"quilty" kirjoitti viestissä
om...
No body in the Solar System is round. I assume that
you'd have to go by some sort of percentage deviation
from a iso-potential surface.

Perhaps he meant "roundish"?

Just off the top of my head, we'd add: Earth's Moon,
Io, Europa, Ganymede, Callisto, Titan, Titania, Triton,
and Charon. If we take it all the way down to Ceres'
size / sphericity it'll be a mess. The big question is,
where's the dividing line and WHY?

Maybe I was just reading between the lines, but I got the impression
that he was going on the principal that planets orbit a star and moons
orbit a planet which orbits said star. That would leave out all of the
moons that you listed.

Since you seem violently against such criteria, what would you suggest
as a criteria for determining whether an object is a planet?

Gravity is proportial to mass. If all objects are put in a same list in the
order of their mass we can see that there are some clear limits of different
groups:
1.Sun is a star, it is a thousand times as massive as the biggest planet
Jupiter.
2. The giant gas planets are clearly one group.
3.The terrestial planets could be considered another group as the smallest
gas planet Uranus is 14.6 times more massive than Earth. However both these
groups are clearly planets. Both groups have roughly as massive metal and
stone cores.
4. The moons, asteroids, comets and kuiper belt objects(KBO) are clearly
smaller in size. The smallest planet Mercury is 4,5 times more massive than
biggest of them, our Moon.
5. Pluto is 18.4 times lighter than the smallest planet Mercury, so it is
not a planet by weight. It is clearly a Kuiper belt object, the biggest, but
only slightly bigger than the next 100 KBOs known today and belongs to that
group. There are many moons bigger than Pluto. Pluto is called a planet only
because it was found years before other KBOs