Portal:Solar System

The Solar System Portal

The Solar System is the gravitationally bound system of the Sun and the objects that orbit it. It was formed 4.6 billion years ago when a dense region of a molecular cloud collapsed, forming the Sun and a protoplanetary disc. The Sun is an ordinary main sequence star that maintains a balanced equilibrium by the fusion of hydrogen into helium at its core, releasing this energy from its outer photosphere.

The largest objects that orbit the Sun are the eight planets. In order from the Sun, they are four terrestrial planets (Mercury, Venus, Earth and Mars); two gas giants (Jupiter and Saturn); and two ice giants (Uranus and Neptune). All terrestrial planets have solid surfaces. Inversely, all giant planets do not have a definite surface, as they are mainly composed of gases and liquids. Over 99.86% of the Solar System's mass is in the Sun and nearly 90% of the remaining mass is in Jupiter and Saturn.

There is a strong consensus among astronomers that the Solar System has at least eight dwarf planets: Ceres, Pluto, Haumea, Quaoar, Makemake, Gonggong, Eris, and Sedna. There are a vast number of small Solar System bodies, such as asteroids, comets, centaurs, meteoroids, and interplanetary dust clouds. Some of these bodies are in the asteroid belt (between Mars's and Jupiter's orbit) and the Kuiper belt (just outside Neptune's orbit). Six planets, six dwarf planets, and other bodies have orbiting natural satellites, which are commonly called 'moons'.

The Solar System is constantly flooded by the Sun's charged particles, the solar wind, forming the heliosphere. Around 75–90 astronomical units, the solar wind is halted, resulting in the heliopause. This is the boundary of the Solar System to interstellar space. The outermost region of the Solar System is the theorized Oort cloud, the source for long-period comets, extending 2,000–200,000 astronomical units (0.032–3.2 light-years). The closest star to the Solar System, Proxima Centauri, is 4.25 light-years away. Both stars belong to the Milky Way galaxy. (Full article...)

Selected article –

Voyager 2 picture of Uranus' rings
The rings of Uranus were discovered on March 10, 1977, by James L. Elliot, Edward W. Dunham, and Douglas J. Mink. Two additional rings were discovered in 1986 by the Voyager 2 spacecraft, and two outer rings were found in 2003–2005 by the Hubble Space Telescope. A number of faint dust bands and incomplete arcs may exist between the main rings. The rings are extremely dark—the Bond albedo of the rings' particles does not exceed 2%. They are likely composed of water ice with the addition of some dark radiation-processed organics. The majority of Uranus's rings are opaque and only a few kilometres wide. The ring system contains little dust overall; it consists mostly of large bodies 0.2–20 m in diameter. The relative lack of dust in the ring system is due to aerodynamic drag from the extended Uranian exosphere—corona. The rings of Uranus are thought to be relatively young, at not more than 600 million years. The mechanism that confines the narrow rings is not well understood. The Uranian ring system probably originated from the collisional fragmentation of a number of moons that once existed around the planet. After colliding, the moons broke up into numerous particles, which survived as narrow and optically dense rings only in strictly confined zones of maximum stability. (Full article...)

Selected picture

  • Solar eclipse of 1999 August 11
    Credit: Luc Viatour
    The solar eclipse of 1999 August 11, as seen from France. This was the most viewed total eclipse in human history, although some areas offered impaired visibility due to adverse weather conditions. The path of the Moon's shadow began in the Atlantic Ocean, before traversing Cornwall, northern France, southern Germany, Austria, Hungary and northern Serbia. Its maximum was in Romania, and it continued across the Black Sea, Turkey, Iran, southern Pakistan and India.
  • Moons of the Solar System
    Image credit: NASA, Deuar, TotoBaggins, KFP
    A natural satellite is an object that orbits a planet or other body larger than itself and which is not man-made. Such objects are often called moons. Shown here are 28 of the 240 moons of the Solar System, including those of the dwarf planets Pluto and Eris as well as that of asteroid 243 Ida. The Earth is included for scale.
  • Mars
    Photograph credit: European Space Agency
    Mars is the fourth planet from the Sun and is known as the "Red Planet" due to its reddish appearance as seen from Earth. The planet is named after Mars, the Roman god of war. A terrestrial planet, Mars has a thin atmosphere and surface features reminiscent both of the impact craters of the Moon and the volcanoes, valleys, deserts and polar ice caps of the Earth. The planet has the highest mountain in the Solar System, Olympus Mons, as well as the largest canyon, Valles Marineris. Mars's rotation period and seasonal cycles are also similar to those of the Earth. Of all the planets in the Solar System other than Earth, Mars is the most likely to harbour liquid water and perhaps life. There are ongoing investigations assessing Mars's past potential for habitability, as well as the possibility of extant life. Future astrobiology missions are planned, including NASA's Mars 2020 rover and the European Space Agency (ESA)'s Rosalind Franklin rover. In November 2016, NASA reported finding a large amount of underground ice in the Utopia Planitia region of the planet. The volume of water detected has been estimated to be equivalent to the volume of water in Lake Superior. Mars has two moons, Phobos and Deimos, which are small and irregularly shaped.

