Facts about Pluto's 2006 demotion
- 08
Pluto's demotion in 2006 reduced the solar system's planetary count from nine to eight, making it the first celestial body stripped of planetary status since Mercury was briefly reclassified in the 1600s.
- 07
Four years after Pluto's 2006 demotion, astronomers discovered that the dwarf planet possesses five known moons, more than any other similarly-sized body in the Kuiper Belt.
- 06
About 100 dwarf planets have been catalogued in the Kuiper Belt since Pluto's 2006 demotion, fundamentally reshaping how astronomers classify icy bodies beyond Neptune's orbit.
- 05
Pluto's reclassification removed it from a nine-planet solar system that had existed in textbooks since 1930, when Clyde Tombaugh first discovered it.
- 04
Neil deGrasse Tyson became the public face of Pluto's demotion, frequently explaining the decision in media appearances and later writing a children's book addressing the reclassified dwarf planet.
- 03
Eris, discovered in 2005, proved slightly more massive than Pluto, prompting astronomers to either create a new planet category or demote Pluto during the 2006 IAU decision.
- 02
At the 2006 International Astronomical Union meeting in Prague, Pluto was reclassified as a dwarf planet after astronomers discovered over 1,000 similar icy bodies in the outer solar system.
- 01
The International Astronomical Union established three criteria for planethood in 2006, and Pluto failed the third requirement of clearing its orbital neighborhood of other debris.