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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 system planets, Mercury, Venus, Earth and Mars, are terrestrial planets, being primarily composed of rock and metal. The four outer system 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 26,000 light-years from the center of the Milky Way galaxy in the Orion Arm, which contains most of the visible stars in the night sky. The nearest stars are within the so-called Local Bubble, with the closest Proxima Centauri at 4.25 light-years. ( Full article...)

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Full moon as seen from Earth's northern hemisphere.
Full moon as seen from Earth's northern hemisphere.
The Moon is Earth's only natural satellite. At about one-quarter the diameter of Earth (comparable to the width of Australia), it is the largest natural satellite in the Solar System relative to the size of its planet, the fifth largest satellite in the Solar System overall, and is larger than any known dwarf planet. Orbiting Earth at an average distance of 384,400 km (238,900 mi), or about 30 times Earth's diameter, its gravitational influence slightly lengthens Earth's day and is the main driver of Earth's tides. The Moon is classified as a planetary-mass object and a differentiated rocky body, and lacks any significant atmosphere, hydrosphere, or magnetic field. Its surface gravity is about one-sixth of Earth's (0.1654  g); Jupiter's moon Io is the only satellite in the Solar System known to have a higher surface gravity and density.

The Moon's orbit around Earth has a sidereal period of 27.3 days. During each synodic period of 29.5 days, the amount of visible surface illuminated by the Sun varies from none up to 100%, resulting in lunar phases that form the basis for the months of a lunar calendar. The Moon is tidally locked to Earth, which means that the length of a full rotation of the Moon on its own axis causes its same side ( the near side) to always face Earth, and the somewhat longer lunar day is the same as the synodic period. That said, 59% of the total lunar surface can be seen from Earth through shifts in perspective due to libration. ( Full article...)

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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 Colonization ˑ Discovery timelineˑ Exploration ˑ Moons ˑ Planetariums

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)
Makemake
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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Italicized articles are on dwarf planets or major moons.

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