Solar System

Solar System
A true-color image of the Solar System with sizes, but not distances, to scale. The order of the planets are from right to left.
The Sun, planets, and dwarf planets[a]
(distances not to scale)
Age4.568 billion years
System mass1.0014 Solar masses
Nearest star
Nearest known planetary system
Proxima Centauri system (4.25 ly)
Planetary system
Semi-major axis of outer known planet(Neptune)
30.10 AU
(4.5 bill. km; 2.8 bill. mi)
Distance to Kuiper cliff50 AU
Stars1 (Sun)
Known planets
Known dwarf planets
Known natural satellites
Known minor planets1,199,224[b][2]
Known comets4,402[b][2]
Identified rounded satellites19
Orbit about Galactic Center
Invariable-to-galactic plane inclination60.19° (ecliptic)
Distance to Galactic Center27,000 ± 1,000 ly
Orbital speed220 km/s; 136 mi/s
Orbital period225–250 myr
Star-related properties
Spectral typeG2V
Frost line≈5 AU[3]
Distance to heliopause≈120 AU
Hill sphere radius≈1–3 ly

The Solar System[c] is the gravitationally bound system of the Sun and the objects that orbit it. Of the bodies that orbit the Sun directly, the largest are the four gas and ice giants and the four terrestrial planets, followed by an unknown number of dwarf planets and innumerable small Solar System bodies. Of the bodies that orbit the Sun indirectly—the natural satellites—two are larger than Mercury, the smallest terrestrial planet, and one is nearly as large.[d]

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 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 more massive than the terrestrials. The two largest planets, 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 substances with relatively high melting points compared with hydrogen and helium, called volatiles, such as water, ammonia and methane. All eight have nearly circular orbits that lie close to the plane of the Earth's orbit, called the ecliptic.

The Solar System also contains smaller objects.[e] 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 the Moon. 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.

Beyond them lies a class of minor planets called detached objects. Within these populations, some objects are large enough to have rounded under their own gravity and thus to be planets under some definitions, though there is considerable debate as to how many such objects there will prove to be.[9] Such objects are 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, the scattered-disk objects Gonggong and Eris, and Sedna.[e] 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 4.25 light-years.

Structure and composition


Animations of the Solar System's inner planets and outer planets orbiting; the latter animation is 100 times faster than the former. Jupiter is three times as far from the Sun as Mars.

Most large objects in orbit around the Sun lie near the plane of Earth's orbit, known as the ecliptic. The planets are very close to the ecliptic, whereas comets and Kuiper belt objects are frequently at significantly greater angles to it.[10][11] Most of the planets in the Solar System have secondary systems of their own, being orbited by planetary objects called natural satellites, or moons (two of which, Titan and Ganymede, are larger than the planet Mercury). The four giant planets have planetary rings, thin bands of tiny particles that orbit them in unison. Most of the largest natural satellites are in synchronous rotation, with one face permanently turned toward their parent.[12]

As a result of the formation of the Solar System, planets (and most other objects) orbit the Sun in the same direction that the Sun is rotating (counter-clockwise, as viewed from above Earth's north pole).[13] There are exceptions, such as Halley's Comet.[14] Most of the larger moons orbit their planets in prograde direction; Neptune's moon Triton is the largest to orbit in the opposite, retrograde manner.[15] Most larger objects rotate around their own axes in the prograde direction, though the rotation of Venus is retrograde.[16]

To a good first approximation, Kepler's laws of planetary motion describe the orbits of objects about the Sun.[17]: 433–437  Kepler's first law states that each object travels along an ellipse with the Sun at one focus. On an elliptical orbit, a body's distance from the Sun varies over the course of its year. A body's closest approach to the Sun is called its perihelion, whereas its most distant point from the Sun is called its aphelion.[18]: 9-6 

The orbits of the planets are nearly circular, but many comets, asteroids, and Kuiper belt objects follow highly elliptical orbits. Kepler's second law states that the angular momentum of an object remains constant as it orbits the Sun, meaning that an object will speed up as it approaches the Sun and slow down as it moves farther away, in a quantitatively predictable manner. Kepler's third law states that for an object in an elliptical orbit, the time it takes to go around in that orbit is proportional to the three-halves power of the orbit's semi-major axis. Kepler's laws only account for the influence of the Sun's gravity upon an orbiting body, not the gravitational pulls of different bodies upon each other. These additional perturbations can be accounted for using numerical models.[18]: 9-6 

Although the Sun dominates the system by mass, it accounts for only about 2% of the angular momentum.[19][20] The planets, dominated by Jupiter, account for most of the rest of the angular momentum due to the combination of their mass, orbit, and distance from the Sun, with a possibly significant contribution from comets.[19]


The overall structure of the charted regions of the Solar System consists of the Sun, four relatively small inner planets surrounded by a belt of mostly rocky asteroids, and four giant planets surrounded by the Kuiper belt of mostly icy objects. Astronomers sometimes informally divide this structure into separate regions. The inner Solar System includes the four terrestrial planets and the asteroid belt. The outer Solar System is beyond the asteroids, including the four giant planets.[21] Since the discovery of the Kuiper belt, the outermost parts of the Solar System are considered a distinct region consisting of the objects beyond Neptune.[22]

The principal component of the Solar System is the Sun, a G2 main-sequence star that contains 99.86% of the system's known mass and dominates it gravitationally.[23] The Sun's four largest orbiting bodies, the giant planets, account for 99% of the remaining mass, with Jupiter and Saturn together comprising more than 90%. The remaining objects of the Solar System (including the four terrestrial planets, the dwarf planets, moons, asteroids, and comets) together comprise less than 0.002% of the Solar System's total mass.[f]

The Sun is composed of roughly 98% hydrogen and helium,[27] as are Jupiter and Saturn.[28][29] A composition gradient exists in the Solar System, created by heat and light pressure from the Sun; those objects closer to the Sun, which are more affected by heat and light pressure, are composed of elements with high melting points. Objects farther from the Sun are composed largely of materials with lower melting points.[30] The boundary in the Solar System beyond which those volatile substances could condense is known as the frost line, and it lies at roughly five times the Earth's distance from the Sun.[3]

The objects of the inner Solar System are composed mostly of rock,[31] the collective name for compounds with high melting points, such as silicates, iron or nickel, that remained solid under almost all conditions in the protoplanetary nebula.[32] Jupiter and Saturn are composed mainly of gases, the astronomical term for materials with extremely low melting points and high vapour pressure, such as hydrogen, helium, and neon, which were always in the gaseous phase in the nebula.[32] Ices, like water, methane, ammonia, hydrogen sulfide, and carbon dioxide,[31] have melting points up to a few hundred kelvins.[32] They can be found as ices, liquids, or gases in various places in the Solar System, whereas in the nebula they were either in the solid or gaseous phase.[32] Icy substances comprise the majority of the satellites of the giant planets, as well as most of Uranus and Neptune (the so-called "ice giants") and the numerous small objects that lie beyond Neptune's orbit.[31][33] Together, gases and ices are referred to as volatiles.[34]

Distances and scales

The astronomical unit [AU] (150,000,000 km; 93,000,000 mi) would be the distance from the Earth to the Sun if the planet's orbit were perfectly circular.[35] For comparison, the radius of the Sun is 0.0047 AU (700,000 km; 400,000 mi).[36] Thus, the Sun occupies 0.00001% (10−5 %) of the volume of a sphere with a radius the size of Earth's orbit, whereas Earth's volume is roughly one millionth (10−6) that of the Sun. Jupiter, the largest planet, is 5.2 astronomical units (780,000,000 km; 480,000,000 mi) from the Sun and has a radius of 71,000 km (0.00047 AU; 44,000 mi), whereas the most distant planet, Neptune, is 30 AU (4.5×109 km; 2.8×109 mi) from the Sun.[29][37]

With a few exceptions, the farther a planet or belt is from the Sun, the larger the distance between its orbit and the orbit of the next nearer object to the Sun. For example, Venus is approximately 0.33 AU farther out from the Sun than Mercury, whereas Saturn is 4.3 AU out from Jupiter, and Neptune lies 10.5 AU out from Uranus. Attempts have been made to determine a relationship between these orbital distances, like the Titius–Bode law[38] and Johannes Kepler's model based on the Platonic solids,[39] but ongoing discoveries have invalidated these hypotheses.[40]

Some Solar System models attempt to convey the relative scales involved in the Solar System on human terms. Some are small in scale (and may be mechanical—called orreries)—whereas others extend across cities or regional areas.[41] The largest such scale model, the Sweden Solar System, uses the 110-metre (361 ft) Ericsson Globe in Stockholm as its substitute Sun, and, following the scale, Jupiter is a 7.5-metre (25-foot) sphere at Stockholm Arlanda Airport, 40 km (25 mi) away, whereas the farthest current object, Sedna, is a 10 cm (4 in) sphere in Luleå, 912 km (567 mi) away.[42][43]

If the Sun–Neptune distance is scaled to 100 metres (330 ft), then the Sun would be about 3 cm (1.2 in) in diameter (roughly two-thirds the diameter of a golf ball), the giant planets would be all smaller than about 3 mm (0.12 in), and Earth's diameter along with that of the other terrestrial planets would be smaller than a flea (0.3 mm or 0.012 in) at this scale.[44]

Logarithmic depiction of the Solar System's location
The Sun's, planets', dwarf planets' and moons' size to scale

Formation and evolution

See caption
Photo of a planetary disk, the inner ring has a radius equal to the distance of Earth from the Sun

The Solar System formed 4.568 billion years ago from the gravitational collapse of a region within a large molecular cloud.[g] This initial cloud was likely several light-years across and probably birthed several stars.[46] As is typical of molecular clouds, this one consisted mostly of hydrogen, with some helium, and small amounts of heavier elements fused by previous generations of stars. As the region that would become the Solar System, known as the pre-solar nebula,[47] collapsed, conservation of angular momentum caused it to rotate faster. The centre, where most of the mass collected, became increasingly hotter than the surrounding disc.[46] As the contracting nebula rotated faster, it began to flatten into a protoplanetary disc with a diameter of roughly 200 AU (30 billion km; 19 billion mi)[46] and a hot, dense protostar at the centre.[48][49] The planets formed by accretion from this disc,[50] in which dust and gas gravitationally attracted each other, coalescing to form ever larger bodies. Hundreds of protoplanets may have existed in the early Solar System, but they either merged or were destroyed or ejected, leaving the planets, dwarf planets, and leftover minor bodies.[51][52]

Due to their higher boiling points, only metals and silicates could exist in solid form in the warm inner Solar System close to the Sun, and these would eventually form the rocky planets of Mercury, Venus, Earth, and Mars. Because metallic elements only comprised a very small fraction of the solar nebula, the terrestrial planets could not grow very large. The giant planets (Jupiter, Saturn, Uranus, and Neptune) formed further out, beyond the frost line, the point between the orbits of Mars and Jupiter where material is cool enough for volatile icy compounds to remain solid. The ices that formed these planets were more plentiful than the metals and silicates that formed the terrestrial inner planets, allowing them to grow massive enough to capture large atmospheres of hydrogen and helium, the lightest and most abundant elements. Leftover debris that never became planets congregated in regions such as the asteroid belt, Kuiper belt, and Oort cloud.[51] The Nice model is an explanation for the creation of these regions and how the outer planets could have formed in different positions and migrated to their current orbits through various gravitational interactions.[53]

Colorful shell which has an almost eye like appearance. The center shows the small central star with a blue circular area that could represent the iris. This is surrounded by an iris like area of concentric orange bands. This is surrounded by an eyelid shaped red area before the edge where plain space is shown. Background stars dot the whole image.
The Helix Nebula, a planetary nebula similar to what the Sun will create when it enters its white dwarf stage.

