http://books.google.co.th/books?id=eOoC0NjWW6sC&lpg=PA14&dq=Dwarf%20Planets&pg=PP1#v=onepage&q=Dwarf%20Planets&f=false
http://books.google.co.th/books?id=-31_iuRiMjcC&lpg=PA22&dq=Dwarf%20Planets&pg=PP1#v=on
http://www.amazon.com/When-Planet-Not-Story-Pluto/dp/0618898328/ref=sr_1_4?s=books&ie=UTF8&qid=1282030303&sr=1-4epage&q=Dwarf%20Planets&f=false
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