Close Encounters with Another Galaxy

The outer reaches of our solar system may have been shaped long ago by a close encounter with another star that tore up both nascent planetary systems like colliding buzz saws, astronomers said today.
The dramatic encounter, if it occurred, might even have deposited an alien world into our midst.
 The scenario was devised to describe unexplained observations of the solar system but is based on speculation about actual events. The resulting computer simulations suggest a range [of] possible outcomes for a close celestial brush shortly after the planets formed, about 4.5 billion years ago.

[4,500,000,000 years ago the enormous Angona system began its approach to the neighborhood of this solitary sun. The center of this great system was a dark giant of space, solid, highly charged, and possessing tremendous gravity pull. -Urantia Paper 57 (1934)]