Beyond the Kuiper Belt are six objects with strange orbits that all point roughly in the same direction—and that could be the result of the gravitational tugs of a large, undiscovered planet in the solar system. If it’s truly out there, how did we miss it?
Astronomers, for one thing, estimate the planet it would be far enough away to make it extremely dim, thousands of times dimmer than Pluto. Even the most powerful telescopes could take some time to find it, even with directions. Which doesn’t mean we won't try. Neptune, after all, was discovered after irregularities in Uranus' orbit led astronomers to theorize that an unknown body was affecting the orbit through gravitational interaction.