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Pluto and its biggest moon, Charon  (Source: NASA)
Pluto gets new classification: Plutoid

After being demoted from a planet to a dwarf planet by the International Astronomical Union (IAU) two years ago, the IAU has announced the term "plutoid" will be given to Pluto and similar dwarf planets.  Members of the IAU argued amongst themselves for two years, confused on how to classify dwarf stars like Pluto.  

Only dwarfs orbiting further than Neptune can be classified as a plutoid, and they must also circle the sun and be large enough to have their own gravitational field.  Pluto's permanent classification as a plutoid now means Neptune is the outermost planet in Earth's solar system; one complete orbit around the sun takes almost 165 years.

"Plutoids are celestial bodies in orbit around the sun at a distance greater than that of Neptune that have sufficient mass for their self-gravity to overcome rigid body forces so that they assume a hydrostatic equilibrium (near-spherical) shape, and that have not cleared the neighborhood around their orbit," said the IAU.

Pluto and Eris remain the only plutoids at the moment, but astronomers expect to find other small bodies that meet the qualifications to be a plutoid.

The controversy over Pluto's planet status has been strong for years, and the IAU-created plutoid classification most likely will not end the debate.  In fact, it is unlikely the debate regarding Pluto's status and what it should be classified as will never end, and defining it as a "plutoid" will only add fuel to the fire.

Many astronomers remain angry that Pluto, considered a planet for around 70 years, could have its status demoted so easily by the IAU.  Text book publishers and teachers must now begin to teach students that Pluto lost its planet status and is now a plutoid, along with describing the new classification.

The IAU has been the sole organization responsible for classifying all planetary bodies for more than a decade.



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So maybe Neptune is a Plutoid as well?
By SYR on 6/18/2008 6:06:52 PM , Rating: 2
Hmm. The definition of planet requires the body to clear its orbit. Pluto crosses Neptune's orbit. Pluto is not a moon of Neptune. Neptune has thus not "cleared" its orbit. Put it all together and we must conclude that Neptune is not a planet. The count is down to 7.

A little more of a stretch and... Look at all of those asteroids sitting between Mars and Jupiter. It might be argued that neither Mars nor Jupiter have truly "cleared" their orbits, but merely reached equilibrium with each other and the debris in between. Now we're down to 5.

But wait. What about all of those comets whizzing through the neighborhood? Whose supposedly clean orbits do they intersect with? Maybe there are really no planets at all; just a bunch of plutoids dancing about the Sun.




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