->> Such a condition exists only for Earth's moon, or so I
->> thought.  It may have been that at the time Clarke made his
->> argument, those outer moons of Jupiter had not yet been
->> discovered?

 DW> Maybe so. The condition, for a jovian satellite, boils down
 DW> to the orbital radius being more than about 23 million
 DW> kilometres. Satellite IX (Hades) exceds this limit, and is
 DW> listed in my 1971 issue of the Rubber Bible. I don't know
 DW> exactly when it was discovered. I am sure that other
 DW> satellites, even further out, have been discovered since.
 DW> When did Clarke make his argument.

Oh, gosh, I don't know.  I was doing good (if I was right) to recall that
it was Clarke who made the argument.

My recollection, though, is that it was based on both criteria.  The only
moon with a concave orbit, plus the largest moon-to-planet mass ratio.

---