XPost: sci.space.policy   
   From: henry@spsystems.net   
      
   In article <1076439012.127427@haldjas.folklore.ee>,   
   Sander Vesik   wrote:   
   >> ...A close encounter with a planet can split a rubble pile   
   >> into a pair of rubble piles, by tidal interaction.  (In fact, one of the   
   >> points offered in support of the rubble-pile hypothesis is precisely that   
   >> we see a suspiciously large number of double asteroids, which ought to be   
   >> fairly rare unless there is some specific mechanism that creates them.)   
   >   
   >But if you have two piles of rubble orbiting each other, then surely   
   >tidal forces would over time convert these to fuzzy rubble-balls that would   
   >then coalesce into a single body?   
      
   Tidal forces within such a system will probably fairly quickly lock the   
   spin of each rubble ball to their orbit around each other, but the effect   
   of that on the spacing between them is quasi-random.  (For forward spins   
   it will move them outward, but there's no special tendency for such small   
   bodies to have forward spins.)  And if they're formed by fission of a   
   single body, they'll probably start out nearly locked anyway, so any   
   effect will be small.   
      
   Once that's happened, only solar tidal effects will change the spacing of   
   the system, and those will be very slow -- too slow, in an environment   
   where close planetary encounters happen frequently.   
   --   
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