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Rare Exoplanet Found Orbiting Brown Dwarfs in Polar Path
WASHINGTON – In a scene reminiscent of the iconic film “Star Wars,” where Luke Skywalker observes twin suns on Tatooine, astronomers have now identified a real-world celestial body with an even more peculiar configuration. This newly discovered exoplanet, designated 2M1510 (AB) b, is a circumbinary planet, but instead of orbiting two stars, it circles a pair of brown dwarfs. Adding to its uniqueness, this planet’s orbit is significantly tilted, following a polar orbit, a phenomenon rarely observed in planetary systems.
Unconventional Celestial System
Brown dwarfs, sometimes called “failed stars,” are celestial objects that exist in the mass range between the largest gas giant planets and the smallest stars. They lack the necessary mass to sustain stable nuclear fusion like stars, yet they are considerably more massive than planets and emit a faint luminosity. Using the Very Large Telescope in Chile, researchers with the European Southern Observatory detected this unusual planet approximately 120 light-years away from Earth.
Planet Details and Orbital Path
This newly found exoplanet is estimated to be a gas giant with a mass at least four to five times that of Earth. It orbits two closely bound brown dwarfs, each around 35 times the mass of Jupiter. For context, a light-year is equal to roughly 5.9 trillion miles (9.5 trillion km). The two brown dwarfs in this system are gravitationally linked and orbit each other at a distance of only 4% of the Earth-Sun separation. The planet 2M1510 (AB) b orbits this binary pair. A third, more distant brown dwarf exists in the same system but its gravitational influence on the inner pair is negligible due to its distance, approximately 250 times the Earth-Sun separation.
Circumbinary Planets: A Rare Class
Among the roughly 5,800 confirmed exoplanets beyond our solar system, only 16 are classified as circumbinary planets. Notably, all previously known circumbinary planets orbit ordinary stars, not brown dwarfs. This discovery marks the first instance of a planet found orbiting a pair of these substellar objects.
Polar Orbit: A Unique Trajectory
The orbit of this planet is also exceptional. Unlike typical planetary orbits that align with the orbital plane of their host stars, this planet exhibits a nearly perpendicular orbit – a polar orbit. This means the planet’s path is significantly inclined relative to the plane in which the two brown dwarfs orbit each other. The planet takes at least 100 days to complete one revolution around the brown dwarf pair.
Polar Orbits Explained
Thomas Baycroft, lead author of the study published in Science Advances and a doctoral student in astronomy at the University of Birmingham, explained the concept using an Earth analogy: “A satellite in a polar orbit around Earth passes over the north and south poles. Its orbit is inclined at 90 degrees relative to Earth’s rotation axis.” No planet in our solar system possesses a polar orbit. While some known exoplanets do have such orbits, they all orbit single stars, not binary systems.
Tatooine vs. Reality
Binary systems, like the fictional Tatooine system in “Star Wars”, involve two stars or brown dwarfs orbiting each other. However, the view from this newly discovered planet would differ from Luke Skywalker’s fictional vista.
Visual Perspective
Baycroft noted, “This would contrast with the Tatooine depiction. Both brown dwarfs would appear identical and red. As brown dwarfs, they are generally dimmer than our sun, although their apparent brightness in the sky would depend on the planet’s proximity to them.” These particular binary brown dwarfs each have a mass roughly 4% of the sun’s and are only about 0.1% as luminous.
Expanding Knowledge of Planetary Systems
Amaury Triaud, astrophysicist at the University of Birmingham and co-author, highlighted the significance of the finding: “This appears to be an extraordinary arrangement for a planetary system. Perhaps the most significant finding since the initial discovery of exoplanets has been the sheer diversity of planetary systems. They consistently surprise us, and this is excellent, as it offers incredible opportunities for learning.”
While scientists had previously theorized about the possibility of exoplanets in polar orbits around binary systems, this discovery offers the first compelling observational evidence, according to Triaud.