NEPTUNE THE BLUE PLANET
Named after the Roman god of the sea, Neptune is the eighth planet from the Sun in the Solar System, and the fourth-largest planet by diameter, 30,598 miles (49,244 km), the third-most-massive planet, and the densest giant planet. Neptune is 17 times the mass of Earth, slightly more massive than its near-twin Uranus. Neptune is denser and physically smaller than Uranus because its greater mass causes more gravitational compression of its atmosphere. Neptune orbits the Sun once every 164.8 years at an average distance of 4.5 billion km (2.8 billion miles).
Neptune is not visible to the naked eye and is the only planet in the Solar System found by mathematical prediction rather than by empirical observation. Unexpected changes in the orbit of Uranus led Alexis Bouvard to deduce that its orbit was subject to gravitational pull by an unknown planet. After Bouvard's death, the position of Neptune was predicted from his observations, independently, by John Couch Adams and Urbain Le Verrier. Neptune was subsequently observed with a telescope on 23 September 1846 by Johann Galle within a degree of the position predicted by Le Verrier. Its largest moon, Triton, was discovered shortly thereafter, though none of the planet's remaining 13 known moons were located telescopically until the 20th century. The planet's distance from Earth gives it a very small apparent size, making it challenging to study with Earth-based telescopes. Neptune was visited by Voyager 2, when it flew by the planet on 25 August 1989. The advent of the Hubble Space Telescope and large ground-based telescopes with adaptive optics has recently allowed for additional detailed observations from afar. The known moons of Neptune, named after lesser sea gods, are Triton, Thalassa, Naiad, Nereid, Neso, Proteus, Hippocamp, Despina, Galatea, Halimede, Laomedeia, Psamathe, Larissa and Sao.
Triton is the largest Neptunian moon, comprising more than 99.5% of the mass in orbit around Neptune, and it is the only one massive enough to be spheroidal. 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 spiraling inward because of tidal acceleration. It will eventually be torn apart, in about 3.6 billion years. In 1989, Triton was the coldest object that had yet been measured in the Solar System, with estimated temperatures of -391 °F (−235 °C).
Like Jupiter and Saturn, Neptune's atmosphere is composed primarily of hydrogen and helium, along with traces of hydrocarbons and possibly nitrogen, though it contains a higher proportion of "ices" such as water, ammonia and methane. However, similar to Uranus, its interior is primarily composed of ices and rock; Uranus and Neptune are normally considered "ice giants". Traces of methane in the outermost regions in part account for the planet's blue appearance.
In contrast to the hazy, relatively featureless atmosphere of Uranus, Neptune's atmosphere has active and visible weather patterns. For example, at the time of the Voyager 2 flyby in 1989, the planet's southern hemisphere had a Great Dark Spot comparable to the Great Red Spot on Jupiter. These weather patterns are driven by the strongest sustained winds of any planet in the Solar System, with recorded wind speeds as high as 2,100 km/h (580 m/s; 1,300 mph). Because of its great distance from the Sun, Neptune's outer atmosphere is one of the coldest places in the Solar System, with temperatures at its cloud tops approaching -360 °F (-218 °C). Temperatures at the planet's center are approximately 9,300 °F (5,100 °C).
Neptune has a planetary ring system, though one much less substantial than that of Saturn. Discovered in 1984, then later confirmed by Voyager 2, the rings may consist of ice particles coated with silicates or carbon-based material, which most likely gives them a reddish hue.
#Neptune #Astronomy #Planet #SolarSystem #NeptuneMoons #SpaceExploration