From: twomack@chiark.greenend.org.uk   
      
   In article <420a2ed8$0$70247$ed2619ec@ptn-nntp-reader03.plus.net>,   
   Ian Stirling   wrote:   
      
   >You of course need to pay attention to errors and rounding.   
      
   Well, yes ... I'm slightly surprised to find that, if I put massless   
   sample bodies in a variety of circular orbits around a point-mass   
   Iapetus, not only do the far-out ones rapidly escape into independent   
   Saturn orbits, but the closest-in ones [1000 to 2500km] have also left   
   orbit, on classical petal patterns, within 10^8 seconds.   
      
   Is this likely to be an integrator artefact?  I'm re-running with half   
   the time step (I was using 1000 seconds, which seemed pretty   
   conservative); I have no intuition about the N-body problem, but for   
   lower orbits *around a point mass* to be less stable than higher ones   
   seems implausible.   
      
   Tom   
      
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