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Pluto (planet)

Pluto (planet)

: For more uses of the term Pluto, see Pluto (disambiguation). Pluto is the ninth planet in the solar system. Discovered in 1930 and immediately classified as a planet, its status is currently under dispute. Pluto has an eccentric orbit that is highly inclined in respect to the other planets and takes it inside the orbit of Neptune. Its largest moon is Charon, discovered in 1978; two smaller moons were discovered in 2005. Pluto's astronomical symbol is a P-L monogram, . This represents both the first two letters of the name Pluto and the initials of Percival Lowell, the man who lent his name to the observatory that was used to find Pluto. An alternate symbol resembles that of Neptune, but has a circle in place of the middle spoke in the top center. Due to its size and unusual orbit, there has been debate regarding Pluto's classification as a major or a minor planet, and there is increasing momentum for recognizing "dual status." Pluto is classified as a trans-Neptunian object. As of July 31, 2005, one other trans-Neptunian object, , had been found that is larger than Pluto.

Discovery and naming

Pluto was discovered by the astronomer Clyde Tombaugh at the Lowell Observatory in Arizona on February 18, 1930 after an extensive search when he compared photographic plates taken on January 23 and 29. After the observatory obtained confirming photographs, the news of the discovery was telegraphed to the Harvard College Observatory on March 13, 1930. The planet was later found on photographs dating back to March 19, 1915. Tombaugh was searching for a "Planet X" to explain discrepancies in the predicted orbit of Neptune. It is now known these discrepancies were an artifact of the slightly incorrect value then assumed for the mass of Neptune. In the matter of Pluto the discretion of naming the new object belonged to Lowell Observatory and its director, Vesto Melvin Slipher, who, in the words of Tombaugh, was "urged to suggest a name for the new planet before someone else did". Soon suggestions began to pour in from all over the world. Constance Lowell, Percival's widow who had delayed the search through her lawsuit, proposed Zeus, then Lowell, and finally her own first name, none of which met with any enthusiasm. One young couple even wrote to ask that the planet be named after their newborn child. Mythological names were much to the fore: Cronus and Minerva (proposed by the New York Times, unaware that it had been proposed for Uranus some 150 years earlier) were high on the list. Also there were Artemis, Athene, Atlas, Cosmos, Hera, Hercules, Icarus, Idana, Odin, Pax, Persephone, Perseus, Prometheus, Tantalus, Vulcan, Zymal, and many more. One complication was that many of the mythological names had already been allotted to the numerous asteroids. Virtually all the female names had been used up, and male names were usually reserved for objects with unusual orbits. The name retained for the planet is that of the Roman god Pluto, and it is also intended to evoke the initials of the astronomer Percival Lowell, who predicted that a planet would be found beyond Neptune. The name was first suggested by Venetia Burney, at the time an eleven-year-old girl from Oxford, England. Over the breakfast table, one morning her grandfather, who worked at Oxford University's Bodleian Library, was reading about the discovery of the new planet in the Times newspaper. He asked his granddaughter what she thought would be good name for it. Venetia thought that as it was so cold and so distant it should be named after the Roman God of the underworld. Professor Herbert Hall Turner cabled his colleagues in America with this suggestion, and after favourable consideration which was almost unanimous, the name Pluto was officially adopted and an announcement made by Slipher on May 1, 1930. The Chinese, Korean, Japanese, and Vietnamese now call the planet 冥王星. Because Pluto was nowhere near the asteroid belt (trans-Neptunian objects would not be discovered until much later), it never got an asteroidal provisional designation; had it obtained one, it would probably have been "1930 BD".

Orbit

provisional designation Pluto's orbit is unlike those of the other planets. It is highly inclined above the plane of the ecliptic, and highly eccentric (non-circular). The eccentricity of its orbit is such that it crosses the orbit of Neptune, and making Pluto only the eighth-most distant planet from the Sun for part of each orbit; the most recent occurrence of this phenomenon lasted from February 7, 1979 through February 11, 1999. Mathematical calculations indicate that the previous occurrence only lasted fourteen years from July 11, 1735 to September 15, 1749. However, the same calculations indicate that Pluto was the eighth-most distant planet between April 30, 1483 and July 23, 1503, which is almost exactly the same length as the 1979 to 1999 period. Recent studies suggest each crossing of Pluto to inside Neptune's orbit lasts alternately for approximately thirteen and twenty years with minor variations. 1503 compared to the other planets]]Pluto orbits in a 3:2 orbital resonance with Neptune. When Neptune approaches Pluto from behind their gravity start to pull on each other slightly, resulting in an interaction between their positions in orbit of the same sort that produces Trojan points. Since the orbits are eccentric, the 3:2 periodic ratio is favoured because this means Neptune always passes Pluto when they're almost farthest apart. Half a Pluto orbit later, when Pluto is nearing its closest approach, it initially seems as if Neptune is about to catch up to Pluto. But Pluto speeds up due to the gravitational acceleration from the Sun, stays ahead of Neptune, and pulls ahead until they meet again on the other side of Pluto's orbit. Beginning in the 1990s, other trans-Neptunian objects have been discovered, and a certain number of these also have a 3:2 orbital resonance with Neptune. TNOs with this orbital resonance are named "plutinos", after Pluto.

Physical characteristics

More than 75 years after its discovery, many facts about Pluto remain unknown, mainly due to the fact that it is the only planet that has not been visited by human spacecraft and that it is too far away for in-depth investigations with telescopes from earth. What is known are the few physical properties listed below.

Mass and size

Pluto is not only smaller and much less massive than every other planet, at less than 0.2 lunar masses it is also smaller and less massive than seven moons: Ganymede, Titan, Callisto, Io, Earth's Moon, Europa and Triton. However, Pluto is more than twice the diameter, and a dozen times the mass, of Ceres, the largest minor planet in the asteroid belt, and it was larger than any other object known in the trans-Neptunian Kuiper belt until was announced in 2005. See List of solar system objects by mass and List of solar system objects by radius. Pluto's mass and diameter could only be estimated for many decades after its discovery. The discovery of its satellite Charon in 1978 enabled a determination of the mass of the Pluto-Charon system by simple application of Newton's formulation of Kepler's third law. Later Pluto's diameter was measured when it was occulted by Charon, and its disk can now be resolved by telescopes using adaptive optics.

Atmosphere

Pluto's thin atmosphere is most likely nitrogen and carbon monoxide, in equilibrium with solid nitrogen and carbon monoxide ices on the surface. As Pluto moves away from its perihelion and farther from the Sun, more of its atmosphere freezes. Pluto was found to have an atmosphere from an occultation observation in 1988. When an object with no atmosphere occults a star, the star abruptly disappears; in the case of Pluto, the star dimmed out gradually. From the rate of dimming, the atmosphere was determined to have a pressure of 0.15 Pa, roughly 1/700,000 that of earth. In 2002, another occultation of a star by Pluto was observed and analyzed by teams led by Bruno Sicardy of the Paris Observatory [http://calys.obspm.fr/~sicardy/pluton/pr_obs_en.html] and by Jim Elliot of MIT [http://web.mit.edu/newsoffice/2002/pluto.html] and Jay Pasachoff of Williams College [http://www.williams.edu/admin/news/releases.php?id=162]. Surprisingly, the atmosphere was estimated to have a pressure of 0.3 Pa, even though Pluto was further from the Sun than in 1988, and hence should be colder and have a less dense atmosphere. The current best hypothesis is that the south pole of Pluto came out of shadow for the first time in 120 years in 1987, and extra nitrogen sublimated from a polar cap. It will take decades for the excess nitrogen to condense out of the atmosphere.

