It looks as though our solar system actually has 10 planets, not 9. Another planet was discovered farther out from the sun than pluto. It is thought to be relatively the same size as pluto (pluto is 2,250 km accross, this is thought to be 2,000 km accross) but could turn out to be bigger. It does have an orbit around the sun. Officially, it's not a planet yet.
You can read the news article here.
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-Dan
DiNoMyTe!