Pluto, Pronunciation /ˈpluːtoʊ/ , formal designation 134340 Pluto, is the tenth-largest body observed directly orbiting the Sun. Classified as a planet from its 1930 discovery, in 2006 the International Astronomical Union (IAU) declared it a dwarf planet instead;
Pluto is composed primarily of rock and ice and is relatively small: approximately a fifth the mass of the Earth's Moon and a third its volume. It has an eccentric and highly inclined orbit that takes it from 30 to 49 AU (4.47.4 billion km) from the Sun. This causes Pluto to periodically come closer to the Sun than Neptune.
Pluto and its largest moon, Charon, are sometimes treated together as a binary system because the barycentre of their orbits does not lie within either body. The IAU has yet to formalise a definition for binary dwarf planets, and until it passes such a ruling, they classify Charon as a moon of Pluto. Pluto has two known smaller moons, Nix and Hydra, discovered in 2005. From its discovery in 1930 until 2006, Pluto was considered the Solar System's ninth planet. In the late 1970s, following the discovery of minor planet 2060 Chiron in the outer Solar System and the recognition of Pluto's very low mass, its status as a major planet began to be questioned. Later, in the early 21st century, many objects similar to Pluto were discovered in the outer Solar System, notably the scattered disc object Eris, which is 27% more massive than Pluto. On August 24, 2006, the IAU defined the term "planet" for the first time. 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 continue to hold that Pluto should be classified as a planet.
Discovered by Clyde W. Tombaugh in February 18, 1930
MPC designation 134340 Pluto
Minor planet, category dwarf planet, TNO, plutoid, KBO, plutino
Adjective Plutonian
Orbital characteristics, Epoch J2000
Aphelion 7,375,927,931 km, (49.305 032 87) AU
Perihelion 4,436,824,613 km, (29.658 340 670) AU
Semi-major axis 5,906,376,272 km,(39.481686 770) 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
Inclination 17.141 75°
11.88° to Sun's equator
Longitude of ascending node 110.303 47°
Argument of perihelion 113.763 29°
Satellites 3 (Charon, Nix, Hydra)
Physical characteristics
Mean radius 1,153 ± 10 km, (0.18) Earths
Surface area 1.665 × 107 km², (0.0330 Earths
Volume 6,39 × 109 km³, (0.00590 Earths
Mass (1.305 ± 0.007) × 1022 kg, (0.0021) Earths,
0.178 moon
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 133.046 ± 0.014°
North pole declination −6.145 ± 0.014°
Albedo 0.490.66 (varies by 35%)
Surface temp.
Kelvin min mean max 33 K 44 K 55 K
Apparent magnitude up to 13.65 (mean is 15.1)
Absolute magnitude (H) −0.7
Angular diameter 0.065" to 0.115"
Atmosphere
Surface pressure 0.30 Pa (summer maximum)
Composition nitrogen, methane
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4:05
Pluto, Charon, Nix & Hydra - Solar system in picturesby 20Bond097,508 views
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