XPost: sci.space.policy   
   From: spam@merlyn.demon.co.uk   
      
   JRS:  In article , seen in   
   news:sci.space.policy, Henry Spencer  posted at   
   Sun, 15 Feb 2004 23:04:56 :-   
   >In article <7L+C+NC9oiLAFwEA@merlyn.demon.co.uk>,   
   >Dr John Stockton   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.)   
   >>   
   >>Why a pair of rubble piles?  Half a rubble pile is still a rubble pile,   
   >>and should itself be split (ignoring the presumably improbable case of   
   >>an encounter virtually tangent to the Roche limit).   
   >   
   >If memory serves -- I didn't pay close attention to the details -- the   
   >two-way split of a rubble pile is a non-trivial interaction between tidal   
   >forces and the rotation of the original rubble pile, and generally does   
   >not involve further splitting of the resulting two piles.   
   >   
   >Multi-way splits of fragile bodies are certainly possible, as witness SL9,   
   >but they generally don't leave the fragments in orbit around each other.   
      
   OK, I can easily enough believe that if the spin rate gives a   
   centrifugal effect non-negligible in comparison with surface gravity,   
   then the break-up will occur at a greater distance, and that the   
   subsequent distribution of angular momentum from spin into spin + spin +   
   orbital will leave the new spins insufficient for further break-up.   
      
   "The satellite is here assumed not to be spinning." is now added to my   
   Roche material in gravity3.htm.   
      
   --   
    © John Stockton, Surrey, UK.  ?@merlyn.demon.co.uk   Turnpike v4.00   MIME. ©   
    Web   - FAQqish topics, acronyms & links;   
    some Astro stuff via astro.htm, gravity0.htm; quotes.htm; pascal.htm; &c, &c.   
    No Encoding. Quotes before replies. Snip well. Write clearly. Don't Mail News.   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)