Pluto

134340 Pluto
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 byClyde W. Tombaugh
Discovery siteLowell Observatory
Discovery dateFebruary 18, 1930
Designations
Designation
(134340) Pluto
Pronunciation/ˈplt/
Named after
Pluto
AdjectivesPlutonian /plˈtniən/[1]
Symbol♇ (historically astronomical, now mostly astrological) or ⯓ (mostly astrological)
Orbital characteristics[2][b]
Epoch J2000
Earliest precovery dateAugust 20, 1909
Aphelion
  • 49.305 AU
  • (7.37593 billion km)
  • February 2114
Perihelion
  • 29.658 AU
  • (4.43682 billion km)[3]
  • (September 5, 1989)[4]
  • 39.482 AU
  • (5.90638 billion km)
Eccentricity0.2488
366.73 days[3]
4.743 km/s[3]
14.53 deg
Inclination
  • 17.16°
  • (11.88° to Sun's equator)
110.299°
113.834°
Known satellites5
Physical characteristics
Dimensions2,376.6±1.6 km (observations consistent with a sphere, predicted deviations too small to be observed)[5]
Mean radius
Flattening<1%[7]
  • 1.774443×107 km2[c]
  • 0.035 Earths
Volume
  • (7.057±0.004)×109 km3[d]
  • 0.00651 Earths
Mass
Mean density
1.854±0.006 g/cm3[6][7]
1.212 km/s[f]
  • −6.38680 d
  • −6 d, 9 h, 17 m, 00 s
[8]
  • −6.387230 d
  • −6 d, 9 h, 17 m, 36 s
Equatorial rotation velocity
47.18 km/h
122.53° (to orbit)[3]
North pole right ascension
132.993°[9]
North pole declination
−6.163°[9]
Albedo0.52 geometric[3]
0.72 Bond[3]
Surface temp. min mean max
Kelvin 33 K 44 K (−229 °C) 55 K
13.65[3] to 16.3[10]
(mean is 15.1)[3]
−0.44[11]
0.06″ to 0.11″[3][g]
Atmosphere
Surface pressure
1.0 Pa (2015)[7][12]
Composition by volumeNitrogen, 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 only 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).

  1. ^ "Plutonian". Oxford English Dictionary (Online ed.). Oxford University Press. (Subscription or participating institution membership required.)
  2. ^ Cite error: The named reference TOP2013 was invoked but never defined (see the help page).
  3. ^ a b c d e f g h i j k Cite error: The named reference Pluto Fact Sheet was invoked but never defined (see the help page).
  4. ^ Cite error: The named reference jpl-ssd-horizons was invoked but never defined (see the help page).
  5. ^ 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.
  6. ^ 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.
  7. ^ 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.
  8. ^ Seligman, Courtney. "Rotation Period and Day Length". Archived from the original on September 29, 2018. Retrieved June 12, 2021.
  9. ^ a b Cite error: The named reference Archinal was invoked but never defined (see the help page).
  10. ^ Cite error: The named reference AstDys-Pluto was invoked but never defined (see the help page).
  11. ^ Cite error: The named reference jpldata was invoked but never defined (see the help page).
  12. ^ 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
  13. ^ Cite error: The named reference Physorg April 19, 2011 was invoked but never defined (see the help page).
  14. ^ Cite error: The named reference T&M was invoked but never defined (see the help page).

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