The simplest explanation is that the ninth planet had a close encounter with one of the other gas giants, and that it was pulled from the sun's gravitational pull as a result. But was it Saturn or Jupiter that did the deed? In the new study, researchers took a look at the orbits of the two planet's moons, looking for evidence that they could exist in their current trajectory after such a violent encounter.
"Our evidence points to Jupiter," lead author Ryan Cloutier, a PhD candidate at the University of Toronto, said in a statement.
"Ultimately, we found that Jupiter is capable of ejecting the fifth giant planet while retaining a moon with the orbit of Callisto. On the other hand, it would have been very difficult for Saturn to do so because Iapetus would have been excessively unsettled, resulting in an orbit that is difficult to reconcile with its current trajectory," Cloutier said.
This isn't the first time Jupiter has been fingered as an old school planetary bully, either. For a few years now, scientists have been throwing around something called the Grand Tack theory. It proposes that Jupiter, caught up in the pull of interplanetary dust just after its formation, made its way towards the sun. When it caught up with Saturn, the two planets pulled each other back to their current positions.
In March, another study suggested that Jupiter's Grand Tack through the solar system may have been responsible for destroying an entire set of planets that once orbited our sun.
If that really happened, we may have Jupiter to thank for our existence -- since it made room for Earth to form. But there's still something unsettling about a planet that habitually evicted its neighbors into interstellar space.