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Pluto

Pluto

The Columbia Encyclopedia, 6th ed. | 2011 | Copyright

Pluto in astronomy, a dwarf planet and the first Kuiper belt, or transneptunian, object (see comet ) to be discovered (1930) by astronomers. Pluto has an elliptical orbit usually lying beyond that of Neptune . Although Pluto was long regarded as a planet, since the discovery (beginning in 1992) of other Kuiper belt objects, including one with a diameter larger than that of Pluto, astronomers have recognized the need to reclassify Pluto, and in 2006 the International Astronomical Union (IAU) ended official recognition of Pluto as a planet.

Pluto's mean distance from the sun is 3.67 billion mi (5.91 billion km), and its period of revolution is about 248 years. Since Pluto has an orbit that is more elliptical and tilted than those of the planets (eccentricity .250, inclination 17°), at its closest point to the sun it passes inside the orbit of Neptune; between 1979 and 1999 it was closer to the sun than Neptune was. It will remain farther from the sun for 220 years, when it will again pass inside Neptune's orbit. Its surface consists largely of frozen nitrogen. It is thought to have a rocky, silicate core; its thin atmosphere probably contains nitrogen, carbon monoxide, and methane. Its surface temperature is estimated to be about -360°F (-218°C), a temperature at which most gases exist in the frozen state.

The existence of an unknown planet beyond the orbit of Neptune was first proposed by Percival Lowell on the basis of observed perturbations of the orbits of Uranus and Neptune. He began searching for such a planet in 1905, although he did not publish his calculations of its predicted position until 1914. Independent calculations were published by W. H. Pickering and others. In 1929, the search for a ninth planet was resumed at Lowell Observatory , and on Feb. 18, 1930, using photographic plates and a blink microscope , Clyde W. Tombaugh discovered an object whose motion was consistent with that of a transneptunian planet.

In 1978, American astronomers James Christy and Robert Harrington discovered the moon Charon. Two smaller, more distant moons, Hydra and Nix, were reported in 2005 by American astronomers Hal Weaver and S. Alan Stern, and another small moon was reported in 2011 by American astronomer Mark Showalter. Pluto's diameter is c.1,400 mi (2,300 km), Charon's is c.748 mi (1,203 km), and the radius of Charon's orbit is 12,200 mi (19,640 km); Charon completes one orbit in about 6.4 earth days. Hydra and Nix have diameters of less than 100 mi (160 km). Pluto and Charon both keep the same side facing one another at all times because they rotate synchronously as Charon orbits Pluto. No spacecraft has yet visited Pluto, and it and its moons are too distant for precise telescopic observation, so little is known for certain about their size, composition, surface, and other aspects.

As an increasing number of Kuiper belt objects were discovered after 1992, many astronomers came to believe that Pluto, rather than being a planet, was really an unusually large and close Kuiper belt object. In 1999, however, the IAU reaffirmed that Pluto was a planet because of its size and its satellite, something no other transneptunian object was then known to have, but subsequent discoveries brought Pluto's status into question once again. One Kuiper belt object, now named Eris (and originally nicknamed Xena), whose orbit extends to roughly three times the distance of Pluto's, has an estimated diameter (1,500 mi/2,400 km) slightly larger than that of Pluto and also has a moon. It was the discovery of Eris in particular that ultimately led to Pluto's classification (2006), along with Eris and Ceres , as a dwarf planet; transneptunian dwarf planets are now classified as plutoids.

Bibliography: See W. Hoyt, Planets X and Pluto (1980); S. A. Stern and J. Mitton, Pluto and Charon (1999); B. W. Jones, Pluto (2010).

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Pluto

A Dictionary of Astronomy | 1997 | Copyright

Pluto (symbol p̱) The smallest of the nine ‘traditional’ planets in the Solar System, and the farthest from the Sun. In 2006 the International Astronomical Union introduced a new definition which categorizes Pluto as a dwarf planet rather than one of the major planets; Pluto is now assigned the minor planet number (134340). This reclassification recognizes the fact that Pluto has many characteristics which distinguish it from the eight planets from Mercury to Neptune. It is far smaller than any of those, with a diameter of only 2390 km, less than that of our Moon. Its orbit has a greater inclination than any of the major planets, 17°.1 to the ecliptic, and its orbit is also the most elliptical (eccentricity 0.25). At aphelion Pluto lies 7375 million km from the Sun, but only 4425 million km at perihelion, inside the orbit of Neptune; it last reached perihelion in 1989. Its mean opposition magnitude is +15. Pluto was discovered in 1930 by C. W.Tombaugh. Its rotation axis is tilted at 122°.5 to its orbital plane, so that its rotation is retrograde, and it presents its poles and its equator alternately towards the Sun and the Earth as it moves around its orbit. Its axial rotation period, 6.387 days, is the same as the orbital period of its satellite, Charon, so that Pluto always keeps the same face towards Charon. As seen from Earth, Pluto and Charon underwent a series of mutual occultations in 1985–90. Two much smaller and more distant moons, Hydra and Nix, were discovered by the Hubble Space Telescope in 2005.

