Why Is Pluto No Longer Considered a Planet?

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Discussion Overview

The discussion centers around the reclassification of Pluto and the implications of the International Astronomical Union's new definition of a planet. Participants explore the criteria for planetary status, the reasons behind Pluto's reclassification, and the potential consequences of the new definition on other celestial bodies.

Discussion Character

  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • Some participants note that Pluto is no longer considered a planet due to the International Astronomical Union's updated definition of "planet."
  • One participant mentions that there were discussions about including additional celestial bodies as planets, suggesting that 12 bodies might meet the new criteria.
  • Another participant argues that the new definition is problematic, as it relies on the concept of a body having "cleared out" its orbit, which they believe could lead to inconsistencies, such as potentially disqualifying Neptune.
  • Concerns are raised about the implications of the new definition, with one participant humorously suggesting that it could reduce the solar system to only one planet, Mercury, due to the presence of numerous near-Earth objects.

Areas of Agreement / Disagreement

Participants express differing views on the validity and implications of the new planetary definition. There is no consensus on whether the reclassification of Pluto is justified or whether the criteria are adequate.

Contextual Notes

The discussion highlights the ambiguity and potential limitations of the new definition, particularly regarding the criteria for clearing an orbit and its application to other celestial bodies.

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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