Pluto prototype

On August 24, 2006, the International Astronomical Union (IAU) decided to reclassify Pluto as a dwarf planet, requiring that a planet must "clear the neighbourhood around its orbit." The General Assembly of the IAU further resolved to recognize Pluto as the prototype of a new (as yet unnamed) category of trans-Neptunian objects which the IAU planned on naming a "pluton" or a "plutonian object". The former was rejected, in part because "pluton" is actually a pre-existing geology term, and many geological experts wrote in complaints pointing this out, and the latter was rejected as well due to the pre-existing definition of "Plutonian". Many astronomers are continuing to use the term "ice dwarf" to describe such objects, following the precedent of calling the four largest planets "gas giants".

A Pluto-prototype trans-Neptunian object is one which:

is both a dwarf planet; and
orbits the sun at a greater distance on average than Neptune.

**Plutonian Dwarf Planets**
Name	Pluto	Eris
Diameter	2306±20 km	2400±100 km
Mass in kg compared to Earth	~1.305×10²² kg .0022	~1.5×10²² kg (est.) .0025
Mean equatorial radius* in km	0.180 1,148.07	0.19 ~1,200
Volume*	0.005	0.007
Density (in Mg/m	2.0
Equatorial gravity (in m/s²)	0.60
Escape velocity (in km/s)	1.2
Rotation period (d) (in sidereal days)	-6.38718 (retrograde)
Orbital radius^* (AU) semi-major axis in km	29.66-49.30 39.48168677 5,906,376,200	37.77-97.56 67.6681 10,210,000,000
Orbital period^*(a) (in sidereal Years)	248.09	557
Mean orbital speed (in km/s)	4.7490	3.436
Orbital Eccentricity	0.24880766	0.44177
Orbital inclination	17.14175°	44.187°
Inclination of the equator from the orbit (see Axial tilt)	119.61°
Mean surface temperature (in K)	40	30
Number of natural satellites	3	1
Date of Discovery	February 18, 1930	October 21, 2003^[1]