QUESTION:
I was wondering if our solar system actually be two solar systems which 
collided long ago.  I was wondering this since every nine years, 
Planet X comes into our solar system for about six months.  

ANSWER from Rhodri Evans on October 13, 1995:
There is no planet X as far as we know, so I don't know what you are 
referring to. We do not know exactly how our Solar System formed, but it 
was definitely from the left over material from another star which exploded 
some 5 billion years ago.

Rhodri Evans,
Yerkes Observatory (KAO group),
The University of Chicago,