    This picture is a true-colour image of Mars, taken from a distance of about 240,000 kilometres (150,000 mi) by the OSIRIS instrument on ESA's Rosetta spacecraft, during its February 2007 flyby of the planet. The image was generated using OSIRIS's orange (red), green and blue filters.
  • Credit: Philipp Salzgeber
    Comet Hale–Bopp sails across the sky in the vicinity of Pazin in Istria, Croatia. To the lower right of the comet the Andromeda Galaxy is also faintly visible. The comet was visible to the naked eye for a record 18 months, twice as long as the Great Comet of 1811. At perihelion, it shone brighter than any star in the sky except Sirius, and its two tails stretched 30-40 degrees across the sky. The passage of Hale-Bopp was notable also for inciting a degree of panic about comets not seen for decades. Rumours that the comet was being followed by an alien spacecraft inspired a mass suicide among followers of the Heaven's Gate cult.
  • Magellan (spacecraft)
    Credit: NASA/Jet Propulsion Laboratory
    These images are composites of the complete radar image collection obtained by the Magellan mission. The Magellan spacecraft was launched aboard Space Shuttle Atlantis in May 1989 and began mapping the surface of Venus in September 1990. The spacecraft continued to orbit Venus for four years, returning high-resolution images, altimetry, thermal emissions and gravity maps of 98 percent of the surface. Magellan spacecraft operations ended on October 12, 1994, when the radio contact was lost with the spacecraft during its controlled descent into the deeper portions of the Venusian atmosphere.
  • Mars
    Credit: NASA
    Mars, the fourth planet from the Sun, is named after the Roman god of war because of its blood red color. Mars has two small, oddly-shaped moons, Phobos and Deimos, named after the sons of the Greek god Ares. At some point in the future Phobos will be broken up by gravitational forces. The atmosphere on Mars is 95% carbon dioxide. In 2003 methane was also discovered in the atmosphere. Since methane is an unstable gas, this indicates that there must be (or have been within the last few hundred years) a source of the gas on the planet.
  • Lunar rover
    Photo credit: Harrison Schmitt
    Astronaut Eugene Cernan makes a short test drive of the lunar rover (officially, Lunar Roving Vehicle or LRV) during the early part of the first Apollo 17 extravehicular activity. The LRV was only used in the last three Apollo missions, but it performed without any major problems and allowed the astronauts to cover far more ground than in previous missions. All three LRVs were abandoned on the Moon.
  • Photo credit: Cassini orbiter
    A close-up of 10 km (6.2 mi) high mountains within the equatorial ridge on Saturn's moon Iapetus, photographed by the Cassini orbiter. Above the middle of the image can be seen a place where an impact has exposed the bright ice beneath the dark overlying material. The image was taken on September 10, 2007, with the Cassini spacecraft narrow-angle camera at a distance of approximately 3,870 km (2,400 mi) from Iapetus.
  • Photograph: John Vermette
    C/2014 Q2 (Lovejoy) is a long-period comet discovered in 2014 by Australian astronomer Terry Lovejoy using a 0.2-meter (8 in) Schmidt–Cassegrain telescope. It was discovered at apparent magnitude 15 in the southern constellation of Puppis, and is the fifth comet discovered by Lovejoy. Its blue-green glow is the result of organic molecules and water released by the comet fluorescing under the harsh UV and optical light of the sun as it passes through space.
  • Sunspot
    Credit: NASA/TRACE
    A TRACE image of sunspots on the surface, or photosphere, of the Sun from September 2002, is taken in the far ultraviolet on a relatively quiet day for solar activity. However, the image still shows a large sunspot group visible as a bright area near the horizon. Although sunspots are relatively cool regions on the surface of the Sun, the bright glowing gas flowing around the sunspots have a temperature of over one million °C (1.8 million °F). The high temperatures are thought to be related to the rapidly changing magnetic field loops that channel solar plasma.
  • Photo: NASA
    A true-color image of Io, one of the moons of Jupiter, taken by the Galileo spacecraft. The dark spot just left of the center is the erupting volcano Prometheus. The whitish plains on either side of it are coated with volcanically deposited sulfur dioxide frost, whereas the yellower regions contain a higher proportion of sulfur.
  • The Blue Marble
    Photo credit: The Apollo 17 crew
    The Blue Marble is a famous photograph of Earth. NASA officially credits the image to the entire Apollo 17 crew — Eugene Cernan, Ronald Evans and Jack Schmitt — all of whom took photographic images during the mission. Apollo 17 passed over Africa during daylight hours and Antarctica is also illuminated. The photograph was taken approximately five hours after the spacecraft's launch, while en route to the Moon. Apollo 17, notably, was the last manned lunar mission; no humans since have been at a range where taking a "whole-Earth" photograph such as "The Blue Marble" would be possible.
  • Photograph: NASA/Dan Burbank
    Comet Lovejoy is a long-period comet and Kreutz Sungrazer which was discovered in 2011. Named after its discoverer, Terry Lovejoy, the comet was nicknamed "The Great Christmas Comet" owing to it becoming visible near Christmas.