Appearance

Pluto's apparent magnitude is fainter than 14 m and therefore a telescope is required for observation. To be easily seen, a telescope of around 30 cm aperture is desirable. It looks star-like even in very big telescopes, because its angular diameter is only 0.15″. The colour of Pluto is light brown with a very slight tint of yellow.

Pluto's moons

apparent magnitude Pluto has three known natural satellites: Charon, first identified in 1978, and two smaller, as yet unnamed moons discovered in 2005.

Charon

The Pluto-Charon system is noteworthy for being the only planet/moon system in the solar system whose barycenter lies above the planet's surface, thus prompting some astronomers to label it a double planet (a term complicated by the discovery of two more Plutonian moons). The Pluto-Charon system is also unusual among planetary systems in that they are tidally locked to each other: Charon always presents the same face to Pluto, and Pluto also always presents the same face to Charon. The discovery of Charon allowed astronomers to determine the mass of the Pluto-Charon pair from their observed orbital period and separation by a straightforward application of Kepler's third law of planetary motion. The mass was found to be lower than even the lowest earlier estimates. The discovery also led astronomers to alter their estimate of Pluto's size. Originally, it was believed that Pluto was larger than Mercury but smaller than Mars, but that calculation was based on the premise that a single object was being observed. Once it was realized that there were in fact two objects instead of one, the estimated size of Pluto was revised downward. Today, with modern adaptive optics, Pluto's disc can be resolved and thus its size can be directly determined. adaptive optics Charon's discovery also resulted in the calculation of Pluto's albedo being revised upward; since the planet was now seen as being far smaller than originally estimated, by necessity its capacity to reflect light must be greater than what had been formerly believed. Current estimates place Pluto's albedo as marginally less than that of Venus, which is fairly high. Previously, some researchers had theorized that Pluto and its moon Charon were moons of Neptune that were knocked out of Neptunian orbit when Triton was captured. Triton, the largest moon of Neptune, which shares many atmospherical and geological composition similarities with Pluto, may once have been a Kuiper belt object in a solar orbit, and today it is widely accepted that Pluto never orbited Neptune. An occultation of a star by Charon in 2005, observed in South America by teams from MIT-Williams College, the Paris Observatory, and the Southwest Research Institute has led to improved knowledge of Charon's parameters.

The outer moons

Charon (right) & S/2005 P 1 (bright dot on left)]] Two additional moons were imaged by astronomers working with the Hubble Space Telescope on May 15, 2005, and have received provisional designations of S/2005 P 1 and S/2005 P 2. They were confirmed with "precovery" Hubble images from June 14, 2002. Observations suggest they orbit Pluto at at least twice the distance Charon does. P2 stays about 49,000km from the planet, P1 lies even further away at 65,000km. The two candidate moons seem to orbit Pluto in an anti-clockwise direction. Preliminary observations are also consistent with the outer moons lying in the same orbital plane as Charon, and orbiting at distances two and three times farther away, with orbital resonances of 4:1 and 6:1 with Charon. Both objects appear to be on the order of 50-150 km in diameter, compared to Charon's 1,200 km, and are thought to have masses less than 0.3% of Charon's (or 0.03% of Pluto's mass). The discovery team plans follow-up observations with Hubble in February 2006 to work out the precise orbits, but ground-based observatories will attempt to image the moons as well. Once the orbits are confirmed, the moons can be given permanent names. [http://www.nasa.gov/vision/universe/solarsystem/hubble_pluto.html] [http://news.bbc.co.uk/2/hi/science/nature/4396546.stm]

Exploration of Pluto

Little is known about Pluto because of its great distance from Earth and because no exploratory spacecraft have visited Pluto yet. The Voyager 1 probe was originally intended to visit Pluto, but due to budget cuts and lack of interest — before the discovery of Pluto's moon, size, and atmosphere — the flyby was scrapped in order to facilitate a close flyby of Saturn's moon Titan. The first spacecraft to visit Pluto will be NASA's New Horizons, a mission led by the Southwest Research Institute and the Johns Hopkins Applied Physics Laboratory. The mission's launch window is between January 11 and February 14, 2006. Assuming it launches within the first 23 days of the window, it will benefit from a gravity assist from Jupiter, and arrive at Pluto in July 2015. New Horizons weighs half a ton and will travel at speeds reaching 43,000 km/h (27,000 mph). It will use a remote sensing package that includes imaging instruments and a radio science investigation, as well as spectroscopic and other experiments, to characterize the global geology and morphology of Pluto and its moon Charon, map their surface composition and characterize Pluto's neutral atmosphere and its escape rate. The mission plan also calls for a flyby of one or more Kuiper belt objects by 2022. The New Horizons mission replaced the Pluto Kuiper Express mission, which was cancelled in 2000 because of increasing costs and launch vehicle delays.

The Pluto debate

Planet X?

The planet Pluto was originally discovered in 1930 in the course of a search for a body sufficiently massive to account for supposed anomalies in the orbits of Uranus and Neptune. Once it was found, its faintness and failure to show a visible disc cast doubt on the idea that it could be Lowell's Planet X. Lowell had made a prediction of Pluto's position in 1915 which had turned out to be fairly close to its actual position at that time; however Ernest W. Brown concluded almost immediately that this was a coincidence, and this view is retained today. Lowell had also made earlier, different predictions of Planet X's position beginning in 1902. [http://www.phys-astro.sonoma.edu/people/faculty/tenn/asphistory/1994.html] In the following decades estimates of the Plutonian mass and diameter were the subject of debate as telescopes and imaging systems improved. The consensus steadily favored smaller masses and diameters as time passed. Indeed, one observer waggishly pointed out that if the trend were extrapolated, the planet seemed to be in danger of vanishing altogether, a remark which proved possibly prophetic in light of later debates over Pluto's status as a "planet". In an attempt to reconcile Pluto's small apparent size with its identification as Planet X, the theory of specular reflection was proposed. This held that observers were measuring only the diameter of a bright spot on the highly reflective surface of a much larger planet which could thereby be massive without having an exceptionally high density. The uncertainty was conclusively resolved by the discovery of Pluto's satellite Charon in 1978. This made it possible to determine the combined mass of the Pluto-Charon system which turned out to be lower even than that anticipated by skeptics of the specular reflection theory, which was then rendered completely untenable. The accepted figure for Pluto's diameter today makes it considerably smaller than the Moon, with only a fraction of the Moon's mass on account of its being largely composed of ice. More recently, measurements of the path of Voyager 2 have shown that Neptune has a lower mass than previously believed and that when this lower mass is taken into account there is no anomalous movement of Uranus or Neptune. Thus Pluto's discovery and Lowell's 1915 prediction were largely coincidental as Pluto actually has no role in what were believed to be anomalies in Neptune and Uranus' motion. Pluto's discovery was mostly due to the thoroughness and diligence of Tombaugh's search, which he continued for some time after the discovery and left him satisfied that no other planet of a comparable magnitude existed. While Pluto's identification as Planet X began to be doubted soon after its discovery, and for some decades afterwards some considered that a hypothetical tenth planet might be the true Planet X which supposedly caused anomalies in Uranus and Neptune's position, Pluto's identity as the solar system's ninth planet was unquestioned until the 1990s.

Minor planet?

