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 formed 4.6 billion years ago from the gravitational collapse of a giant interstellar molecular cloud. The vast majority (99.86%) of the system's mass is in the Sun, with most of the remaining mass contained in the planet Jupiter. The planetary system around the Sun contains eight planets. The four inner system planets—Mercury, Venus, Earth and Mars—are terrestrial planets, being composed primarily of rock and metal. The four giant planets of the outer system are substantially larger and more massive than the terrestrials. The two largest, Jupiter and Saturn, are gas giants, being composed mainly of hydrogen and helium; the next two, Uranus and Neptune, are ice giants, being composed mostly of volatile substances with relatively high melting points compared with hydrogen and helium, such as water, ammonia, and methane. All eight planets have nearly circular orbits that lie near the plane of Earth's orbit, called the ecliptic.
There are an unknown number of smaller dwarf planets and innumerable small Solar System bodies orbiting the Sun. Six of the major planets, the six largest possible dwarf planets, and many of the smaller bodies are orbited by natural satellites, commonly called "moons" after Earth's Moon. Two natural satellites, Jupiter's moon Ganymede and Saturn's moon Titan, are larger than Mercury, the smallest terrestrial planet, though less massive, and Jupiter's moon Callisto is nearly as large. Each of the giant planets and some smaller bodies are encircled by planetary rings of ice, dust and moonlets. The asteroid belt, which lies between the orbits of Mars and Jupiter, contains objects composed of rock, metal and ice. Beyond Neptune's orbit lie the Kuiper belt and scattered disc, which are populations of objects composed mostly of ice and rock.
In the outer reaches of the Solar System lies a class of minor planets called detached objects. There is considerable debate as to how many such objects there will prove to be. Some of these objects are large enough to have rounded under their own gravity and thus to be categorized as dwarf planets. Astronomers generally accept about nine objects as dwarf planets: the asteroid Ceres, the Kuiper-belt objects Pluto, Orcus, Haumea, Quaoar, and Makemake, and the scattered-disc objects Gonggong, Eris, and Sedna. Various small-body populations, including comets, centaurs and interplanetary dust clouds, freely travel between the regions of the Solar System.
The solar wind, a stream of charged particles flowing outwards from the Sun, creates a bubble-like region of interplanetary medium 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 4.2441 light-years. (Full article...)
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Photo credit: The Apollo 17 crewThe 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.
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.
Photo credit: Cassini orbiterFalse-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.
The transit of Mercury across the face of the Sun that took place in November 2006. Mercury appears as a black speck in the Sun's lower center-right region; the black areas on the left and right edges are sunspots. The transit was first recorded by French astronomer Pierre Gassendi on November 7, 1631. Transits of Mercury take place in May or November, at intervals of 7, 13, or 33 years, with the next one scheduled to appear in May 2016.
Image credit: NASAA radar image of the surface of Venus, centered at 180 degrees east longitude. This composite image was created from mapping by the Magellan probe, supplemented by data gathered by the Pioneer orbiter, with simulated hues based on color images recorded by Venera 13 and 14. No probe has been able to survive more than a few hours on Venus's surface, which is completely obscured by clouds, because the atmospheric pressure is some 90 times that of the Earth's, and its surface temperature is around 450 °C (842 °F).
Image credit: SeavAn 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.
Credit: Philipp SalzgeberComet 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.- 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, 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.
Photograph credit: Neil ArmstrongTranquility Base is the landing site of the Apollo 11 mission on the Moon where, on July 20, 1969, humans first landed and walked on a celestial body other than the Earth. This photograph was taken at Tranquility Base by Neil Armstrong, the Apollo 11 commander, and depicts crewmember Buzz Aldrin with scientific equipment he had just deployed on the lunar surface. In the background on the right of the image is the lunar module, Eagle; the United States flag planted at the site during the mission was blown over the next day by the exhaust of the ascent rocket.- 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.
Photograph credit: NASA / JPL–Caltech / University of ArizonaAlthough Mars is smaller than the Earth and 50 percent farther from the Sun, its climate has important similarities with the Earth, such as the presence of polar ice caps, seasonal changes and observable weather patterns. This image shows layered deposits in Planum Boreum, in the north polar region of Mars, which formed from a 3-kilometre-thick (2 mi) stack of dusty water-ice layers about 1,000 km (600 mi) across. The layers record information about the climate of the planet stretching back several million years. Erosion has created scarps and troughs that expose the layering. The tan-colored layers are the dusty water ice of the polar layered deposits, however a section of bluish layers is visible below them. These bluish layers contain sand-sized rock fragments that likely formed a large polar dunefield before the overlying dusty ice was deposited. This photograph, depicting an area approximately 1.3 km (0.8 mi) across, was captured by the HiRISE camera on board NASA's Mars Reconnaissance Orbiter.
Photo credit: Cassini orbiterA 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.
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.
Credit: Cassini probeJupiter 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.
Photo credit: Spirit roverA 360° panorama taken during the descent from the summit of Husband Hill, one of the Columbia Hills in Gusev crater, Mars. This stitched image is composed of 405 individual images taken with five different filters on the panoramic camera over the course of five Martian days.
Credit: William AndersEarthrise, 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.