Within 50 million years, the pressure and density of hydrogen in the centre of the protostar became great enough for it to begin thermonuclear fusion.[54] The temperature, reaction rate, pressure, and density increased until hydrostatic equilibrium was achieved: the thermal pressure counterbalancing the force of gravity. At this point, the Sun became a main-sequence star.[55] The main-sequence phase, from beginning to end, will last about 10 billion years for the Sun compared to around two billion years for all other phases of the Sun's pre-remnant life combined.[56] Solar wind from the Sun created the heliosphere and swept away the remaining gas and dust from the protoplanetary disc into interstellar space. As helium accumulates at its core the Sun is growing brighter;[57] early in its main-sequence life its brightness was 70% that of what it is today.[58]

The Solar System will remain roughly as it is known today until the hydrogen in the core of the Sun has been entirely converted to helium, which will occur roughly 5 billion years from now. This will mark the end of the Sun's main-sequence life. At that time, the core of the Sun will contract with hydrogen fusion occurring along a shell surrounding the inert helium, and the energy output will be greater than at present. The outer layers of the Sun will expand to roughly 260 times its current diameter, and the Sun will become a red giant. Because of its increased surface area, the surface of the Sun will be cooler (2,600 K (2,330 °C; 4,220 °F) at its coolest) than it is on the main sequence.[56]

The expanding Sun is expected to vaporize Mercury and render Earth uninhabitable. Eventually, the core will be hot enough for helium fusion; the Sun will burn helium for a fraction of the time it burned hydrogen in the core. The Sun is not massive enough to commence the fusion of heavier elements, and nuclear reactions in the core will dwindle. Its outer layers will be ejected into space, leaving behind a dense white dwarf, half the original mass of the Sun but only the size of Earth.[59] The ejected outer layers will form what is known as a planetary nebula, returning some of the material that formed the Sun—but now enriched with heavier elements like carbon—to the interstellar medium.[60]


The Sun is the Solar System's star and by far its most massive component. Its large mass (332,900 Earth masses),[61] which comprises 99.86% of all the mass in the Solar System,[62] produces temperatures and densities in its core high enough to sustain nuclear fusion of hydrogen into helium.[63] This releases an enormous amount of energy, mostly radiated into space as electromagnetic radiation peaking in visible light.[64][65]

Because the Sun fuses hydrogen into helium, it is a main-sequence star. More specifically, it is a G2-type main-sequence star, where the type designation refers to its effective temperature. Hotter main-sequence stars are more luminous. The Sun's temperature is intermediate between that of the hottest stars and that of the coolest stars. Stars brighter and hotter than the Sun are rare, whereas substantially dimmer and cooler stars, known as red dwarfs, make up about 75% of the stars in the Milky Way.[66][67]

The Sun is a population I star; it has a higher abundance of elements heavier than hydrogen and helium ("metals" in astronomical parlance) than the older population II stars.[68] Elements heavier than hydrogen and helium were formed in the cores of ancient and exploding stars, so the first generation of stars had to die before the universe could be enriched with these atoms. The oldest stars contain few metals, whereas stars born later have more. This high metallicity is thought to have been crucial to the Sun's development of a planetary system because the planets form from the accretion of "metals".[69]

Interplanetary medium

The vast majority of the Solar System consists of a near-vacuum known as the interplanetary medium. Along with light, the Sun radiates a continuous stream of charged particles (a plasma) known as the solar wind. This stream of particles spreads outwards at speeds from 900,000 kilometres per hour (560,000 mph) to 2,880,000 kilometres per hour (1,790,000 mph),[70] creating a tenuous atmosphere that permeates the interplanetary medium out to at least 100 AU (15 billion km; 9.3 billion mi) (see § Heliosphere).[71] Activity on the Sun's surface, such as solar flares and coronal mass ejections, disturbs the heliosphere, creating space weather and causing geomagnetic storms.[72] The largest structure within the heliosphere is the heliospheric current sheet, a spiral form created by the actions of the Sun's rotating magnetic field on the interplanetary medium.[73][74]

Earth's magnetic field stops its atmosphere from being stripped away by the solar wind.[75] Venus and Mars do not have magnetic fields, and as a result the solar wind is causing their atmospheres to gradually bleed away into space.[76] Coronal mass ejections and similar events blow a magnetic field and huge quantities of material from the surface of the Sun. The interaction of this magnetic field and material with Earth's magnetic field funnels charged particles into Earth's upper atmosphere, where its interactions create aurorae seen near the magnetic poles.[77]

The heliosphere and planetary magnetic fields (for those planets that have them) partially shield the Solar System from high-energy interstellar particles called cosmic rays. The density of cosmic rays in the interstellar medium and the strength of the Sun's magnetic field change on very long timescales, so the level of cosmic-ray penetration in the Solar System varies, though by how much is unknown.[78]

The interplanetary medium is home to at least two disc-like regions of cosmic dust. The first, the zodiacal dust cloud, lies in the inner Solar System and causes the zodiacal light. It may have been formed by collisions within the asteroid belt brought on by gravitational interactions with the planets; a more recent proposed origin is the planet Mars.[79] The second dust cloud extends from about 10 AU (1.5 billion km; 930 million mi) to about 40 AU (6.0 billion km; 3.7 billion mi), and was probably created by collisions within the Kuiper belt.[80][81]

Inner Solar System

Overview of the Inner Solar System up to the Jovian System.

The inner Solar System is the region comprising the terrestrial planets and the asteroid belt.[82] Composed mainly of silicates and metals,[83] the objects of the inner Solar System are relatively close to the Sun; the radius of this entire region is less than the distance between the orbits of Jupiter and Saturn. This region is also within the frost line, which is a little less than 5 AU (750 million km; 460 million mi) from the Sun.[10]

Inner planets

The terrestrial planets of the Solar System: Mercury, Venus, Earth and Mars, sized to scale

The four terrestrial or inner planets have dense, rocky compositions, few or no moons, and no ring systems. They are composed largely of refractory minerals such as the silicates—which form their crusts and mantles—and metals such as iron and nickel which form their cores. Three of the four inner planets (Venus, Earth and Mars) have atmospheres substantial enough to generate weather; all have impact craters and tectonic surface features, such as rift valleys and volcanoes. The term inner planet should not be confused with inferior planet, which designates those planets that are closer to the Sun than Earth is (i.e. Mercury and Venus).[84]


Mercury (0.4 AU (60 million km; 37 million mi) from the Sun) is the closest planet to the Sun. The smallest planet in the Solar System (0.055 MEarth), Mercury has no natural satellites. The dominant geological features are impact craters or basins with ejecta blankets, the remains of early volcanic activity including magma flows, and lobed ridges or rupes that were probably produced by a period of contraction early in the planet's history.[85] Mercury's very tenuous atmosphere consists of solar-wind particles trapped by Mercury's magnetic field, as well as atoms blasted off its surface by the solar wind.[86][87] Its relatively large iron core and thin mantle have not yet been adequately explained. Hypotheses include that its outer layers were stripped off by a giant impact, or that it was prevented from fully accreting by the young Sun's energy.[88][89]

There have been searches for "Vulcanoids", asteroids in stable orbits between Mercury and the Sun, but none have been discovered.[90][91]


Venus (0.7 AU (100 million km; 65 million mi) from the Sun) is close in size to Earth (0.815 MEarth) and, like Earth, has a thick silicate mantle around an iron core, a substantial atmosphere, and evidence of internal geological activity. It is much drier than Earth, and its atmosphere is ninety times as dense. Venus has no natural satellites. It is the hottest planet, with surface temperatures over 400 °C (752 °F), mainly due to the amount of greenhouse gases in the atmosphere.[92] The planet has no magnetic field that would prevent depletion of its substantial atmosphere, which suggests that its atmosphere is being replenished by volcanic eruptions.[93] A relatively young planetary surface displays extensive evidence of volcanic activity, but is devoid of plate tectonics. It may undergo resurfacing episodes on a time scale of 700 million years.[94]


Earth (1 AU (150 million km; 93 million mi) from the Sun) is the largest and densest of the inner planets, the only one known to have current geological activity, and the only place where life is known to exist.[95] Its liquid hydrosphere is unique among the terrestrial planets, and it is the only planet where plate tectonics has been observed. Earth's atmosphere is radically different from those of the other planets, having been altered by the presence of life to contain 21% free oxygen.[96][97] The planetary magnetosphere shields the surface from solar and cosmic radiation, limiting atmospheric stripping and maintaining habitability.[98] It has one natural satellite, the Moon, the only large satellite of a terrestrial planet in the Solar System.


Mars (1.5 AU (220 million km; 140 million mi) from the Sun) is smaller than Earth and Venus (0.107 MEarth). It has an atmosphere of mostly carbon dioxide with a surface pressure of 6.1 millibars (0.088 psi; 0.18 inHg); roughly 0.6% of that of Earth but sufficient to support weather phenomena.[99] Its surface, peppered with volcanoes, such as Olympus Mons, and rift valleys, such as Valles Marineris, shows geological activity that may have persisted until as recently as 2 million years ago.[100] Its red colour comes from iron oxide (rust) in its soil.[101] Mars has two tiny natural satellites (Deimos and Phobos) thought to be either captured asteroids,[102] or ejected debris from a massive impact early in Mars's history.[103]

Asteroid belt

Linear map of the Inner Solar System, showing many asteroid populations

Asteroids except for the largest, Ceres, are classified as small Solar System bodies[e] and are composed mainly of refractory rocky and metallic minerals, with some ice.[104][105] They range from a few metres to hundreds of kilometres in size. Asteroids smaller than one meter are usually called meteoroids and micrometeoroids (grain-sized), with the exact division between the two categories being debated over the years.[106] As of 2017, the IAU designates asteroids having diameter between about 30 micrometres and 1 metre as micrometeroids, and terms smaller particles "dust".[107]

The asteroid belt occupies the orbit between Mars and Jupiter, between 2.3 and 3.3 AU (340 and 490 million km; 210 and 310 million mi) from the Sun. It is thought to be remnants from the Solar System's formation that failed to coalesce because of the gravitational interference of Jupiter.[108] The asteroid belt contains tens of thousands, possibly millions, of objects over one kilometre in diameter.[109] Despite this, the total mass of the asteroid belt is unlikely to be more than a thousandth of that of Earth.[26] The asteroid belt is very sparsely populated; spacecraft routinely pass through without incident.[110]


Ceres (2.77 AU (414 million km; 257 million mi) from the Sun) is the largest asteroid, a protoplanet, and a dwarf planet.[e] It has a diameter of slightly under 1,000 km (620 mi), and a mass large enough for its own gravity to pull it into a spherical shape. Ceres was considered a planet when it was discovered in 1801, but as further observations revealed additional asteroids, it became common to consider it as one of the minor rather than major planets.[111] It was then reclassified again as a dwarf planet in 2006 when the IAU definition of planet was established.[112]: 218 

Pallas and Vesta

Pallas (2.77 AU from the Sun) and Vesta (2.36 AU from the Sun) are the largest asteroids in the asteroid belt, after Ceres. They are the other two protoplanets that survive more or less intact. At about 520 km (320 mi) in diameter, they were large enough to have developed planetary geology in the past, but both have suffered large impacts and been battered out of being round.[113][114][115] Fragments from impacts upon these two bodies survive elsewhere in the asteroid belt, as the Pallas family and Vesta family. Both were considered planets upon their discoveries in 1802 and 1807 respectively, and then like Ceres generally considered as minor planets with the discovery of more asteroids. Some authors today have begun to consider Pallas and Vesta as planets again, along with Ceres, under geophysical definitions of the term.[5]

Asteroid groups

Asteroids in the asteroid belt are divided into asteroid groups and families based on their orbital characteristics. Kirkwood gaps are sharp dips in the distribution of asteroid orbits that correspond to orbital resonances with Jupiter.[116] Asteroid moons are asteroids that orbit larger asteroids. They are not as clearly distinguished as planetary moons, sometimes being almost as large as their partners (e.g. that of 90 Antiope). The asteroid belt includes main-belt comets, which may have been the source of Earth's water.[117]

