Planet Nine is a hypothetical planet in the outer region of the Solar System. Its gravitational influence could explain a statistical anomaly in the distribution of orbits for a group of distant trans-Neptunian objects (TNOs) found mostly beyond the Kuiper belt in the scattered disc region. This undiscovered super-Earth-sized planet would have an estimated mass of ten Earths, a diameter two to four times that of Earth, and an elongated orbit lasting approximately 15,000 years. To date, efforts have failed to directly observe Planet Nine.

Speculation about the possible existence of a ninth planet began in 2014. Astronomers Chad Trujillo and Scott S. Sheppard noted the similarities in the orbits of Sedna and 2012 VP113 and several other objects. In early 2016, Konstantin Batyginand Michael E. Brown described how the similar orbits of six TNOs could be explained by Planet Nine and proposed a possible orbit for the planet. This hypothesis could also explain TNOs with orbits perpendicular to the inner planets and others with extreme inclinations, as well as the tilt of the Sun’s axis.

Batygin and Brown suggest that Planet Nine could be the core of a primordial giant planet that was ejected from its original orbit by Jupiter during the genesis of the Solar System. Others have proposed that the planet was captured from another star, is a captured rogue planet, or that it formed on a distant orbit and was scattered onto an eccentric orbit by a passing star.  *Wiki