  • Retrograde and direct motion
    Image credit: Seav
    An animated image showing the apparent retrograde motion of Mars in 2003 as seen from Earth. All the true planets appear to periodically switch direction as they cross the sky. Because Earth completes its orbit in a shorter period of time than the planets outside its orbit, we periodically overtake them, like a faster car on a multi-lane highway. When this occurs, the planet will first appear to stop its eastward drift, and then drift back toward the west. Then, as Earth swings past the planet in its orbit, it appears to resume its normal motion west to east.
  • Jupiter is the fifth planet from the Sun and by far the largest within the Solar System. It is 318 times more massive than Earth, with a diameter 11 times that of Earth, and with a volume 1300 times that of Earth. Its best known feature is the Great Red Spot, a storm larger than Earth, which was first observed by Galileo four centuries ago. This picture, taken by the Cassini orbiter was one of 26 thousand images taken of Jupiter during the course of its flyby and is the most detailed global color portrait of the planet ever produced.
  • Lunar distance
    Model: Nickshanks
    Lunar distance is a measurement of the distance from the Earth to the Moon. This diagram shows the distance, averaging 384,400 km (238,900 mi), to scale, as well as the Earth and the Moon (scroll to see the entire image).
  • Sun
    Diagram credit: Kelvin Ma
    The Sun is the star at the center of the Solar System. It is a nearly perfect sphere of hot plasma, heated to incandescence by nuclear-fusion reactions in its core, radiating the energy mainly as visible light and infrared radiation. It is by far the most important source of energy for life on Earth. Its diameter is about 1.39 million kilometres (860,000 mi), or 109 times that of Earth. Its mass is about 330,000 times that of Earth, and accounts for about 99.86 percent of the total mass of the Solar System. Roughly three-quarters of the Sun's mass consists of hydrogen; the rest is mostly helium, with much smaller quantities of heavier elements, including oxygen, carbon, neon, and iron. This diagram illustrates the general structure of the Sun, with all features drawn to scale.
  • Animation: NASA/JPL/University of Arizona
    A 14-frame clip showing the atmosphere of Jupiter as viewed from the NASA probe Cassini. Taken over a span of 24 Jupiter rotations between October 31 and November 9, 2000, this clip shows various patterns of motion across the planet. The Great Red Spot rotates counterclockwise, and the uneven distribution of its high haze is obvious. To the east (right) of the Red Spot, oval storms, like ball bearings, roll over and pass each other. East-west bands adjacent to each other move at different rates. Strings of small storms rotate around northern-hemisphere ovals. The large grayish-blue "hot spots" at the northern edge of the white Equatorial Zone change over time as they proceed eastward across the planet. Ovals in the north rotate counter to those in the south. Small, very bright features appear quickly and randomly in turbulent regions, possibly lightning storms. The smallest visible features at the equator are about 600 km (370 miles) across.
  • Credit: William Anders
    Earthrise, the first occasion in which humans saw the Earth seemingly rising above the surface of the Moon, taken during the Apollo 8 mission on December 24, 1968. This view was seen by the crew at the beginning of its fourth orbit around the Moon, although the first photograph taken was in black-and-white. Note that the Earth is in shadow here. A photo of a fully lit Earth would not be taken until the Apollo 17 mission.
  • Photo credit: Luc Viatour
    Full moon is a lunar phase that occurs when the Moon is on the opposite side of the Earth from the Sun, and when the three celestial bodies are aligned as closely as possible to a straight line. At this time, as seen by viewers on Earth, the hemisphere of the Moon that is facing the Earth (the near side) is fully illuminated by sunlight and appears round. Only during a full moon is the opposite hemisphere of the Moon, which is not visible from Earth (the far side), completely unilluminated.
  • Photo credit: Cassini orbiter
    False-color mosaic shows the entire hemisphere of Iapetus (1,468 km or 912 mi across) visible from the Cassini orbiter on the outbound leg of its encounter with the two-toned moon of Saturn in September 2007. The central longitude of the trailing hemisphere is 24 degrees to the left of the image's center. It is hypothesized that the moon's two-toned nature is due to the sublimation of various ices evaporated from the warmer parts of the surface.
  • Neptune
    Photograph credit: NASA / JPL
    Neptune is the eighth and farthest known planet from the Sun in the Solar System. In the Solar System, it is the fourth-largest planet by diameter, the third-most-massive planet and the densest giant planet. Neptune is 17 times the mass of Earth, slightly more massive than its near-twin Uranus. Neptune is denser and physically smaller than Uranus because its greater mass causes more gravitational compression of its atmosphere. Neptune orbits the Sun once every 164.8 years at an average distance of 30.1 au (4.5 billion km; 2.8 billion mi). It is named after the Roman god of the sea and has the astronomical symbol ♆, a stylised version of the god Neptune's trident.

