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.

  • Evidence of early planetary shake-up
    on September 10, 2018 at 3:12 pm

    Scientists have studied an unusual pair of asteroids and discovered that their existence points to an early planetary rearrangement in our solar system. […]

  • New exoplanet found very close to its star
    on September 5, 2018 at 8:19 pm

    Using data from NASA's Kepler Space Telescope, an international team has discovered a new exoplanet twice the size of Earth. It orbits its star every six days and is thus very close to it, about 10 times closer than Mercury is to the Sun. […]

  • Collective gravity, not Planet Nine, may explain...
    on June 4, 2018 at 5:17 pm

    Bumper car-like interactions at the edges of our solar system -- and not a mysterious ninth planet -- may explain the dynamics of strange bodies called 'detached objects,' according to a new study. […]

  • From car engines to exoplanets
    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. […]


Phys.org - latest science and technology news stories Phys.org internet news portal provides the latest news on science including: Physics, Nanotechnology, Life Sciences, Space Science, Earth Science, Environment, Health and Medicine.

  • Giant planets around young star raise questions...
    on October 15, 2018 at 1:43 pm

    Researchers have identified a young star with four Jupiter and Saturn-sized planets in orbit around it, the first time that so many massive planets have been detected in such a young system. The system has also set a new record for the most extreme range of orbits yet observed: the outermost planet is more than a thousand times further from the star than the innermost one, which raises interesting questions about how such a system might have formed. […]

  • Five in a row—the planets align in the night sky
    on October 12, 2018 at 12:05 pm

    For the second time this year, the five brightest planets can be seen at the same time. You can catch them by looking towards the western sky after sunset. The planets will form a line rising up from the horizon. […]

  • The stuff that planets are made of
    on October 10, 2018 at 12:01 pm

    UZH researchers have analyzed the composition and structure of faraway exoplanets using statistical tools. Their analysis indicates whether a planet is Earth-like, made up of pure rock, or a water-world. The larger the planet, the more hydrogen and helium surround it. […]

  • The threat of centaur solar system objects for...
    on October 10, 2018 at 10:48 am

    Astrophysicists Mattia Galiazzo and Rudolf Dvorak from the University of Vienna, in collaboration with Elizabeth A. Silber (Brown University, U.S.) investigated the long-term path development of centaurs, solar system minor bodies that originally have orbits between Jupiter and Neptune. The researchers have estimated the number of close encounters and impacts with the terrestrial planets after the so-called Late Heavy Bombardment about 3.8 billion years ago, as well as the possible sizes of […]

  • Astronomers find first compelling evidence for a...
    on October 3, 2018 at 6:00 pm

    A pair of Columbia University astronomers using NASA's Hubble Space Telescope and Kepler Space Telescope have assembled compelling evidence for the existence of a moon orbiting a gas-giant planet 8,000 light-years away. […]