Based on their calculations, they think Jupiter could have done those planets in. The massive gas giant would have messed with the orbits of all of the not-quite-planets forming in the life-giving dust of the early solar system. Once a couple of the unwieldy space rocks collided, it would cause a chain reaction of destruction. And based on simulations using the dimensions of a known super-Earth, the researchers believe that any planets in Jupiter's wake would be crushed by the onslaught of debris after just 20,000 years.