Mass and size



Pluto's mass and diameter could only be estimated for many decades after its discovery. Initially it was thought to be quite large, with a mass comparable to Earth, but over time the estimates were revised sharply downward as observations were refined. Indeed, in 1980 A.J. Dessler published a tongue-in-cheek analysis of Pluto's historical mass estimates and predicted that it would soon disappear completely.[6]

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 disc can now be resolved by telescopes using adaptive optics.

Pluto is not only smaller and much less massive than any planet, but 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, a dwarf planet in the asteroid belt, and it was larger than any other object known in the trans-Neptunian Kuiper belt until 2003 UB313 was announced in 2005. See List of solar system objects by mass and List of solar system objects by radius.

   

Atmosphere

Pluto's thin atmosphere is most likely made up of nitrogen, methane, 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 and falls to the ground. When it returns to a closer proximity to the sun, the temperature of Pluto's solid surface will increase, causing the nitrogen ice to sublimate into gas—creating an anti-greenhouse effect. Much as sweat evaporating from the surface of human skin, this sublimation has a cooling effect and scientists have recently discovered,[7] by use of the Submillimeter Array, that Pluto's temperature is 10 kelvins less than they expected.

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[8] and by Jim Elliot of MIT[9] and Jay Pasachoff of Williams College.[10] 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.

Composition

The surface of Pluto is remarkably heterogeneous, as evidenced by its lightcurve, maps of its surface constructed from Hubble Space Telescope observations, and by periodic variations in its infrared spectra. The face of Pluto oriented toward Charon has more methane ice, while the opposite face has more ices of nitrogen and carbon monoxide.

Pluto's moons

Main article: Pluto's natural satellites
Pluto has three known natural satellites: Charon, first identified in 1978 by astronomer James Christy; and two smaller moons, Nix and Hydra, that were discovered in 2005.


Diagram of the Plutonian system. P 1 is Hydra, and P 2 is Nix.


Charon



The Pluto-Charon system is noteworthy for being the only system in the solar system whose barycenter lies above the primary's surface. This and the large size of Charon relative to Pluto prompted some astronomers to label it a dwarf double planet.

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.
Pluto and its largest satellite Charon
Enlarge

Charon's discovery also resulted in the calculation of Pluto's albedo being revised upward; since Pluto 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. 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.

Nix and Hydra

Two additional moons were imaged by astronomers working with the Hubble Space Telescope on May 15, 2005, and received provisional designations of S/2005 P 1 and S/2005 P 2. They were confirmed with a series of "precovery" Hubble images from June 2002 through May 2003, which led to their orbits being determined. Additional follow-up observations were made in February and March 2006, confirming the orbit solutions. The International Astronomical Union officially christened Pluto's newest moons Nix (or Pluto II, the inner of the two moons, formerly P 2) and Hydra (Pluto III, the outer moon, formerly P 1), on June 21, 2006.

These small moons orbit Pluto at approximately two and three times the distance of Charon: Nix at 48,700 kilometres and Hydra at 64,800 kilometers from the barycenter of the system. They have nearly circular prograde orbits in the same orbital plane as Charon, and are very close to (but not in) 4:1 and 6:1 mean motion orbital resonances with Charon.

Hydra is sometimes brighter than Nix and thus may be larger in some dimensions; alternately different parts of its surface may vary in brightness. Their sizes are not known but can be estimated from likely albedos. The moons' spectral similarity with Charon suggests a 35% albedo similar to Charon's; this results in diameter estimates of 46 kilometers for Nix and 61 kilometers for the brighter orientation of Hydra. Likely upper limits on their diameters can be estimated by assuming the 4% albedo of the darkest Kuiper Belt objects; these bounds are 137 ± 11 km and 167 ± 10 km respectively. At the larger end of this range, the inferred masses are less than 0.3% of Charon's mass, or 0.03% of Pluto's.[11]

With the discovery of the two small moons, Pluto may possess a time variable ring system. Small body impacts can create debris that can form into a ring system. After deep optical survey from the Advanced Camera for Surveys, ACS, of the Hubble Space Telescope, no ring system was detected. If such a system exists, it is either tenuous like the Rings of Jupiter, or it is tightly confined to less than 1000km in width. This may become a problem for the New Horizons space probe. There is potential for micrometeorite damage that can damage or disable the probe.[12]

Limits on additional moons

In imaging the Plutonian system, the Hubble observations placed limits on any additional moons. With 90% confidence, no additional moons larger than 12 km1 exist beyond the glare of Pluto 5 arcseconds from the dwarf planet, assuming Charon-like albedo of 0.38; at a 50% confidence level the limit is 8 kilometers.[13]

1Or a maximum of 37 kilometers with an albedo of 0.04

This is a striking distribution. Moons could potentially orbit Pluto up to the 53% (or 69%, if retrograde) of the Hill sphere radius (stable gravitational zone of influence) of 6.0 million kilometers. For example, Psamathe orbits Neptune at 40% of the Hill radius. In the case of Pluto, only the inner 3% of the zone is known to be occupied by satellites. In the discoverers’ terms, the Plutonian system appears to be "highly compact and largely empty."

