Aug. 24, 2006: Pluto Is Demoted
The IAU set a formal planet definition and created the dwarf-planet category after Pluto failed the orbit-clearing test.
- On Monday, August 24, 2026, the International Astronomical Union marks the 20th anniversary of the 2006 vote that reclassified Pluto as a dwarf planet, ending its status as the solar system's ninth planet.
- Facing pressure from the 2005 discovery of Eris, the IAU formed a Planet Definition Committee and established criteria requiring bodies to achieve hydrostatic equilibrium and gravitational dominance within their orbits.
- Paul Byrne, a planetary astronomer at the University of Washington in St Louis, critiques these criteria, stating, "Nature doesn't care what we call Pluto," and advocates for geophysical-based definitions.
- Because its orbit crosses Neptune's and shares space with Kuiper Belt objects, Pluto fails the third IAU requirement, making the "cleared neighborhood" mandate the most controversial aspect of the definition.
- As the 20-year anniversary passes, some researchers debate whether to revisit the 2006 decision while anticipating the discovery of more potential planets far from the Sun in coming years.
12 Articles
12 Articles
On August 24, 2006, the world was surprised by the degradation of a planet in the solar system. From that date there were only eight planets.
Aug. 24, 2006: Pluto is demoted
After much discussion and debate, an International Astronomical Union (IAU) vote on Aug. 24, 2006, reclassified Pluto as a dwarf planet. “Throw away the placemats. Grab a magic marker for the classroom charts. Take a pair of scissors to the solar system mobile,” crowed the New York Times coverage. While sentiment from the general publicContinue reading "Aug. 24, 2006: Pluto is demoted" The post Aug. 24, 2006: Pluto is demoted appeared first on A…
Pluto became a dwarf planet 20 years ago today
Pluto is the largest of many small bodies in the outer solar system. That's partly why it was demoted from major planet to dwarf planet in 2006. The post Pluto became a dwarf planet 20 years ago today first appeared on EarthSky.
It's been 20 years since Pluto lost planet status. Will it ever get its title back?
In August of 2006, astronomers at the International Astronomical Union (IAU) democratically voted to reclassify Pluto as a dwarf planet — but 20 years later, with our greater knowledge and understanding of planetary systems, is it time to revisit the controversial decision? Should Pluto be called a planet again?For several years before the IAU vote, there had been agitators among the astronomical community lobbying for our solar system's nine wo…
In August 2006, astronomers adopted the criteria defining what a planet is.
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