Interesting. By that definition Mars wouldn't have moons at all, because Phobos and Deimos are way too small. And the four giants would have only a few moons instead of an armada.

I had a rather radical idea: Why not say that a moon can be a planet? Right now we say that something like Luna or Charon is either a moon or a planet. But we don't even have an official definition of the term "moon". What if we said: The term "planet" is referring to the physical nature of the object itself, and the term "moon" is referring to its role within a system of interacting bodies? This would have the following consequences, for example:

1) Luna is a terrestrial planet, because of its physical composition and mass. And it is a moon, because it has the terrestrial planet Earth as a planetary senior-partner.

2) Io, Europa, Ganymede, Callisto are terrestrial planets. And they are moons of the jovian planet Jupiter.

3) Triton is a dwarf planet. And it is a moon of the neptunian planet Neptune.

4) Charon is a dwarf planet. And it is a moon of the dwarf planet Pluto.

Okay, now I have an unrelated question: The gravitational pull of the sun regarding the orbit of Luna is bigger than the gravitational pull of the Earth, which is why Luna's orbit is always concave towards the sun. But why are the tidal forces caused by Luna regarding the oceans on Earth bigger than the tidal forces caused by the sun?