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SESK: Stuff Everyone Should Know · sesk.info/astro-pluto-2006-reclassification

In what year did the IAU reclassify Pluto as a dwarf planet?

The decision was made in 2006.

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  1. 2006 ✔
  2. 1930
  3. 2015

Why: IAU members adopted a formal Solar System planet definition in 2006. Under it, Pluto became a dwarf planet; 1930 was its discovery year, and 2015 was the New Horizons flyby.

Huh, didn't know that: Discoveries of Pluto-like worlds beyond Pluto helped trigger reconsideration of the planet definition.

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Pluto kept circling the issue even after the classification changed.
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References

Answer: 2006. IAU members adopted a formal Solar System planet definition in 2006. Under it, Pluto became a dwarf planet; 1930 was its discovery year, and 2015 was the New Horizons flyby.

  1. Pluto and Dwarf Planets science.nasa.gov/dwarf-planets
    the IAU reclassified Pluto as a dwarf planet in 2006.
    Checked 2026-10-10.

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