An Aside - Are There Alien Worlds in Our Own Solar System?

I came across an interesting article: "Did Our Sun Capture Alien Worlds? Close Encounter May Explain Some Objects Beyond Neptune." Seems many billions of years ago our sun may have had a "side-swipe" with another solar system - resulting in our picking up some alien riders. Through a telescope one can see galaxies in the midst of a collision, and others heading toward one. Why not with solar systems as well?

Reference:

University Of Utah. "Did Our Sun Capture Alien Worlds? Close Encounter May Explain Some Objects Beyond Neptune." ScienceDaily 9 December 2004. 4 November 2007 .