David Nesvorny from Colorado’s Southwest Research Institute reached the conclusion after performing around 6,000 computer simulations about the formation of the solar system, nearly all of which required the extra planet to work. Almost all of the simulations that factored in only the planets we know of in our solar system showed the four gas giants violently destroying one another. In the few simulations in which they survived, several of the rocky planets, such as Earth, were destroyed instead.