April 9, 2009
The solar system oscillates past the galactic plane 2.7 times every rotation around the center of the Milky Way galaxy. This plane has lots of matter which can strike the earth. And these oscillations correspond with mass extinctions in earth's history. Of course it take the solar system 225 - 250 millions years to go around so, barring any rogue asteroids hitting us, we've got some time.