1990s Starting in September of 1992 scientists began discovering hundreds of other bodies in the area of the solar system beyond the orbit of Neptune. The second of these, after Pluto and Pluto's moon Charon, was . The continued discovery of these objects, especially of plutinos, rekindled a debate that goes on to this day: is Pluto a major planet or simply one of the largest trans-Neptunian objects? Trans-Neptunian objects are considered to be minor planets, so the question arose whether to consider Pluto to be one too. This planetary sciences debate landed in newspaper headlines, editorials, and on the Internet in the mid- to late-1990s. Thoughts that Pluto might be "demoted" to non-planet status created an emotional response in certain sectors of the public. Such news outlets as the BBC News Online, the Boston Globe, and USA Today all printed stories noting that the International Astronomical Union was considering dropping Pluto's planetary status. "Save Pluto" websites sprang up, and school children sent letters to astronomers and the IAU. On February 3 1999, Brian Marsden of the Minor Planet Center inadvertently fueled the debate when he issued an editorial in the [http://cfa-www.harvard.edu/iau/mpec/J99/J99C03.html Minor Planet Electronic Circular 1999-C03] noting that the 10,000th minor planet was about to be numbered and this called for a large celebration (the IAU celebrates every thousandth numbered minor planet in some way). He suggested that Pluto be honored with the number 10,000, giving it "dual citizenship" of sorts as both a major and a minor planet. Between the media reports and the Minor Planet Electronic Circulars, IAU General Secretary Joannes Anderson issued a press release that same day, stating there were no plans to change Pluto's planetary status. Eventually, the number 10,000 was assigned to an "ordinary" asteroid, 10000 Myriostos. The debate centers on how a "planet", from the Greek for "wanderer", is an appellation that depends upon an object's particular size, formation, or orbit. Some argue that not only is Pluto a major planet but also some moons like Titan, Europa or Triton, or even the larger asteroids. Some argue that an astronomical object more than about 360 km in diameter, at which point the object has a tendency to become round under its own gravity, should be known as a major planet; this would include several moons and a handful of asteroids. Isaac Asimov suggested the term mesoplanet be used for planetary objects intermediate in size between Mercury, the smallest terrestrial planet with a diameter of 4879.4 km and Ceres, the largest known asteroid with a mean diameter of 950 km, which would include Pluto but not most moons.

New discoveries

Continuing discoveries in the transneptunian region keep rekindling the debate. In 2002, 50000 Quaoar was discovered, with a 1280 km diameter, making it a bit more than half the size of Pluto. Another recent discovery, 90482 Orcus, is probably even larger. In 2004 the discoverers of 90377 Sedna, an extremely distant object well beyond the other known transneptunian objects, placed an upper limit of 1800 km on its diameter, close to Pluto's 2320 km. On July 29, 2005, a Trans-Neptunian object called was announced, which on the basis of its magnitude and simple albedo considerations is assumed to be larger than Pluto. This caused its discoverers to call it the "10th planet" of the solar system, although there is no consensus yet on whether to call it a planet, and others consider the new discovery to be the strongest argument yet for demoting Pluto to the status of a minor planet. could be the largest object yet discovered in the solar system since Neptune in 1846. The last remaining distinguishing feature of Pluto is now its large moon, Charon, and its atmosphere; these characteristics may not, however, be unique to Pluto: several other transneptunian objects are known to have satellites; and 's spectrum suggests that it has a similar surface composition to Pluto, as well as a moon discovered in September of 2005. There is some historical precedent for "demoting" a "planet" in the light of subsequent discoveries. The first four asteroids (1 Ceres, 2 Pallas, 3 Juno and 4 Vesta) were considered to be planets for several decades (in part because their sizes were not accurately known at the time). However, in 1845, the first new asteroid in 38 years was discovered (5 Astraea), just one year before Neptune, and soon every year brought more asteroid discoveries. It was soon recognized that Ceres and the others were just the most prominent members of a populous asteroid belt, and although asteroids are also known as "minor planets", they are no longer considered "planets". Some see in this a precedent for noting that Pluto is just the most prominent member of the Kuiper belt. On the other hand, it may very well be that regardless of future astronomical discoveries, Pluto will remain grandfathered as a planet in much the same way that Europe is considered a separate continent for historical reasons although geographically it makes more sense, from first principles, to consider both Europe and Asia to comprise the single continent of Eurasia.

Pluto in popular culture


- Donald W. Horner, in Their Winged Destiny (1912), described spaceflight to Alpha Centauri by astronauts who, as they leave the solar system, pass a planet beyond Neptune.
- Mickey Mouse's dog Pluto first appeared in the 1930 cartoon The Chain Gang; it was adapted into Minnie Mouse's dog Rover, and shortly thereafter became Mickey's Pluto, being named for the planet.
- Stanton Coblentz's In Plutonian Depths (Wonder Stories Quarterly, Spring 1931) was the first story to take advantage of the newly discovered and named world.
- In H. P. Lovecraft's Cthulhu mythos stories (1928–), the Mi-go are a fictional alien race with a base on Pluto, called Yuggoth and Iukkoth in the stories. There are some stories, though, that identify Yuggoth with a huge world situated beyond Pluto on an orbit perpendicular to the ecliptic.
- In Robert A. Heinlein's novel Have Space Suit-Will Travel (1958), Pluto is used by aliens as a remote base for Earth exploration. In Heinlein's story Sky Lift (1953), a torch-ship pilot flies on a mercy mission to Pluto.
- In Larry Niven's novel World of Ptavvs (1966), Pluto was theorized to have been a moon of Neptune until it was knocked out of orbit by an interstellar craft.
- Martinex of the Guardians of the Galaxy is the last survivor of a human colony in Pluto. His ancestors were African. The character first appeared in January, 1969 and operates in the 31st century.
- In the 1974 Japanese anime series Space Battleship Yamato, also known as Star Blazers, the eponymous starship destroys an alien base on Pluto and fights a subsequent battle in an asteroid belt beyond Pluto. Eighteen years later astronomers confirmed the existence of the real-life Kuiper belt.
- In the Doctor Who (1963–) serial The Sun Makers (1977), set far in the future, Pluto is covered with vast cities that are warmed by artificial suns, but access to sunlight is controlled by a sinister ruling elite.
- In John DeChancie's Starrigger series (1983), Pluto is the location of our solar system's dimensional gate to the interstellar Skyway.
- Pluto is featured in Kim Stanley Robinson's novel Icehenge (1985), in which a mysterious artificial structure is found on the planet's north pole.
- In the computer game Star Control II (1990), and consequently in The Ur-Quan Masters, the Spathi Captain Fwiffo can be found on Pluto.
- The final section of Dave Sim's graphic novel Minds (Cerebus the Aardvark, Volume 10, 1996) takes place on Pluto.
- Christine Lavin's song Planet X (1996) is a good-natured protest against suggestions that Pluto is not a planet.
- In the Japanese anime series Cowboy Bebop (1998), it is mentioned that a "supermax" maximum security penitentiary is located on Pluto.
- In the game Starsiege (1999), Pluto is destroyed at the end of the game.
- The television show Futurama (1999-2003) has featured Pluto on occasion, mainly as a habitat for penguins.
- In the television show Aqua Teen Hunger Force (2000), two of the show's "Villains", Oglethorpe and Emory (The Plutonians), are from Pluto.
- In the cartoon Fairly Oddparents (2001–) Cosmo destroys Pluto with a button the president lost.
- In the anime Bishoujo Senshi Sailor Moon, Sailor Pluto is the third Outer Senshi to be discovered, and her talisman is the Garnet Orb. She guards the gates of time, and her Greek god equivalent is Hades, the lord of the underworld, which she derives her attacks from (e.g. Dead Scream). On her forehead, she bears the planet's symbol and her image colour is black (sometimes purple).
- In the game Epoch Star (2004), Pluto is the home planet of the Anthropite civilization.
- In the second part of a BBC drama documentary called [http://www.bbc.co.uk/sn/tvradio/programmes/spaceodyssey/ Space Odyssey: Voyage to the Planets] (2004) Pluto is the penultimate destination on a hypothetical human space flight to planets of the Solar System
- In the PC Game Freelancer, one of the start movies shows Pluto Being Destroyed by an alien race 800 years before the game starts.

