Though it's not technically an "exoplanet," it's certainly an alien world that's been causing some buzz this year. Planet Nine is a hypothetical planet at the edge of our solar system that would take an incredible 10,000 to 20,000 years to orbit the sun. Through modeling and simulations, the researchers say that the existence of Planet Nine could help explain the motion of objects in the Kuiper Belt, an icy realm beyond Neptune. The research was done by the California Insititute of Technology's Konstantin Batygin and Mike Brown; Brown is best known for finding several nearly Pluto-sized objects in the outer solar system.
WATCH VIDEO: How the Mysterious Planet 9 is Tilting Our Solar System