Clyde Tombaugh discovered Pluto in 1930 at Lowell Observatory in Flagstaff. Here's how Pluto won - and lost - its planetary ...
According to the IAU, a planet must: Orbit the sun (Pluto does this). Be spherical in shape (Pluto is round due to its gravity). Clear its orbit of other debris (Pluto fails this). Pluto shares ...
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