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Portal:Solar System

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Solar System

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The Solar System is the gravitationally bound system of the planets and the Sun plus other objects that orbit it, either directly or indirectly. Of the objects that orbit the Sun directly, the largest eight are the planets, with the remainder being smaller objects, such as dwarf planets and small Solar System bodies. Of the objects that orbit the Sun indirectly, the moons, 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, 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 are several dozen to possibly tens of thousands of objects large enough that they have been rounded by their own gravity. Such objects are categorized as dwarf planets. Identified dwarf planets include the asteroid Ceres and the trans-Neptunian objects Pluto and Eris. 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, at least four of the 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.

Selected article

Callisto, the third largest moon in the Solar System
Callisto is a moon of the planet Jupiter, discovered in 1610 by Galileo Galilei. It is the third-largest moon in the Solar System and the second largest in the Jovian system, after Ganymede. It is not a part of the orbital resonance that affects three inner Galilean satellites—Io, Europa and Ganymede—and thus does not experience appreciable tidal heating. Callisto rotates synchronously with its orbital period, so the same hemisphere is always turned toward Jupiter. It is composed of approximately equal amounts of rock and ices, with a mean density of about 1.83 g/cm3. Compounds detected spectroscopically on the surface include water ice, carbon dioxide, silicates, and organic compounds. Investigation by the Galileo spacecraft revealed that Callisto may have only partially differentiated interior covered by a thick icy crust and possibly a subsurface ocean of liquid water at depths greater than 100 km. Prominent surface features include multi-ring structures, variously shaped impact craters, and chains of craters and associated scarps, ridges and deposits. Callisto is surrounded by an extremely thin atmosphere composed of carbon dioxide and probably molecular oxygen, as well as by a rather dense ionosphere. (more...)

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Did you know...

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?

Mars as seen by the Hubble Space Telescope

  • ... that troilite, a form of pyrrhotite, is extremely rare on Earth but is abundant on Mars (pictured)?

In the news

Wikinews Space portal
  • July 31: Total lunar eclipse occurs in July 2018
  • July 19: US astronomers announce discovering ten tiny Jovian satellites
  • May 7: NASA's InSight lander and MarCO craft launch in new mission to Mars
  • April 21: NASA launches exoplanet-hunting satellite TESS
  • April 3: China's Tiangong-1 space station crashes into Pacific
  • March 17: British scientist Stephen Hawking dies aged 76
  • January 6: Mysterious dimming of Tabby's star likely due to space dust, not alien superstructures, say scientists
  • November 3: Astronomers report dwarf star with unexpectedly giant planet
  • September 6: Peggy Whitson, record-breaking 'American space ninja', returns to Earth
  • July 17: Sun's mood swings not so strange after all, say scientists
  • July 14: Astronomers discover smallest known star
  • June 8: Astronomers reveal discovery of the hottest gas giant exoplanet known yet

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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)
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

Bold articles are featured.
Italicized articles are on dwarf planets or major moons.

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