Pluto
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Pluto Astronomical symbol of Pluto Reconstructed map of Pluto, approximately true colour, and at highest resolution possible with current methods
Reconstructed map of Pluto, approximately true colour, and at highest resolution possible with current methods
Discovery
Discovered by: Clyde W. Tombaugh
Discovery date: February 18, 1930
Orbital characteristics
Epoch J2000
Aphelion distance: 7,375,927,931 km
(49.305 032 87 AU)
4,583,200,123 miles
Perihelion distance: 4,436,824,613 km
(29.658 340 67 AU)
2,756,921,611 miles
Semi-major axis: 5,906,376,272 km
(39.481 686 77 AU)
3,670,060,865 miles
Orbital circumference: 36.530 Tm
244.186 AU
Eccentricity: 0.248 807 66
Sidereal period: 90,613.3055 day
(248.09 yr)
Synodic period: 366.73 day
Avg. orbital speed: 4.666 km/s
Max. orbital speed: 6.112 km/s
Min. orbital speed: 3.676 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
Physical characteristics
Mean radius: 1195 km [1]
(19% of Earth, or
742.5 miles)
Surface area: 1.795×107 km²
(0.033 Earths)
Volume: 7.15×109 km³
(0.0066 Earths)
Mass: (1.305±0.007)×1022 kg [2]
(0.0021 Earths)
Mean density: 2.03±0.06 g/cm³ [3]
Equatorial surface gravity: 0.58 m/s²
(0.059 gee)
Escape velocity: 1.2 km/s
0.74 mi/s
Sidereal rotation period: −6.387230 day
(6 d 9 h 17 m 36 s)
Rotation velocity at equator: 47.18 km/h (at the equator)
Axial tilt: 119.591 ± 0.014° (to orbit)[1][2]
Right ascension of North pole: 133.046 ± 0.014°[1]
Declination of North pole: -6.145 ± 0.014°[1]
Albedo: 0.49–0.66 (varies by 35%) [4] [5]
Surface temp.:
Kelvin
min mean max
33 K 44 K 55 K
Adjectives: Plutonian
Atmosphere
Surface pressure: 0.30 pascals (summer maximum)
Composition: nitrogen, methane
Pluto (IPA: /ˈplu.toʊ/), also designated 134340 Pluto, is the second-largest known dwarf planet in the Solar System and the tenth-largest body observed directly orbiting the Sun. Originally considered a planet, Pluto has since been recognised as the largest member of a distinct region called the Kuiper belt. Like other members of the belt, it is primarily composed 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 orbit that takes it from 29 to 49 AU (4.3–7.3 billion km / 2.7–4.5 billion mi) from the Sun, and is highly inclined with respect to the planets. As a result, Pluto occasionally comes closer to the Sun than the planet Neptune.
Pluto and its largest satellite, Charon, are often considered a binary system because the barycentre of their orbits does not lie within either body.[3] However, the International Astronomical Union (IAU) has yet to formalise a definition for binary dwarf planets, and until it passes such a ruling, Charon remains a moon of Pluto.[4] Pluto has two known smaller moons, Nix and Hydra, discovered in 2005.[5]
From the time of its discovery in 1930 until 2006, Pluto was considered the Solar System's ninth planet. In the late 20th and early 21st centuries, however, many objects similar to Pluto were discovered in the outer solar system, most notably the scattered disc object Eris, which is 27% more massive than Pluto.[6] On August 24, 2006 the IAU defined the term "planet" for the first time. This definition excluded Pluto from planethood, and reclassified it under the new category of dwarf planet along with Eris and Ceres.[7] After the reclassification, Pluto was added to the list of minor planets and given the number 134340.[8][9]