August 24, 2006 was a dark day for Pluto enthusiasts. It was on that day that the International Astronomical Union established three conditions a celestial body must meet in order to be considered a planet. A planet must orbit around the sun, it must be massive enough to be rounded by its own gravity, and it must have “cleared the neighborhood” around its orbit, which means, simply put, that it must have a certain amount of gravitational pull.
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