Portal:Solar System

The Solar System Portal

The Solar System consists of the Sun and the objects that orbit it. The name comes from Sōl, the Latin name for the Sun. It formed about 4.6 billion years ago when a dense region of a molecular cloud collapsed, creating the Sun and a protoplanetary disc from which the orbiting bodies assembled. The fusion of hydrogen into helium inside the Sun's core releases energy, which is primarily emitted through its outer photosphere. This creates a decreasing temperature gradient across the system. Over 99.86% of the Solar System's mass is located within the Sun.

The most massive objects that orbit the Sun are the eight planets. Closest to the Sun in order of increasing distance are the four terrestrial planets – Mercury, Venus, Earth and Mars. Only the Earth and Mars orbit within the Sun's habitable zone, where liquid water can exist on the surface. Beyond the frost line at about five astronomical units (AU), are two gas giants – Jupiter and Saturn – and two ice giants – Uranus and Neptune. Jupiter and Saturn possess nearly 90% of the non-stellar mass of the Solar System.

There are a vast number of less massive objects. There is a strong consensus among astronomers that the Solar System has at least nine dwarf planets: Ceres, Orcus, Pluto, Haumea, Quaoar, Makemake, Gonggong, Eris, and Sedna. Six planets, seven dwarf planets, and other bodies have orbiting natural satellites, which are commonly called 'moons', and range from sizes of dwarf planets, like Earth's Moon, to moonlets. There are 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).

Between the bodies of the Solar System is an interplanetary medium of dust and particles. The Solar System is constantly flooded by outflowing charged particles from the solar wind, forming the heliosphere. At around 70–90 AU from the Sun, the solar wind is halted by the interstellar medium, resulting in the heliopause. This is the boundary to interstellar space. The Solar System extends beyond this boundary with its outermost region, the theorized Oort cloud, the source for long-period comets, extending to a radius of 2,000–200,000 AU. The Solar System currently moves through a cloud of interstellar medium called the Local Cloud. The closest star to the Solar System, Proxima Centauri, is 4.25 light-years (269,000 AU) away. Both are within the Local Bubble, a relatively small 1,000 light-years wide region of the Milky Way. (Full article...)

Selected article –

Europa (moon).

Europa is the sixth-nearest and fourth-largest natural satellite of the planet Jupiter. Europa was discovered in 1610 by Galileo Galilei (and independently by Simon Marius), and named for a mythical Phoenician noblewoman, Europa, who was courted by Zeus. It is the smallest of the four Galilean moons - slightly smaller than Earth's Moon and is the sixth-largest moon in the Solar System. Europa has a tenuous atmosphere composed primarily of molecular oxygen. Its surface is composed of ice and is one of the smoothest in the Solar System. This young surface is striated by cracks and streaks, while craters are relatively infrequent. The apparent youth and smoothness of the surface have led to the hypothesis that a water ocean exists beneath it, which could conceivably serve as an abode for extraterrestrial life. Although by 2007 only flyby missions have visited the moon, the intriguing character of Europa has led to several ambitious exploration proposals. The Galileo mission provided the bulk of current data on Europa, while the Jupiter Icy Moons Orbiter, canceled in 2005, would have targeted Europa, Ganymede and Callisto. Conjecture on extraterrestrial life has ensured a high profile for the moon and has led to steady lobbying for future missions. (Full article...)

