Planet 09 – National Geographic Kids Magazine

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.[1][4][5] 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.[6][7] To date, efforts have failed to directly observe Planet Nine.[8][9]

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.[4] 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.[1] This hypothesis could also explain TNOs with orbits perpendicular to the inner planets[1] and others with extreme inclinations,[10] as well as the tilt of the Sun’s axis.[11]

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.[12][13] Others have proposed that the planet was captured from another star,[14] is a captured rogue planet,[15] or that it formed on a distant orbit and was scattered onto an eccentric orbit by a passing star.[1][16][17]  *Wiki