Jupiter likely hoyed giant planet out of solar system

Looks like, for Jupiter, our solar system wasn't big enough to fit in another giant planet.

Astrophysicists at the University of Toronto have found that a close encounter with Jupiter, about four billion years ago, may have resulted in another planet's ejection from the Solar System altogether.

The existence of a fifth giant gas planet at the time of the Solar System's formation - in addition to Jupiter, Saturn, Uranus and Neptune that we know of today - was first proposed in 2011. But if it did exist, how did it get pushed out?

For years, scientists have suspected the ouster was either Saturn or Jupiter. "Our evidence points to Jupiter," said lead author Ryan Cloutier.

Planet ejections occur as a result of a close planetary encounter in which one of the objects accelerates so much that it breaks free from the massive gravitational pull of the Sun. However, earlier studies which proposed that giant planets could possibly eject one another did not consider the effect such violent encounters would have on minor bodies, such as the known moons of the giant planets, and their orbits.

"Ultimately, we found that Jupiter is capable of ejecting the fifth giant planet while retaining a moon with the orbit of Callisto," said Cloutier, adding "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."

The study is published in The Astrophysical Journal.