Clyde Tombaugh discovered Pluto in 1930 at Lowell Observatory in Flagstaff. Here's how Pluto won - and lost - its planetary ...

If you answered "Pluto's planethood," your grasp ... satisfy one of three newly defined criteria to be a planet. They were: The body must orbit its host star, just as Earth and Jupiter orbit ...

Pluto fails the third criterion because its orbit overlaps with objects in the Kuiper Belt, a region of icy bodies beyond Neptune. So, a new class of celestial object — the dwarf planet — came ...

The International Astronomical Union reclassified Pluto as a dwarf planet because it does not clear its orbit of other debris. Pluto was the little planet that could — until it couldn’t.