Pluto - Planet or Moon?

[aussie1st]

The reason for Pluto demotion from what I have read

The key difference between planets and dwarf planets is that while both are required to orbit the Sun and be of large enough mass that their own gravity pulls them into a nearly round shape, dwarf planets are not required to "clear their neighborhood" of other celestial bodies.

http://en.wikipedia.org/wiki/Solar_...06_IAU_Resolution_on_the_Definition_of_Planet

Basically the term of "clearing their neighborhood"

 

[angryangy]

This is a much better way of understanding things. 2003 UB313 ("Xena") possesses all the characteristics that people judge Pluto to require to be a planet; it too has at least one tiny satellite (S/2005 (2003 UB313) 1, nicknamed "Gabrielle"), it is larger than Pluto and part of its orbit actually brings it closer to the Sun than Neptune.

Indeed, the asteroid Ceres (which can be considered a dwarf planet) was considered a planet for some time after its discovery. One might say that Pluto has been considered a planet for so long because it was too far away for anyone to be able to prove otherwise.