Global InformationPluto information
 Pluto, imaged by the New Horizons spacecraft, July 2015.[a] The most prominent feature in the image, the bright, youthful plains of Tombaugh Regio and Sputnik Planitia, can be seen at right. It contrasts the darker, cratered terrain of Belton Regio at lower left | |||||||||
| Discovery | |||||||||
|---|---|---|---|---|---|---|---|---|---|
| Discovered by | Clyde W. Tombaugh | ||||||||
| Discovery site | Lowell Observatory | ||||||||
| Discovery date | February 18, 1930 | ||||||||
| Designations | |||||||||
Designation | (134340) Pluto | ||||||||
| Pronunciation | /ˈpluːtoʊ/ ⓘ | ||||||||
Named after | Pluto | ||||||||
Minor planet category |
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| Adjectives | Plutonian /pluːˈtoʊniən/[1] | ||||||||
| Symbol |  (historically astronomical, now mostly astrological) or  (mostly astrological) | ||||||||
| Orbital characteristics[2][b] | |||||||||
| Epoch J2000 | |||||||||
| Earliest precovery date | August 20, 1909 | ||||||||
| Aphelion |
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| Perihelion |
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Semi-major axis |
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| Eccentricity | 0.2488 | ||||||||
Orbital period (sidereal) |
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Orbital period (synodic) | 366.73 days[3] | ||||||||
Average orbital speed | 4.743 km/s[3] | ||||||||
Mean anomaly | 14.53 deg | ||||||||
| Inclination |
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Longitude of ascending node | 110.299° | ||||||||
Argument of perihelion | 113.834° | ||||||||
| Known satellites | 5 | ||||||||
| Physical characteristics | |||||||||
| Dimensions | 2,376.6±1.6 km (observations consistent with a sphere, predicted deviations too small to be observed)[5] | ||||||||
Mean radius |
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| Flattening | <1%[7] | ||||||||
Surface area |
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| Volume |
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| Mass |
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Mean density | 1.854±0.006 g/cm3[6][7] | ||||||||
Surface gravity |
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Escape velocity | 1.212 km/s[f] | ||||||||
Synodic rotation period |
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Sidereal rotation period |
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Equatorial rotation velocity | 47.18 km/h | ||||||||
Axial tilt | 122.53° (to orbit)[3] | ||||||||
North pole right ascension | 132.993°[9] | ||||||||
North pole declination | −6.163°[9] | ||||||||
| Albedo | 0.52 geometric[3] 0.72 Bond[3] | ||||||||
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Apparent magnitude | 13.65[3] to 16.3[10] (mean is 15.1)[3] | ||||||||
Absolute magnitude (H) | −0.44[11] | ||||||||
Angular diameter | 0.06″ to 0.11″[3][g] | ||||||||
| Atmosphere | |||||||||
Surface pressure | 1.0 Pa (2015)[7][12] | ||||||||
| Composition by volume | Nitrogen, methane, carbon monoxide[13] | ||||||||
Pluto (minor-planet designation: 134340 Pluto) is a dwarf planet in the Kuiper belt, a ring of bodies beyond the orbit of Neptune. It is the ninth-largest and tenth-most-massive known object to directly orbit the Sun. It is the largest known trans-Neptunian object by volume, by a small margin, but is less massive than Eris. Like other Kuiper belt objects, Pluto is made primarily of ice and rock and is much smaller than the inner planets. Pluto has roughly one-sixth the mass of Earth's moon, and one-third its volume.
Pluto has a moderately eccentric and inclined orbit, ranging from 30 to 49 astronomical units (4.5 to 7.3 billion kilometers; 2.8 to 4.6 billion miles) from the Sun. Light from the Sun takes 5.5 hours to reach Pluto at its orbital distance of 39.5 AU (5.91 billion km; 3.67 billion mi). Pluto's eccentric orbit periodically brings it closer to the Sun than Neptune, but a stable orbital resonance prevents them from colliding.
Pluto has five known moons: Charon, the largest, whose diameter is just over half that of Pluto; Styx; Nix; Kerberos; and Hydra. Pluto and Charon are sometimes considered a binary system because the barycenter of their orbits does not lie within either body, and they are tidally locked. The New Horizons mission was the first spacecraft to visit Pluto and its moons, making a flyby on July 14, 2015, and taking detailed measurements and observations.
Pluto was discovered in 1930 by Clyde W. Tombaugh, making it by far the first known object in the Kuiper belt. It was immediately hailed as the ninth planet, but it was always the odd object out,[14]: 27 and its planetary status was questioned when it was found to be much smaller than expected. These doubts increased following the discovery of additional objects in the Kuiper belt starting in the 1990s, and particularly the more massive scattered disk object Eris in 2005. In 2006, the International Astronomical Union (IAU) formally redefined the term planet to exclude dwarf planets such as Pluto. Many planetary astronomers, however, continue to consider Pluto and other dwarf planets to be planets.
Cite error: There are <ref group=lower-alpha> tags or {{efn}} templates on this page, but the references will not show without a {{reflist|group=lower-alpha}} template or {{notelist}} template (see the help page).
- ^ "Plutonian". Oxford English Dictionary (Online ed.). Oxford University Press. (Subscription or participating institution membership required.)
- ^ Cite error: The named reference
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Pluto Fact Sheetwas invoked but never defined (see the help page). - ^ Cite error: The named reference
jpl-ssd-horizonswas invoked but never defined (see the help page). - ^ a b Nimmo, Francis; et al. (2017). "Mean radius and shape of Pluto and Charon from New Horizons images". Icarus. 287: 12–29. arXiv:1603.00821. Bibcode:2017Icar..287...12N. doi:10.1016/j.icarus.2016.06.027. S2CID 44935431.
- ^ a b Stern, S.A.; Grundy, W.; McKinnon, W.B.; Weaver, H.A.; Young, L.A. (2017). "The Pluto System After New Horizons". Annual Review of Astronomy and Astrophysics. 2018: 357–392. arXiv:1712.05669. Bibcode:2018ARA&A..56..357S. doi:10.1146/annurev-astro-081817-051935. S2CID 119072504.
- ^ a b c d Stern, S.A.; et al. (2015). "The Pluto system: Initial results from its exploration by New Horizons". Science. 350 (6258): 249–352. arXiv:1510.07704. Bibcode:2015Sci...350.1815S. doi:10.1126/science.aad1815. PMID 26472913. S2CID 1220226.
- ^ Seligman, Courtney. "Rotation Period and Day Length". Archived from the original on September 29, 2018. Retrieved June 12, 2021.
- ^ a b Cite error: The named reference
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jpldatawas invoked but never defined (see the help page). - ^ Amos, Jonathan (July 23, 2015). "New Horizons: Pluto may have 'nitrogen glaciers'". BBC News. Archived from the original on October 27, 2017. Retrieved July 26, 2015.
It could tell from the passage of sunlight and radiowaves through the Plutonian "air" that the pressure was only about 10 microbars at the surface
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