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Thursday, October 10, 2013

SCHOOL PROJECT IDEAS (3) : Presentation on Neptune

Neptune from Voyager 2 with Great Dark Spot


Neptune is the eighth and farthest planet from the Sun in the Solar System. It is the fourth-largest planet by diameter and the third-largest by mass. Among the gaseous planets in the solar system, Neptune is the most dense. Neptune is 17 times the mass of Earth and is slightly more massive than its near-twin Uranus, which is 15 times the mass of Earth but not as dense. On average, Neptune orbits the Sun at a distance of 30.1 approximately 30 times the Earth–Sun distance. Named for the Roman God of the sea, its astronomical symbol is ♆, a stylised version of the god Neptune's trident.

Internal structure
Neptune's internal structure resembles that of Uranus. Its atmosphere forms about 5% to 10% of its mass and extends perhaps 10% to 20% of the way towards the core, where it reaches pressures of about 10 GPa, or about 100,000 times that of the earth's atmosphere. Increasing concentrations of methane,ammonia and water are found in the lower regions of the atmosphere
The mantle reaches temperatures of 2,000 K to 5,000 K. It is equivalent to 10 to 15 Earth masses and is rich in water, ammonia and methane. As is customary in planetary science, this mixture is referred to as icy even though it is a hot, highly dense fluid. This fluid, which has a high electrical conductivity, is sometimes called a water-ammonia ocean.At a depth of 7000 km, the conditions may be such that methane decomposes into diamond crystals that then precipitate toward the core. The mantle may consist of a layer of ionic water where the water molecules break down into a soup of hydrogen and oxygen ions, and deeper down superionic water in which the oxygen crystallises but the hydrogen ions float around freely within the oxygen lattice.
The core of Neptune is composed of iron, nickel and silicates, with an interior model giving a mass about 1.2 times that of the Earth.The pressure at the centre is 7 Mbar (700 GPa), about twice as high as that at the centre of the Earth, and the temperature may be 5,400 K.

                                                                   The internal structure of Neptune:

                                                   1. Upper atmosphere, top clouds

                                                   2. Atmosphere consisting of hydrogen, helium and                                                                                        methane gas
                                                   3. Mantle consisting of water, ammonia and methane ices
                                                   4. Core consisting of rock (silicates and nickel-iron)

Combined colour and near-infared image of Neptune, showing bands of methane in its atmosphere, and four of its moons -  Proteus, Larissa, Galatea, and Dispena.

Neptune has 14 known moons.The largest by far, comprising more than 99.5% of the mass in orbit around Neptune and the only one massive enough to be spheroidal, is Triton, discovered by William Lassel just 17 days after the discovery of Neptune itself. Unlike all other large planetary moons in the Solar System, Triton has a retrograde orbit, indicating that it was captured rather than forming in place; it was probably once a dwarf planet in the Kuiper belt. It is close enough to Neptune to be locked into a synchronous rotation, and it is slowly spiralling inward because of tidal acceleration. It will eventually be torn apart, in about 3.6 billion years, when it reaches the Roche Limit. In 1989, Triton was the coldest object that had yet been measured in the solar system,with estimated temperatures of 38 K(−235 °C).

Neptune's moon Proteus

Voyager 2 mosaic of Triton

Neptune (top) and Triton (bottom)


In 1989, the Great Dark Spot, an anti-cyclonic storm system spanning 13000×6600 km,was discovered by NASA's Voyager 2 spacecraft. The storm resembled the Great Red Spot of Jupiter. Some five years later, on 2 November 1994, the Hubble Space Telescope did not see the Great Dark Spot on the planet. Instead, a new storm similar to the Great Dark Spot was found in the planet's northern hemisphere.
The Scooter is another storm, a white cloud group farther south than the Great Dark Spot. Its nickname is due to the fact that when first detected in the months before the 1989 Voyager 2 encounter it moved faster than the Great Dark Spot.Subsequent images revealed even faster clouds. The Small Dark Spot is a southern cyclonic storm, the second-most-intense storm observed during the 1989 encounter. It initially was completely dark, but as Voyager 2 approached the planet, a bright core developed and can be seen in most of the highest-resolution images.

The  Great Dark Spot (top), Scooter (middle white cloud),and  the Small Dark Spot (bottom), with contrast exaggerated.

  The Great Dark Spot, as imaged by Voyager 2


Neptune has a planetary ring system, though one much less substantial than that of Saturn. The rings may consist of ice particles coated with silicates or carbon-based material, which most likely gives them a reddish hue.The three main rings are the narrow Adams Ring, 63,000 km from the centre of Neptune, the Le Verrier Ring, at 53,000 km, and the broader, fainter Galle Ring, at 42,000 km. A faint outward extension to the Le Verrier Ring has been named Lassell; it is bounded at its outer edge by the Arago Ring at 57,000 km.

Neptune's rings, taken by Voyager 2



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