One of our planets is missing: Scientists say solar system may have once included a 5th 'giant'

Have you seen this planet?

It's complicated.

Numbers and theories, computer simulations and gravitational lensing (don't ask because we have no idea).

Discovery News is reporting that scientists believe a fifth "giant planet" - in addition to Jupiter, Saturn, Uranus, and Neptune - once was part of our solar system. The theory is supported by a new set of computer simulations by David Nesvorny of the Southwest Research Institute in Boulder, Colo. According to the website:

Nesvorny models place a fifth hefty planet, several dozen times the mass of the Earth at various possible locations in the outer solar system: midway between Saturn and Uranus, and just beyond Neptune. In this game of orbital musical chairs, the fifth planet was ejected after a tussle with Jupiter –- sort of a celestial King Kong vs. Godzilla.

This is where "gravitational lensing" and other things that we will never understand come into play. Just in case you're curious, though:

First, it is known that Uranus and Neptune are too far from the sun for them to have formed in their present locations. There simply has not been enough time and materials for them to agglomerated into 15-Earth mass worlds. Uranus and Neptune must have formed closer into the sun and then migrated outward.

This implies that the early solar system was very chaotic. Smaller bodies, the planetesimals, were gravitationally kicked around and the exchange of momentum widened the orbits of the outer planets. Our moon bears the scars of this rough and tumble period called the Late Heavy Bombardment, of about 4 billion years ago.

The planetesimal debris was then snowplowed outward to form the Kupier belt, where Pluto dwells. Kuiper belt objects are not spread out uniformly in but are clustered into three distinct populations. This means that the belt was; extensively sculpted by the gravitational influence of the giant planets.

Relax. We won't be having a quiz later.