It is now known for quite some time that our ninth planet, Pluto, is actually part of the Kuiper belt. The largest, recent discovery in the Kuiper belt is 2003 UB313, nicknamed Xena. It has led scientists to question the definition of the term "planet", as it is larger than Pluto and has already been called a tenth planet by some sources.
The current expectation is that the largest Kuiper belt objects, including Pluto, may be relabeled "dwarf planets" or something like it. The answer is apparently due in September.
Author Robert Roy Britt of LiveScience Blogs says: "If all goes as it should — meaning if astronomers can put aside their quibbles and vote "yes" — in 20 years Pluto will probably still be popular with children, but rather than being known as the ninth planet, it'll be known as the first object ever discovered in that sea of dozens or maybe even hundreds of dwarf planets that will have been found by then."
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