Jupiter trojans are located in either of Jupiter's L4 or L5 points (gravitationally stable regions leading and trailing a planet in its orbit); the term trojan is also used for small bodies in any other planetary or satellite Lagrange point. Hilda asteroids are in a 2:3 resonance with Jupiter; that is, they go around the Sun three times for every two Jupiter orbits.[118] The inner Solar System contains near-Earth asteroids, many of which cross the orbits of the inner planets.[119] Some of them are potentially hazardous objects.[120]

Outer 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

The outer region of the Solar System is home to the giant planets and their large moons. The centaurs and many short-period comets also orbit in this region. Due to their greater distance from the Sun, the solid objects in the outer Solar System contain a higher proportion of volatiles, such as water, ammonia, and methane than those of the inner Solar System because the lower temperatures allow these compounds to remain solid.[51]

Outer planets

The outer planets Jupiter, Saturn, Uranus and Neptune, compared to the inner planets Earth, Venus, Mars and Mercury at the bottom right

The four outer planets, also called giant planets or Jovian planets, collectively make up 99% of the mass known to orbit the Sun.[f] Jupiter and Saturn are together more than 400 times the mass of Earth and consist overwhelmingly of the gases hydrogen and helium, hence their designation as gas giants.[121] Uranus and Neptune are far less massive—less than 20 Earth masses (MEarth) each—and are composed primarily of ices. For these reasons, some astronomers suggest they belong in their own category, ice giants.[122] All four giant planets have rings, although only Saturn's ring system is easily observed from Earth. The term superior planet designates planets outside Earth's orbit and thus includes both the outer planets and Mars.[84]

The ring–moon systems of Jupiter, Saturn, and Uranus are like miniature versions of the Solar System; that of Neptune is significantly different, having been disrupted by the capture of its largest moon Triton.[123]


Jupiter (5.2 AU (780 million km; 480 million mi) from the Sun), at 318 MEarth, is 2.5 times the mass of all the other planets put together. It is composed largely of hydrogen and helium. Jupiter's strong internal heat creates semi-permanent features in its atmosphere, such as cloud bands and the Great Red Spot. The planet possesses a 4.2–14 Gauss strength magnetosphere that spans 22–29 million km, making it, in certain respects, the largest object in the Solar System.[124] Jupiter has 80 known satellites. The four largest, Ganymede, Callisto, Io, and Europa, are called the Galilean moons: they show similarities to the terrestrial planets, such as volcanism and internal heating.[125] Ganymede, the largest satellite in the Solar System, is larger than Mercury; Callisto is almost as large.


Saturn (9.5 AU (1.42 billion km; 880 million mi) from the Sun), distinguished by its extensive ring system, has several similarities to Jupiter, such as its atmospheric composition and magnetosphere. Although Saturn has 60% of Jupiter's volume, it is less than a third as massive, at 95 MEarth. Saturn is the only planet of the Solar System that is less dense than water. The rings of Saturn are made up of small ice and rock particles.[126] Saturn has 83 confirmed satellites composed largely of ice. Two of these, Titan and Enceladus, show signs of geological activity;[127] they, as well as five other Saturnian moons (Iapetus, Rhea, Dione, Tethys, and Mimas), are large enough to be round. Titan, the second-largest moon in the Solar System, is bigger than Mercury and the only satellite in the Solar System to have a substantial atmosphere.[128][129]


Uranus (19.2 AU (2.87 billion km; 1.78 billion mi) from the Sun), at 14 MEarth, has the lowest mass of the outer planets. Uniquely among the planets, it orbits the Sun on its side; its axial tilt is over ninety degrees to the ecliptic. This gives the planet extreme seasonal variation as each pole points toward and then away from the Sun.[130] It has a much colder core than the other giant planets and radiates very little heat into space.[131] As a consequence, it has the coldest planetary atmosphere in the Solar System.[132] Uranus has 27 known satellites, the largest ones being Titania, Oberon, Umbriel, Ariel, and Miranda.[133] Like the other giant planets, it also possesses a ring system and magnetosphere.


Neptune (30.1 AU (4.50 billion km; 2.80 billion mi) from the Sun), though slightly smaller than Uranus, is more massive (17 MEarth) and hence more dense. It radiates more internal heat than Uranus, but not as much as Jupiter or Saturn.[134] Neptune has 14 known satellites. The largest, Triton, is geologically active, with geysers of liquid nitrogen.[135] Triton is the only large satellite with a retrograde orbit, which indicates that it did not form with Neptune, but was probably captured from the Kuiper belt.[136] Neptune is accompanied in its orbit by several minor planets, termed Neptune trojans, that either lead or trail the planet by about one-sixth of the way around the Sun, positions known as Lagrange points.[137]


The centaurs are icy comet-like bodies whose orbits have semi-major axes greater than Jupiter's (5.5 AU (820 million km; 510 million mi)) and less than Neptune's (30 AU (4.5 billion km; 2.8 billion mi)). The largest known centaur, 10199 Chariklo, has a diameter of about 250 km (160 mi).[138] The first centaur discovered, 2060 Chiron, has also been classified as a comet (95P) because it develops a coma just as comets do when they approach the Sun.[139]


Comet Hale–Bopp seen in 1997

Comets are small Solar System bodies,[e] typically only a few kilometres across, composed largely of volatile ices. They have highly eccentric orbits, generally a perihelion within the orbits of the inner planets and an aphelion far beyond Pluto. When a comet enters the inner Solar System, its proximity to the Sun causes its icy surface to sublimate and ionise, creating a coma: a long tail of gas and dust often visible to the naked eye.[140]

Short-period comets have orbits lasting less than two hundred years. Long-period comets have orbits lasting thousands of years. Short-period comets are thought to originate in the Kuiper belt, whereas long-period comets, such as Hale–Bopp, are thought to originate in the Oort cloud. Many comet groups, such as the Kreutz sungrazers, formed from the breakup of a single parent.[141] Some comets with hyperbolic orbits may originate outside the Solar System, but determining their precise orbits is difficult.[142] Old comets whose volatiles have mostly been driven out by solar warming are often categorised as asteroids.[143]

Trans-Neptunian region

Distribution and size of trans-Neptunian objects
Size comparison of some large TNOs with Earth: Pluto and its moons, Eris, Makemake, Haumea, Sedna, Gonggong, Quaoar, Orcus, Salacia, and 2002 MS4.

Inside the orbit of Neptune is the planetary region of the Solar System. Beyond the orbit of Neptune lies the area of the "trans-Neptunian region", with the doughnut-shaped Kuiper belt, home of Pluto and several other dwarf planets, and an overlapping disc of scattered objects, which is tilted toward the plane of the Solar System and reaches much further out than the Kuiper belt. The entire region is still largely unexplored. It appears to consist overwhelmingly of many thousands of small worlds—the largest having a diameter only a fifth that of Earth and a mass far smaller than that of the Moon—composed mainly of rock and ice. This region is sometimes described as the "third zone of the Solar System", enclosing the inner and the outer Solar System.[144]

Kuiper belt

The Kuiper belt is a great ring of debris similar to the asteroid belt, but consisting mainly of objects composed primarily of ice.[145] It extends between 30 and 50 AU (4.5 and 7.5 billion km; 2.8 and 4.6 billion mi) from the Sun. It is composed mainly of small Solar System bodies, although the largest few are probably large enough to be dwarf planets.[9] There are estimated to be over 100,000 Kuiper belt objects with a diameter greater than 50 km (30 mi), but the total mass of the Kuiper belt is thought to be only a tenth or even a hundredth the mass of Earth.[25] Many Kuiper belt objects have multiple satellites,[146] and most have orbits that take them outside the plane of the ecliptic.[147]

The Kuiper belt can be roughly divided into the "classical" belt and the resonant trans-Neptunian objects.[145] The latter have orbits whose periods are in a simple ratio to that of Neptune: for example, going around the Sun twice for every three times that Neptune does, or once for every two. The classical belt consists of objects having no resonance with Neptune, and extends from roughly 39.4 to 47.7 AU (5.89 to 7.14 billion km; 3.66 to 4.43 billion mi).[148] Members of the classical Kuiper belt are sometimes called "cubewanos", after the first of their kind to be discovered, originally designated 1992 QB1; they are still in near primordial, low-eccentricity orbits.[149]

Pluto and Charon

The dwarf planet Pluto (with an average orbit of 39 AU (5.8 billion km; 3.6 billion mi) from the Sun) is the largest known object in the Kuiper belt. When discovered in 1930, it was considered to be the ninth planet; this changed in 2006 with the adoption of a formal definition of planet. Pluto has a relatively eccentric orbit inclined 17 degrees to the ecliptic plane and ranging from 29.7 AU (4.44 billion km; 2.76 billion mi) from the Sun at perihelion (within the orbit of Neptune) to 49.5 AU (7.41 billion km; 4.60 billion mi) at aphelion. Pluto has a 2:3 resonance with Neptune, meaning that Pluto orbits twice round the Sun for every three Neptunian orbits. Kuiper belt objects whose orbits share this resonance are called plutinos.[150]

Charon, the largest of Pluto's moons, is sometimes described as part of a binary system with Pluto, as the two bodies orbit a barycentre of gravity above their surfaces (i.e. they appear to "orbit each other"). Beyond Charon, four much smaller moons, Styx, Nix, Kerberos, and Hydra, orbit within the system.[151]


Besides Pluto, astronomers generally agree that at least four other Kuiper belt objects are dwarf planets,[9] with additional bodies have also been proposed:[152]

  • Makemake (45.79 AU average from the Sun), although smaller than Pluto, is the largest known object in the classical Kuiper belt (that is, a Kuiper belt object not in a confirmed resonance with Neptune). Makemake is the brightest object in the Kuiper belt after Pluto. Discovered in 2005, it was officially named in 2009.[153] Its orbit is far more inclined than Pluto's, at 29°.[154] It has one known moon.[155]
  • Haumea (43.13 AU average from the Sun) is in an orbit similar to Makemake, except that it is in a temporary 7:12 orbital resonance with Neptune.[156] Like Makemake, it was discovered in 2005.[157] It has two known moons, Hiʻiaka and Namaka, and rotates so quickly (once every 3.9 hours) that it is stretched into an ellipsoid.[158]
  • Quaoar (43.69 AU average from the Sun) is the second-largest known object in the classical Kuiper belt, after Makemake. Its orbit is significantly less eccentric and inclined than those of Makemake or Haumea.[156] It has one known moon, Weywot.[159]
  • Orcus (39.40 AU average from the Sun) is in the same 2:3 orbital resonance with Neptune that Pluto is in, and is the largest such object after Pluto itself.[156] Its eccentricity and inclination are similar to Pluto's, but its perihelion lies about 120° from that of Pluto. Thus, the phase of Orcus's orbit is opposite to Pluto's: Orcus is at aphelion (most recently in 2019) around when Pluto is at perihelion (most recently in 1989) and vice versa.[160] For this reason, it has been called the anti-Pluto.[161][162] It has one known moon, Vanth.[163]

Scattered disc

The scattered disc object Sedna and its orbit within the Solar System.

The scattered disc, which overlaps the Kuiper belt but extends out to about 200 AU, is thought to be the source of short-period comets. Scattered-disc objects are thought to have been ejected into erratic orbits by the gravitational influence of Neptune's early outward migration. Most scattered disc objects (SDOs) have perihelia within the Kuiper belt but aphelia far beyond it (some more than 150 AU from the Sun). SDOs' orbits are also highly inclined to the ecliptic plane and are often almost perpendicular to it. Some astronomers consider the scattered disc to be merely another region of the Kuiper belt and describe scattered disc objects as "scattered Kuiper belt objects".[164] Some astronomers also classify centaurs as inward-scattered Kuiper belt objects along with the outward-scattered residents of the scattered disc.[165]

Eris and Gonggong

Eris (67.78 AU average from the Sun) is the largest known scattered disc object, and caused a debate about what constitutes a planet, because it is 25% more massive than Pluto[166] and about the same diameter. It is the most massive of the known dwarf planets. It has one known moon, Dysnomia. Like Pluto, its orbit is highly eccentric, with a perihelion of 38.2 AU (roughly Pluto's distance from the Sun) and an aphelion of 97.6 AU, and steeply inclined to the ecliptic plane.

