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Name: Deborah
Status: educator
Grade: N/A
Location: NV
Country: N/A
Date: 4/29/2005

Is there a set of specific requirements that is used to classify a planet as a planet versus an asteroid, etc? I have a student who is doing a research project on the discussion of whether Pluto is truly a planet.

There is no border line between 'planet' and 'minor planet', although there have been attempts to clarify the situation.

One suggestion of a line was 1000 kilometres in diameter, and some astronomers do use this 'de facto' definition, but the International Astronomical Union (IAU) looked into the matter a few years ago but has never made a decision.

Even if some forth-coming IAU decision decides that Pluto is a minor planet [asteroid], history will inevitably keep it a major planet.

Howard Barnes.

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