User:Alastor Moody/Dwarf planet

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Pluto, a former planet and considered a planet for 76 years, was reclassified as a dwarf planet in 2006.
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Pluto, a former planet and considered a planet for 76 years, was reclassified as a dwarf planet in 2006.

Since the discovery of Pluto in 1930, Pluto has widely been known to be considered as the ninth planet of the solar system. But in August 2006, astronomers and members from the International Astronomical Union (IAU) decided to re-define the term, "planet". The result ended up with Pluto demoted from planetary status to a "dwarf planet".

The term, "dwarf planets" is an official category making the boundary of the difference between a planet and a small solar system body. A celestial objects to be a dwarf planet must...

  • Is in orbit around the Sun.
  • Is not a satellite of a planet, or other nonstellar body.
  • Does not produce energy by nuclear fusion.
  • Has sufficient mass so that it assumes a hydrostatic equilibrium (nearly round) shape.
  • Has not "cleared the neighborhood" around its orbit.

[edit] List of Dwarf Planets

The current dwarf planets are Pluto (a former planet), Ceres, and 136199 Eris.

Dwarf planets
Name 1 Ceres Pluto Eris
Region of Solar system Asteroid belt Kuiper belt Scattered disc
Category Asteroid Plutino Scattered disc object
Diameter 975×909 km 2306±20 km 2400±100 km
Mass in kg
compared to Earth
9.5Template:E kg
.00016
~1.305Template:E kg
.0022
~1.5Template:E kg (est.)
Mean equatorial radius*
in km
0.0738
471
0.180
1,148.07
0.19
~1,200
Volume*
in km3
0.00042
0.005
0.007
Density (in g/cm3) 2.08 2.0
Equatorial gravity (in m/s2) 0.27 0.60
Escape velocity (in km/s) 0.51 1.2
Rotation period (d)
(in sidereal days)
0.3781 -6.38718
(retrograde)
Orbital radius* (AU)
mean
mean in km
2.5-2.9
2.766
413,715,000
39.5
39.48168677
5,906,376,200
37.77-97.56
67.6681
10,210,000,000
Orbital period*(a)
(in sidereal Years)
4.599 248.09 557
Mean orbital speed
(in km/s)
17.882 4.7490 3.436
Orbital Eccentricity 0.080 0.24880766 0.44177
Orbital inclination 10.587° 17.14175° 44.187°
Inclination of the equator from the orbit
(see Axial tilt)
119.61°
Mean surface temperature (in K) 167 40 30
Number of moons 0 3 1

[edit] External links

The Solar System
Image:Eight Planets.png
Star: The Sun
Planets: Mercury - Venus - Earth - Mars - Jupiter - Saturn - Uranus - Neptune
Dwarf planets: Ceres - Pluto - 2003 UB313
Other: Moon - Asteroid belt - Comets - Kuiper belt - Scattered disc - Oort cloud
See also astronomical objects and the solar system's list of objects, sorted by radius or mass.