Talk:136199 Eris

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[edit] Accurate Size

If Eris is bigger then Mercury it isn't a dwarf planet, because Mercury itself is a pure planet. --ยง Alastor Moody (T + C) 06:14, 20 September 2006 (UTC)

The classification as a dwarf planet is not only based on size (The following is from en:Definition of planet):
The IAU therefore resolves that planets and other bodies in our Solar System, except satellites, be defined into three 
distinct  categories in the following way:
.
(1) A "planet"1 is a celestial body that: (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome  
rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighbourhood 
around its orbit.
.
(2) A "dwarf planet" is a celestial body that: (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to 
overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape2, (c) has not cleared the 
neighbourhood around its orbit, and (d) is not a satellite.
.
(3) All other objects3 except satellites orbiting the Sun shall be referred to collectively as "Small Solar System Bodies".
.
Footnotes:
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1 The eight planets are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. 
2 An IAU process will be established to assign borderline objects into either "dwarf planet" and other categories.
3 These currently include most of the Solar System asteroids, most Trans-Neptunian Objects (TNOs), comets, and other small bodies.
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The IAU further resolves:
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Pluto is a "dwarf planet" by the above definition and is recognized as the prototype of a new category of trans-Neptunian objects.