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Dwarf Planet Pluto

Solar System Explanation ::-- Sun|| Solar Planet || Mercury Planet || Jupitor Planet || Venus Planet || Earth Planet || Uranus Planet || Saturn Planet || Mars Planet || Neptune Planet || Dwarf Planet || Astroids || Comet ||

Pluto, formal designation 134340 Pluto, is the second-most-massive known dwarf planet in the Solar System (after Eris) and the tenth-most-massive body observed directly orbiting the Sun. Originally classified as the ninth planet from the Sun, Pluto was recategorized as a dwarf planet and plutoid due to the discovery that it is one of several large bodies within the newly charted Kuiper belt.[i]
Like other members of the Kuiper belt, Pluto is composed primarily of rock and ice and is relatively small: approximately a fifth the mass of the Earth's Moon and a third its volume. It has an eccentric and highly inclined orbit that takes it from 30 to 49 AU (4.4–7.4 billion km) from the Sun. This causes Pluto to periodically come closer to the Sun than Neptune. As of 2011, it is 32.1 AU from the Sun.

From its discovery in 1930 until 2006, Pluto was classified as a planet. In the late 1970s, following the discovery of minor planet 2060 Chiron in the outer Solar System and the recognition of Pluto's relatively low mass, its status as a major planet began to be questioned. In the late 20th and early 21st century, many objects similar to Pluto were discovered in the outer Solar System, notably the scattered disc object Eris in 2005, which is 27% more massive than Pluto. On August 24, 2006, the International Astronomical Union (IAU) defined what it means to be a "planet" within the Solar System. This definition excluded Pluto as a planet and added it as a member of the new category "dwarf planet" along with Eris and Ceres. After the reclassification, Pluto was added to the list of minor planets and given the number 134340. A number of scientists continue to hold that Pluto should be classified as a planet.
Pluto has four known moons, the largest being Charon discovered in 1978, along with Nix and Hydra, discovered in 2005, and the provisionally named S/2011 P 1, discovered in 2011.Pluto and Charon are sometimes described as a binary system because the barycenter of their orbits does not lie within either body. However, the IAU has yet to formalise a definition for binary dwarf planets, and as such Charon is officially classified as a moon of Pluto.

Pluto Discovery

In the 1840s, using Newtonian mechanics, Urbain Le Verrier predicted the position of the then-undiscovered planet Neptune after analysing perturbations in the orbit of Uranus. Subsequent observations of Neptune in the late 19th century caused astronomers to speculate that Uranus' orbit was being disturbed by another planet besides Neptune. In 1906, Percival Lowell, a wealthy Bostonian who had founded the Lowell Observatory in Flagstaff, Arizona in 1894, started an extensive project in search of a possible ninth planet, which he termed "Planet X". By 1909, Lowell and William H. Pickering had suggested several possible celestial coordinates for such a planet. Lowell and his observatory conducted his search until his death in 1916, but to no avail. Unknown to Lowell, on March 19, 1915, his observatory had captured two faint images of Pluto, but did not recognise them for what they were. Lowell was not the first to unknowingly photograph Pluto. There are sixteen known pre-discoveries, with the oldest being made by the Yerkes Observatory on August 20, 1909.
Due to a ten-year legal battle with Constance Lowell, Percival's widow, who attempted to wrest the observatory's million-dollar portion of his legacy for herself, the search for Planet X did not resume until 1929, when its director, Vesto Melvin Slipher, summarily handed the job of locating Planet X to Clyde Tombaugh, a 23-year-old Kansas man who had just arrived at the Lowell Observatory after Slipher had been impressed by a sample of his astronomical drawings.
Tombaugh's task was to systematically image the night sky in pairs of photographs taken two weeks apart, then examine each pair and determine whether any objects had shifted position. Using a machine called a blink comparator, he rapidly shifted back and forth between views of each of the plates to create the illusion of movement of any objects that had changed position or appearance between photographs. On February 18, 1930, after nearly a year of searching, Tombaugh discovered a possible moving object on photographic plates taken on January 23 and January 29 of that year. A lesser-quality photograph taken on January 21 helped confirm the movement. After the observatory obtained further confirmatory photographs, news of the discovery was telegraphed to the Harvard College Observatory on March 13, 1930.

