Why Is Pluto No Longer Considered a Planet?

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SUMMARY

The International Astronomical Union (IAU) redefined the criteria for classifying celestial bodies as planets, leading to Pluto's reclassification. According to the new definition, a planet must have "cleared out" its orbit, a criterion Pluto does not meet due to its overlapping orbit with Neptune. This decision has sparked debate, as some argue that other celestial bodies, including Neptune, may also fail to meet this definition. The discussion highlights the complexities of planetary classification and the potential implications for our understanding of the solar system.

PREREQUISITES
  • Understanding of the International Astronomical Union's (IAU) planetary classification criteria
  • Familiarity with celestial mechanics, particularly orbital dynamics
  • Knowledge of the characteristics of dwarf planets, including Pluto and Ceres
  • Awareness of the historical context of planetary definitions
NEXT STEPS
  • Research the IAU's official definition of a planet and its implications
  • Explore the characteristics and classification of dwarf planets like Ceres
  • Investigate the concept of "clearing the orbit" in celestial mechanics
  • Examine the ongoing debates and alternative classifications in planetary science
USEFUL FOR

Astronomy enthusiasts, educators, and students interested in planetary science and classification debates will benefit from this discussion.

poppop24
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Please explain why there is no pluto any more
 
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The International Astronomical Union recently changed the official definition of "planet." Pluto does not meet this new definition. Pluto still exists, but it is no longer considered a planet.

- Warren
 
Last edited:
The alternatives were (basically) to include three new planets, or take away Pluto, and the later was chosen...
 
I doubt it will last for long, though. The new definition is very sketchy, and depends upon a body having "cleared out" the immediate vicinity of its orbit. Pluto was not disqualified because of its size, or the eccentricity of its ellipse, or its inclination to the orbital plane, but because it crosses Neptune's orbital radius. By this definition, Neptune (having failed to "clear out" Pluto from its orbit) should also be disqualified.

In fact, because there are still thousands of NEO's whizzing about the inner solar system, many of them crossing inside the orbit of Venus, the new definition may reduce the entire solar system to only one planet: Mercury!
 
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