Pluto was declared not a planet on August 24, 2006 , when the International Astronomical Union reclassified it as a dwarf planet.

Quick Scoop

Before that vote, Pluto had been considered the ninth planet for 76 years. The change happened after astronomers set a new definition for a planet, and Pluto did not meet all the criteria because it has not cleared its neighboring region of other objects.

Key date

  • August 24, 2006 : Pluto was officially reclassified.

If you want, I can also give you the one-sentence reason Pluto lost planet status.