From: henry@spsystems.net   
      
   In article ,   
   Jonathan Brimsfield  wrote:   
   >I am looking for the name of the area or group from which Jupiter, et al   
   >can nudge space rocks towards earth. I am *NOT* referring to the Asteroid   
   >Belt between Mars and Jupiter.   
      
   Unfortunately, that *is* the group in question.  There are zones within   
   the asteroid belt where resonances with Jupiter make orbits evolve very   
   rapidly and chaotically.  When an asteroid's orbit, evolving very slowly   
   by more subtle processes, enters one of those zones, it can be driven into   
   the inner solar system quite quickly.  If this process continues, the low   
   end of the orbit will soon be driven low enough to intersect the Sun...   
   but if the asteroid makes a close encounter with one of the inner planets   
   first, that can kick it out of the resonance, leaving a reasonably stable   
   orbit which is wholly or partly in the inner solar system.  And that in   
   turn gives it time to have some chance of actually hitting one of the   
   inner planets.   
   --   
   MOST launched 30 June; first light, 29 July; 5arcsec    | Henry Spencer   
   pointing, 10 Sept; first science, early Oct; all well.  | henry@spsystems.net   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)