See also


- Pluto in astrology
- Solar eclipses on Pluto

References


- Henderson, Mark (Oct. 30, 2005). "Pluto may lose status of planet". New Straits Times, p. F17.

External links


- [http://nssdc.gsfc.nasa.gov/planetary/factsheet/plutofact.html NASA's Pluto fact sheet]
- [http://www.studyworksonline.com/cda/content/article/0%2C%2CEXP666_NAV4-42_SAR920,00.shtml StudyWorks! Online: Is Pluto a Planet?] - summarizes the pros and the cons of classifying Pluto as a planet
- David H. Freedman, [http://www.theatlantic.com/issues/98feb/pluto.htm "When is a Planet Not a Planet?"], Atlantic Monthly, February 1998.
- [http://pluto.jhuapl.edu/ NASA's Pluto-Kuiper Belt Mission] - launching in early 2006.
- [http://www.sfsite.com/~silverag/pluto.html Pluto in Science Fiction] - Bibliography of science fiction which is set on Pluto.
- [http://www.expreso.co.cr/centaurs/astronom/crossings/Plutocross.html Pluto/Neptune crossings]
- [http://space.com/scienceastronomy/051031_pluto_moons.html Space.com article on second and third moons]
- [http://hubblesite.org/newscenter/newsdesk/archive/releases/2005/19/ NASA's Hubble Reveals Possible New Moons Around Pluto ] – Hubble Press Release
- [http://www.washingtonpost.com/wp-dyn/content/article/2005/10/31/AR2005103101426.html Possible New Moons]
- [http://www.nature.com/cgi-taf/DynaPage.taf?file=/nature/journal/v424/n6945/abs/nature01762_fs.html Elliot et al., The recent expansion of Pluto's atmosphere]
- [http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2005AJ....129.1718P&db_key=AST&data_type=HTML&format=&high=43809decd514756 Pasachoff et al., "The Structure of Pluto's Atmosphere from the 2002 August 21 Stellar Occultation," Astron. J., 129, 1718-1723.] Category:Trans-Neptunian objects ko:명왕성 ms:Pluto ja:冥王星 simple:Pluto (planet) th:ดาวพลูโต zh-min-nan:Mê-ông-chheⁿ

Pluto (disambiguation)

Pluto can refer to the following:
- Pluto is the name of an object regarded by many as the ninth planet by average distance in our Solar System. There is an on-going debate as to its actual status, but it is officially regarded by the IAU as a planet.
- Pluto is the Roman god of the Underworld, for which the planet above is named.
- Plouto, a nymph in Greek mythology, was sometimes spelled "Pluto". She is not the same character as the Roman god mentioned above.
- Pluto is fictional Mickey Mouse's pet dog.
- Plutocracy
- Pluto is a fictional giant green-black horned robot that fought Astro Boy in order to become the world's mightiest robot.
- Pluto is a thriller/mystery manga by Naoki Urasawa based on events from Astro Boy.
- Project Pluto, an American nuclear powered cruise missile.
- Operation Pluto (Pipe-Lines Under The Oceans) was a major project undertaken during World War II by British scientists and armed forces to carry and deliver gasoline. After testing between Wales and Cornwall, it was operationally laid and used through the English Channel in July 1944 and in Pas-de-Calais later. It was the forefather of all flexible pipes used in the development of offshore oil fields.
- PLUTO, a nuclear reactor at the Atomic Energy Research Establishment at Harwell, Oxfordshire
- PLUTO is one of the largest and oldest Italian Linux User Groups.
- Pluto, in computer programming, is the second Italian metasyntactic variable commonly used.
- "Pluto" is the title of the movement added to Gustav Holst's The Planets suite, composed in 1996 by Brad Spitz for the award-winning CD "Nine Worlds", hosted by Patrick Stewart, and featured in the DVD "Patrick Stewart Narrates THE PLANETS epoch 2000".
- "Pluto, the Renewer" is a movement composed by Colin Matthews to add to Gustav Holst's The Planets suite.
- Pluto was a German car manufacturer between the world wars.
- Pluto Press is a British publishing house.
- Pluto is a song by nerdcore rap group 2 Skinnee J's from their 1998 album Super Mercado.
- Sailor Pluto is the codename of the character Setsuna Meioh in the Sailor Moon franchise. ja:プルート simple:Pluto

1930

1930 (MCMXXX) is a common year starting on Wednesday.

Events

January-February


- January 6 - The first diesel-engine automobile trip is completed (Indianapolis, Indiana, to New York City).
- February 18 - While studying photographs taken in January, Clyde Tombaugh discovers Pluto
- February 18 - Elm Farm Ollie becomes the first cow to fly in an airplane and also the first cow to be milked in an airplane.

March


- March 2 - Mohandas Gandhi informs British viceroy of India that civil disobedience would begin nine days later
- March 5 - Danish painter Einar Wegener goes through a sexual reassignment surgery and takes the name Lili Elbe
- March 6 - first frozen foods of Clarence Birdseye go on sale in Springfield, Massachusetts, USA
- March 12 - Mohandas Gandhi sets off to a 200-mile protest march towards the sea with 78 followers to protest the British monopoly on salt - more will join them during the Salt March that ends in April 5
- March 28 - Constantinople and Angora change their names to Istanbul and Ankara
- March 29 - Heinrich Brüning is appointed German Reichskanzler
- March 31 - The Motion Pictures Production Code is instituted, imposing strict guidelines on the treatment of sex, crime, religion and violence in motion pictures for the next forty years

April-May


- April 5 - In an act of civil disobedience, Mahatma Gandhi breaks British law after marching to the sea and making salt.
- April 6 - Hostess Twinkies are invented.
- April 21 - Fire in Ohio State Penitentiary near Columbus kills 320
- April 22 - The United Kingdom, Japan and the United States sign the London Naval Treaty regulating submarine warfare and limiting shipbuilding.
- April 28 - The first night game in organized baseball history takes place in Independence, Kansas.
- May 4/May 5 - Mohandas Gandhi is arrested again
- May 15 - Aboard a Boeing tri-motor, Ellen Church becomes the first airline stewardess (the flight was from Oakland, California to Chicago, Illinois).
- May 17 - French Prime Minister André Tardieu decides to withdraw the remaining French troops from the Rheinland. They depart by June 30
- May 20 - Sergei Eisenstein arrives in New York City
- May 24 - Amy Johnson lands in Darwin, Australia becoming the first woman to fly solo from England to Australia (she left on May 5 for the 11,000 mile flight).
- May 30 - Sergei Eisenstein arrives in Hollywood to work for Paramount Pictures - they part ways by October

June-August


- June 9 - Chicago Tribune journalist Alfred Lingle is shot in Chicago, Illinois, USA. Newspapers promise $55,000 reward for information. Liddle is later found to have had contacts to organized crime
- June 17 - U.S. President Herbert Hoover signs the Smoot-Hawley Tariff Act into law.
- June 17 - Bonus Army: Around a thousand World War I veterans mass at the United States Capitol as the U.S. Senate considers a bill that would give them certain benefits.
- June 21 - One-year conscription comes into force in France
- July 7 - Lapua Movement marches in Helsinki, Finland
- July 7 - Building of the Boulder Dam (now known as Hoover Dam) is started.
- July 13 - The first soccer World Cup starts: Lucien Laurent scores the first goal, for France against Mexico
- July 26 - Charles Creighton and James Hargis of Missouri begin their return journey to Los Angeles - driving 11 555 km using only a reverse gear. The trip lasts the next 42 days
- July 30 - Uruguay beat Argentina 4-2 in the first soccer World Cup Final
- July 31 - The radio mystery program The Shadow airs for the first time.
- August 7 - Richard Bedford Bennett becomes Canada's eleventh prime minister.
- August 9 - Betty Boop premiers in the animated film Dizzy Dishes.
- August 12 - Turkish troops move into Persia to fight Kurdish insurgents
- August 27 - Military junta takes over in Peru