More selected articles

Selected picture

Image 1
Tvashtar Paterae
Photo credit: New Horizons probe
An animation of an eruption by the Tvashtar Paterae volcanic region on the innermost of Jupiter's Galilean moons, Io. The ejecta plume is 330 km (205 mi) high, though only its uppermost half is visible in this image, as its source lies over the moon's limb on its far side. This animation consists of a sequence of five images taken by NASA's New Horizons probe on March 1, 2007, over the course of eight minutes from 23:50 UTC.
Image 2
Lunar phase
Image: Tom Ruen
An animation of the phases of the Moon. As the Moon revolves around the Earth, the Sun lights the Moon from a different side, creating the different phases. In the image, the Moon appears to get bigger as well as "wobble" slightly. Tidal locking synchronizes the Moon's rotation period on its axis to match its orbital period around the earth. These two periods nearly cancel each other out, except that the Moon's orbit is elliptical. This causes its orbital motion to speed up when closer to the Earth, and slow down when farther away, causing the Moon's apparent diameter to change, as well as the wobbling motion observed.
Image 3
Hyperion
Photo credit: Cassini orbiter
Hyperion, a moon of Saturn, is one of the largest highly irregular (non-spherical) bodies in the Solar System. Enhanced image processing was used to bring out details and color differences in this photo taken by the Cassini orbiter. Hyperion is entirely saturated with deep, sharp-edged craters that give it the appearance of a giant sponge. Dark material fills the bottom of each crater.
Image 4
Jupiter
Credit: Cassini probe
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.
Image 5
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.
Image 6
Saturn
Photo credit: Cassini orbiter
Saturn eclipsing the Sun, as seen by the Cassini orbiter. Individual rings seen in this image include (in order, starting from most distant): E ring, Pallene ring (visible very faintly in an arc just below Saturn), G ring, Janus/Epimetheus ring (faint), F ring (narrow brightest feature), Main rings (A,B,C), and D ring (bluish, nearest Saturn). Interior to the G ring and above the brighter main rings is the pale dot of Earth.
Image 7
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.
Image 8
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.
Image 9
Comet Hale–Bopp
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.
Image 10
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.
Image 11
Iapetus
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.
Image 12
Iapetus
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.
Image 13
C/2011 W3 (Lovejoy)
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.
Image 14
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.
Image 15
Transit of Mercury
Photo: Mila Zinkova
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 16
Full moon
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.
Image 17
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.
Image 18
Moon
Photograph credit: Gregory H. Revera
The Moon is the only natural satellite of Earth and the fifth largest moon in the Solar System. Owing to its synchronous rotation around Earth, the Moon always shows essentially the same face: its near side, which is marked by dark volcanic maria, as well as the bright ancient crustal highlands and the prominent impact craters. However, variations in the Moon's orbital speed due to its orbital eccentricity cause a libration of several degrees of longitude; the alignment of the Moon's orbital plane causes a similar libration in latitude. The Moon was first reached in September 1959 by the Soviet Union's unmanned Luna 2, followed by the first successful soft landing by Luna 9 in 1966. The United States Apollo program achieved the only manned lunar missions to date, including Apollo 8 in 1968, the first manned orbital mission, as well as Apollo 11, the first of six manned landings between 1969 and 1972.

This picture shows the near side of the Moon close to its greatest northern ecliptic latitude, so the southern craters are especially prominent. Tranquility Base, Apollo 11's landing site, is located near the mid-right in the photograph.
Image 19
Apollo 8
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.
Image 20
Io
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.
Image 21
Cassini–Huygens
Photograph credit: NASA / JPL / Space Science Institute
The Cassini–Huygens space-research project involved a collaboration between NASA, the European Space Agency, and the Italian Space Agency to send a probe to study the planet Saturn and its system, including its rings and its natural satellites.

This natural-color mosaic image, combining thirty photographs, was taken by the Cassini orbiter over the course of approximately two hours on 23 July 2008 as it panned its wide-angle camera across Saturn and its ring system as the planet approached equinox. Six moons are pictured in the panorama, with the largest, Titan, visible at the bottom left.
Image 22
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.
Image 23
Tranquility Base
Photograph credit: Neil Armstrong
Tranquility 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.

General images
The following are images from various Solar System-related articles on Wikipedia.