 

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 Charon or Pluto's size and atmosphere — the flyby was scrapped in order to facilitate a close flyby of Saturn's moon Titan.

In 1989, NASA also considered sending Voyager 2 to Pluto using a gravitational assist from Neptune, but this would not permit the best flyby of Triton for scientific observations. It was eventually decided to calculate the Neptune and Triton visit for the best results around that planet, regardless of the consequences to the craft's final trajectory.

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 launched on January 19, 2006 (while Pluto was still classified as a Planet). It will benefit from a gravity assist from Jupiter, and the closest approach to Pluto will be on July 14, 2015, 11:59 UTC. Observations of Pluto will start 5 months prior to closest approach and will continue for at least a month after the encounter.

New Horizons will use a remote sensing package that includes imaging instruments and a radio science investigation tool, 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. New Horizons would also photograph the surfaces of Pluto and Charon. 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. If launched, Pluto Kuiper Express was to reach Pluto around 2012, and the Kuiper Belt around 2017.

Planetary status


Planet X?
Main article: Planet X

Pluto was originally discovered in 1930 in the course of a search for a body sufficiently massive to account for perceived anomalies in the orbits of Uranus and Neptune. Once it was found, its faintness and lack of a visible disk cast doubt on the idea that it could be Percival Lowell's Planet X. Lowell had made a prediction of Pluto's position in 1915 which was 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.[14]

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.

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 greater mass than previously believed and that when the updated 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 diligence of Tombaugh's search.

Reclassification to a dwarf planet

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. Due to its small size and unusual orbit, however, there is some debate regarding Pluto's classification as a major or as a minor planet, which included some momentum for recognizing dual status.[15] Pluto is one of the largest known members of the main Kuiper Belt, the area of the solar system beyond the orbit of Neptune; one scattered Kuiper Belt object, 2003 UB313, has been found that is larger than Pluto, and they have several companions (as of August 2006 there are 783 KBOs) in the Kuiper Belt, including 2003 EL61 and 2005 FY9.

The Kuiper belt is believed to be the source for all short-period comets, and Pluto, like other Kuiper Belt objects, shares features in common with comets. The solar wind is gradually sublimating Pluto's surface into space, in the manner of a comet.[16] If Pluto were placed near the Sun, it would develop a tail, like comets do.[17]

Hundreds of other Kuiper Belt objects have been discovered since September 1992, the first being (15760) 1992 QB1. The continued discovery of these objects, especially that of plutinos, rekindled the debate on Pluto's status as 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 also.[citation needed] 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.[citation needed] "Save Pluto" websites sprang up, and school children sent letters to astronomers and the IAU.[18]

On February 3, 1999, Brian Marsden of the Minor Planet Center inadvertently fueled the debate when he issued an editorial in the 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.[19]

Between the media reports and the Minor Planet Electronic Circulars, IAU General Secretary Johannes Andersen issued a press release that same day, stating there were no plans to change Pluto's planetary status.[20] Eventually, the number 10,000 was assigned to an "ordinary" asteroid, 10000 Myriostos.

The debate centered on whether a "planet", from the Greek for "wanderer", is an appellation that depends upon an object's particular size, formation, or orbit. Some argued that not only was Pluto a major planet but also some moons like Titan, Europa or Triton, or even the larger asteroids were as well.[citation needed] Others argued that the term "minor planet" should refer to an astronomical object more than about 360 kilometers in diameter, at which point the object has a tendency to become round under its own gravity;[citation needed] 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 4,879.4 kilometres and Ceres, the largest known asteroid with a mean diameter of 950 kilometers.[citation needed] This definition would include Pluto but not most moons.

Pluto had qualified as a planet under a draft definition[21] that had been proposed by a committee of the IAU, but which was not accepted by the IAU General Assembly. The re-classification adopted by the assembly, however, has been disputed by some members who had left the conference on the grounds that the timetable had been "hijacked" with only 4% of eligible voters being left in the conference room at the time the resolution was adopted [22].

New discoveries



Continuing discoveries in the Trans-Neptunian region kept rekindling the debate. In 2002, 50000 Quaoar was discovered, with a 1,280 kilometers diameter, making it a bit more than half the size of Pluto. Another discovery, 90482 Orcus, was probably even larger. In 2004 the discoverers of 90377 Sedna, an extremely distant object well beyond the other known Trans-Neptunian objects, placed an upper limit of 1,800 kilometers on its diameter, close to Pluto's 2,320 kilometers.

