Yes, Dan. Please write another book! *g*
If you must include the story of a visiting planet/ball of matter, please include this explanation:
the Solar system will periodically pass through regions of dense particle matter. We are currently in the bubble of relatively clear space.
Of course, there is also the possibility that when our solar system passed through a dense particle(and then some) cloud, that it could have disrupted the orbits of our own rocky and icy neighbors in the Oort, Kuiper and asteroid belts. :) It may even explain Mars' present a-bit-off orbit from the other terrestrial planets.
Marcia