuration,” explained Amaury Triaud, a professor at the University of Birmingham and co-author of the study. “As such, it is a big surprise.”

Most planets known to orbit binary stars travel in the same plane as the stars orbit each other—similar to how planets in our solar system roughly align with the Sun’s equator. This new planet, however, travels in an orbit perpendicular to its host stars, like a vertical loop crossing over the north and south poles of the binary system.

The researchers detected the planet indirectly by observing its gravitational effects on the orbits of the brown dwarfs. After careful analysis and elimination of alternative explanations, they concluded that a planet in a polar orbit was the only scenario consistent with their observations.

This unusual configuration matters beyond its novelty. It provides crucial insights into how planets form and the diversity of planetary systems in our galaxy. Theoretical models had suggested such configurations were possible, and astronomers had previously detected discs of gas and dust capable of forming planets in polar orientations around binary stars—but this is the first confirmed planet in such an arrangement.

The 2M1510 system is located relatively close to Earth in astronomical terms. The pair of brown dwarfs was first discovered in 2018 by Professor Triaud and colleagues using SPECULOOS (Search for habitable Planets EClipsing ULtra-cOOl Stars), another facility at the Paranal Observatory.

While the exact mass and orbital period of the planet remain uncertain, the team estimates that if the planet orbits close to the boundary of stability around the binary, it would have a mass approximately 10 times that of Earth and circle the brown dwarfs once every 100 days.

Researchers hope to further study the system with additional observations to refine the planet’s characteristics. Professor Triaud believes this discovery demonstrates what remains to be found in our cosmic neighborhood: “Overall, I think this shows to us astronomers, but also to the public at large, what is possible in the fascinating Universe we inhabit.”

The research was published in Science Advances with contributions from researchers at the University of Birmingham in the United Kingdom, University of Cambridge, and institutions in Portugal and France.