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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.

  • TESS discovers three new planets nearby,...
    on July 29, 2019 at 3:13 pm

    NASA's Transiting Exoplanet Survey Satellite, or TESS, has discovered three new worlds that are among the smallest, nearest exoplanets known to date. The planets orbit a star just 73 light years away and include a small, rocky super-Earth and two sub-Neptunes -- planets about half the size of our own icy giant.

  • Atmosphere of midsize planet revealed by Hubble,...
    on July 2, 2019 at 8:46 pm

    Two NASA space telescopes have identified the detailed chemical 'fingerprint' of a planet between the sizes of Earth and Neptune. No planets like this can be found in our own solar system, but they are common around other stars.

  • How icy outer solar system satellites may have...
    on June 25, 2019 at 1:33 pm

    Beyond the orbit of the planet Neptune, there are a multitude of icy and rocky small bodies, smaller than planets but larger than comets. These likely formed at the same time as the Solar System, and understanding their origin could provide important clues as to how the entire Solar System originated. Using sophisticated computer simulations and observations of TNOs, astronomers have shown how these so-called trans-Neptunian Objects (or TNOs) may have formed.

  • Astronomers find 'Forbidden' planet in 'Neptunian...
    on May 28, 2019 at 11:30 pm

    An exoplanet smaller than Neptune with its own atmosphere has been discovered in a region close to its star where no Neptune-sized planets would normally be found.

  • Neptune's moon Triton fosters rare icy union
    on May 22, 2019 at 6:17 pm

    Astronomers using the Gemini Observatory explore Neptune's largest moon Triton and observe, for the first time beyond the lab, an extraordinary union between carbon monoxide and nitrogen ices. The discovery offers insights into how this volatile mixture can transport material across the moon's surface via geysers, trigger seasonal atmospheric changes, and provide a context for conditions on other distant, icy worlds.


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.

  • Analysis of Galileo's Jupiter entry probe reveals...
    on October 15, 2019 at 5:31 pm

    The entry probe of the Galileo mission to Jupiter entered the planet's atmosphere in 1995 in fiery fashion. As the probe descended from Mach 50 to Mach 1 and generated enough heat to cause plasma reactions on its surface, it relayed data about the burning of its heat shield that differed from the effects predicted in fluid dynamics models. New work examines what might have caused such a discrepancy.

  • For newborn planets, solar systems are naturally...
    on October 10, 2019 at 2:11 pm

    Numerical simulations by a group of astronomers, led by Mario Flock from the Max Planck Institute for Astronomy, have shown that young planetary systems are naturally "baby-proof": Physical mechanisms combine to keep young planets in the inner regions from taking a fatal plunge into the star. Similar processes also allow planets to be born close to stars—from pebbles trapped in a region close to the star. The research, which has been published in the journal Astronomy & Astrophysics, […]

  • Exoplanet and cosmology discoveries awarded Nobel...
    on October 9, 2019 at 10:22 am

    ESA congratulates 2019 Nobel Prize in Physics laureates Michel Mayor and Didier Queloz, who have been awarded the prestigious prize for the first discovery of an exoplanet orbiting a solar-type star, and James Peebles, honoured for the theoretical framework of cosmology used to investigate the Universe on its largest scales.

  • Exoplanet orbits its star every 18 hours
    on October 3, 2019 at 1:20 pm

    In the past decade, thousands of planets have been discovered beyond our solar system. These planets have provided astronomers with the opportunity to study planetary systems that defy our preconcieved notions. This includes particularly massive gas giants that are many times the size of Jupiter (aka "super-Jupiters"). And then there are those that orbit particularly close to their suns, otherwise known as "hot Jupiters."

  • What moons in other stellar systems reveal about...
    on October 3, 2019 at 1:09 pm

    What is the difference between a planet-satellite system as we have with the Earth and moon, versus a binary planet—two planets orbiting each other in a cosmic do-si-do?