September-December


- September 6 - Josef Felix Urileu makes a successful military coup in Argentina
- September 8 - 3M begins marketing Scotch transparent tape.
- September 12 - Wilfred Rhodes end his 1110-game first-class career by taking 5 for 95 for H.D.G. Leveson Gower's XI against the Australians.
- September 14 - National socialists win 107 seats in German parliament - 18.3% of all the votes makes them second largest party
- September 16 - overthrow of Hipólito Yrigoyen, President of Argentina.
- October 5 - British Airship R101 crashed in France en-route to India on its maiden voyage.
- October 24 - Brazil - Revolution of 1930 by Getúlio Dornelles Vargas
- November 1 - William Joseph Dess is born in New Castle, PA to Joseph and Mary Dess.
- November 2 - Haile Selassie is crowned emperor of Ethiopia.
- November 25 - An earthquake in the Izu Peninsula of Japan kills 223 people and destroys 650 buildings
- December 2 - Great Depression: US President Herbert Hoover goes before Congress and asks for a US$150 million public works program to help generate jobs and stimulate the economy.
- December 19 - Merap volcano erupts - 1300 dead
- December 24 - In London, Harry Grindell Matthews demonstrates his devide to project pictures to the clouds
- December 28 - Mohandas Gandhi leaves for Britain for negotiations

Unknown dates


- British White Paper demands restrictions on Jewish immigration into Palestine
- Rafael Leónidas Trujillo takes over in the Dominican Republic
- The Federal Bureau of Narcotics replaces the Narcotics Division of the Prohibition Unit.
- Walther Bothe and H. Becker discover the neutron.
- Abkhazia and Georgia, autonomous republics of the Soviet Union, are merged.
- The University of Queensland starts the pitch drop experiment.
- Jake paralysis outbreak occurs in United States.

Births

January-February


- January 2 - Julius LaRosa, American singer
- January 20 - Buzz Aldrin, American pilot and astronaut
- January 23 - Derek Walcott, West Indian writer, Nobel Prize laureate
- January 26 - John Straffen, British serial killer
- January 29 - Bobby Bland, American singer
- January 30 - Gene Hackman, American actor
- February 27 - Peter Stone, American writer (d. 2003)
- February 28 - Leon Neil Cooper, American physicist, Nobel Prize laureate

March


- March 3 - Heiner Geißler, German politician
- March 6 - Allison Hayes, American actress (d. 1977)
- March 6 - Lorin Maazel, French-born conductor
- March 7 - Antony Armstrong-Jones, Lord Snowdon
- March 10 - Claude Bolling, French jazz pianist and composer
- March 15 - Zhores Ivanovich Alferov, Russian physicist, Nobel Prize laureate
- March 17 - James Irwin, astronaut (d. 1991)
- March 19 - Ornette Coleman, American musician
- March 22 - Pat Robertson, American televangelist
- March 22 - Stephen Sondheim, American composer and lyricist
- March 24 - David Dacko, first President of the Central African Republic (d. 2003)
- March 24 - Steve McQueen, American actor, film director, and producer (d. 1980)
- March 25 - John Keel, American author
- March 26 - Sandra Day O'Connor, U.S. Supreme Court Justice
- March 27 - David Janssen, American actor (d. 1980)
- March 28 - Jerome Isaac Friedman, American physicist, Nobel Prize laureate
- March 30 - John Astin, American actor
- March 30 - Rolf Harris, Australian-born entertainer
- March 30 - Peter Marshall, American game show host

April


- April 3 - Helmut Kohl, Chancellor of Germany
- April 8 - Carlos Hugo of Bourbon-Parma, Duke of Parma, French-born fascist
- April 10 - Pertti "Spede" Olavi Pasanen, Finnish television personality (d. 2001)
- April 11 - Anton LaVey, American religious leader (d. 1997)
- April 15 - Vigdís Finnbogadóttir, President of Iceland
- April 16 - Herbie Mann, American jazz flutist (d. 2003)
- April 21 - Silvana Mangano, Italian actress (d. 1989)
- April 25 - Paul Mazursky, American director and writer
- April 29 - Jean Rochefort, French actor

May-August


- May 4 - Roberta Peters, American soprano
- May 8 - Heather Harper, Irish soprano
- May 9 - Joan Sims, English actress (d. 2001)
- May 10 - Pat Summerall, American football player and broadcaster
- May 15 - Jasper Johns, American painter
- May 19 - Lorraine Hansberry, American playwright (d. 1965)
- May 21 - Malcolm Fraser, twenty-second Prime Minister of Australia
- May 22 - John Barth, American writer
- May 22 - Harvey Milk, American politician and civil rights activist (d. 1978)
- May 31 - Clint Eastwood, American actor, director, and producer
- June 2 - Charles Conrad, astronaut (d. 1999)
- June 8 - Robert Aumann, German-born mathematician, recipient of the Nobel Prize in Economics
- June 9 - Monique Serf, French musician (d. 1997)
- June 12 - Jim Nabors, American actor, musician, and comedian
- June 17 - Brian Statham, English cricketer (d. 2000)
- June 22 - Yuri Artyukhin, cosmonaut (d. 1998)
- June 27 - Ross Perot, American billionaire and politician
- July 2 - Carlos Menem, President of Argentina
- July 3 - Carlos Kleiber, Austrian conductor (d. 2004)
- July 4 - George Steinbrenner, baseball team owner
- July 11 - Harold Bloom, American literary critic
- July 15 - Jacques Derrida, Algerian-born French literary critic (d. 2004)
- July 25 - Maureen Forrester, Canadian contralto
- July 25 - Murray Chapple, New Zealand cricket captains (d. 1985)
- August 1 - Pierre Bourdieu, French sociologist
- August 5 - Neil Armstrong, astronaut
- August 12 - George Soros, Hungarian-born businessman
- August 17 - Ted Hughes, English poet (d. 1998)
- August 21 - Princess Margaret, Countess of Snowdon (d. 2002)
- August 25 - Sir Sean Connery, Scottish actor
- August 30 - Warren Buffett, American investor

September-December


- September 3 - Cherry Wilder, New Zealand author (d. 2002)
- September 7 - King Baudouin I of Belgium (d. 1993)
- September 25 - Shel Silverstein, American author, poet, and humorist (d. 1999)
- September 26 - Fritz Wunderlich, German tenor (d. 1966)
- September 30 - Ray Charles, American singer and musician (d. 2004)
- October 1 - Sir Richard Harris, Irish actor (d. 2002)
- October 5 - Anne Haddy, Australian actress (d. 1999)
- October 5 - Pavel Popovich, cosmonaut
- October 5 - Reinhard Selten, German economist, Nobel Prize laureate
- October 6 - Hafez al-Assad, President of Syria (d. 2000)
- October 8 - Tōru Takemitsu, Japanese composer (d. 1996)
- October 10 - Yves Chauvin, French chemist, Nobel Prize laureate
- October 10 - Harold Pinter, English playwright, Nobel Prize laureate
- October 11 - Sam Johnson, American politician
- October 17 - Robert Atkins, American nutritionist (d. 2003)
- October 28 - Bernie Ecclestone, English auto racing tycoon
- October 30 - Timothy Findley, Canadian author (d. 2002)
- November 14 - Edward White, astronaut (d. 1967)
- November 16 - Chinua Achebe, Nigerian writer
- November 24 - Bob Friend, baseball player
- December 1 - Joachim Hoffmann, German historian (d. 2002)
- December 2 - Gary Becker, American economist, Nobel Prize laureate
- December 6 - Daniel Lisulo, Prime Minister of Zambia

Planet

A planet is generally considered to be a relatively large mass of accreted matter in orbit around a star that is not a star itself. The name comes from the Greek term πλανήτης, planētēs, meaning "wanderer", as ancient astronomers noted how certain lights moved across the sky in relation to the other stars. Based on historical consensus, the International Astronomical Union (IAU) lists nine planets in our solar system. Since the term "planet" has no precise scientific definition, however, many astronomers contest that figure. Some say it should be lowered to eight by removing Pluto from the list, whilst others claim it should be raised to fifteen, twenty, or even higher.

