There are eight classical planets in our solar system, from speedy Mercury to distant Neptune. There are also numerous dwarf planets, such as Pluto and Ceres. While we continue to find more dwarf planets, there are some hints that another large planet could lurk far beyond Neptune. This Planet Nine is thought to be a "super-Earth," about five times the mass of our planet, which would make it about twice as large as Earth. But despite several searches for the planet, it has not yet been found.