If so, it’s the 10th planet... not the 9th.
Are the planets of the solar system, that's 8. Once we got better data, we realized that while Pluto had sufficient gravity to coalesce into a sphere, it was not large enough clear itself of planetesimals, therefore did not meet the definition of a planet. Astronomers being a sentimental lot created a new (but unnecessary) classification for Pluto, Eris and Ceres.
Well Pluto got demoted some years back