pluto

Physical data

Diameter

Oblateness

Inclination of equator to orbit

Axial rotation period (sidereal)

2390 km

0

122°.5

6.387 days

Mean density

Mass (Earth = 1)

Volume (Earth = 1)

Mean albedo (geometric)

Escape velocity

1.8g/cm3

0.0022

0.007

0.3

1.3km/s

Orbital data

Mean distance from Sun

106 km

AU

Eccentricity of orbit

Inclination of orbit to ecliptic

Orbital period (sidereal)

5906.4

39.48

0.25

17°.1

247.9 years

Pluto has an extremely thin atmosphere with a surface pressure of about 10 μbar, composed of methane, possibly with some nitrogen and carbon monoxide. This atmosphere may be seasonal, forming when the planet heats up and releases surface volatiles around the time of perihelion. Methane may escape from the atmosphere near perihelion, so that Pluto behaves somewhat like a comet. Its mean surface temperature is estimated at -220°C. Pluto is thought to have a large rocky core, probably surrounded by a layer of frozen water and other icy materials, and a surface layer of methane. Pluto is now regarded as simply the largest of the sub‐group of trans‐Neptunian objects known as Plutinos.
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PLUTO

The Oxford Companion to World War II | 2001 | | Copyright

PLUTO, acronym derived from the phrase Pipe Line Under The Ocean. Experiments began in 1942 by the British HQ, Combined Operations, to find a means of pumping petrol through flexible pipes laid across the floor of the English Channel. A trial pipe was laid across the Bristol Channel and four pipes, unwound from large drums (CONUNDRUMS) towed by tugs, were laid from the Isle of Wight to Cherbourg when the port was captured after the Normandy landings in June 1944 (see OVERLORD). In January 1945 another 16 pipes were laid from Dungeness to Ambleteuse, delivering up to 4,000 gallons a day. During the assault phase of the Normandy landings (see OVERLORD) petrol was pumped ashore from tankers direct to storage tanks by means of buoyed pipe lines, an operation codenamed TOMBOLA. The British terminus was at Port-en-Bessin, the American at St Honorine.
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I. C. B. DEAR and M. R. D. FOOT. "PLUTO." The Oxford Companion to World War II. 2001. Encyclopedia.com. 28 May. 2012 <http://www.encyclopedia.com>.

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Pluto

A Dictionary of Earth Sciences | 1999 | | Copyright

Pluto The ninth and outermost planet of the solar system, its orbit an average 39.44 AU from the Sun and highly eccentric, sometimes carrying it inside the orbit of Neptune. Its distance from Earth ranges from 4293.7 × 106km to 7533.3 × 106km. Pluto is the smallest planet (much smaller than the Moon), with a radius of 1137 km; volume 0.616 × 1010 km3; mass 0.0125 × 1024 kg; mean density 2050 kg/m3; surface gravity 0.66 (Earth = 1); visual albedo 0.3; blackbody temperature 42.7 K. The atmosphere is very thin, with a surface pressure of about 0.003 bar, and composed of methane and nitrogen. The average surface temperature is about 50 K. It has one satellite, Charon, so large that some astronomers consider Pluto and Charon a minor double-planet system. Pluto was discovered in 1930 by Clyde Tombaugh.
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AILSA ALLABY and MICHAEL ALLABY. "Pluto." A Dictionary of Earth Sciences. 1999. Encyclopedia.com. 28 May. 2012 <http://www.encyclopedia.com>.

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Pluto

World Encyclopedia | 2005 | Copyright

Pluto Smallest and outermost planet of the Solar System. Independently, William H. Pickering and Percival Lowell calculated the possible existence of Pluto. The planet was eventually located (1930) by Clyde Tombaugh – within 5° of Lowell's predicted position. Pluto seems to have a mottled surface with light and dark regions, and signs of polar caps. The surface is covered with icy deposits consisting of 98% nitrogen, with traces of methane, and also probably water, carbon dioxide and carbon monoxide. Pluto has a single moon, Charon, which is so large that some astronomers consider Pluto/Charon as a double planet.

http://lpl.arizona.edu/nineplanets/nineplanets/pluto.html; http://wr.usgs.gov
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PLUTO

