Observed on Aug. 24, Pluto Demoted Day remembers the vote that shrank the solar system’s planet count from nine to eight.
In 2006, the International Astronomical Union met in Prague and approved a definition of planet requiring an object to orbit the sun, be nearly round and clear its orbital neighborhood. Pluto met the first two rules but shares its distant region with other icy bodies, so it became a dwarf planet instead.
The decision upset many Pluto fans, but it also showed science changing in public. Pluto was not gone; astronomers had simply learned more about where it belongs.
– Staff report with AI assist*, The Today 100
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