This hypothesized ninth planet (not you, sorry Pluto) might explain the unusual commonalities of extreme trans-Neptunian objects (ETNOs) 100s of AU from the sun. These ETNOs (such as dwarf planets and sednoids) have remarkably aligned orbits, suggest the existence of an undiscovered celestial body, dubbed Planet Nine, influencing them gravitationally.
There’s the even more hypothetical and highly theoretical Planet Eleven. It’s so obscure there aren’t even rumors about it.