Why Isn't Pluto a Planet? — fromquarkstoquasars.com

A planet must meet a minimum size requirement in order to be classified as such. After all, that’s why Pluto is now considered a dwarf planet, right? Well, not exactly. Pluto’s reclassification as a dwarf planet in 2006 was a source of much controversy. Pluto had been in the science books for years; millions of children grew up knowing it as the tiny ninth planet of our solar system. But, seemingly abruptly, the International Astronomical Union defined (or redefined) what it means to be a planet within our solar system. The verdict set forth on August 24th, 2006 was the end of a lengthy debate beginning in the late 1970s.

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