Dwarf Planet
Characteristics, & Facts
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dwarf planet, body, other than a natural satellite (moon), that orbits the Sun and that is, for practical purposes, smaller than the planet Mercury yet large enough for its own gravity to have rounded its shape substantially. The International Astronomical Union (IAU) adopted this category of solar system bodies in August 2006, designating Pluto, the even more-remote object Eris, and the asteroid Ceres as the first members of the category. Unlike major planets, these bodies are not massive enough to have swept up most smaller nearby bodies by gravitational attraction; they thus failed to grow larger. The IAU agreed to establish a process for determining which other bodies presently known or to be discovered are dwarf planets. In June 2008 the IAU created a new category, plutoids, within the dwarf planet category. Plutoids are dwarf planets that are farther from the Sun than Neptune. All the dwarf planets except Ceres are plutoids; because of its location in the asteroid belt, Ceres is not. For a discussion of the formal conditions set out by the IAU for a body to be a dwarf planet, see planet.
The table provides a list of dwarf planets.
name
mean distance from Sun (AU)
orbital period (years)
diameter (km)
year of discovery
notable features
Official dwarf planets*
*As defined by the International Astronomical Union.
Ceres
2.77
4.61
980 × 910
1801
largest known asteroid; first asteroid discovered
Pluto
39.5
247.69
2,370
1930
has five moons
Haumea
43.19
283.84
980 × 750 × 500
2003
rotates every 3.9 hours; has elongated shape
Makemake
45.48
306.17
1,500
2005
reddish in colour
Eris
67.84
558.77
2,326
2003
surface coated with methane ice
Notable candidate dwarf planets
Orcus
39.22
245.62
946
2004
named after Roman god of the underworld
2003 AZ84
39.36
246.94
686
2003
has one moon
Ixion
39.70
250.18
650
2001
named after Greek mythological king sentenced to roll a wheel through the underworld
90568 (2004 GV9)
42.10
273.13
677
2004
discovered by U.S. robotic telescopes searching for near-Earth asteroids
55636 (2002 TX300)
43.28
284.69
<800
2002
possible fragment formed from collision with Haumea
Quaoar
43.61
287.97
844
2002
named after the creator god of the Tongva Indians
55565 (2002 AW197)
47.12
323.49
735
2002
discovered by U.S. astronomers at Palomar Observatory
Sedna
488.98
10,812.82
<1,600
2003
has extremely eccentric orbit that takes it as far as 975 AU from the Sun
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