“Planet Nine” is theorized to be 10 times larger than Earth and is supposedly located somewhere in the outer reaches of our solar system, but it may not be a real planet after all, but instead a massive disc of smaller objects lying just beyond Neptune that exerts the same gravitational force as a super-Earth-sized planet. This mysterious planet is thought to be located so far from the Sun that it reflects very little light, and scientists have based its existence based on the strange clustered orbits of a group of trans-Neptunian Objects (TNOs), which includes Pluto. Read more for another video and additional information.
“When combined with a simplified model of the solar system, the gravitational forces of the disc can account for the unusual orbital architecture exhibited by some objects at the outer reaches of the solar system. Theirs is not, they concede, the first theory involving such a disc, but it is the first, they say, which explains the significant features of the observed orbits while accounting for the mass and gravity of the other eight planets in our solar system,” according to Cosmos Magazine.