-> My recollection, though, is that it was based on both criteria.  The only mo 
-> with a concave orbit, plus the largest moon-to-planet mass ratio. 
  
That makes sense. 
  
I have been thinking about the "Greek" and "Trojan"
asteroids. We don't 
normally think of them as satellites of Jupiter, but they do go around 
the planet in roughly circular paths. And their trajectories are most 
definitely always concave to the sun. 
  
                                 dow 
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