Pluto Orbit and rotation

Pluto's orbital period is 248 Earth years. Its orbital characteristics are substantially different from those of the planets, which follow nearly circular orbits around the Sun close to a flat reference plane called the ecliptic. In contrast, Pluto's orbit is highly inclined relative to the ecliptic (over 17°) and highly eccentric (elliptical). This high eccentricity means a small region of Pluto's orbit lies nearer the Sun than Neptune's. The Pluto–Charon barycentre came to perihelion on September 5, 1989,[j] and was last closer to the Sun than Neptune between February 7, 1979 and February 11, 1999. Detailed calculations indicate that the previous such occurrence lasted only fourteen years, from July 11, 1735 to September 15, 1749, whereas between April 30, 1483 and July 23, 1503, it had also lasted 20 years. The durations of the relationship vary because of the varying speed of motion of Neptune along its orbit; the relationship between the orbits themselves varies much more slowly, as Neptune's orbit precesses and otherwise evolves.

Although this repeating pattern may suggest a regular structure, in the long term Pluto's orbit is in fact chaotic. While computer simulations can be used to predict its position for several million years (both forward and backward in time), after intervals longer than the Lyapunov time of 10–20 million years, calculations become speculative: Pluto's tiny size makes it sensitive to unmeasurably small details of the Solar System, hard-to-predict factors that will gradually disrupt its orbit. Millions of years from now, Pluto may well be at aphelion, at perihelion or anywhere in between, with no way for us to predict which. This does not mean Pluto's orbit itself is unstable, but its position on that orbit is impossible to determine so far ahead. Several resonances and other dynamical effects keep Pluto's orbit stable, safe from planetary collision or scattering.

pluto planet

Pluto Mass and size

Pluto's mass is 1.31×1022 kg, less than 0.24 percent that of the Earth, while its diameter is 2,306 (+/- 20) km, or roughly 66% that of the Moon. Pluto's atmosphere complicates determining its true solid size within a certain margin.
Astronomers, assuming Pluto to be Lowell's Planet X, initially calculated its mass based on its presumed effect on Neptune and Uranus. In 1955 Pluto was calculated to be roughly the mass of the Earth, with further calculations in 1971 bringing the mass down to roughly that of Mars. In 1976, Dale Cruikshank, Carl Pilcher and David Morrison of the University of Hawaii calculated Pluto's albedo for the first time, finding that it matched that for methane ice; this meant Pluto had to be exceptionally luminous for its size and therefore could not be more than 1 percent the mass of the Earth. Pluto's albedo is 1.3–2.0 times greater than that of Earth.
The discovery of Pluto's satellite Charon in 1978 enabled a determination of the mass of the Pluto–Charon system by application of Newton's formulation of Kepler's third law. Once Charon's gravitational effect was measured, Pluto's true mass could be determined. Observations of Pluto in occultation with Charon allowed scientists to establish Pluto's diameter more accurately, while the invention of adaptive optics allowed them to determine its shape more accurately.

Among the objects of the Solar System, Pluto is much less massive than the terrestrial planets, and at less than 0.2 lunar masses, it is also less massive than seven moons: Ganymede, Titan, Callisto, Io, Earth's Moon, Europa and Triton. Pluto is more than twice the diameter and a dozen times the mass of the dwarf planet Ceres, the largest object in the asteroid belt. It is less massive than the dwarf planet Eris, a trans-Neptunian object discovered in 2005. Given the error bars in the different size estimates, it is currently unknown whether Eris or Pluto has the larger diameter. Both Pluto and Eris are estimated to have solid-body diameters of about 2330 km. Determinations of Pluto's size are complicated by its atmosphere, and possible hydrocarbon haze.

Pluto Satellites

Pluto has four known natural satellites: Charon, first identified in 1978 by astronomer James Christy; Nix and Hydra, both discovered in 2005, and S/2011 P 1 (provisional name, also known as P4), identified by the Hubble Space Telescope in 2011.
The Plutonian moons are unusually close to Pluto, compared to other observed systems. Moons could potentially orbit Pluto up to 53% (or 69%, if retrograde) of the Hill sphere radius, the stable gravitational zone of Pluto's influence. 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", although others have pointed out the possibility of additional objects, including a small ring system.