Image 1Pierre-Simon Laplace, one of the originators of the nebular hypothesis (from Formation and evolution of the Solar System)
Image 2Location of the Solar System within the Milky Way (from Formation and evolution of the Solar System)
Image 3An artist's impression of the Oort cloud, a region still well within the sphere of influence of the Solar System, including a depiction of the much further inside Kuiper belt (inset); the sizes of objects are over-scaled for visibility. (from Solar System)
Image 4Orbit classification of Kuiper belt objects. Some clusters that is subjected to orbital resonance are marked. (from Solar System)
Image 5The Sun in true white color (from Solar System)
Image 6A color enhanced photopgraph from the Moon of a range of components of the Solar System. The three dots at the lower left are from left to right the planets Saturn, Mars, and Mercury, and in the middle of the picture rises the Sun's corona over the dark limb of the Moon, which is from the right lit by earthshine. (from Solar System)
Image 7Solar system diagram by Emanuel Bowen in 1747, when neither Uranus, Neptune, nor the asteroid belts had yet been discovered. Orbits of planets are to scale, but the orbits of moons and the sizes of bodies are not. (from Solar System)
Image 8Diagram of the Sun's magnetosphere and helioshealth (from Solar System)
Image 9Animations of the Solar System's outer planets orbiting. This animation is 100 times faster than the inner planet animation. (from Solar System)
Image 10Diagram of the Milky Way, with galactic features and the relative position of the Solar System labeled. (from Solar System)
Image 11The motion of 'lights' moving across the sky is the basis of the classical definition of planets: wandering stars. (from Solar System)
Image 12Hubble image of protoplanetary discs in the Orion Nebula, a stellar nursery approximately 25 ly across and estimated to be similar to the primordial nebula from which the Sun formed (from Formation and evolution of the Solar System)
Image 13The sparse plasma (blue) and dust (white) in the tail of comet Hale–Bopp are being shaped by pressure from solar radiation and the solar wind, respectively.
Image 14Comparison of the distances between planets, with the white bar showing orbital variations. The size of the planets is not to scale. (from Solar System)
Image 15The current orbits of Sedna, 2012 VP113, Leleākūhonua (pink), and other very distant objects (red, brown and cyan) along with the predicted orbit of the hypothetical Planet Nine (dark blue) (from Solar System)
Image 16Relative 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)
Image 17Plot of objects around the Kuiper belt and other asteroid populations. J, S, U and N denotes Jupiter, Saturn, Uranus and Neptune. (from Solar System)
Image 18Artist's conception of a protoplanetary disk (from Formation and evolution of the Solar System)
Image 19Simulation 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)
Image 20The four terrestrial planets Mercury, Venus, Earth and Mars (from Solar System)
Image 21The outer planets Jupiter, Saturn, Uranus and Neptune, compared to the inner planets Earth, Venus, Mars, and Mercury at the bottom right (from Solar System)
Image 22The four largest asteroids: Ceres, Vesta, Pallas, Hygiea. Only Ceres and Vesta have been visited by a spacecraft and thus have a detailed picture. (from Solar System)
Image 23Animations of the Solar System's inner planets orbiting. Each frame represents 2 days of motion. (from Solar System)
Image 24Diagram of the early Solar System's protoplanetary disk, out of which Earth and other Solar System bodies formed (from Solar System)
Image 25The planets, zodiacal light and meteor shower (top left of image) (from Solar System)
Image 26The Solar System (left) within the interstellar medium, with the different regions and their distances on a logarithmic scale (from Solar System)
Image 27Diagram of the Local Interstellar Cloud, the G-Cloud and surrounding stars. As of 2022, the exact position of the Solar System within the interstellar clouds remains an unresolved question in astronomy. (from Solar System)
Image 28The Ring Nebula, a planetary nebula similar to what the Sun will become (from Formation and evolution of the Solar System)
Image 29Overview of the inner Solar System up to Jupiter's orbit (from Solar System)
Image 30Relative orbital distances in the Solar System visualized as a condensed rectangle (from Solar System)
Image 31The orbital eccentricities and inclinations of the scattered disc population compared to the classical and resonant Kuiper belt objects (from Solar System)
Image 32Meteor 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)
Image 33Artist's conception of the giant impact thought to have formed the Moon (from Formation and evolution of the Solar System)
Image 34Neptune 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)
Image 35The current Sun compared to its peak size in the red-giant phase (from Solar System)

Did you know –

...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?

...that the Battle of Szkłów in 1654 occurred during a solar eclipse?

...that NASA engineer Harvey Allen's "Blunt Body Theory" made possible the design of heat shields that protected the Mercury, Gemini and Apollo astronauts?

...that the Explorer 32 satellite was able to determine the density of the upper atmosphere through ground-based observations of the effect of drag on the satellite?

...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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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) · Geology · Atmosphere · Exploration (New Horizons)

Haumea: Moons (Hi'iaka, Namaka) · Ring

Quaoar: Weywot · Rings

Makemake: S/2015 (136472) 1

Gonggong: Xiangliu

Eris: Dysnomia

Sedna

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

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