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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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RE: But Wait;
By masher2 (blog) on 6/13/2008 11:56:58 AM , Rating: 3
> "I for one, because of Pluto's strategic orbit crossing paths with Neptune, will always classify it as a planet"

In other words -- because Pluto does something no other planet's a planet? Come again?

RE: But Wait;
By Titanius on 6/13/2008 12:13:08 PM , Rating: 1
Not because of what it does, because of where it is located, sometimes closer to the sun than Neptune is.

RE: But Wait;
By jbartabas on 6/13/2008 12:27:26 PM , Rating: 2
Again, you totally missed the point: Ceres is much closer to the Sun than Neptune is, and it is not a planet. The distance to the Sun has no implication in terms of being a planet or a dwarf planet.

The distance to the Sun comes into play to distinguish between various types of dwarf planets. And the distance is defined in terms of semi-axis of the ellipse.

RE: But Wait;
By masher2 (blog) on 6/13/2008 12:27:36 PM , Rating: 2
Ceres is located much closer to the sun than Pluto and is also large enough to maintain a spherical shape. Why not call it a planet as well then?

RE: But Wait;
By Titanius on 6/13/2008 11:01:30 PM , Rating: 1
Ceres is located much closer to the sun than Pluto and is also large enough to maintain a spherical shape. Why not call it a planet as well then?

Why not?

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