Neptune

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Neptune : the planet eighth in order from the sun — Webster

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Neptune is the eighth and farthest known planet from the Sun in the Solar System. In the Solar System, it is the fourth-largest planet by diameter, the third-most-massive planet, and the densest giant planet. 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 and slightly larger than Neptune. Neptune orbits the Sun once every 164.8 years at an average distance of 30.1 astronomical units (4.50×109 km). It is named after the Roman god of the sea and has the astronomical symbol ♆, a stylised version of the god Neptune’s trident.

Neptune is not visible to the unaided 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 perturbation by an unknown planet. Neptune was subsequently observed with a telescope on 23 September 1846 by Johann Galle within a degree of the position predicted by Urbain Le Verrier. Its largest moon, Triton, was discovered shortly thereafter, though none of the planet’s remaining known 14 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.

Neptune’s composition can be compared and contrasted with the Solar System’s other giant planets. Like Jupiter and Saturn, Neptune’s atmosphere is composed primarily of hydrogen and helium, along with traces of hydrocarbons and possibly nitrogen, but it contains a higher proportion of “ices” such as water, ammonia, and methane. However, its interior, like that of Uranus, is primarily composed of ices and rock, which is why Uranus and Neptune are normally considered “ice giants” to emphasise this distinction. 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 kilometres per hour (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 55 K (−218 °C). Temperatures at the planet’s center are approximately 5,400 K (5,100 °C). Neptune has a faint and fragmented ring system (labelled “arcs”), which was first detected during the 1960s and confirmed by Voyager 2. — Wikipedia

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Neptune News -- ScienceDaily Planet Neptune News. Read astronomy articles on Neptune's oddball moon Triton. See images of Neptune and more.

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    on April 4, 2018 at 3:47 pm

    Chemical models developed to help limit the emission of pollutants by car engines are being used to study the atmospheres of hot exoplanets orbiting close to their stars. […]

  • Hubble sees Neptune's mysterious shrinking storm
    on February 15, 2018 at 6:11 pm

    Three billion miles away on the farthest known major planet in our solar system, an ominous, dark storm -- once big enough to stretch across the Atlantic Ocean from Boston to Portugal -- is shrinking out of existence as seen in pictures of Neptune taken by NASA's Hubble Space Telescope. […]

  • Pluto's hydrocarbon haze keeps dwarf planet...
    on November 15, 2017 at 6:09 pm

    The gas composition of a planet's atmosphere generally determines how much heat gets trapped in the atmosphere. For the dwarf planet Pluto, however, the predicted temperature based on the composition of its atmosphere was much higher than actual measurements taken by NASA's New Horizons spacecraft in 2015. A new study proposes a novel cooling mechanism controlled by haze particles to account for Pluto's frigid atmosphere. […]

  • NASA investigates invisible magnetic bubbles in...
    on November 1, 2017 at 7:12 pm

    Forty years ago, the twin Voyagers spacecraft were launched to explore the frontiers of our solar system, and have since made countless discoveries, including finding magnetic bubbles around two of the outer planets. […]