Did Jupiter "bully" another giant planet out of the solar system some 4 billion years ago? Some space scientists think so.

Astrophysicists at the University of Toronto are floating the idea that the solar system could have had another extra planet, if not for a close encounter with Jupiter.

The ejected planet could have been the 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.

Since 2011, space scientists have been toying with the idea of another planet being pushed out of the solar system either by Jupiter or Saturn.

"Our evidence points to Jupiter," said Ryan Cloutier, a PhD candidate in the University of Toronto's department of astronomy and astrophysics and the lead author of a new study just published in The Astrophysical Journal.

How exactly did Jupiter manage to eject a massive planet out of the solar system?

Usually, a planetary ejection is a result of the close encounter between two heavenly bodies, where one of them accelerates so much that it breaks free even from the strong gravitational pull of the Sun, Cloutier said in an article in Astronomy Now.

What made Jupiter's "bullying" of another giant planet more fascinating, and at the same time baffling for space scientists, is that while making this move, the solar system's biggest planet managed to hold on to one of its "allies:" its moon Callisto.

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

"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," he added.