On August 24, 2006, Pluto was demoted as a planet. Nearly ten years later, Caltech researchers, Mike Brown and Konstantin Batygin, have discovered another to take its place: Planet Nine, or Planet X. With a mass 10 times that of Earth and an orbit 20 times that of Neptune, Planet Nine is believed to be the answer to the unusual alignment and eccentric orbits of a handful of dwarf planets in the Kuiper Belt. While all the numbers point to the possibility of another planet in the outer solar system, the race is on to find it. Could Pluto have finally met its replacement?