In a recent article published in Science Magazine, astronomers Mike Brown and Konstantin Batygin have found circumstantial evidence that a Neptune size planet exists in an elliptical orbit beyond Pluto.
Sedna and five other objects in the outer solar system are grouped together as if they are being shepherded by a larger body. Batygin and Brown say there’s only a 0.007% chance, or about one in 15,000, that the clustering could be a coincidence.

See Full Article in Science Magazine