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Pluto (planet)

Pluto Astronomical symbol of Pluto
Nh-pluto-in-true-color 2x JPEG-edit-frame.jpg
Full-disc view of Pluto in near-true color, imaged by New Horizons
Discovery
Discovered by Clyde W. Tombaugh
Discovery date February 18, 1930
Designations
MPC designation 134340 Pluto
Pronunciation Listeni/ˈplt/
Named after
Pluto
Adjectives Plutonian
Orbital characteristics
Epoch J2000
Aphelion
  • 49.305 AU
  • (7,375.93 Gm)
  • February, 2114
Perihelion
  • 29.658 AU
  • (4,436.82 Gm)
  • (September 5, 1989)
  • 39.48 AU
  • (5,906.38 Gm)
Eccentricity 0.2488
  • 248.00 years
  • 90,560 d
366.73 days
Average orbital speed
4.67 km/s
14.53 deg
Inclination
  • 17.16°
  • (11.88° to Sun's equator)
110.299°
113.834°
Known satellites 5
Physical characteristics
Mean radius
  • 1,187±4 km
  • 0.1863 Earths
Flattening <1%
  • 1.77×107 km2
  • 0.035 Earths
Volume
  • (7.006±0.071)×109 km3
  • 0.00647 Earths
Mass
  • (1.303±0.003)×1022 kg
  • 0.00218 Earths
  • 0.177 Moons
Mean density
1.860±0.013 g/cm3
  • 0.620 m/s2
  • 0.063 g
1.212 km/s
Sidereal rotation period
  • 6.387230 d
  • 6 d, 9 h, 17 m, 36 s
Equatorial rotation velocity
47.18 km/h
122.53° (to orbit)
North pole right ascension
132.993°
North pole declination
−6.163°
Albedo 0.49 to 0.66 (geometric, varies by 35%)
Surface temp. min mean max
Kelvin 33 K 44 K (−229 °C) 55 K
13.65 to 16.3
(mean is 15.1)
−0.7
0.06″ to 0.11″
Atmosphere
Surface pressure
1.0 Pa (2015)
Composition by volume Nitrogen, methane, carbon monoxide

Pluto (minor-planet designation: 134340 Pluto) is a dwarf planet in the Kuiper belt, a ring of bodies beyond Neptune. It was the first Kuiper belt object to be discovered.

Pluto was discovered by Clyde Tombaugh in 1930 and was originally considered to be the ninth planet from the Sun. After 1992, its planethood was questioned following the discovery of several objects of similar size in the Kuiper belt. In 2005, Eris, which is 27% more massive than Pluto, was discovered. This led the International Astronomical Union (IAU) to define the term "planet" formally in 2006, during their 26th General Assembly. That definition excluded Pluto and reclassified it as a dwarf planet.

Pluto is the largest and second-most-massive known dwarf planet in the Solar System and the ninth-largest and tenth-most-massive known object directly orbiting the Sun. It is the largest known trans-Neptunian object by volume but is less massive than Eris, a dwarf planet in the scattered disc. Like other Kuiper belt objects, Pluto is primarily made of ice and rock and is relatively small—about one-sixth the mass of the Moon and one-third its volume. It has a moderately eccentric and inclined orbit during which it ranges from 30 to 49 astronomical units or AU (4.4–7.4 billion km) from the Sun. This means that Pluto periodically comes closer to the Sun than Neptune, but a stable orbital resonance with Neptune prevents them from colliding. Light from the Sun takes about 5.5 hours to reach Pluto at its average distance (39.5 AU).


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