The early evolution of the Solar System clearly presents a gap in our understanding. There have been a huge number of simulations done about how the evolution might have gone, and a recent study, investigating into the dynamic instabilities of the early orbits, has reached a stunning conclusion. The startling finale is this: There was a fifth giant planet, about as big as Jupiter, that was simply ejected from the Solar System, so as to lend stability to the entire planetary system.
A Cosmic Billiard Ball Game
The study, led by Dr. David Nesvorny, looks into the instabilities when the Solar System was as young as 600 million years (about a tenth of its current age). As expected the scattering process would be dominated by the giant planets, primarily Jupiter, simply because of its high mass. It would have either gobbled up small objects coming in from the outer Kuiper belt or severely deflected them from their orbits. The problem is that this situation would be reflected in the inner Solar System too. If the orbit of Jupiter stabilized slowly, it would transfer enough momentum to deflect the orbits of Mars, Earth and Venus. They could’ve even collided into one another.
The solution to this colliding billiard ball problem is to make Jupiter jump’ from one orbit to another, in what is called a Jumping Jupiter’ theory. This sudden change of Jupiter’s orbit would prevent it from transferring the large amount of momentum to the inner planets, leaving them as they are found now. However, Dr. Nesvorny found a new anomaly. Every simulation that he did with a jumping Jupiter showed Uranus or Neptune being pushed out of the Solar System. Since we see Uranus and Neptune today, this couldn’t have been the scenario.
A Fifth Giant
But, you can just add a fifth giant planet, which would play role of a leaving planet. Simulations show that this solves every problem. So the inner planets were left untouched, Jupiter jumped, Uranus and Neptune stayed within the Solar System, but a fifth giant planet had to leave the scene. This is what Dr. Nesvorny has to say:
The possibility that the solar system had more than four giant planets initially, and ejected some, appears to be conceivable in view of the recent discovery of a large number of free-floating planets in interstellar space, indicating the planet ejection process could be a common occurrence
Time and time again, that line from Shakespeare comes to memory There are more things in heaven and earth that are dreamt of in your philosophy.