    This picture of Neptune was taken by NASA's Voyager 2 spacecraft in 1989, at a range of 4.4 million miles (7.1 million kilometres) from the planet, approximately four days before closest approach. The photograph shows the Great Dark Spot, a storm about the size of Earth, in the centre, while the fast-moving bright feature nicknamed the "Scooter" and the Small Dark Spot can be seen on the western limb. These clouds were seen to persist for as long as the spacecraft's cameras could resolve them.
  • Pluto
    Photograph: NASA / Johns Hopkins University Applied Physics Laboratory / Southwest Research Institute
    Pluto is a dwarf planet in the Kuiper belt, a ring of bodies beyond Neptune. Discovered by Clyde Tombaugh in 1930, Pluto was originally considered to be the ninth planet from the Sun. Following the discovery of several objects of similar size in the Kuiper belt, its status as a planet was questioned, and in 2006 the International Astronomical Union (IAU) gave a definition of the term "planet" that excluded Pluto. The largest and second-most-massive known dwarf planet in the Solar System, Pluto is primarily made of ice and rock. It is relatively small, with a moderately eccentric and inclined orbit.

    This photograph of Pluto is a composite of four near-true color images taken by the New Horizons spacecraft in 2015. The most prominent feature in the image, the bright, youthful, nitrogen ice plains of Sputnik Planitia, the left lobe of heart-shaped Tombaugh Regio, is at right center. This contrasts with the darker, more cratered terrain of Cthulhu Macula at lower left.
  • Comparison between the habitable zones of the Solar System and Gliese 581 (planet d was later found to not exist). The habitable zone is highly dependent on parent star's luminosity. (from Solar System)
  • Plot of objects around the Kuiper belt and other asteroid populations. J, S, U and N denotes Jupiter, Saturn, Uranus and Neptune. (from Solar System)
  • Animations of the Solar System's inner planets orbiting. Each frame represents 2 days of motion. (from Solar System)
  • Artist's conception of a protoplanetary disk (from Formation and evolution of the Solar System)
  • The current Sun compared to its peak size in the red-giant phase (from Solar System)
  • To-scale diagram of distance between planets, with the white bar showing orbital variations. The size of the planets is not to scale. (from Solar System)
  • Orbit classification of Kuiper belt objects. Some clusters that is subjected to orbital resonance are also marked. (from Solar System)
  • Overview of the inner Solar System up to Jupiter's orbit (from Solar System)
  • The Sun in true white color (from Solar System)
  • Location of the Solar System within the Milky Way (from Formation and evolution of the Solar System)
  • The Ring nebula, a planetary nebula similar to what the Sun will become (from Formation and evolution of the Solar System)
  • The Sun, planets, moons and dwarf planets. The asteroid belt and Kuiper belt are not added because the individual asteroids are too small to be shown on the diagram.
  • Meteor Crater in Arizona. Created 50,000 years ago by an impactor about 50 metres (160 ft) across, it shows that the accretion of the Solar System is not over. (from Formation and evolution of the Solar System)
  • Overview of the evolution of the Sun, a G-type main-sequence star. Around 11 billion years after being formed by the Solar System's protoplanetary disk, the Sun will expand to become a red giant; Mercury, Venus and possibly the Earth will be swallowed. (from Solar System)
  • Diagram of the Sun's magnetosphere and helioshealth (from Solar System)
  • Hubble image of protoplanetary discs in the Orion Nebula, a light-years-wide stellar nursery probably very similar to the primordial nebula from which the Sun formed (from Formation and evolution of the Solar System)
  • Animations of the Solar System's outer planets orbiting. This animation is 100 times faster than the inner planet animation. (from Solar System)