Planetary formation

It is not known with certainty how planets are formed. The prevailing theory is that they are formed from those remnants of a nebula that don't condense under gravity to form a protostar. Instead, these remnants become a thin disc of dust and gas revolving around the protostar and begin to condense about local concentrations of mass within the disc. These concentrations become ever more dense until they collapse inward under gravity to form protoplanets. When the protostar has grown such that it ignites to form a star, its solar wind blows away most of the disc's remaining material. Thereafter there still may be many protoplanets orbiting the star or each other, but over time many will collide, either to form a single larger planet or release material for other larger protoplanets or planets to absorb. Meanwhile, protoplanets that have avoided collisions may become moons of larger planets. With the discovery and observation of planetary systems around stars other than our own, it is becoming possible to elaborate, revise or even replace this account.

Within our solar system

Main article: Solar system The process of naming planets and their features is known as planetary nomenclature. All the currently accepted planets in the solar system are named after Roman gods, except for Uranus (named after a Greek god) and the Earth, which was not seen as a planet by the ancients but rather the centre of the universe. The designated planetary names are near-universal in the Western world, but some non-European languages, such as Chinese, use their own. Moons are also named after gods and characters from classical mythology, or, in the case of Uranus, after Shakespearean characters. Asteroids can be named after anybody or anything at the discretion of their discoverers, subject to approval by the IAU's nomenclature panel.

Accepted planets

Asteroid According to the authority of the IAU, there are nine planets in our solar system. In increasing distance from the Sun they are: #Mercury (astronomical symbol ) #Venus () #Earth () with one confirmed natural satellite, Luna (the Moon) #Mars () with two confirmed natural satellites, Deimos and Phobos #Jupiter () with sixty-three confirmed natural satellites #Saturn () with forty-six confirmed natural satellites #Uranus (Uranus) with twenty-seven confirmed natural satellites #Neptune () with thirteen confirmed natural satellites #Pluto () with three confirmed natural satellites (Charon, S/2005 P 1, S/2005 P 2) However, there is some pressure for Pluto to be reclassified as a Kuiper Belt object, especially in light of the discovery of . This object, however, has not yet received a definitive classification from the IAU.

Other candidates

When Ceres was found orbiting between Mars and Jupiter in 1801, it was initially touted as a planet, but after many smaller objects were found with a similar orbit, it was classified as an asteroid. However, due to its large size (relative to the other asteroids), and its roughly spherical shape, Ceres would be considered a planet by some astronomers' definitions. Similarly, since 1992 many objects have been found in the predicted Kuiper Belt that exists beyond Neptune. Several of the largest of these have challenged the planetary status quo, as they are both spherical and larger than the bodies in the Mars-Jupiter asteroid belt, and are similar in size, orbit and composition to Pluto. However, as yet none have been accepted as planets by the IAU. The most significant of these are (in order of increasing distance from the Sun) 90482 Orcus, , 50000 Quaoar, , , 28978 Ixion, 20000 Varuna, 19521 Chaos, and 90377 Sedna. (However, it should be noted that Sedna is often considered to be beyond the Kuiper Belt; being either a member of the scattered disc or the inner Oort Cloud). Like Ceres before it, Sedna was widely touted as a planet when it was discovered in 2003, as it was the largest object found since Pluto. However, mainly due to its size still being smaller than Pluto's, it did not achieve planetary status from the IAU. However, the discovery in 2005 of (nicknamed Xena), with a size and mass larger than Pluto seems to have forced the issue. As of September 2005 it has not yet been accepted as a planet, but the IAU is expected to announce a definition of a planet by the end of the year, which will either see become a planet, or have Pluto stripped of its status.

Extrasolar planets

:Main article: Extrasolar planet. Of the 173 extrasolar planets (those outside our solar system) discovered to date (October 2005) most have masses which are about the same or larger than Jupiter's. Exceptions include a number of planets discovered orbiting burned-out star remnants called pulsars, such as PSR B1257+12, the planets orbiting the stars Mu Arae, 55 Cancri and GJ 436 which are approximately Neptune-sized [http://www.eso.org/outreach/press-rel/pr-2004/pr-22-04_pf.html], and a planet orbiting Gliese 876 that is estimated to be about 6 to 8 times as massive as the Earth and is probably rocky in origin. It is far from clear if the newly discovered large planets would resemble the gas giants in our solar system or if they are of an entirely different type as yet unknown, like ammonia giants or carbon planets. In particular, some of the newly discovered planets, known as hot Jupiters, orbit extremely close to their parent stars, in nearly circular orbits. They therefore receive much more stellar radiation than the gas giants in our solar system, which makes it questionable whether they are the same type of planet at all. There is also a class of hot Jupiters that orbit so close to their star that their atmospheres are slowly blown away in a comet-like tail: the Chthonian planets. The National Aeronautics and Space Administration of the United States has a program underway to develop a Terrestrial Planet Finder artificial satellite, which would be capable of detecting the planets with masses comparable to terrestrial planets. The frequency of occurrence of these planets is one of the variables in the Drake equation which estimates the number of intelligent, communicating civilizations that exist in our galaxy. Astronomers have recently [http://www.nature.com/news/2005/050711/full/050711-6.html] [http://www.jpl.nasa.gov/news/news.cfm?release=2005-115] detected a planet in a triple star system, a finding that challenges current theories of planetary formation. The planet, a gas giant slightly larger than Jupiter, orbits the main star of the HD 188753 system, in the constellation Cygnus, and is hence known as HD 188753 Ab. The stellar trio (yellow, orange, and red) is about 149 light-years from Earth. The planet, which is at least 14% larger than Jupiter, orbits the main star (HD 188753 A) once every 80 hours or so (3.3 days), at a distance of about 8 Gm, a twentieth of the distance between Earth and the Sun. The other two stars whirl tightly around each other in 156 days, and circle the main star every 25.7 years at a distance from the main star that would put them between Saturn and Uranus in our own Solar System. The latter stars invalidate the leading hot Jupiter formation theory, which holds these planets form at "normal" distances and then migrate inward through some debatable mechanism. This could not have occurred here, the outer star pair disrupting outer planet formation.

Brown dwarf "planets"

The discovery of a planet-sized satellite of a brown dwarf has blurred the distinction between "planet" and "moon." A brown dwarf, though a star in theory, in practice is often described as in between a planet and a star. It is formally defined by the IAU by its official statement that "Substellar objects with true masses above the limiting mass for thermonuclear fusion of deuterium are "brown dwarfs", no matter how they formed nor where they are located." To the IAU, the question of whether an object in orbit around a brown dwarf is a "planet" or a "moon" was simply not relevant, as it does not use the term "moon," only "satellite" and as yet has no official definition for "planet."

