Facts about Pluto's Demotion to Dwarf Planet
- 05
Alan Stern, the principal investigator of NASA's New Horizons mission to Pluto, was a vocal critic of the IAU demotion and has continued to contest the dwarf planet classification.
- 04
Only around 424 IAU members cast votes on Pluto's demotion to dwarf planet, a small fraction of the total IAU membership at the time.
- 03
After Pluto's demotion, it was placed into the same category as Eris, a similarly sized trans-Neptunian object whose discovery helped prompt the reclassification.
- 02
Pluto's demotion introduced a new three-part definition of 'planet' requiring a body to orbit the Sun, have sufficient mass for a spherical shape, and have cleared its orbital neighborhood.
- 01
The International Astronomical Union formally redefined 'planet' in August 2006, reclassifying Pluto as a 'dwarf planet' by a vote of IAU members in Prague.