The Milky Way is the galaxy that contains the Solar System, with the name describing the galaxy's appearance from Earth: a hazy band of light seen in the night sky formed from stars that cannot be individually distinguished by the naked eye. The term Milky Way is a translation of the Latin via lactea, from the Greek γαλαξίας κύκλος (galaxías kýklos, 'milky circle'). From Earth, the Milky Way appears as a band because its disk-shaped structure is viewed from within. Galileo Galilei first resolved the band of light into individual stars with his telescope in 1610. Until the early 1920s, most astronomers thought that the Milky Way contained all the stars in the Universe. Following the 1920 Great Debate between the astronomers Harlow Shapley and Heber Curtis, observations by Edwin Hubble showed that the Milky Way is just one of many galaxies.
This picture shows a portion of the Milky Way as seen from Cerro Paranal in Chile, home to the European Southern Observatory (ESO)'s Very Large Telescope, depicting the region spanning the constellations from Sagittarius to Scorpius. The colourful nebulae surrounding Rho Ophiuchi and Antares can be seen to the right, while the dusty lane of the galaxy runs obliquely through the image, dotted with reddish objects such as the Lagoon and Trifid Nebulae. This region of the Milky Way also includes the Galactic Center, likely containing a supermassive black hole, Sagittarius A*.
Diagram: Kelvin SongA diagram of Jupiter showing a model of the planet's interior, with a rocky core overlaid by a deep layer of liquid metallic hydrogen and an outer layer predominantly of molecular hydrogen. Jupiter's true interior composition is uncertain. For instance, the core may have shrunk as convection currents of hot liquid metallic hydrogen mixed with the molten core and carried its contents to higher levels in the planetary interior. Furthermore, there is no clear physical boundary between the hydrogen layers—with increasing depth the gas increases smoothly in temperature and density, ultimately becoming liquid.
Photo credit: Luc ViatourFull 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.
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.
The Sun is the star at the center of the Solar System. It is a nearly perfect sphere of plasma, heated by nuclear fusion of hydrogen into helium in its core, with internal convective motion that generates a magnetic field via a dynamo process. It is by far the most important source of energy for life on Earth. Its diameter is about 1.39 million kilometres (860,000 miles) or 109 times that of Earth, while its mass is about 330,000 times that of Earth. It accounts for about 99.86% 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 false-color photograph of the Sun was taken by the Atmospheric Imaging Assembly instrument on NASA's Solar Dynamics Observatory (SDO) at a wavelength of 304 angstroms, in the extreme ultraviolet region of the electromagnetic spectrum.
Photo credit: Fir0002Comet C/2006 P1 (McNaught), as seen from Swifts Creek, Victoria, Australia. This non-periodic comet, the brightest in over 40 years, was discovered on August 7, 2006 by British-Australian astronomer Robert H. McNaught. It was first visible in the northern hemisphere, reaching perihelion on January 12, 2007 at a distance of 0.17 AU.
The Helix Nebula, a planetary nebula similar to what the Sun will create when it enters its white dwarf stage (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)
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)
The four terrestrial planets Mercury, Venus, Earth and Mars. (from Solar System)
The orientation of the Solar System's motion (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)
Distribution and size of trans-Neptunian objects (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)
Harrison H. Schmitt, an astronaut in the Apollo 17 mission, with the Moon and Earth in the background (from Solar System)
Plot of objects around the Kuiper belt and other asteroid populations, the J, S, U and N denotes Jupiter, Saturn, Uranus and Neptune (from Solar System)
The Sun's, planets', dwarf planets' and moons' size to scale, labelled. Distance of objects is not to scale (from Solar System)
The detached object Sedna and its orbit within the Solar System. (from Solar System)
The zodiacal light, caused by interplanetary dust (from Solar System)
Artist's conception of the giant impact thought to have formed the Moon (from Formation and evolution of the Solar System)
Location of the Solar System within the Milky Way (from Formation and evolution of the Solar System)
Comet Hale–Bopp seen in 1997 (from Solar System)
Artistic depiction of the Solar System's heliosphere (from Solar System)
Artist's conception of a protoplanetary disk (from Formation and evolution of the Solar System)
The Sun in true white color (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)
Beyond the heliosphere is the interstellar medium, consisting of various clouds of gases. The Solar System currently moves through the Local Interstellar Cloud, here shown along with neighbouring clouds and the two closest unaided visible stars. (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)
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)
Linear map of the inner Solar System, showing many asteroid populations (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 JupiterOrbit of JupiterOrbit of SaturnOrbit of UranusOrbit of Neptune(from Formation and evolution of the Solar System)
Overview of the Inner Solar System up to the Jovian System (from Solar System)
The Ring nebula, a planetary nebula similar to what the Sun will become (from Formation and evolution of the Solar System)
Pierre-Simon Laplace, one of the originators of the nebular hypothesis (from Formation and evolution of the Solar System)
Artist's impression of the early Solar System's protoplanetary disk, out of which Earth and other Solar System bodies formed (from Solar System)
Did you know –
- ...that New York's Panther Mountain (pictured) was the site of a prehistoric meteor crash?
- ...that the Beethoven crater in the Beethoven quadrangle on Mercury is the eleventh largest named impact crater in the Solar System?
- ...that the planet Mars appears red primarily because of a ubiquitous layer of dust containing nanophase ferric oxides?
- ...that the 1997 volcanic eruption of Pillan Patera on Jupiter's moon Io was the largest effusive eruption ever witnessed?
- ...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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In the news
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Major topics
Solar System: Planets (Definition · Planetary habitability · Terrestrial planets · Gas giants · Rings) · Dwarf planets (Plutoid) · Colonization · Discovery timelineˑ Exploration · Moons · Planetariums
- 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 1/2ˑ 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)
- Makemake
- 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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