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Portal:Solar System

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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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Artist's impression of 90377 Sedna
Artist's impression of 90377 Sedna
90377 Sedna is a trans-Neptunian object currently about three times as far from the Sun as Neptune. For the majority of its orbit it is the most distant known object in the Solar System other than long-period comets. Roughly two-thirds the size of Pluto, Sedna is hypothetically large enough to be rounded by its own gravity, and thus would qualify as a dwarf planet under current definitions. However, its distance makes determining its shape difficult. Spectroscopy has revealed that Sedna's surface composition is similar to that of some other trans-Neptunian objects, being largely a mixture of water, methane, and nitrogen ices with tholins. Its surface is one of the reddest in the Solar System. Its exceptionally long and elongated orbit, taking approximately 12,000 years to complete, and distant point of closest approach to the Sun have led to much speculation as to its origin. Astronomer Mike Brown, who co-discovered Sedna in 2003, believes it to be the most scientifically important trans-Neptunian object found to date, as understanding its peculiar orbit is likely to yield valuable information about the origin and early evolution of the Solar System. ( Full article...)

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The original scalloped margin dome, known as "The Tick"

  • ...that although NASA originally thought that there was only one scalloped margin dome on the planet Venus (pictured), they have since discovered hundreds of them?


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The Sun Mercury Venus The Moon Earth Mars Phobos and Deimos Ceres The main asteroid belt Jupiter Moons of Jupiter Saturn Moons of Saturn Uranus Moons of Uranus Neptune Moons of Neptune Pluto Moons of Pluto Haumea Moons of Haumea Makemake The Kuiper Belt Eris Dysnomia The Scattered Disc The Hills Cloud The Oort CloudSolar System Template Final.png

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

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

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