Portal:Solar System
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Portal:Solar System

The Solar System Portal

The Sun and planets of the Solar System (distances not to scale)

The Solar System is the gravitationally bound system of the Sun and the objects that orbit it, either directly or indirectly. Of the objects that orbit the Sun directly, the largest are the eight planets, with the remainder being smaller objects, the dwarf planets and small Solar System bodies. Of the objects that orbit the Sun indirectly--the natural satellites--two are larger than the smallest planet, Mercury.

The Solar System formed 4.6 billion years ago from the gravitational collapse of a giant interstellar molecular cloud. The vast majority of the system's mass is in the Sun, with the majority of the remaining mass contained in Jupiter. The four smaller inner planets, Mercury, Venus, Earth and Mars, are terrestrial planets, being primarily composed of rock and metal. The four outer planets are giant planets, being substantially more massive than the terrestrials. The two largest planets, Jupiter and Saturn, are gas giants, being composed mainly of hydrogen and helium; the two outermost planets, Uranus and Neptune, are ice giants, being composed mostly of substances with relatively high melting points compared with hydrogen and helium, called volatiles, such as water, ammonia and methane. All eight planets have almost circular orbits that lie within a nearly flat disc called the ecliptic.

The Solar System also contains smaller objects. The asteroid belt, which lies between the orbits of Mars and Jupiter, mostly contains objects composed, like the terrestrial planets, of rock and metal. Beyond Neptune's orbit lie the Kuiper belt and scattered disc, which are populations of trans-Neptunian objects composed mostly of ices, and beyond them a newly discovered population of sednoids. Within these populations, some objects are large enough to have rounded under their own gravity, though there is considerable debate as to how many there will prove to be. Such objects are categorized as dwarf planets. The only certain dwarf planet is Pluto, with another trans-Neptunian object, Eris, expected to be, and the asteroid Ceres at least close to being a dwarf planet. In addition to these two regions, various other small-body populations, including comets, centaurs and interplanetary dust clouds, freely travel between regions. Six of the planets, the six largest possible dwarf planets, and many of the smaller bodies are orbited by natural satellites, usually termed "moons" after the Moon. Each of the outer planets is encircled by planetary rings of dust and other small objects.

The solar wind, a stream of charged particles flowing outwards from the Sun, creates a bubble-like region in the interstellar medium known as the heliosphere. The heliopause is the point at which pressure from the solar wind is equal to the opposing pressure of the interstellar medium; it extends out to the edge of the scattered disc. The Oort cloud, which is thought to be the source for long-period comets, may also exist at a distance roughly a thousand times further than the heliosphere. The Solar System is located in the Orion Arm, 26,000 light-years from the center of the Milky Way galaxy. (Full article...)

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Voyager 2 showing Neptune's full ring system with the highest sensitivity
Voyager 2 showing Neptune's full ring system with the highest sensitivity
The rings of Neptune were first detected in 1980, but only identified in 1989 by the Voyager 2 spacecraft. The rings are tenuous, faint and dusty, and resemble the rings of Jupiter more closely than those of Saturn or Uranus. Neptune possesses five known rings, each named for an astronomer who contributed important work on the planet: the Galle, Le Verrier, Lassell, Arago and Adams rings. Neptune also has a faint unnamed ring coincident with the orbit of Neptunian moon Galatea. The rings of Neptune are made of extremely dark material, likely organic compounds processed by radiation similar to that found in the rings of Uranus. The proportion of dust in the rings (between 20 and 70%) is high, while their optical depth is low, at less than 0.1. Uniquely, the Adams ring is divided into five discrete arcs, named Fraternité, Égalité 1 and 2, Liberté, and Courage. The arcs occupy a narrow range of orbital longitudes and are remarkably stable, having changed only slightly since their initial detection in 1980. How the arcs maintain stability is still under debate. However, their stability is probably related to the resonant interaction between the Adams ring and its inner shepherd moon, Galatea. (Full article...)

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Great Comet of 1577

  • ...that the passing of the Great Comet of 1577 (pictured) caused almost century-long debate, during which Galileo argued that comets were merely optical illusions?


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The SunMercuryVenusThe MoonEarthMarsPhobos and DeimosCeresThe main asteroid beltJupiterMoons of JupiterSaturnMoons of SaturnUranusMoons of UranusNeptuneMoons of NeptunePlutoMoons of PlutoHaumeaMoons of HaumeaMakemakeThe Kuiper BeltErisDysnomiaThe Scattered DiscThe Hills CloudThe Oort CloudSolar System Template Final.png

Solar System: Planets (Definition ? Planetary habitability ? Terrestrial planets ? Gas giants ? Rings) ? Dwarf planets (Plutoid) ? Moons ? Exploration ? Colonization ? Discovery timeline

Sun: Sunspot ? Solar wind ? Solar flare ? Solar eclipse
Mercury: Geology ? Exploration (Mariner 10 ? MESSENGER ? BepiColombo) ? Transit
Venus: Geology ? Atmosphere ? Exploration (Venera ? Mariner program 2/5/10 ? Pioneer ? Vega 1/2? Magellan ? Venus Express) ? Transit
Earth: History ? Geology ? Geography ? Atmosphere ? Rotation
Moon: Geology ? Selenography ? Atmosphere ? Exploration (Luna ? Apollo 8/11) ? Orbit ? Lunar eclipse
Mars: Moons (Phobos ? Deimos) ? Geology ? Geography ? Atmosphere ? Exploration (Mariner ? Mars ? Viking 1/2 ? Pathfinder ? MER)
Ceres: Exploration (Dawn)
Jupiter: Moons (Amalthea, Io ? Europa ? Ganymede ? Callisto) ? Rings ? Atmosphere ? Magnetosphere ? Exploration (Pioneer 10/11 ? Voyager 1/2 ? Ulysses ? Cassini ? Galileo ? New Horizons)
Saturn: Moons (Mimas ? Enceladus ? Tethys ? Dione ? Rhea ? Titan ? Iapetus) ? Rings ? Exploration (Pioneer 11 ? Voyager 1/2 ? Cassini-Huygens)
Uranus: Moons (Miranda ? Ariel ? Umbriel ? Titania ? Oberon) ? Rings ? Exploration (Voyager 2)
Neptune: Moons (Triton) ? Rings ? Exploration (Voyager 2)
Planets beyond Neptune
Pluto: Moons (Charon, Nix, Hydra, Kerberos, Styx) ? Exploration (New Horizons)
Haumea: Moons (Hi'iaka, Namaka)
Eris: Dysnomia
Small bodies: Meteoroids ? Asteroids (Asteroid belt) ? Centaurs ? TNOs (Kuiper belt ? Scattered disc ? Oort cloud) ? Comets (Hale-Bopp ? Halley's ? Hyakutake ? Shoemaker-Levy 9)
Formation and evolution of the Solar System: History of Solar System formation and evolution hypotheses ? Nebular hypothesis
See also: Featured content ? Featured topic ? Good articles ? List of objects

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Italicized articles are on dwarf planets or major moons.

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