Interstellar planets

Interstellar planets are rogues in interstellar space, not gravitationally linked to any given solar system. No interstellar planet is known to date, but their existence is considered a likely hypothesis based on computer simulations of the origin and evolution of planetary systems, which often include the ejection of bodies of significant mass. Such objects are not formally called planets, however, since the IAU has not defined the term "planet".

Definition and classification of planets

Much like "continent", "planet" is a word without a precise definition, with history and culture playing as much of a role as geology and astrophysics. Recent definitions have been vague and imprecise; The American Heritage Dictionary, for instance, formerly defined a planet as: :A nonluminous celestial body larger than an asteroid or comet, illuminated by light from a star, such as the sun, around which it revolves. In the solar system there are nine known planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto.' However, for some time that definition has been viewed by many as inadequate. The eight largest planets (which are also the eight nearest to the Sun) are universally recognised as such, and for this reason are often universally referred to as "major planets", but there is controversy over Pluto and other smaller objects.

Suggested wide definitions

Since the discoveries of many of the objects in the Kuiper belt and around other stars, there has been a concerted push amongst scientists to come up with a precise definition of what constitutes a planet. In 1999, the IAU set up a working group to develop a scientifically plausible recommendation, but as of August, 2005 they had not reached a conclusion. After the discovery of (informally called "Xena"), a member of the committee, Alan Stern, has said that the group wanted "to get something done, pronto". He also informed journalists that a "consensus" in the group was moving towards the following definition: :A planet is a body that directly orbits a star, is large enough to be round because of self gravity, and is not so large that it triggers nuclear fusion in its interior. Note that this definition also covers disputes at the upper end of a planet's size, which provides the extra benefit of forming a barrier between planets and brown dwarfs. Many consider this definition the best option as it sets up divisions based on physical characteristics rather than an arbitrary size limit. It is also somewhat universal in its application where other definitions have been crafted mainly to sort our own solar system into simple categories (such as placing the size limit as just under Mars, Mercury or Pluto). Depending how it is interpreted, objects counted as planets under such a new system would include some or all of the objects listed above, with potentially many more yet to be found. Gibor Basri, head of astronomy at the University of Berkeley, has suggested a similar definition and has also proposed the terms "fusor" (any object that achieves fusion in its core) and "planemo" (an object that is round from self-gravity but not a fusor) to help improve the astronomical nomenclature. Under Basri's definition: :A planet is a planemo orbiting a fusor These definitions have the advantage of creating a group including larger moons (which share many characteristics with the smaller planets) and also covering large free-roaming objects, which some astronomers think should be included in the definition of a planet. Basri has also suggested 'liberal use of adjectives' such as "major", "beltway", "dwarf", "giant", "super" and "historical".[http://astron.berkeley.edu/%7Ebasri/defineplanet/Mercury.htm] Others have suggested categories of planet/planemo based on composition such as "rock" (composed mainly of silicate), "gas" (composed mainly of hydrogen and helium), and "ice" (composed mainly of oxygen and carbon).

Suggested narrow definitions

There are alternate suggestions which would instead reduce the number of planets in the system. Upon his discovery of Sedna, Mike Brown of Caltech suggested a definition which would exclude both Sedna and Pluto from being classified as planets, proposing the following: :A planet is any body in the solar system that is more massive than the total mass of all of the other bodies in a similar orbit [http://www.gps.caltech.edu/~mbrown/sedna/#What%20is%20the%20definition%20of%20a%20planet?] This definition generally plays down the importance of size, but instead focuses on the formation of the proposed planet. Under this definition, no Kuiper Belt objects (including Pluto) would be considered planets. Brown's wish to "demote" Pluto prompted many to criticize him for setting out to create a purely scientific definition for a term which had an existing popular (albeit 'flawed') application. Upon his discovery of , Brown indicated he had become a convert to this way of thinking, and proposed that whatever definition of planet be adopted, it should include both Pluto and any Kuiper Belt object found to be larger than Pluto. [http://www.gps.caltech.edu/~mbrown/planetlila/index.html]

Further classification

Astronomers distinguish between minor planets, such as asteroids, comets, and trans-Neptunian objects; and major (or true) planets. Planets within Earth's solar system can be divided into categories according to composition.
- Terrestrial or rocky: Planets that are similar to Earth — with bodies largely composed of rock: Mercury, Venus, Earth, Mars
- Jovian or gas giant: Those with a composition largely made up of gaseous material: Jupiter, Saturn, Uranus, Neptune. Uranian planets, or ice giants, are a sub-class of gas giants, distinguished from true Jovians by their depletion in hydrogen and helium and a significant composition of rock and ice.
- Icy: Sometimes a third category is added to include bodies like Pluto, whose composition is primarily ice; this category of "icy" bodies also includes many non-planetary bodies such as the icy moons of the outer planets of our solar system (e.g. Triton). Many consider the Earth and its Moon to be a double planet, for several reasons:
- The Moon, as measured by its diameter, is 1.5 times larger than Pluto.
- The gravitational force of the Sun on the Moon is larger than the gravitational force of the Earth on the Moon by a factor of approx. 2.2. (This is not a unique situation in the solar system. The Sun's gravity is also stronger than the primary's on Jupiter's moon S/2003 J 2; Uranus' moon S/2001 U 2; Neptune's moons S/2002 N 4 and Psamathe; and several asteroid moons. However, Luna is the sole case of this phenomenon affecting an object of planetary mass.)

See also


- Definition of planet
- Planetary habitability
- Planetary science
- Planemo
- Planetoid
- Brown Dwarf
- Planets in science fiction
- Prograde and retrograde motion
- Skies of other planets

References


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External links


- [http://www.nineplanets.org/ NinePlanets.org] - tour of the solar system
- [http://www.iau.org International Astronomical Union]
- [http://www.fourmilab.ch/cgi-bin/uncgi/Solar/ Solar System Live] (an interactive orrery)
- [http://janus.astro.umd.edu/javadir/orbits/ssv.html Solar System Viewer] (animation)
- [http://www.sky-pics.net/ Pictures of the solar system]
- [http://gw.marketingden.com/planets/sun.html Renderings of the planets]
- [http://planetquest.jpl.nasa.gov/ NASA Planet Quest]
- [http://www.ciw.edu/IAU/div3/wgesp/definition.html Working definition of "planet"] from IAU WGESP — the lower bound remained a matter of consensus in February 2003
- Dan Green's page on [http://cfa-www.harvard.edu/cfa/ps/icq/ICQPluto.html planet classification]
- [http://www.spacedaily.com/news/outerplanets-04b.html Gravity Rules: The Nature and Meaning of Planethood]; S. Alan Stern; March 22, 2004
- [http://www.iau.org/IAU/FAQ/PlutoPR.html On the status of Pluto]; IAU, February 3, 1999
- als:Planet ko:행성 ms:Planet ja:惑星 simple:Planet th:ดาวเคราะห์ zh-min-nan:He̍k-chheⁿ

Charon (moon)

