An astronomer has proposed the existence of an unseen planet in the distant outskirts of the solar system. It would explain the peculiar motions of Kuiper belt objects.
"A planet four times the size of Earth may be skirting the edges of the solar system beyond Pluto, according to new research. Too distant to be easily spotted by Earth-based telescopes, the unseen planet could be gravitationally tugging on small icy objects past Neptune, helping explain the mystery of those objects' peculiar orbits."
"The claim comes from Rodney Gomes, a noted astronomer at the National Observatory of Brazil in Rio de Janeiro."