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An image of Jupiter taken by the Hubble Space Telescope
Full-disc view of Jupiter in natural color in April 2014

Jupiter is the fifth planet from the Sun and the largest in the Solar System. It is a giant planet with a mass one-thousandth that of the Sun, but two-and-a-half times that of all the other planets in the Solar System combined. Jupiter and Saturn are gas giants; the other two giant planets, Uranus and Neptune, are ice giants. Jupiter has been known to astronomers since antiquity. It is named after the Roman god Jupiter. When viewed from Earth, Jupiter can reach an apparent magnitude of −2.94, bright enough for its reflected light to cast shadows, and making it on average the third-brightest natural object in the night sky after the Moon and Venus.

Jupiter is primarily composed of hydrogen with a quarter of its mass being helium, though helium comprises only about a tenth of the number of molecules. It may also have a rocky core of heavier elements, but like the other giant planets, Jupiter lacks a well-defined solid surface. Because of its rapid rotation, the planet's shape is that of an oblate spheroid (it has a slight but noticeable bulge around the equator). The outer atmosphere is visibly segregated into several bands at different latitudes, resulting in turbulence and storms along their interacting boundaries. A prominent result is the Great Red Spot, a giant storm that is known to have existed since at least the 17th century when it was first seen by telescope. Surrounding Jupiter is a faint planetary ring system and a powerful magnetosphere. Jupiter has 79 known moons, including the four large Galilean moons discovered by Galileo Galilei in 1610. Ganymede, the largest of these, has a diameter greater than that of the planet Mercury.

Selected general articles

  • True-color image taken by the Galileo orbiter
    Image of Ganymede's anti-Jovian hemisphere taken by the Galileo orbiter (contrast is enhanced). Lighter surfaces, such as in recent impacts, grooved terrain and the whitish north polar cap at upper right, are enriched in water ice.

    Ganymede /ˈɡænɪmd/ (Jupiter III) is the largest and most massive moon of Jupiter and in the Solar System. The ninth largest object in the Solar System, it is the largest without a substantial atmosphere. It has a diameter of 5,268 km (3,273 mi) and is 8% larger than the planet Mercury, although only 45% as massive. Possessing a metallic core, it has the lowest moment of inertia factor of any solid body in the Solar System and is the only moon known to have a magnetic field. It is the third of the Galilean moons, the first group of objects discovered orbiting another planet, and the seventh satellite outward from Jupiter. Ganymede orbits Jupiter in roughly seven days and is in a 1:2:4 orbital resonance with the moons Europa and Io, respectively.

    Ganymede is composed of approximately equal amounts of silicate rock and water ice. It is a fully differentiated body with an iron-rich, liquid core, and an internal ocean that may contain more water than all of Earth's oceans combined. Its surface is composed of two main types of terrain. Dark regions, saturated with impact craters and dated to four billion years ago, cover about a third of the satellite. Lighter regions, crosscut by extensive grooves and ridges and only slightly less ancient, cover the remainder. The cause of the light terrain's disrupted geology is not fully known, but was likely the result of tectonic activity due to tidal heating.

    Ganymede's magnetic field is probably created by convection within its liquid iron core. The meager magnetic field is buried within Jupiter's much larger magnetic field and would show only as a local perturbation of the field lines. The satellite has a thin oxygen atmosphere that includes O, O2, and possibly O3 (ozone). Atomic hydrogen is a minor atmospheric constituent. Whether the satellite has an ionosphere associated with its atmosphere is unresolved. Read more...
  • Hs-2010-20-a-web print.jpg

    The 2010 Jupiter impact event was a bolide impact event on Jupiter by an object estimated to be about 8–13 meters in diameter. The impactor may have been an asteroid, comet, centaur, extinct comet, or temporary satellite capture. Read more...
  • Jupiter

    The planet Jupiter, the largest planet in the solar system, is a popular backdrop for science fiction stories and films. Early works of science fiction used Jupiter itself as a location for stories, but modern science has shown that the planet has no solid surface one could land on and that its atmosphere, temperature, high gravity and intense radiation is hostile to human life. As a result, the Jovian system as a whole, including both the space around Jupiter and its very extensive system of moons, is a more common setting for science fiction. Read more...
  • Galilean moons of Jupiter

    Jupiter's extensive system of natural satellites – in particular the four large Galilean moons (Io, Europa, Ganymede and Callisto) – has been a common science fiction setting. Read more...
  • Artist's rendering of the Europa Clipper spacecraft.

    Europa Clipper is an interplanetary mission in development by NASA comprising an orbiter. Set for a launch between 2022 and 2025, the spacecraft is being developed to study the Galilean moon Europa through a series of flybys while in orbit around Jupiter.

    This mission is a scheduled flight of the Planetary Science Division, designated a Large Strategic Science Mission, and funded under the Planetary Missions Program Office's Solar System Exploration program as its second flight. It is also supported by the new Ocean Worlds Exploration Program. Europa Clipper will perform follow-up studies to those made by the Galileo spacecraft during its eight years in Jupiter orbit, which indicated the existence of a subsurface ocean underneath Europa. Plans to send a spacecraft to Europa were initially conceived with projects such as Europa Orbiter and Jupiter Icy Moons Orbiter, in which a spacecraft would be injected into orbit around Europa. However, due to the strong impact of radiation from Jupiter's magnetosphere in Europan orbit, it was decided that it would be safer to inject a spacecraft into an elliptical orbit around Jupiter and make 45 close flybys of the moon instead. The mission began as a joint investigation between the Jet Propulsion Laboratory and the Applied Physics Laboratory.

    The mission will complement ESA's Jupiter Icy Moons Explorer launching in 2022, which will fly-by Europa twice and Callisto multiple times before moving into orbit around Ganymede. Launching around the same time as the Europa Clipper, the Jupiter Icy Moons Explorer will have a cruise phase some three times as long. Read more...
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