  • Linear map of the inner Solar System, showing many asteroid populations (from Solar System)
  • Diagram of the Local Interstellar Cloud, the G-Cloud and surrounding stars. As of 2022, the precise location of the Solar System in the clouds is an open question in astronomy. (from Solar System)
  • The orbital eccentricities and inclinations of the scattered disc population compared to the classical and resonant Kuiper belt objects (from Solar System)
  • Diagram of the Milky Way, with galactic features and the relative position of the Solar System labelled. (from Solar System)
  • The outer planets Jupiter, Saturn, Uranus and Neptune, compared to the inner planets Earth, Venus, Mars, and Mercury at the bottom right (from Solar System)
  • The motion of 'lights' moving across the sky is the basis of the classical definition of planets: wandering stars. (from Solar System)
  • Relative size of the Sun as it is now (inset) compared to its estimated future size as a red giant (from Formation and evolution of the Solar System)
  • Comet Hale–Bopp seen in 1997 (from Solar System)
  • The four terrestrial planets Mercury, Venus, Earth and Mars (from Solar System)
  • Diagram of the early Solar System's protoplanetary disk, out of which Earth and other Solar System bodies formed (from Solar System)
  • The Solar System within the interstellar medium, with the different regions and their distances on a steped horizontal distance scale (from Solar System)
  • Artist's conception of the giant impact thought to have formed the Moon (from Formation and evolution of the Solar System)
  • The orbits of Sedna, 2012 VP113, Leleākūhonua, and other very distant objects along with the predicted orbit of the hypothetical Planet Nine (from Solar System)
  • Pierre-Simon Laplace, one of the originators of the nebular hypothesis (from Formation and evolution of the Solar System)
  • Solar phenomena play a dominant role in the Solar System's dynamics (from Solar System)
  • Simulation showing outer planets and Kuiper belt:
    a) Before Jupiter/Saturn 2:1 resonance
    b) Scattering of Kuiper belt objects into the Solar System after the orbital shift of Neptune
    c) After ejection of Kuiper belt bodies by Jupiter
      Orbit of Jupiter
      Orbit of Saturn
      Orbit of Uranus
      Orbit of Neptune
    (from Formation and evolution of the Solar System)
  • True-scale Solar System diagram made by Emanuel Bowen in 1747. At that time, Uranus, Neptune, nor the asteroid belts have been discovered yet. (from Solar System)
  • Neptune and its moon Triton, taken by Voyager 2. Triton's orbit will eventually take it within Neptune's Roche limit, tearing it apart and possibly forming a new ring system. (from Formation and evolution of the Solar System)

Did you know –

  • ...that the Solar Sentinels, a NASA spacecraft designed to study the Sun, will have to survive at distances from the Sun only one-quarter of Earth's distance?
  • ...that just over 50 kilometres above its surface, the atmosphere of Venus has very similar pressure and temperature as does Earth, making it the most Earth-like area in the Solar System?
  • ...that the south pole of the planet Mercury is located in the Bach quadrangle?
  • ...that the Sweden Solar System is currently the world's largest scale model of the Solar System?
  • ...that the dominant feature in the Shakespeare quadrangle is the 1300 km wide Caloris Planitia, the largest and best preserved impact basin on Mercury observed by the spacecraft Mariner 10?
  • ...that the nearly circular shape of Lukanga Swamp, a wetland covering 2,600 km² in Central Province, Zambia, has led to speculation that it may be a crater formed by the impact of a meteorite?

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Makemake
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Formation and evolution of the Solar System: History of Solar System formation and evolution hypotheses · Nebular hypothesis
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