Unusual planet discovered in an orbit that has never been seen before

In a finding that reshapes what we thought we knew about how planets move, astronomers have discovered a planet that orbits at a perfect right angle – 90 degrees – around two stars.

This type of orbit, called a polar orbit, has been suggested in theory and hinted at through indirect observations. But until now, there was no solid evidence that such a planet existed.

The discovery comes from scientists at the University of Birmingham, who made the observation using the European Southern Observatory’s Very Large Telescope (VLT) in Chile.

The exoplanet, named 2M1510 (AB) b, circles a rare pair of brown dwarfs – objects larger than gas-giant planets like Jupiter but not massive enough to qualify as full-fledged stars.

Strange planet in a unique system

Planets that orbit two stars – like Tatooine from Star Wars – are not unheard of. Several of them have been identified in recent years. But they tend to orbit in the same flat plane that the two stars share as they revolve around each other. What sets this new planet apart is its highly tilted, perpendicular path.

“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.

The host system, known as 2M1510, is no ordinary binary. It’s only the second known pair of brown dwarfs that eclipse each other from Earth’s viewpoint.

Because of these eclipses, the system provided ideal conditions for astronomers to closely track shifts in motion. This made it possible to detect the tug of a hidden planet with a surprising orbit.

Tilted orbit around two brown dwarfs

The planet’s configuration is a triple rarity. It orbits not just any binary, but a binary brown dwarf, and does so in a polar orbit.

These orbits were previously thought to be possible based on computer models and evidence of tilted planet-forming discs. But this is the first time astronomers have found a planet that actually moves in such a way.

“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 Amaury Triaud, a professor at the University of Birmingham.

An accidental discovery

The researchers did not originally set out to find this type of planet. They were studying the brown dwarfs themselves, collecting data using the Ultraviolet and Visual Echelle Spectrograph (UVES) on the VLT.

The brown dwarf system had been discovered in 2018 by Triaud and colleagues using another instrument called SPECULOOS, also located at ESO’s Paranal Observatory.

While refining the physical and orbital characteristics of the binary, the experts noticed irregular movements – small wobbles and shifts that didn’t match predictions.

Those unexplained changes led the team to suspect a hidden third object was influencing the system.

A surprising turn of events

“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,” said Baycroft.

Triaud noted that the discovery was serendipitous, as the observations were not collected to seek such a planet, or its unusual orbital configuration. “As such, it is a big surprise.”

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

The rare planet opens up new possibilities in our understanding of how planets form and behave, especially in unusual systems. It’s a reminder that space doesn’t always follow the rules we expect.

Mystery of the new planet’s orbit

The discovery also raises new questions about how planets form and settle into their orbits. Most known planets – especially those in binary systems – tend to follow predictable, flat paths. So how did 2M1510 (AB) b end up in such an unusual position?

Scientists suspect that gravitational interactions during the system’s early years may have tilted the planet’s orbit, but the exact mechanism remains unclear.

Finding a planet on a polar orbit challenges long-held assumptions about how orderly and consistent planetary systems are supposed to be. It suggests that nature may allow for a much greater variety of planetary arrangements than we’ve seen so far.

The full study was published in the journal Science Advances.

Image Credit: ESO/L. Calçada

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