There are rogue planets that have been knocked out of orbit just chilling out in the universe, and they could do the same to another planet.
These rogue planets do not orbit a star, and so it's pretty hard to glimpse them – in fact we don't actually know if there are any nearby at all. Statistically speaking, however, they are not close enough to be a concern and really we're a pretty small target given the size of the solar system.
@spacepictureloversspecial
