Scientists at the Cardiff Centre for Astrobiology built a computer model of our solar system's movement and found that it "bounces" up and down through the plane of the galaxy. As we pass through the densest part of the plane, gravitational forces from the surrounding giant gas and dust clouds dislodge comets from their paths. The comets plunge into the solar system, some of them colliding with the earth. The Cardiff team found that we pass through the galactic plane every 35 to 40 million years, increasing the chances of a comet collision tenfold.[note: this is the same idea advocated by the late Gene Shoemaker; also, this stands as an alternative to the Nemesis model for periodicity in the impact record]
Nemesis: Does the Sun Have a ‘Companion’?
SPACE dot COM | 03 April 2001 | By Robert Roy Britt
Posted on 02/10/2003 11:03:23 AM PST by vannrox
http://www.freerepublic.com/focus/f-news/839980/posts
Could An Asteroid Hit Planet Earth, Again?
Science Daily | 1-20-2008 | Planetary Society
Posted on 01/30/2008 3:46:10 PM PST by blam
http://www.freerepublic.com/focus/f-news/1962278/posts
Earth-sized planet predicted beyond Pluto
Cosmos Magazine | Friday, February 29, 2008 | Agence France-Presse
Posted on 03/20/2008 11:43:43 PM PDT by SunkenCiv
http://www.freerepublic.com/focus/f-chat/1989253/posts