  | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
      | 
   
   
    | • | 
    Most
    on long elliptical orbits 
     | 
     | 
   
   
     | 
   
   
     | 
    – | 
    Short
    period comets – go to outer solar 
     | 
     | 
   
   
     | 
    system 
     | 
     | 
   
   
     | 
   
   
     | 
    • | 
    “Jupiter
    family” still ~ in plane of ecliptic 
     | 
     | 
   
   
     | 
   
   
     | 
    • | 
    “Halley
    family” are highly inclined to ecliptic 
     | 
     | 
   
   
     | 
   
   
     | 
    – | 
    Longer
    period ones go out thousands of AU 
     | 
     | 
   
   
     | 
   
   
     | 
    • | 
    Most
    of these are highly inclined to ecliptic 
     | 
     | 
   
   
     | 
   
   
    | • | 
    Become
    active only in inner solar system 
     | 
   
   
     | 
   
   
     | 
    – | 
    Made
    of volatile ices and dust 
     | 
     | 
   
   
     | 
   
   
     | 
    – | 
    Sun
    heats and vaporizes ice, releasing dust 
     | 
     | 
   
   
     | 
   
   
     | 
    – | 
    “Dirty
    snowball” model 
     | 
     |