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Pluto
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Pluto
Discovered by
Clyde W. Tombaugh
Discovery date
February 18, 1930
MPC designation
134340 Pluto
Pronunciation
i/'plu?to?/,
Named after
Pluto
Minor planet
category
dwarf planet* TNO* plutoid* KBO* plutino
Adjective
Plutonian
Epoch J2000
Aphelion
7,311,000,000 km* 48.871 AU
Perihelion
4,437,000,000 km* 29.657 AU
(1989 Sep 05)
Semi-major axis
5,874,000,000 km* 39.264 AU
Eccentricity
0.248 807 66
Orbital period
90,613.305 days* 248.09 years* 14,164.4 Pluto solar days
Synodic period
366.73 days
Average orbital speed
4.666 km/s
Mean anomaly
14.86012204°
Inclination
17.141 75°* 11.88° to Sun's equator
Longitude of ascending node
110.303 47°
Argument of perihelion
113.763 29°
Satellites
5
Mean radius
1153 ± 10 km* 0.18 Earths* 1161 km (solid)
Surface area
1.665×107 km2* 0.033 Earths
Volume
6.39×109 km3* 0.0059 Earths
Mass
(1.305 ± 0.007)×1022 kg* 0.00218 Earths* 0.178 Moons
Mean density
2.03 ± 0.06 g/cm3
Equatorial surface gravity
0.658 m/s2* 0.067 g
Escape velocity
1.229 km/s
Sidereal rotation
period
-6.387 230 day* 6 d 9 h 17 m 36 s
Equatorial rotation velocity
47.18 km/h
Axial tilt
119.591 ± 0.014° (to orbit)
North pole right ascension
312.993°
North pole declination
6.163°
Albedo
0.49–0.66 (geometric, varies by 35%)
Surface temp.
Kelvin
min
mean
max
33 K
44 K
55 K
Apparent magnitude
13.65 to 16.3
(mean is 15.1)
Absolute magnitude (H)
-0.7
Angular diameter
0.065" to 0.115"
Surface pressure
0.30 Pa (summer maximum)
Composition
nitrogen, methane, carbon monoxide
Pluto, formal designation 134340 Pluto, is the second-most-massive known dwarf planet in the Solar System (after Eris) and the tenth-most-massive body observed directly orbiting the Sun. Originally classified as the ninth planet from the Sun, Pluto was recategorized as a dwarf planet and plutoid owing to the discovery that it is only one of several large bodies within the Kuiper belt.Like other members of the Kuiper belt, Pluto is composed primarily of rock and ice and is relatively small: approximately one-sixth the mass of the Earth's Moon and one-third its volume. It has an eccentric and highly inclined orbit that takes it from 30 to 49 AU (4.4–7.4 billion km) from the Sun. This causes Pluto to periodically come closer to the Sun than Neptune. As of 2011, it is 32.1 AU from the Sun.From its discovery in 1930 until 2006, Pluto was classified as a planet. In the late 1970s, following the discovery of minor planet 2060 Chiron in the outer Solar System and the recognition of Pluto's relatively low mass, its status as a major planet began to be questioned. In the late 20th and early 21st centuries, many objects similar to Pluto were discovered in the outer Solar System, notably the scattered disc object Eris in 2005, which is 27% more massive than Pluto. On August 24, 2006, the International Astronomical Union (IAU) defined what it means to be a "planet" within the Solar System. This definition excluded Pluto as a planet and added it as a member of the new category "dwarf planet" along with Eris and Ceres. After the reclassification, Pluto was added to the list of minor planets and given the number 134340. A number of scientists hold that Pluto should continue to be classified as a planet, and that other dwarf planets should be added to the roster of planets along with Pluto.Pluto has five known moons, the largest being Charon discovered in 1978, along with Nix and Hydra, discovered in 2005, and the provisionally named S/2011 P 1, discovered in 2011. Another discovery was announced on 11 July 2012, provisionally designated S/2012 (134340) 1, bringing the total number of identified satellites orbiting Pluto to five. Pluto and Charon are sometimes described as a binary system because the barycenter of their orbits does not lie within either body. However, the IAU has yet to formalise a definition for binary dwarf planets, and as such Charon is officially classified as a moon of Pluto.
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