According to this brief article, two astrophysicists think they found evidence of a gas giant in our solar system
much bigger than Jupiter:
The name of the planet is Tyche. The scientists are John Matese and Daniel Whitmire, from the University of Louisiana at Lafayette. According to them, this colossus is hiding in the Oort Cloud—the asteroid beehive that forms the outer shell of our home system, one light-year in radius. They claim that data already captured by NASA's Wide-field Infrared Survey Explorer proves its existence. It only needs to be analyzed... over the next two years.