Charon (shar'-un or kair'-un, Greek Χάρων) is the largest satellite of Pluto. It was discovered by astronomer James Christy on June 22, 1978 by carefully examining highly magnified images of Pluto on photographic plates taken a couple of months before and noticing that a slight bulge appeared periodically. Later, the bulge was confirmed on plates dating back to April 29, 1965. It received the temporary designation S/1978 P 1, according to the then-recently instituted convention. It is not to be confused with the similarly named 2060 Chiron, another object in the outer solar system with an orbit between those of Saturn and Uranus. With the discovery in 2005 of two other moons of Pluto (S/2005 P 1 and S/2005 P 2), Charon is now also referred to as Pluto I. Christy chose the name "Charon" for the moon, and this was officially accepted by the IAU in 1985. In Greek mythology, Charon was the ferryman of the dead, a figure with close ties to the god Pluto. However, Christy pronounced it differently. The ch of the mythological figure is pronounced as a k sound, like the ch in Christy's name. However, the ch in the moon's name is an sh sound, after the Christy's wife Charlene (nicknamed "Char"). The sh pronunciation is now standard among astronomers, in spite of the pleas of classicists. The discovery of Charon allowed astronomers to more accurately calculate Pluto's mass and size. Charon revolves around Pluto in 6.387 days, the same period as Pluto's rotation. The two objects are gravitationally locked (tidal locking) so they each keep the same face towards the other. Charon's diameter is 1,205 km (748.8 miles), just over half the size of Pluto. It has 1/7th the mass of Pluto, and a surface area of 4,560,000 km2. Unlike Pluto, which is covered with nitrogen ice, the Charonian surface appears to be coated with water ice. Due to the unusually small difference in size between it and Pluto, Pluto and Charon are sometimes considered to be a double planet. They are also sometimes thought of as not a planet and a satellite, but as the first two Trans-Neptunian objects. Simulation work published in 2005 by Robin Canup suggested that Charon could have formed by a giant impact around 4.5 billion years ago, with a Kuiper belt object between 1600 and 2000 kilometres in diameter striking Pluto at a speed of 1 kilometre per second and Charon coalescing from the ring of debris kicked up by the collision. There is less evidence for this theory than there is for the similar theory regarding Earth's Moon, however, most notably a lack of information regarding the composition of the two bodies. On July 11, 2005 Charon occulted the magnitude 14 star 2UCAC 2625 7135. The event was seen by three independent teams using several telescopes across southern South America. It was the first Charon occultation since 1980. The MIT-Williams College (Williamstown, Massachusetts) team (including James Elliot, Amanda Gulbis, Michael Person, Elisabeth Adams, and Susan Kern of MIT and Jay Pasachoff, Bryce Babcock, Steven Souza, and Joseph Gangestad of Williams College, working with colleagues already located in Chile and Brazil) used the 6.5 metre Clay Telescope at the Las Campanas Observatory , the 8-m Gemini South telescope on Cerro Pachón, the 2.5-m DuPont Telescope at Las Campanas, and a 0.84-m telescope of the Cerro Armazones Observatório, all in Chile and, though clouded out, a telescope at the Brazilian national observatory; they used four Portable Occultation, Eclipse, and Transit electronic-camera Systems (POETS) provided through a grant from NASA. A team headed by Bruno Sicardy of the Paris Observatory in France used one of the 8-m telescopes of the European Southern Observatory's Very Large Telescope in Chile as well as several smaller telescopes, including two that were clouded out at the same Brazilian national observatory. A team from the Southwest Research Institute in Boulder, Colorado (including Leslie Young and Elliot Young), used two telescopes in Chile, including the 4-m Blanco telescope at the Cerro Tololo Inter-American Observatory. The scientists from all the teams used information from this occultation to determine Charon's gravity, radius, and density to unprecedented precision; the results of the MIT-Williams and Paris teams appeared in the journal Nature in January 2006. The moon, along with Pluto, is to be visited by the New Horizons mission in 2015.

External links


- James W. Christy and Robert S. Harrington, "The satellite of Pluto," [http://adsabs.harvard.edu//full/seri/AJ.../0083//0001005.000.html The Astronomical Journal 83 (1978) 1005]
- Marc W. Buie, [http://www.lowell.edu/users/buie/pluto/chphases.html Phases of Charon as seen from Pluto], Lowell Observatory
- [http://news.bbc.co.uk/2/hi/science/nature/4230918.stm Hubble reveals new map of Pluto], BBC News, 12 September 2005
- IAU Circular No. 3241 [http://cfa-www.harvard.edu/iauc/03200/03241.html] describing the discovery Category:Trans-Neptunian objects Category:Pluto's moons ja:カロン (衛星) simple:Charon

Monogram

]] A monogram is a motif made by overlapping or combining two or more letters or other graphemes to form one symbol. Monograms are often made by combining the initials of an individual or a company. Monograms may be used as recognizable symbols or logos. An individual's monogram is often a very fancy piece of art for adorning luggage, clothing, and so forth. Some monograms, like the interrobang, are not used for companies. These, rather, are used as letters, punctuation, and the like. ja:モノグラム

Percival Lowell

Percival Lowell (March 13, 1855 – November 12, 1916) was a wealthy amateur astronomer who was convinced that there were canals on Mars, and was the founder of Lowell Observatory in Flagstaff, Arizona.

Biography

Percival Lowell came from the distinguished Boston Lowell family. In addition to his own accomplishments, his younger brother Abbott was president of Harvard University, and his sister Amy Lowell was a well-known Imagist poet and critic. Percival Lowell graduated from Harvard University in 1876 with distinction in mathematics, and traveled extensively through the Far East before deciding to study Mars and astronomy as a full-time career. He was particularly interested in the supposed canals of Mars, as drawn by Giovanni Schiaparelli, who was director of the Milan Observatory and an esteemed Italian astronomer. In 1894 he moved to Flagstaff, Arizona. At an altitude of over 7000 feet, and with few cloudy nights, it was an excellent site for astronomical observations. For the next fifteen years he studied Mars extensively, and drew intricate drawing of the surface markings as he perceived them. Lowell published his views in three books: Mars (1895), Mars and Its Canals (1906), and Mars As the Abode of Life (1908). He thereby instigated the long-held belief that Mars had once sustained intelligent life forms. His works include a detailed description of what he termed the 'non-natural features' of the planet's surface, including especially a full account of the 'canals,' single and double; the 'oases,' as he termed the dark spots at their intersections; and the varying visibility of both, depending partly on the Martian seasons. He upheld the theory of the canals having been constructed for the purpose of 'husbanding' Mars's scanty water-supply. Lowell's greatest contribution to planetary studies came during the last 8 years of his life, which he devoted to the search for Planet X, which was the designation for a planet beyond Neptune. The search continued for a number of years after his death at Flagstaff in 1916; the new planet, named Pluto, was discovered by Clyde Tombaugh in 1930. The symbol for the planet is a stylized "PL" (♇), chosen in part to honor Lowell. It is interesting to note, that predictions of a planet beyond Neptune were based on discrepancies between the predicted and observed positions of Neptune and Uranus, and the erroneous assumption that such discrepancies were caused by the gravitational influence of an unknown planet. In fact, the discrepancies were due to erroneous values for the masses of Neptune and Uranus; with modern precise values, the discrepancies disappear, and in any case it is now known that the mass of Pluto is far too small to exert any appreciable gravitational influence on other planets.

External links


-
- [http://www.lowell.edu/ Lowell Observatory] Lowell, Percival Lowell, Percival Lowell, Percival Lowell, Percival Lowell, Percival Lowell, Percival Lowell, Percival ja:パーシヴァル・ローウェル th:เปอร์ซิวัล โลเวลล์

Trans-Neptunian object

A trans-Neptunian object (TNO) is any object in the solar system which orbits the sun at a greater distance on average than Neptune. The Kuiper belt, Scattered disk, and Oort cloud are names for three divisions of this volume of space. Pluto and its moon Charon are trans-Neptunian objects, and if Pluto had been discovered today, it might not have been called a planet. (See the definition of Planet.) The orbit of each of the planets is affected by the gravitational influences of all the other planets. Discrepancies in the early 1900s between the observed and expected orbits of the k