Gonggong (67.38 AU average from the Sun) is in an orbit similar to Eris, except that it is in a 3:10 resonance with Neptune.[167] It has one known moon, Xiangliu.[168]

Farthest regions

The point at which the Solar System ends and interstellar space begins is not precisely defined because its outer boundaries are shaped by two forces, the solar wind and the Sun's gravity. The limit of the solar wind's influence is roughly four times Pluto's distance from the Sun; this heliopause, the outer boundary of the heliosphere, is considered the beginning of the interstellar medium.[71] The Sun's Hill sphere, the effective range of its gravitational dominance, is thought to extend up to a thousand times farther and encompasses the hypothetical Oort cloud.[169]


Artistic depiction of the Solar System's heliosphere

The heliosphere is a stellar-wind bubble, a region of space dominated by the Sun whose boundaries occur where the solar wind collides with the interstellar medium.[170] This collision occurs at the termination shock, which is roughly 80–100 AU from the Sun upwind of the interstellar medium and roughly 200 AU from the Sun downwind.[171] Here the wind slows dramatically, condenses and becomes more turbulent,[171] forming a great oval structure known as the heliosheath. This structure has been theorized to look and behave very much like a comet's tail, extending outward for a further 40 AU on the upwind side but tailing many times that distance downwind.[172] Evidence from the Cassini and Interstellar Boundary Explorer spacecraft has suggested that it is forced into a bubble shape by the constraining action of the interstellar magnetic field,[173][174] but the actual shape remains unknown.[175]

The outer boundary of the heliosphere, the heliopause, is the point at which the solar wind finally terminates and is the beginning of interstellar space.[71] Voyager 1 and Voyager 2 passed the termination shock and entered the heliosheath at 94 and 84 AU from the Sun, respectively.[176][177] Voyager 1 was reported to have crossed the heliopause in August 2012, and Voyager 2 in December 2018.[178][179]

The shape and form of the outer edge of the heliosphere is likely affected by the fluid dynamics of interactions with the interstellar medium as well as solar magnetic fields prevailing to the south, e.g. it is bluntly shaped with the northern hemisphere extending 9 AU farther than the southern hemisphere.[171] Beyond the heliopause, at around 230 AU, lies the bow shock, a plasma "wake" left by the Sun as it travels through the Milky Way.[180]

Detached objects

Sedna (with an average orbit of 520 AU from the Sun) is a large, reddish object with a gigantic, highly elliptical orbit that takes it from about 76 AU at perihelion to 940 AU at aphelion and takes 11,400 years to complete. Mike Brown, who discovered the object in 2003, asserts that it cannot be part of the scattered disc or the Kuiper belt because its perihelion is too distant to have been affected by Neptune's migration. He and other astronomers consider it to be the first in an entirely new population, sometimes termed "distant detached objects" (DDOs), which also may include the object 2000 CR105, which has a perihelion of 45 AU, an aphelion of 415 AU, and an orbital period of 3,420 years.[181] Brown terms this population the "inner Oort cloud" because it may have formed through a similar process, although it is far closer to the Sun.[182] Sedna is very likely a dwarf planet, though its shape has yet to be determined. The second unequivocally detached object, with a perihelion farther than Sedna's at roughly 81 AU, is 2012 VP113, discovered in 2012. Its aphelion is only about half that of Sedna's, at 458 AU.[183][184]

Oort cloud

Artist conception of the Oort cloud, with a disc-shaped inner cloud and a spherical outer cloud extending to about 100,000 AU or 1.5 ly, making the planetary system of about 100 AU too small to distinguish.

The Oort cloud is a hypothetical spherical cloud of up to a trillion icy objects that is thought to be the source for all long-period comets and to surround the Solar System at roughly 50,000 AU (around 1 light-year (ly)) from the Sun, and possibly to as far as 100,000 AU (1.87 ly). It is thought to be composed of comets that were ejected from the inner Solar System by gravitational interactions with the outer planets. Oort cloud objects move very slowly, and can be perturbed by infrequent events, such as collisions, the gravitational effects of a passing star, or the galactic tide, the tidal force exerted by the Milky Way.[185][186]


Much of the Solar System is still unknown. The Sun's gravitational field is estimated to dominate the gravitational forces of surrounding stars out to about two light-years (125,000 AU). Lower estimates for the radius of the Oort cloud, by contrast, do not place it farther than 50,000 AU.[187] Most of the mass is orbiting in the region between 3,000 and 100,000 AU.[188] Despite discoveries such as Sedna, the region between the Kuiper belt and the Oort cloud, an area tens of thousands of AU in radius, is still virtually unmapped. Learning about this region of space is difficult, because it depends upon inferences from those few objects whose orbits happen to be perturbed such that they fall closer to the Sun, and even then, detecting these objects has often been possible only when they happened to become bright enough to register as comets.[189] Objects may yet be discovered in the Solar System's uncharted regions.[190] The furthest known objects, such as Comet West, have aphelia around 70,000 AU from the Sun,[191] but as the Oort cloud becomes better known, this may change.

Galactic context

Position of the Solar System within the Milky Way
Diagram of the Milky Way with the position of the Solar System marked by a yellow arrow and a red dot in the Orion Arm, the dot roughly covering the large surrounding celestial area dominated by the Radcliffe Wave and Split linear structures (formerly Gould Belt).[192]

The Solar System is located in the Milky Way, a barred spiral galaxy with a diameter of about 100,000 light-years containing more than 100 billion stars.[193] The Sun resides in one of the Milky Way's outer spiral arms, known as the Orion–Cygnus Arm or Local Spur.[194] The Sun lies about 26,660 light-years from the Galactic Centre,[195] and its speed around the center of the Milky Way is about 220 km/s, so that it completes one revolution every 240 million years.[193] This revolution is known as the Solar System's galactic year.[196] The solar apex, the direction of the Sun's path through interstellar space, is near the constellation Hercules in the direction of the current location of the bright star Vega.[197] The plane of the ecliptic lies at an angle of about 60° to the galactic plane.[h]

The Solar System's location in the Milky Way is a factor in the evolutionary history of life on Earth. Its orbit is close to circular, and orbits near the Sun are at roughly the same speed as that of the spiral arms.[199][200] Therefore, the Sun passes through arms only rarely. Because spiral arms are home to a far larger concentration of supernovae, gravitational instabilities, and radiation that could disrupt the Solar System, this has given Earth long periods of stability for life to evolve.[199] However, the changing position of the Solar System relative to other parts of the Milky Way could explain periodic extinction events on Earth, according to the Shiva hypothesis or related theories, but this remains controversial.[201][202] The Solar System lies well outside the star-crowded environs of the galactic centre. Near the centre, gravitational tugs from nearby stars could perturb bodies in the Oort cloud and send many comets into the inner Solar System, producing collisions with potentially catastrophic implications for life on Earth. The intense radiation of the galactic centre could also interfere with the development of complex life.[199]

Celestial neighbourhood

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.

The Solar System is surrounded by the Local Interstellar Cloud, although it is not clear if it is embedded in the Local Interstellar Cloud or if it lies just outside the cloud's edge.[203][204] Multiple other interstellar clouds also exist in the region within 300 light-years of the Sun, known as the Local Bubble.[204] The density of all matter in the local neighborhood is 0.097±0.013 M·pc−3.[205]

Within ten light-years of the Sun there are relatively few stars, the closest being the triple star system Alpha Centauri, which is about 4.4 light-years away and in the Local Bubble's G-Cloud. Alpha Centauri A and B are a closely tied pair of Sun-like stars, whereas the closest to Earth, the small red dwarf Proxima Centauri, orbits the pair closer at a distance of 0.2 light-year. In 2016, a potentially habitable exoplanet was confirmed to be orbiting Proxima Centauri, called Proxima Centauri b, the closest confirmed exoplanet to the Sun.[206] The next closest known fusors and rogue planets to the Sun are the red dwarf Barnard's Star (at 5.9 ly), the nearest brown dwarfs of the binary Luhman 16 system (6.6 ly), the closest known rogue or free-floating planetary-mass object at less than 10 Jupiter masses the sub-brown dwarf WISE 0855−0714,[207] (7 ly), as well as the red dwarfs Wolf 359 (7.8 ly) and Lalande 21185 (8.3 ly).

The next closest at 8.6 ly is Sirius, the brightest star in Earth's night sky, with roughly twice the Sun's mass, orbited by the closest white dwarf to Earth, Sirius B. Other stars within ten light-years are the binary red-dwarf system Luyten 726-8 (8.7 ly) and the solitary red dwarf Ross 154 (9.7 ly).[208][209] The closest solitary Sun-like star to the Solar System is Tau Ceti at 11.9 light-years. It has roughly 80% of the Sun's mass but only about half of its luminosity.[210]

The nearest and unaided-visible group of stars beyond the immediate celestial neighbourhood is the Ursa Major Moving Group at roughly 80 light-years, which is within the Local Bubble, like the nearest as well as unaided-visible star cluster the Hyades, which lie at its edge. The Local Bubble is an hourglass-shaped cavity or superbubble in the interstellar medium roughly 300 light-years across. The bubble is suffused with high-temperature plasma, suggesting that it may be the product of several recent supernovae.[211] The Local Bubble is a small superbubble compared to the neighbouring wider Radcliffe Wave and Split linear structures (formerly Gould Belt), each of which are some thousands of light-years in length.[192] All these structures are part of the Orion Arm, which contains most of the stars in the Milky Way that are visible to the unaided eye. The closest star-forming regions are the Corona Australis Molecular Cloud, the Rho Ophiuchi cloud complex and the Taurus Molecular Cloud; the latter lies just beyond the Local Bubble and is part of the Radcliffe wave.[212]

Comparison with extrasolar systems

Compared to many extrasolar systems, the Solar System stands out in lacking planets interior to the orbit of Mercury.[213][214] The known Solar System also lacks super-Earths, planets between one and ten times as massive as the Earth,[213] although the hypothetical Planet Nine, if it does exist, could be a super-Earth beyond the Solar System as we understand it today.[215] Uncommonly, it has only small rocky planets and large gas giants; elsewhere planets of intermediate size are typical—both rocky and gas—so there is no "gap" as seen between the size of Earth and of Neptune (with a radius 3.8 times as large). Also, these super-Earths have closer orbits than Mercury.[213] This led to the hypothesis that all planetary systems start with many close-in planets, and that typically a sequence of their collisions causes consolidation of mass into few larger planets, but in case of the Solar System the collisions caused their destruction and ejection.[216]

The orbits of Solar System planets are nearly circular. Compared to other systems, they have smaller orbital eccentricity.[213] Although there are attempts to explain it partly with a bias in the radial-velocity detection method and partly with long interactions of a quite high number of planets, the exact causes remain undetermined.[213][217]


This section is a sampling of Solar System bodies, selected for size and quality of imagery, and sorted by volume. Some large objects are omitted here (notably the seven large trans-Neptunian objects Eris, Haumea, Makemake, Gonggong, Quaoar, Sedna, and Orcus) because they have not yet been imaged in high quality.

