Explanation

The International Astronomical Union (IAU) downgraded the status of Pluto to that of a dwarf planet because it did not meet the three criteria the IAU uses to define a full-sized planet. Essentially Pluto meets all the criteria except one- it “has not cleared its neighboring region of other objects.” In August 2006 the International Astronomical Union (IAU) downgraded the status of Pluto to that of “dwarf planet.”