Question: Will another planet ever come into our solar system?

Iain Bethune answered on 25 Jun 2015:

There are two answers to this:

1) We may well find other planets (or at least dwarf planets) that already exist within our solar system that we have not yet detected. Especially in the outer regions of the solar system called the Kuiper belt, there are probably dozens of objects like Sedna, Makemake and other recently discovered dwarf planets.

2) There are possibly other planets that were ejected from other solar systems due to violent collisions or gravitational interactions, which could be travelling across interstellar space and could enter our solar system. The odds of one of these arriving in the solar system is very low (since the interstellar void is much much bigger than the solar system.