Solar System
The Sun in white light.jpg
Jupiter and its shrunken Great Red Spot.jpg
Jewel of the Solar System.jpg
Uranus as seen by NASA's Voyager 2 (remastered).png
Neptune - Voyager 2 (29347980845) flatten crop.jpg
The Blue Marble (remastered).jpgVenus from Mariner 10.jpg
OSIRIS Mars true color.jpg
Ganymede - Perijove 34 Composite.png
Titan in true color.jpg
Mercury in true color.jpg
Io highest resolution true color.jpg
(moon of Jupiter)
(moon of Saturn)
(moon of Jupiter)
(moon of Jupiter)
(moon of Earth)
Triton moon mosaic Voyager 2 (large).jpg
Pluto in True Color - High-Res.jpg
PIA07763 Rhea full globe5.jpg
Voyager 2 picture of Oberon.jpg
Iapetus as seen by the Cassini probe - 20071008.jpg
(moon of Jupiter)
(moon of Neptune)
(dwarf planet)
(moon of Uranus)
(moon of Saturn)
(moon of Uranus)
(moon of Saturn)
Charon in True Color - High-Res.jpg
PIA00040 Umbrielx2.47.jpg
Ariel (moon).jpg
Dione in natural light.jpg
Ceres - RC3 - Haulani Crater (22381131691) (cropped).jpg
Vesta in natural color.jpg
(moon of Pluto)
(moon of Uranus)
(moon of Uranus)
(moon of Saturn)
(moon of Saturn)
(dwarf planet)
(belt asteroid)
Potw1749a Pallas crop.png
PIA17202 - Approaching Enceladus.jpg
Proteus (Voyager 2).jpg
Mimas Cassini.jpg
Hyperion true.jpg
Iris asteroid eso.jpg
(belt asteroid)
(moon of Saturn)
(moon of Uranus)
(moon of Neptune)
(moon of Saturn)
(moon of Saturn)
(belt asteroid)
Phoebe cassini.jpg
PIA12714 Janus crop.jpg
PIA09813 Epimetheus S. polar region.jpg
Rosetta triumphs at asteroid Lutetia.jpg
Prometheus 12-26-09a.jpg
PIA21055 - Pandora Up Close.jpg
(253) mathilde crop.jpg
(moon of Saturn)
(moon of Saturn)
(moon of Saturn)
(belt asteroid)
(moon of Saturn)
(moon of Saturn)
(belt asteroid)
Leading hemisphere of Helene - 20110618.jpg
243 Ida (cropped).jpg
UltimaThule CA06 color 20190516.png
Phobos colour 2008.jpg
Comet 67P True color.jpg
Comet Hartley 2 (super crop).jpg
(moon of Saturn)
(belt asteroid)
(Kuiper belt object)
(moon of Mars)
(moon of Mars)

Hartley 2

Humanity's perspective

Andreas Cellarius's illustration of the Copernican system, from the Harmonia Macrocosmica (1660)
Buzz Aldrin on the Moon during the Apollo 11 mission

Humanity's knowledge of the Solar System has grown incrementally over the centuries. Most people up to the Late Middle AgesRenaissance believed Earth to be stationary at the centre of the universe and categorically different from the divine or ethereal objects that moved through the sky. Although the Greek philosopher Aristarchus of Samos had speculated on a heliocentric reordering of the cosmos, Nicolaus Copernicus was the first person known to have developed a mathematically predictive heliocentric system.[218][219] Heliocentrism did not triumph immediately over geocentrism, but the work of Copernicus had its champions, notably Johannes Kepler. Using a heliocentric model that improved upon Copernicus by allowing orbits to be elliptical as well as circular, and the precise observational data of Tycho Brahe, Kepler produced the Rudolphine Tables, which enabled accurate computations of the positions of the then-known planets. Pierre Gassendi used them to predict a transit of Mercury in 1631, and Jeremiah Horrocks did the same for a transit of Venus in 1639. This provided a strong vindication of heliocentrism and Kepler's elliptical orbits.[220][221]

In the 17th century, Galileo publicized the use of the telescope in astronomy; he and Simon Marius independently discovered that Jupiter had four satellites in orbit around it.[222] Christiaan Huygens followed on from these observations by discovering Saturn's moon Titan and the shape of the rings of Saturn.[223] In 1677, Edmond Halley observed a transit of Mercury across the Sun, leading him to realise that observations of the solar parallax of a planet (more ideally using the transit of Venus) could be used to trigonometrically determine the distances between Earth, Venus, and the Sun.[224] Halley's friend Isaac Newton, in his magisterial Principia Mathematica of 1687, demonstrated that celestial bodies are not quintessentially different from Earthly ones: the same laws of motion and of gravity apply on Earth and in the skies.[17]: 142 

The term "Solar System" entered the English language by 1704, when John Locke used it to refer to the Sun, planets, and comets.[225] In 1705, Halley realised that repeated sightings of a comet were of the same object, returning regularly once every 75–76 years. This was the first evidence that anything other than the planets repeatedly orbited the Sun,[226] though Seneca had theorized this about comets in the 1st century.[227] Careful observations of the 1769 transit of Venus allowed astronomers to calculate the average Earth–Sun distance as 93,726,900 miles (150,838,800 km), only 0.8% greater than the modern value.[228] Uranus, having occasionally been observed since antiquity, was recognized to be a planet beyond Saturn by 1783.[229] In 1838, Friedrich Bessel successfully measured a stellar parallax, an apparent shift in the position of a star created by Earth's motion around the Sun, providing the first direct, experimental proof of heliocentrism.[230] Neptune was identified as a planet some years later, in 1846, thanks to its gravitational pull causing a slight but detectable variation in the orbit of Uranus.[231]

In the 20th century, humans began their space exploration around the Solar System, starting with placing telescopes in space.[232] Since then, humans have landed on the Moon during the Apollo program, one mission (Apollo 13) marked the furthest any human has been away from Earth at 400,171 kilometers (248,655 mi).[233] All eight planets have been visited by space probes; the outer planets are first visited by the Voyager, one of them (Voyager 1) is the furthest object made by humankind and the first in interstellar space.[234] In addition, probes has also returned samples from comets[235] and asteroids,[236] as well as fly through the Sun's corona[237] and fly-by Kuiper belt objects.[238] Six of the planets have or had a dedicated orbiter, except Uranus and Neptune.[239]

See also


  1. ^ The asteroid belt and Kuiper belt are not added because the individual asteroids are too small to be shown on the diagram.
  2. ^ a b As of 2 April 2022.
  3. ^ Capitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Solar System" and "solar system" structures in their naming guidelines document Archived 25 July 2021 at the Wayback Machine. The name is commonly rendered in lower case ('solar system'), as, for example, in the Oxford English Dictionary and Merriam-Webster's 11th Collegiate Dictionary Archived 27 January 2008 at the Wayback Machine.
  4. ^ The two moons larger than Mercury are Ganymede, which orbits Jupiter, and Titan, which orbits Saturn. Although bigger than Mercury, both moons have less than half its mass. In addition, the radius of Jupiter's moon Callisto is over 98% that of Mercury.
  5. ^ a b c d e According to IAU definitions, objects orbiting the Sun are classified dynamically and physically into three categories: planets, dwarf planets, and small Solar System bodies.
    • A planet is any body orbiting the Sun whose mass is sufficient for gravity to have pulled it into a (near-)spherical shape and that has cleared its immediate neighbourhood of all smaller objects. By this definition, the Solar System has eight planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. Because it has not cleared its neighbourhood of other Kuiper belt objects, Pluto does not fit this definition.[4]
    • A dwarf planet is a body orbiting the Sun that is massive enough to be made near-spherical by its own gravity but that has not cleared planetesimals from its neighbourhood and is also not a satellite.[4] Dwarf planets are considered planets by some planetologists but not by the IAU.[5] The IAU has recognized four other bodies in the Solar System as dwarf planets: Ceres, Haumea, Makemake, and Eris.[6][7] Other objects commonly accepted as dwarf planets include Gonggong, Sedna, Orcus, and Quaoar. In a reference to Pluto, other dwarf planets orbiting in the trans-Neptunian region are sometimes called "plutoids",[8] though this term is seldom used.
    • The remaining objects orbiting the Sun are known as small Solar System bodies.[4]
  6. ^ a b The mass of the Solar System excluding the Sun, Jupiter and Saturn can be determined by adding together all the calculated masses for its largest objects and using rough calculations for the masses of the Oort cloud (estimated at roughly 3 Earth masses),[24] the Kuiper belt (estimated at roughly 0.1 Earth mass)[25] and the asteroid belt (estimated to be 0.0005 Earth mass)[26] for a total, rounded upwards, of ~37 Earth masses, or 8.1% of the mass in orbit around the Sun. With the combined masses of Uranus and Neptune (~31 Earth masses) subtracted, the remaining ~6 Earth masses of material comprise 1.3% of the total orbiting mass.
  7. ^ The date is based on the oldest inclusions found to date in meteorites, 4568.2+0.2
    million years, and is thought to be the date of the formation of the first solid material in the collapsing nebula.[45]
  8. ^ If is the angle between the north pole of the ecliptic and the north galactic pole then:

    where = 27° 07′ 42.01″ and = 12h 51m 26.282s are the declination and right ascension of the north galactic pole,[198] whereas = 66° 33′ 38.6″ and = 18h 0m 00s are those for the north pole of the ecliptic. (Both pairs of coordinates are for J2000 epoch.) The result of the calculation is 60.19°.


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External links

Media files used on this page

(c) Gregory H. Revera, CC BY-SA 3.0
Full Moon photograph taken 10-22-2010 from Madison, Alabama, USA. Photographed with a Celestron 9.25 Schmidt-Cassegrain telescope. Acquired with a Canon EOS Rebel T1i (EOS 500D), 20 images stacked to reduce noise. 200 ISO 1/640 sec.
Solar system.jpg
This is a montage of planetary images taken by spacecraft managed by the Jet Propulsion Laboratory in Pasadena, CA. Included are (from top to bottom) images of Mercury, Venus, Earth (and Moon), Mars, Jupiter, Saturn, Uranus and Neptune. The spacecraft responsible for these images are as follows:
  • the Mercury image was taken by Mariner 10,
  • the Venus image by Magellan,
  • the Earth and Moon images by Galileo,
  • the Mars image by Mars Global Surveyor,
  • the Jupiter image by Cassini, and
  • the Saturn, Uranus and Neptune images by Voyager.
  • Pluto is not shown as it is no longer a planet. The inner planets (Mercury, Venus, Earth, Moon, and Mars) are roughly to scale to each other; the outer planets (Jupiter, Saturn, Uranus, and Neptune) are roughly to scale to each other. PIA 00545 is the same montage with Neptune shown larger in the foreground. Actual diameters are given below:
  • Sun (to photosphere) 1,392,684 km
  • Mercury 4,879.4 km
  • Venus 12,103.7 km
  • Earth 12,756.28 km
  • Moon 3,476.2 km
  • Mars 6,804.9 km
  • Jupiter 142,984 km
  • Saturn 120,536 km
  • Uranus 51,118 km
  • Neptune 49,528 km
Crab Nebula.jpg
This is a mosaic image, one of the largest ever taken by NASA's Hubble Space Telescope, of the Crab Nebula, a six-light-year-wide expanding remnant of a star's supernova explosion. Japanese and Chinese astronomers recorded this violent event in 1054 CE, as did, almost certainly, Native Americans.

The orange filaments are the tattered remains of the star and consist mostly of hydrogen. The rapidly spinning neutron star embedded in the center of the nebula is the dynamo powering the nebula's eerie interior bluish glow. The blue light comes from electrons whirling at nearly the speed of light around magnetic field lines from the neutron star. The neutron star, like a lighthouse, ejects twin beams of radiation that appear to pulse 30 times a second due to the neutron star's rotation. A neutron star is the crushed ultra-dense core of the exploded star.

The Crab Nebula derived its name from its appearance in a drawing made by Irish astronomer Lord Rosse in 1844, using a 36-inch telescope. When viewed by Hubble, as well as by large ground-based telescopes such as the European Southern Observatory's Very Large Telescope, the Crab Nebula takes on a more detailed appearance that yields clues into the spectacular demise of a star, 6,500 light-years away.