The Oxford Companion to Ships and the Sea | 2006 | Copyright

PLUTO, the code name given to the ‘Pipe Line Under The Ocean’ laid across the English Channel from Southampton to Cherbourg shortly after the Anglo-American invasion of north-west France on 6 June 1944 during the Second World War (1939–45). It was an entirely British achievement designed to provide a continuous supply of petrol to sustain the Allied armies as they drove the Germans eastwards. Further pipelines were laid as the Allied armies advanced. The pipe through which the petrol flowed was wound on huge floating drums, known as ‘conundrums’, which were then towed across the Channel unwinding the pipe as they progressed.
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dis

The Oxford Pocket Dictionary of Current English | 2009 | Copyright

dis / dis/ inf. • v. (also diss) (dissed, diss·ing) [tr.] act or speak in a disrespectful way toward: he was expelled for dissing the gym teacher. • n. disrespectful talk: the airwaves bristle with the sexual dis of shock jocks.

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Pluto

The Oxford Pocket Dictionary of Current English | 2009 | Copyright

Plu·to / ˈploōtō/ 1. Greek Mythol. the god of the underworld. Also called Hades. 2. Astron. the most remote known planet of the solar system, usually ninth in order from the sun, discovered in 1930 by Clyde Tombaugh.

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Pluto

World Encyclopedia | 2005 | Copyright

Pluto Roman god of the underworld, equivalent to the Greek god Hades. He ruled over the land of the dead and was also a god of wealth, since his realm contained all underground mineral riches.
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Pluto

The Oxford Dictionary of Phrase and Fable | 2006 | | Copyright

Pluto2 (the code-name for) a system of pipelines laid in 1944 to carry petrol supplies from Britain to Allied forces in France. The name is an acronym for Pipe Line Under The Ocean.
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ELIZABETH KNOWLES. "Pluto." The Oxford Dictionary of Phrase and Fable. 2006. Encyclopedia.com. 28 May. 2012 <http://www.encyclopedia.com>.

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Dis

The Concise Oxford Dictionary of Music | 1996 | | Copyright

Dis (Ger.). The note D♯.
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Pluto

Oxford Dictionary of Rhymes | 2007 | Copyright

Pluto •blotto, Giotto, grotto, lotto, motto, Otto, risotto, Watteau •Cocteau •molto, Sholto •pronto, Toronto •Ariosto •auto, Oporto, Porto, quarto •in toto, koto, Kumamoto, Kyoto, photo, Sesotho, Yamamoto •Bhutto, Maputo, Pluto, prosciutto, ritenuto, sostenuto, tenuto •Cousteau • putto • gusto • Pashto •undertow • Erato

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Pluto

The Oxford Dictionary of Abbreviations | 1998 | | Copyright

Pluto (or PLUTO) (ˈpluːtəʊ) pipe line under the ocean (conveying fuel to Allied forces, World War II)
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FRAN ALEXANDER , PETER BLAIR , JOHN DAINTITH , ALICE GRANDISON , VALERIE ILLINGWORTH , ELIZABETH MARTIN , ANNE STIBBS , JUDY PEARSALL , and SARA TULLOCH. "Pluto." The Oxford Dictionary of Abbreviations. 1998. Encyclopedia.com. 28 May. 2012 <http://www.encyclopedia.com>.

FRAN ALEXANDER , PETER BLAIR , JOHN DAINTITH , ALICE GRANDISON , VALERIE ILLINGWORTH , ELIZABETH MARTIN , ANNE STIBBS , JUDY PEARSALL , and SARA TULLOCH. "Pluto." The Oxford Dictionary of Abbreviations. 1998. Encyclopedia.com. (May 28, 2012). http://www.encyclopedia.com/doc/1O25-Pluto.html

FRAN ALEXANDER , PETER BLAIR , JOHN DAINTITH , ALICE GRANDISON , VALERIE ILLINGWORTH , ELIZABETH MARTIN , ANNE STIBBS , JUDY PEARSALL , and SARA TULLOCH. "Pluto." The Oxford Dictionary of Abbreviations. 1998. Retrieved May 28, 2012 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O25-Pluto.html

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Free newspaper and magazine articles

Pluto or bust!(The Space Place)
Magazine article from: The Technology Teacher; 2/1/2005
Pluto: limits on its atmosphere, ice on its moon.
Magazine article from: Science News; 9/26/1987
Pluto Downgraded
Magazine article from: Skeptic (Altadena, CA); 1/1/2007

Facts and information from other sites

Pluto images
Photo of Pluto as seen through the Hubble telescope. (Image by Public Domain, NASA photo)

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