Before Pluto's demotion, a draft proposal by the International Astronomical Union (IAU) in August 2006 actually recommended expanding our solar system from 9 to 12 planets.
The 12-Planet Plan
▫️The original nine: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto.
▫️Three new additions: Ceres (previously an asteroid), Pluto’s largest moon Charon, and Eris (then known as 2003 UB313).
▫️The reasoning: This draft suggested defining a planet largely by its round shape under its own gravity, rather than what else shared its orbital path.
Why It Changed
▫️The vote: Astronomers quickly debated the definition and realized a shape-only rule would soon force the addition of dozens more icy bodies found in the Kuiper Belt.
▫️The new rule: On August 24, 2006, the IAU voted on a strict definition requiring a planet to "clear its neighborhood" of other objects.
▫️The result: Pluto, Ceres, and Eris failed this final test and were placed into a new category called dwarf planets, leaving our solar system with eight official planets.
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