The newly composed image was assembled from 24 individual Wide Field and Planetary Camera 2 exposures taken in October 1999, January 2000, and December 2000. The colors in the image indicate the different elements that were expelled during the explosion. Blue in the filaments in the outer part of the nebula represents neutral oxygen, green is singly-ionized sulfur, and red indicates doubly-ionized oxygen.
The Earth seen from Apollo 17 with transparent background.png
"The Blue Marble" is a famous photograph of the Earth taken on December 7, 1972 by the crew of the Apollo 17 spacecraft en route to the Moon at a distance of about 29,000 kilometers (18,000 statute miles). It shows Africa, Antarctica, and the Arabian Peninsula.
Author/Creator: Me, Licence: Copyrighted free use
SVG replacement for File:Spaceship and the Sun.jpg. A stylized illustration of a spaceship and the sun, based on the description of the emblem of the fictional Galactic Empire in Isaac Asimov's Foundation series ("The golden globe with its conventionalized rays, and the oblique cigar shape that was a space vessel"). This image could be used as a icon for science-fiction related articles.
TheTransneptunians 73AU.svg
Author/Creator: unknown, Licence: CC-BY-SA-3.0
This image shows a view of the trailing hemisphere of Jupiter's ice-covered satellite, Europa, in approximate natural color. Long, dark lines are fractures in the crust, some of which are more than 3,000 kilometers (1,850 miles) long. The bright feature containing a central dark spot in the lower third of the image is a young impact crater some 50 kilometers (31 miles) in diameter. This crater has been named "Pwyll" after the figure from Welsh mythology. Europa is about 3,160 kilometers (1,950 miles) in diameter, or about the size of Earth's moon. This image was taken on September 7, 1996, at a range of 677,000 kilometers (417,900 miles) by the solid state imaging television camera onboard the Galileo spacecraft during its second orbit around Jupiter. The image was processed by Deutsche Forschungsanstalt fuer Luftund Raumfahrt e.V., Berlin, Germany.
Iapetus as seen by the Cassini probe - 20071008.jpg

Iapetus as seen by the Cassini probe.
Original NASA caption: Cassini captures the first high-resolution glimpse of the bright trailing hemisphere of Saturn's moon Iapetus.
This false-color mosaic shows the entire hemisphere of Iapetus (1,468 kilometers, or 912 miles across) visible from Cassini on the outbound leg of its encounter with the two-toned moon in Sept. 2007. The central longitude of the trailing hemisphere is 24 degrees to the left of the mosaic's center.
Also shown here is the complicated transition region between the dark leading and bright trailing hemispheres. This region, visible along the right side of the image, was observed in many of the images acquired by Cassini near closest approach during the encounter.
Revealed here for the first time in detail are the geologic structures that mark the trailing hemisphere. The region appears heavily cratered, particularly in the north and south polar regions. Near the top of the mosaic, numerous impact features visible in NASA Voyager 2 spacecraft images (acquired in 1981) are visible, including the craters Ogier and Charlemagne.
The most prominent topographic feature in this view, in the bottom half of the mosaic, is a 450-kilometer (280-mile) wide impact basin, one of at least nine such large basins on Iapetus. In fact, the basin overlaps an older, similar-sized impact basin to its southeast.
In many places, the dark material--thought to be composed of nitrogen-bearing organic compounds called cyanides, hydrated minerals and other carbonaceous minerals--appears to coat equator-facing slopes and crater floors. The distribution of this material and variations in the color of the bright material across the trailing hemisphere will be crucial clues to understanding the origin of Iapetus' peculiar bright-dark dual personality.
The view was acquired with the Cassini spacecraft narrow-angle camera on Sept. 10, 2007, at a distance of about 73,000 kilometers (45,000 miles) from Iapetus.
The color seen in this view represents an expansion of the wavelengths of the electromagnetic spectrum visible to human eyes. The intense reddish-brown hue of the dark material is far less pronounced in true color images. The use of enhanced color makes the reddish character of the dark material more visible than it would be to the naked eye.
This mosaic consists of 60 images covering 15 footprints across the surface of Iapetus. The view is an orthographic projection centered on 10.8 degrees south latitude, 246.5 degrees west longitude and has a resolution of 426 meters (0.26 miles) per pixel. An orthographic view is most like the view seen by a distant observer looking through a telescope.
At each footprint, a full resolution clear filter image was combined with half-resolution images taken with infrared, green and ultraviolet spectral filters (centered at 752, 568 and 338 nanometers, respectively) to create this full-resolution false color mosaic.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colo.
Author/Creator: ESO, European Southern Observatory, Licence: CC BY 4.0
Artist's impression of "the oldest star of our Galaxy": HE 1523-0901
  • About 13.2 billion years old
  • Approximately 7500 light years far from Earth
  • Published as part of Hamburg/ESO Survey in the May 10 2007 issue of The Astrophysical Journal
Color-enhanced image of Deimos, a moon of Mars, captured by the HiRISE instrument on the Mars Reconnaissance Orbiter on 21 Feb 2009. Cropped from source image.
Titan in true color.jpg
Titan's atmosphere makes Saturn's largest moon look like a fuzzy orange ball in this natural color view from the Cassini spacecraft.

Titan's north polar hood is visible at the top of the image, and a faint blue haze also can be detected above the south pole at the bottom of this view.

This view looks toward the anti-Saturn side of Titan (3,200 miles, or 5,150 kilometers across). North is up. Images taken using red, green and blue spectral filters were combined to create this natural color view. The images were obtained with the Cassini spacecraft wide-angle camera on Jan. 30, 2012 at a distance of approximately 119,000 miles (191,000 kilometers) from Titan. Image scale is 7 miles (11 kilometers) per pixel.
Venus from Mariner 10.jpg
As it sped away from Venus, NASA's Mariner 10 spacecraft captured this seemingly peaceful view of a planet the size of Earth, wrapped in a dense, global cloud layer. But, contrary to its serene appearance, the clouded globe of Venus is a world of intense heat, crushing atmospheric pressure and clouds of corrosive acid.
Prometheus 12-26-09a.jpg
This raw, unprocessed image of Prometheus was taken by Cassini on Dec. 26, 2009.

The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Dec. 26, 2009 at a distance of approximately 59,000 kilometers (36,000 miles) from Prometheus and at a Sun-Prometheus-spacecraft, or phase, angle of 19 degrees. Image scale is 351 meters (1,150 feet) per pixel.

The Cassini Equinox Mission is a joint United States and European endeavor. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter was designed, developed and assembled at JPL. The imaging team consists of scientists from the US, England, France, and Germany. The imaging operations center and team lead (Dr. C. Porco) are based at the Space Science Institute in Boulder, Colo.

For more information about the Cassini Equinox Mission visit, and

The original NASA image has been modified by cropping, doubling the linear pixel density, reducing brightness, and removal of some cosmic ray artifacts.
Io highest resolution true color.jpg
Original Caption Released with Image:

NASA's Galileo spacecraft acquired its highest resolution images of Jupiter's moon Io on 3 July 1999 during its closest pass to Io since orbit insertion in late 1995. This color mosaic uses the near-infrared, green and violet filters (slightly more than the visible range) of the spacecraft's camera and approximates what the human eye would see. Most of Io's surface has pastel colors, punctuated by black, brown, green, orange, and red units near the active volcanic centers. A false color version of the mosaic has been created to enhance the contrast of the color variations.

The improved resolution reveals small-scale color units which had not been recognized previously and which suggest that the lavas and sulfurous deposits are composed of complex mixtures (Cutout A of false color image). Some of the bright (whitish), high-latitude (near the top and bottom) deposits have an ethereal quality like a transparent covering of frost (Cutout B of false color image). Bright red areas were seen previously only as diffuse deposits. However, they are now seen to exist as both diffuse deposits and sharp linear features like fissures (Cutout C of false color image). Some volcanic centers have bright and colorful flows, perhaps due to flows of sulfur rather than silicate lava (Cutout D of false color image). In this region bright, white material can also be seen to emanate from linear rifts and cliffs.

Comparison of this image to previous Galileo images reveals many changes due to the ongoing volcanic activity.

Galileo will make two close passes of Io beginning in October of this year. Most of the high-resolution targets for these flybys are seen on the hemisphere shown here.

North is to the top of the picture and the sun illuminates the surface from almost directly behind the spacecraft. This illumination geometry is good for imaging color variations, but poor for imaging topographic shading. However, some topographic shading can be seen here due to the combination of relatively high resolution (1.3 kilometers or 0.8 miles per picture element) and the rugged topography over parts of Io. The image is centered at 0.3 degrees north latitude and 137.5 degrees west longitude. The resolution is 1.3 kilometers (0.8 miles) per picture element. The images were taken on 3 July 1999 at a range of about 130,000 kilometers (81,000 miles) by the Solid State Imaging (SSI) system on NASA's Galileo spacecraft during its twenty-first orbit.

The Jet Propulsion Laboratory, Pasadena, CA manages the Galileo mission for NASA's Office of Space Science, Washington, DC.

This image and other images and data received from Galileo are posted on the World Wide Web, on the Galileo mission home page at URL Background information and educational context for the images can be found at URL
Kuiper belt plot objects of outer solar system.png
(c) WilyD at English Wikipedia, CC BY-SA 3.0
Objects of the Kuiper belt (blue). Plot displays the known positions of objects in the outer Solar System within 60 astronomical units (AU) from the Sun. Epoch as of January 1, 2015.

 Jupiter trojans (6,178)
 Giant planets: Jupiter (J), Saturn (S), Uranus (U) and Neptune (N)
 Centaurs (44,000)
 Kuiper belt (>1,000)
 Scattered disc
 Neptune trojans (9)

Notes: Orbital elements were converted to positions using MERCURY (Chambers 1999). Distances but not sizes are to scale.
Uranus' icy moon Miranda is seen in this image from Voyager 2 on January 24, 1986. The Voyager project is managed for NASA by the Jet Propulsion Laboratory.
Local Interstellar Clouds with motion arrows.jpg
Our solar journey through space is carrying us through a cluster of very-low-density interstellar clouds. Right now the Sun is inside of a cloud (Local cloud) that is so tenuous that the interstellar gas detected by IBEX is as sparse as a handful of air stretched over a column that is hundreds of light-years long. These clouds are identified by their motions, indicated in this graphic with blue arrows.
Oort cloud Sedna orbit.svg

These four panels show the location of trans-Neptunian object 90377 Sedna, which lies in the farthest reaches of the Solar System.[1] Each panel, moving clockwise from the upper left, successively zooms out to place Sedna in context.

The first panel shows the orbits of the inner planets and Jupiter; and the asteroid belt.

In the second panel, Sedna is shown well outside the orbits of Neptune and the Kuiper belt objects.

Sedna's full orbit is illustrated in the third panel along with the object's location in 2004, nearing its closest approach to the Sun.

The final panel zooms out much farther, showing that even this large elliptical orbit falls inside what was previously thought to be the inner edge of the spherical Oort cloud: a distribution of cold, icy bodies lying at the limits of the Sun's gravitational pull. Sedna's presence suggests that the previously speculated inner disk on the ecliptic does exist.
Vesta in natural color.jpg
Vesta is a colorful world; craters of a variety of ages make splashes of lighter and darker brown against its surface. This photo was processed from data acquired on July 24, 2011, from a distance of about 5200 kilometers, during the third "rotation characterization" observation by Dawn.
The Blue Marble (remastered).jpg
Full disk view of the Earth taken on December 7, 1972, by the crew of the Apollo 17 spacecraft en route to the Moon at a distance of about 29,000 kilometres (18,000 mi). It shows Africa, Antarctica, and the Arabian Peninsula.
Ceres - RC3 - Haulani Crater (22381131691) (cropped).jpg

Approximate true-color image of Ceres, using the F7 ('red'), F2 ('green') and F8 ('blue') filters, projected onto a clear filter image.

Images were acquired by Dawn at 04:13 UT May 4, 2015, at a distance of 13641 km. At the time, Dawn was over Ceres' northern hemisphere. The prominent, bright crater at right is Haulani. The smaller bright spot to its left is exposed on the floor of Oxo. Ejecta from these impacts appears to have exposed high albedo material similar to deposits found on the floor of Occator Crater.