On July 29, 2005, a Trans-Neptunian object called 2003 UB313 (nicknamed "Xena") was announced, which on the basis of its magnitude and simple albedo considerations was assumed to be larger than Pluto. This caused its discoverers to call it the "10th planet" of the solar system, although there was no consensus at the time on whether to call it a planet, and others considered the discovery to be the strongest argument for demoting Pluto to the status of a minor planet. 2003 UB313 was the largest object yet discovered in the solar system since Neptune in 1846, although it is only slightly larger than Pluto. The last remaining distinguishing feature of Pluto was now its large moon, Charon, and its atmosphere; these characteristics are probably not unique to Pluto: several other Trans-Neptunian objects have satellites; and 2003 UB313's spectrum suggests that it has a similar surface composition to Pluto, as well as a moon (nicknamed "Gabrielle"), discovered in September 2005. Trans-Neptunian object 2003 EL61 (nicknamed "Santa") has two moons (one of which is nicknamed "Rudolph") and is the fourth largest TNO behind 2003 UB313, Pluto, and 2005 FY9 (nicknamed "Easterbunny").

Precedents for reclassifying planets

There is historical precedent for reclassifying what was originally called a planet, in the light of subsequent discoveries. Many bodies in the asteroid belt (including 1 Ceres, 2 Pallas, 3 Juno, 4 Vesta) were considered to be planets for several decades (in part because their sizes were not accurately known at the time). In 1845, however, an asteroid (5 Astraea) was discovered for the first time in thirty-eight years. Neptune was discovered a year later, 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" (though Ceres, along with Pluto, was recently reclassified as a "dwarf planet"). Some see in this a precedent for noting that Pluto is just the most prominent member of the Kuiper belt.

As its discoverer reportedly said before his death in 1997: "It's there. Whatever it is. It is there." [23]

International Astronomical Union meeting

    Main article: 2006 redefinition of planet

In order to put these matters to rest, in August 2006, 3,000 astronomers and scientists of the International Astronomical Union (IAU) gathered in Prague, Czech Republic to deliberate. The organization planned to publish an official definition of "planet", ruling on whether to call Pluto a planet, dwarf planet or a Kuiper Belt Object (KBO).[24][25] The draft proposal classified Pluto along with 2003 UB313 and any other spherical TNOs that may be discovered, as planets, although they would have been informally labelled 'plutons'. The asteroid 1 Ceres and Pluto's moon, Charon, would also have been considered planets.

On August 24, 2006, however, the previous draft was reversed, according to the newly passed rule, Pluto was demoted from planetary status to a dwarf planet and is accompanied by Ceres and 2003 UB313 in this category. There are three main conditions for an object to be called a 'planet', according to the IAU resolution.

   1. The object must be in orbit around a star, but not be a star itself.
   2. The object must be massive enough to be a sphere by its own gravitational force.
   3. It must have cleared the neighborhood around its orbit.

Pluto fails to meet these conditions (primarily, condition 3[26]) but will act as a prototype for a yet to be named category of Trans-Neptunian objects.

masa jupitera 1.9 *10 na 27 nek je 2 *10 na 27 kg
daljina od sunca 778,330,000 km nek je onda od zemlje 500 000 000 km (mada to varira ,u stvari je obicno mnogo vishe) znaci 5 *10 na 11 m
dobije se da jupiter ima gravitacioni uticaj kao telo od 8t na 1m. ili telo od 80 kg na 1 dm. ili telo od 0.8 kg na 1cm  ... pshto su pantalone tako raspodeljene da je svaki njihov deo otprilike na 1mm od koze ti onda vidi ... da ne pricamo kako je sve to beznachajno u odnosu na uticaj zemljine gravitacije (ili chak gravitacije meseca i sunca) .shta tek onda reci o plutonu ...

uh
http://en.wikipedia.org/wiki/Jupiter

procitaj sve ako me secanje ne vara tu sam procitao nesto o gravitaciji Jupitera koliko je jaka...

Jesam jednom mozda umesto Jupiter napisao Pluton greskom, mislim plutonovo gravitaciono polje nikako ne utiche... al to nema veze sa "astroloskim zracenjima" koje planete salju i koja uticu na coveka.

ima jupiter veliki gravitacioni uticaj na nebeska tela ,ali nebeska tela nemaju toliko bliske objekte kao ljudi .funkcija kvadrata rastojanja je veoma zanimljiva poshto je nash prostor 3D + vreme .ako bi se astroloshki uticaj prenosio putem polja i on bi morao da opada sa kvadratom rastojanja .prema tome chak i u tom sluchaju bi najvishe zavisili od majchice zemlje