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.

  • Tiny Neptune moon spotted by Hubble may have...
    on February 21, 2019 at 2:50 pm

    After several years of analysis, a team of planetary scientists using NASA's Hubble Space Telescope has at last come up with an explanation for a mysterious moon around Neptune that they discovered with Hubble in 2013. […]

  • Dynamic atmospheres of Uranus, Neptune
    on February 7, 2019 at 4:49 pm

    NASA's Hubble Space Telescope has uncovered another mysterious dark storm on Neptune and provided a fresh look at a long-lived storm circling around the north polar region on Uranus. […]

  • Mystery orbits in outermost reaches of solar...
    on January 21, 2019 at 3:33 pm

    The strange orbits of some objects in the farthest reaches of our solar system, hypothesized by some astronomers to be shaped by an unknown ninth planet, can instead be explained by the combined gravitational force of small objects orbiting the sun beyond Neptune, say researchers. […]

  • Where did the hot Neptunes go? A shrinking planet...
    on December 13, 2018 at 3:13 pm

    'Where did the hot Neptunes go?' This is the question astronomers have been asking for a long time, faced with the mysterious absence of planets the size of Neptune. Researchers have just discovered that one of these planets is losing its atmosphere at a frantic pace. This observation strengthens the theory that hot Neptunes have lost much of their atmosphere and turned into smaller planets called super-Earths. […]

  • Odd bodies, rapid spins keep cosmic rings close
    on November 19, 2018 at 8:59 pm

    Forget those shepherding moons. Gravity and the odd shapes of asteroid Chariklo and dwarf planet Haumea -- small objects deep in our solar system -- can be credited for forming and maintaining their own rings, according new research. […]


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.

  • An exoplanet with an 11-hour orbit
    on February 22, 2019 at 2:31 pm

    The Transiting Exoplanet Survey Satellite (TESS) was launched on April 18 of last year with the primary objective of discovering transiting planets smaller than Neptune around stars bright enough for spectroscopic investigations of their masses and atmospheres. Before TESS there were roughly 385 exoplanets known with masses smaller than Neptune, with orbital periods ranging from less than half-a-day to about two Earth-years. […]

  • Video: Big questions about small worlds
    on February 18, 2019 at 1:00 pm

    Scientists who study the solar system tend to ask big questions: How was our solar system formed? Where did the building blocks of life come from? What hazards from above threaten life on our planet? To find answers, they're looking more and more at small worlds. […]

  • Hubble reveals dynamic atmospheres of Uranus,...
    on February 7, 2019 at 5:20 pm

    During its routine yearly monitoring of the weather on our solar system's outer planets, NASA's Hubble Space Telescope has uncovered a new mysterious dark storm on Neptune and provided a fresh look at a long-lived storm circling around the north polar region on Uranus. […]

  • Video: Jupiter odyssey
    on February 6, 2019 at 1:46 pm

    ESA's Jupiter Icy Moons Explorer, Juice, is set to embark on a seven-year cruise to Jupiter starting May 2022. The mission will investigate the emergence of habitable worlds around gas giants and the Jupiter system as an archetype for the numerous giant planets now known to orbit other stars. […]

  • Giant impacts caused by interplanetary collisions
    on February 5, 2019 at 12:22 pm

    Astronomers have found fresh evidence for significant planetary diversity within a single exoplanet system, suggesting that giant high-speed collisions are partly responsible for planetary evolution. […]