Image Credit: NASA / JPL-Caltech / UCLA / MPS / DLR / IDA / Justin Cowart
Bright scars on a darker surface testify to a long history of impacts on Jupiter's moon Callisto in this image of Callisto from NASA's Galileo spacecraft. The picture, taken in May 2001, is the only complete global color image of Callisto obtained by Galileo, which has been orbiting Jupiter since December 1995. Of Jupiter's four largest moons, Callisto orbits farthest from the giant planet. Callisto's surface is uniformly cratered but is not uniform in color or brightness. Scientists believe the brighter areas are mainly ice and the darker areas are highly eroded, ice-poor material.
Solar system orrery inner planets.gif
Author/Creator: Datumizer, Licence: CC BY-SA 4.0
Orrery showing the motions of the inner four planets of our solar system, starting on A.D. 2018 Jul 06, 16:47:00.0 (Earth aphelion) and ending on A.D. 2019 Jul 04, 22:11:00.0 (Earth aphelion). Each small sphere represents one Julian day. Distances are to scale. Objects are not. The circular rings are spaced 0.5 AU apart.
Jupiter and its shrunken Great Red Spot.jpg
This full-disc image of Jupiter was taken on 21 April 2014 with Hubble's Wide Field Camera 3 (WFC3).
Triton moon mosaic Voyager 2 (large).jpg
Global Color Mosaic of Triton, taken by Voyager 2 in 1989
Voyager 2 picture of Oberon.jpg
Original Caption Released with Image: This Voyager 2 picture of Oberon is the best the spacecraft acquired of Uranus' outermost moon. The picture was taken shortly after 3:30 a.m. PST on Jan. 24, 1986, from a distance of 660,000 kilometers (410,000 miles). The color was reconstructed from images taken through the narrow-angle camera's violet, clear and green filters. The picture shows features as small as 12 km (7 mi) on the moon's surface. Clearly visible are several large impact craters in Oberon's icy surface surrounded by bright rays similar to those seen on Jupiter's moon Callisto. Quite prominent near the center of Oberon's disk is a large crater with a bright central peak and a floor partially covered with very dark material. This may be icy, carbon-rich material erupted onto the crater floor sometime after the crater formed. Another striking topographic feature is a large mountain, about 6 km (4 mi) high, peeking out on the lower left limb. The Voyager project is managed for NASA by the Jet Propulsion Laboratory.
PIA07763 Rhea full globe5.jpg
This giant mosaic reveals Saturn's icy moon Rhea in her full, crater-scarred glory.

This view consists of 21 clear-filter images and is centered at 0.4 degrees south latitude, 171 degrees west longitude.

The giant impact basin Tirawa is seen above and to the right of center. Tirawa, and the even larger basin Mamaldi to its southwest, are both covered in impact craters, indicating they are quite ancient.

The bright, approximately 40-kilometer-wide (25-mile) ray crater seen in many Cassini views of Rhea is located on the right side of this mosaic (at 12 degrees south latitude, 111 degrees west longitude). See PIA07764 for a close-up view of the eastern portion of the bright, ray crater.

There are few signs of tectonic activity in this view. However, the wispy streaks on Rhea that were seen at lower resolution by NASA's Voyager and Cassini spacecraft, were beyond the western (left) limb from this perspective. In high-resolution Cassini flyby images of Dione, similar features were identified as fractures caused by extensive tectonism.

Rhea is Saturn's second-largest moon, at 1,528 kilometers (949 miles) across.

The images in this mosaic were taken with the Cassini spacecraft narrow-angle camera during a close flyby on Nov. 26, 2005. The images were acquired as Cassini approached the moon at distances ranging from 79,190 to 58,686 kilometers (49,206 to 36,466 miles) from Rhea and at a Sun-Rhea-spacecraft, or phase, angle of about 19 degrees. Image scale in the mosaic is 354 meters (1,161 feet) per pixel.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colo.

For more information about the Cassini-Huygens mission visit The Cassini imaging team homepage is at

The NASA image has been processed to enhance contrast and had black panels added to its borders.
Inner solar system objects top view for wiki.png
Author/Creator: Pablo Carlos Budassi, Licence: CC BY-SA 4.0
A top view of asteroid group location in the inner solar system.
Pluto in True Color - High-Res.jpg
Pluto's image taken by New Horizons on July 14, 2015, from a range of 22,025 miles (35,445) kilometers. The striking features on Pluto are clearly visible, including the bright expanse of Pluto's icy, nitrogen-and-methane rich "heart," Sputnik Planitia.

The natural-looking colors result from refined calibration of data gathered by New Horizons' color Multispectral Visible Imaging Camera (MVIC). The processing creates images that would approximate the colors that the human eye would perceive, bringing them closer to “true color” than the images released at the time of the encounter.

The source single-color MVIC scan includes no added data from other New Horizons imagers or instruments.
Submillimeter Array Night.jpg
Author/Creator: Steven Keys, Licence: CC BY 4.0
The Submillimeter Array of radio telescopes at night, lit by flash.
OSIRIS Mars true color.jpg
True color image of Mars taken by the OSIRIS instrument on the ESA Rosetta spacecraft during its February 2007 flyby of the planet. The image was generated using the OSIRIS orange (red), green, and blue filters.
Alternative description: The first true-colour image generated using the OSIRIS orange (red), green and blue colour filters. The image was acquired on 24 February 2007 at 19:28 CET from a distance of about 240 000 km; image resolution is about 5 km/pixel.
Iris asteroid eso.jpg
Author/Creator: ESO/Vernazza et al., Licence: CC BY 4.0
VLT/SPHERE/ZIMPOL images of (7) Iris obtained on October 10 and 11, 2017, and deconvolved with the Mistral algorithm.
Author/Creator: Lexicon, Licence: CC-BY-SA-3.0
Comparison of the largest TNOs: Pluto, Eris, Haumea, Makemake, Gonggong, Quaoar, Sedna, Orcus, Salacia, and 2002 MS4. All but two of these TNOs (Sedna and 2002 MS4) are known to have at least one moon. The top four are IAU-accepted dwarf planets while the bottom six are dwarf-planet candidates that are accepted as dwarf planets by several astronomers.

Text properties for future modifications:

  • Font is Verdana
  • Size is 100 pt for title, 72 pt for objects, 48 pt for moons
  • Colour is FFFFCE
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  • Anti-aliasing (in Photoshop) is Sharp
Solar System Template Final.png
Major Solar System objects. Sizes of planets and Sun are roughly to scale, but distances are not. This is not a diagram of all known moons – small gas giants' moons and Pluto's S/2011 P 1 moon are not shown.
Charon in True Color - High-Res.jpg
Three years after NASA's New Horizons spacecraft gave humankind our first close-up views of Pluto and its largest moon, Charon, scientists are still revealing the wonders of these incredible worlds in the outer solar system. Marking the anniversary of New Horizons' historic flight through the Pluto system on July 14, 2015, mission scientists released the highest-resolution color images of Pluto and Charon.

These natural-color images result from refined calibration of data gathered by New Horizons' color Multispectral Visible Imaging Camera (MVIC). The processing creates images that would approximate the colors that the human eye would perceive, bringing them closer to “true color” than the images released near the encounter.

This image was taken on July 14, 2015, from a range of 46,091 miles (74,176 kilometers). This single color MVIC scan includes no data from other New Horizons imagers or instruments added. The striking features on Charon are clearly visible, including the reddish north-polar region known as Mordor Macula.
Rosetta triumphs at asteroid Lutetia.jpg
Author/Creator: ESA 2010 MPS for OSIRIS Team MPS/UPD/LAM/IAA/RSSD/INTA/UPM/DASP/IDA, Licence: CC BY-SA 2.0
Asteroid 21 Lutetia has been revealed as a battered world of many craters. ESA's Rosetta mission has returned the first close-up images of the asteroid showing it is most probably a primitive survivor from the violent birth of the Solar System.
PIA09813 Epimetheus S. polar region.jpg

The Cassini spacecraft's close flyby of Epimetheus in December 2007 returned detailed images of the moon's south polar region.

The view shows what might be the remains of a large impact crater covering most of this face, and which could be responsible for the somewhat flattened shape of the southern part of Epimetheus (116 kilometers, or 72 miles across) seen previously at much lower resolution.

The image also shows two terrain types: darker, smoother areas, and brighter, slightly more yellowish, fractured terrain. One interpretation of this image is that the darker material evidently moves down slopes, and probably has a lower ice content than the brighter material, which appears more like "bedrock." Nonetheless, materials in both terrains are likely to be rich in water ice.

The images that were used to create this enhanced color view were taken with the Cassini spacecraft narrow-angle camera on Dec. 3, 2007. The views were obtained at a distance of approximately 37,400 kilometers (23,000 miles) from Epimetheus and at a Sun-Epimetheus-spacecraft, or phase, angle of 65 degrees. Image scale is 224 meters (735 feet) per pixel.

The Cassini–Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colo.

For more information about the Cassini–Huygens mission visit The Cassini imaging team homepage is at

The NASA image has been cropped.
Mimas Cassini.jpg
Description from NASA :

In this view captured by NASA's Cassini spacecraft on its closest-ever flyby of Saturn's moon Mimas, large Herschel Crater dominates Mimas, making the moon look like the Death Star in the movie "Star Wars."
Herschel Crater is 130 kilometers, or 80 miles, wide and covers most of the right of this image. Scientists continue to study this impact basin and its surrounding terrain (see PIA12569 and PIA12571).
Cassini came within about 9,500 kilometers (5,900 miles) of Mimas on Feb. 13, 2010. This mosaic was created from six images taken that day in visible light with Cassini's narrow-angle camera on Feb. 13, 2010. The images were re-projected into an orthographic map projection. This view looks toward the area between the region that leads on Mimas' orbit around Saturn and the region of the moon facing away from Saturn. Mimas is 396 kilometers (246 miles) across. This view is centered on terrain at 11 degrees south latitude, 158 degrees west longitude. North is up. This view was obtained at a distance of approximately 50,000 kilometers (31,000 miles) from Mimas and at a sun-Mimas-spacecraft, or phase, angle of 17 degrees. Image scale is 240 meters (790 feet) per pixel.
The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate in Washington. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging team is based at the Space Science Institute, Boulder, Colo.
For more information about the Cassini-Huygens mission visit and The Cassini imaging team homepage is at

The original NASA image has been cropped.
Leading hemisphere of Helene - 20110618.jpg
This raw, unprocessed image of Saturn's moon Helene was taken by Cassini on 18 June 2011 and received on Earth 20 June 2011.

Helene is a trojan moon of Dione. It leads Dione by 60 degrees in their shared orbit. The view looks toward the leading hemisphere of Helene (33 kilometers, 21 miles across). North on Helene is towards the top.

The camera was pointing toward Helene, and the image was taken using the CL1 and CL2 filters. The image has not been validated or calibrated. A validated/calibrated image will be archived with the Planetary Data System in 2012.

The Cassini Solstice Mission is a joint United States and European endeavor. The Jet Propulsion Laboratory (JPL), a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter was designed, developed and assembled at JPL. The imaging team consists of scientists from the US, England, France, and Germany. The imaging operations center and team lead (Dr. C. Porco) are based at the Space Science Institute in Boulder, Colorado.

