What's the difference between a planet.... ?

Question

what's the difference between a planet and.. what ever pluto is (like just space junk or something ?) what are the characteristics that make it a planet, and what qualifies it as a non-planet... (is there a word for that ?)

Answer 1

Pluto is officially a Dwarf Planet. The same as a planet, but smaller and unable to clear the area around it. Still big enough, though, that it's gravity tucked it into a nice, round shape. That's why asteroids and such aren't Dwarf Planets; they are irregularly shaped because they're too small.

Answer 2

Dwarf planet is the term you're thinking of and the only thing that keeps Pluto from being a planet is that it has not cleared it's neighborhood of other objects.

Answer 3

Pluto is a dwarf planet, as well as the other objects in the Kuper Belt system.  A planet has to be a certain size, and must orbit the central star.  

Answer 4

A planet has to be in orbit around a star, high enough gravity to maintain a hydrostatic equilibrium (be round), and have cleared the neighborhood around its orbit (be the biggest thing in its orbit).

Pluto is a dwarf planet.  It's in orbit around a star (and not a satellite of anything else), has enough gravity to be sphereish, but crosses the orbit of Neptune every once in a while, and thus has not "cleared the neighborhood."