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When did the International Astronomical Union reclassify Pluto?
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Pluto
Pluto as observed by the New Horizons spacecraft, July 13, 2015.
The International Astronomical Union (IAU) reclassified Pluto from a planet to a dwarf planet in 2006.12
This decision occurred during the 2006 IAU General Assembly, where members established a formal, scientific definition for a planet. Under these new criteria, a celestial body must orbit the Sun, be massive enough to achieve a spherical shape, and have "cleared the neighborhood" around its orbit of other debris. Pluto was reclassified because, while it is spherical, it lacks the gravitational dominance required to clear its orbital path of other objects.23