The Planet Nine hypothesis states that there’s a massive planet in our Solar System orbiting at a great distance from the Sun.
Nobody’s ever observed the hypothesized planet; the evidence for it lies in a cluster of bodies that orbit the Sun 250 times further out than Earth does. These objects are called e-TNOs, for extreme Trans-Neptunian Objects. According to the hypothesis, Planet Nine’s gravity is responsible for the unusual clustered orbits of these e-TNOs.
Now astronomers have found a distant solar system with its own Planet Nine, and that discovery is breathing new life into the hypothesis.
The planet is named HD 106906 b, and it orbits a binary star 336 light-years away. It has a mass of about 11 Jupiters, and it orbits the stars at a distance of more than 730 times the distance from Earth to the Sun. That’s an extremely distant orbit.
The paper presenting these results is titled “First Detection of Orbital Motion for HD 106906 b: A Wide-separation Exoplanet on a Planet Nine–like Orbit.” The first author is Meiji M. Nguyen from the University of California, Berkeley. It’s published in The Astronomical Journal.
The story of this discovery starts back in 2004 when the Hubble first observed HD 106906 b. At that time, little was known about the system. The Hubble observations were follow-up observations aimed at indirect evidence that a warm dust disk surrounded the star, and astronomers wanted to know more about that disk.