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Originally Posted by umop ap!sdn
Perhaps a moon could be required to meet any 2 of the following criteria:
- Tidal locked to planet
- Circular, prograde orbit
- Spherical
- More than a certain threshhold size or mass
But honestly, I don't see why it's so important to make any such distinction; it is not common knowledge how many moons there are in the solar system and there are no mnemonics AFAIK that attempt to list all of them.  |
Won't work. Every planet (and the Sun) meets the last two criteria. Why the focus on a prograde orbit, by the way? Is there a reason retrograde orbits wouldn't count?
I guess anything orbiting a planet or an asteroid or a KBO is nowadays called a moon (if it's not a ring), and the only way to stop the addition of more ones is perhaps to get a minimum size (mass), either absolute or relative to the parent.