For more information about the Cassini Solstice Mission visit, and

The original NASA image has been modified by cropping, sharpening and lightening shadows.
Logarithmic scale universe.png
Author/Creator: Olaf Frohn, Licence: CC BY-SA 4.0
Logarithmic overview of the universe.
Terrestrial planet sizes2.jpg
This diagram shows the approximate relative sizes of the terrestrial planets, from left to right: Mercury, Venus, Earth and Mars. Distances are not to scale. A terrestrial planet is a planet that is primarily composed of silicate rocks. The term is derived from the Latin word for Earth, "Terra", so an alternate definition would be that these are planets which are, in some notable fashion, "Earth-like". Terrestrial planets are substantially different from gas giants, which might not have solid surfaces and are composed mostly of some combination of hydrogen, helium, and water existing in various physical states. Terrestrial planets all have roughly the same structure: a central metallic core, mostly iron, with a surrounding silicate mantle. Terrestrial planets have canyons, craters, mountains, volcanoes and secondary atmospheres.
243 Ida (cropped).jpg
Author/Creator: Kevin Gill from Nashua, NH, United States, Image Credit: NASA/JPL/Processed by Kevin M. Gill, Licence: CC BY-SA 2.0
For use in the en:Template:SolarSummary template.
Solar system orrery outer planets.gif
Author/Creator: Datumizer, Licence: CC BY-SA 4.0
Orrery showing the motions of the outer four planets of our solar system, starting on A.D. 2018 Apr 17, 11:32:00.0 UT1 (Saturn aphelion) and ending on A.D. 2047 Jul 15, 07:02:00.0 UT1 (Saturn aphelion). Each small sphere represents 100 Julian days. Distances are to scale. Objects are not. The circular rings are spaced 4 AU apart.
Cellarius Harmonia Macrocosmica - Scenographia Systematis Copernicani.jpg

Andreas Cellarius: Harmonia macrocosmica seu atlas universalis et novus, totius universi creati cosmographiam generalem, et novam exhibens. Plate 5.

SCENOGRAPHIA SYSTEMATIS COPERNICANI - Scenography of the Copernican world system.
Jewel of the Solar System.jpg
A swing high above Saturn by NASA's Cassini spacecraft revealed this stately view of the golden-hued planet and its main rings. The view is in natural color, as human eyes would have seen it. This mosaic was made from 36 images in three color filters obtained by Cassini's imaging science subsystem on Oct. 10, 2013. The observation and resulting image mosaic were planned as one of three images for Cassini's 2013 Scientist for a Day essay contest.

Saturn sports differently colored bands of weather in this image. For instance, a bright, narrow wave of clouds around 42 degrees north latitude appears to be some of the turbulent aftermath of a giant storm that reached its violent peak in early 2011. The mysterious six-sided weather pattern known as the hexagon is visible around Saturn's north pole.

When Cassini arrived in 2004, more of the northern hemisphere sported a bluish hue and it was northern winter. The golden tones dominated the southern hemisphere, where it was southern summer. But as the seasons have turned and northern spring is in full swing, the colors have begun to change in each hemisphere as well. Golden tones have started to dominate in the northern hemisphere and the bluish color in the north is now confined to a tighter circle around the north pole. The southern hemisphere has started getting bluer, too.

The rings shown here include Saturn's main rings. The innermost D ring, and the C, B and A rings are easily seen. The F ring is also there, but not easily seen without enhancing the contrast of the image. (Rings were named in order of their discovery rather than their position around Saturn.) The rings also cast a shadow on Saturn at the limb of the planet in the lower right quadrant.

Cassini is currently in a set of tilted orbits known as "inclined orbits" that allow it to swing up over the north pole and below the south pole. Much of Cassini's time is spent close to the equatorial plane, where most of Saturn's rings and moons are located.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology, Pasadena, manages the Cassini-Huygens mission for NASA's Science Mission Directorate in Washington. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging team consists of scientists from the United States, the United Kingdom, France and Germany. The imaging operations center is based at the Space Science Institute in Boulder, Colo.
PIA21055 - Pandora Up Close.jpg
This image from NASA's Cassini spacecraft is one of the highest-resolution views ever taken of Saturn's moon Pandora. Pandora (52 miles, 84 kilometers) across orbits Saturn just outside the narrow F ring.

The spacecraft captured the image during its closest-ever flyby of Pandora on Dec. 18, 2016, during the third of its grazing passes by the outer edges of Saturn's main rings. (For Cassini's closest view prior to this flyby, see PIA07632, which is also in color.)

The image was taken in green light with the Cassini spacecraft narrow-angle camera at a distance of approximately 25,200 miles (40,500 kilometers) from Pandora. Image scale is 787 feet (240 meters) per pixel.

The Cassini-Huygens mission is a cooperative project of NASA, ESA (European Space Agency) and the Italian Space Agency. NASA's Jet Propulsion Laboratory, a division of Caltech in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington. JPL designed, developed and assembled the Cassini orbiter. The Cassini imaging operations center is based at the Space Science Institute in Boulder, Colorado.

For more information about the Cassini-Huygens mission visit and The Cassini imaging team homepage is at
Titania (moon) color, edited.jpg
Original caption: This high-resolution color composite of Titania was made from Voyager 2 images taken Jan. 24, 1986, as the spacecraft neared its closest approach to Uranus. Voyager's narrow-angle camera acquired this image of Titania, one of the large moons of Uranus, through the violet and clear filters. The spacecraft was about 500,000 kilometers (300,000 miles) away; the picture shows details about 9 km (6 mi) in size. Titania has a diameter of about 1,600 km (1,000 mi). In addition to many scars due to impacts, Titania displays evidence of other geologic activity at some point in its history. The large, trenchlike feature near the terminator (day-night boundary) at middle right suggests at least one episode of tectonic activity. Another, basinlike structure near the upper right is evidence of an ancient period of heavy impact activity. The neutral gray color of Titania is characteristic of the Uranian satellites as a whole. The Voyager project is managed for NASA by the Jet Propulsion Laboratory.
Proteus (Voyager 2).jpg
Proteus is the second largest moon of Neptune behind the mysterious Triton. Proteus was discovered only in 1989 by the Voyager 2 spacecraft. This is unusual since Neptune has a smaller moon - Nereid - which was discovered 33 years earlier from Earth. The reason Proteus was not discovered sooner is that its surface is very dark and it orbits much closer to Neptune. Proteus has an odd box-like shape and were it even slightly more massive, its own gravity would cause it to reform itself into a sphere.

Original NASA caption: This image of Neptune's satellite 1989N1 was obtained on Aug. 25, 1989 from a range of 146,000 kilometers (91,000 miles). The resolution is about 2.7 kilometers (1.7 miles) per line pair.

The satellite, seen here about half illuminated, has an average radius of some 200 kilometers (120 miles). It is dark (albedo 6 percent) and spectrally grey. Hints of crater-like forms and groove-like lineations can be discerned. The apparent graininess of the image is caused by the short exposure necessary to avoid significant smear.
Oort cloud.png
Author/Creator: Pablo Carlos Budassi, Licence: CC BY-SA 4.0
Spherical cloud of icy planetesimals surrounding the Sun at distances from 2,000 to 200,000 AU (beyond the heliosphere) - Two regions: a disc-shaped inner Oort cloud and a spherical outer Oort cloud - Affected by the gravitational pull of the Milky Way and of passing stars (occasionally sending comets to the inner Solar System) - Still theoretical as no confirmed direct observations of it has been made yet -
Comet Hale-Bopp 1995O1.jpg
Author/Creator: E. Kolmhofer, H. Raab; Johannes-Kepler-Observatory, Linz, Austria (, Licence: CC BY-SA 3.0
Image of comet C/1995 O1 (Hale-Bopp), taken on 1997 April 04, with a 225mm f/2.0 Schmidt Camera (focal length 450mm) on Kodak Panther 400 color slide film with an exposure time of 10 minutes. The field shown is about 6.5°x6.5°. At full resolution, the stars in the image appear slightly elongated, as the camera tracked the comet during the exposure.
Inner solar system linear map.png
Author/Creator: Pablo Carlos Budassi, Licence: CC BY-SA 4.0
A map of planets and asteroid groups of the inner solar system. Distances from sun are to scale, object sizes are not.
Aldrin Apollo 11 original.jpg

  • Short description: Astronaut Buzz Aldrin on the moon
  • Full description: Astronaut Buzz Aldrin, lunar module pilot, stands on the surface of the moon near the leg of the lunar module, Eagle, during the Apollo 11 moonwalk. Astronaut Neil Armstrong, mission commander, took this photograph with a 70mm lunar surface camera. While Armstrong and Aldrin descended in the lunar module to explore the Sea of Tranquility, astronaut Michael Collins, command module pilot, remained in lunar orbit with the Command and Service Module, Columbia. The picture features additionally to Aldrin, in his visor as reflections, Armstrong, Earth,[1] the lander, as well as the placed flag and instruments.
  • This is the actual photograph as exposed on the moon by Armstrong. He held the camera slightly rotated so that the camera frame did not include the top of Aldrin's portable life support system ("backpack"). A communications antenna mounted on top of the backpack is also cut off in this picture. When the image was released to the public, it was rotated clockwise to restore the astronaut to vertical for a more harmonious composition, and a black area was added above his head to recreate the missing black lunar "sky". The edited version is the one most commonly reproduced and known to the public, but the original version, above, is the authentic exposure. A full explanation with illustrations can be seen at the Apollo Lunar Surface Journal.
The Sun in white light.jpg
Author/Creator: Matúš Motlo, Licence: CC BY-SA 4.0
The Sun photographed on the 8th of May, 2019 in white light (true color). Sunspots AR2740 (to the right) and AR2741 (to the left) visible. Some other interesting features include faculae, white spots near AR2741, limb darkening, and tiny convection cells called granules all across its surface.
PIA22835: Two Interstellar Travelers

This illustration shows the position of NASA's Voyager 1 and Voyager 2 probes, outside of the heliosphere, a protective bubble created by the Sun that extends well past the orbit of Pluto. Voyager 1 crossed the heliopause, or the edge of the heliosphere, in August 2012. Heading in a different direction, Voyager 2 crossed another part of the heliopause in November 2018.

One of the annotated images below shows plasma flow lines both inside and outside the heliopause. The direction of the solar plasma is different from the direction of the interstellar plasma.

The Voyager spacecraft were built by JPL, which continues to operate both. JPL is a division of Caltech in Pasadena. California. The Voyager missions are a part of the NASA Heliophysics System Observatory, sponsored by the Heliophysics Division of the Science Mission Directorate in Washington. For more information about the Voyager spacecraft, visit and
Solar System true color (captions).jpg
Author/Creator: CactiStaccingCrane, Licence: CC BY-SA 4.0
Finally... the true color of the Solar System, with captions! Dwarf planets are sorted by radius ascending from top down, with four main classifications from right to left: Asteroid belt (Ceres, above the Jovian moons), Kuiper belt (Orcus, Quaoar, Makemake, Haumea, Pluto), scattered disk (Gonggong, Eris), and detached objects (Sedna)
Planet and moon credits: User:MotloAstro (Sun); NASA (Mercury, Venus, Earth, Jupiter [with ESA], Saturn, Uranus, Neptune, Io, Europa, Ganymede, Callisto, Mimas, Enceladus, Tethys, Dione, Rhea, Titan, Iapetus, Miranda, Ariel, Umbriel, Titania, Oberon, Triton); ESA (Mars); User:Grevera (Moon)
Dwarf planets + moons credit: NASA and ESA
Milky Way Arms ssc2008-10.svg
Artist's conception of the Milky Way galaxy as seen from far Galactic North (in Coma Berenices) by NASA/JPL-Caltech/R. Hurt [1] annotated with arms (colour-coded according to Milky Way article) as well as distances from the Solar System and galactic longitude with corresponding constellation.
Ganymede - Perijove 34 Composite.png
Author/Creator: NASA/JPL-Caltech/SwRI/MSSS/Kevin M. Gill, Licence: CC BY 2.0
Ganymede photographed by Juno in 2021, Projected from the perspective of '3.
Comet Hartley 2 (super crop).jpg
Image of Comet Hartley 2. This image was captured by NASA's EPOXI mission between Nov. 3 and 4, 2010, during the spacecraft's flyby of comet Hartley 2. It was captured using the spacecraft's Medium-Resolution Instrument.
Hyperion true.jpg
Approximately true-color mosaic of Saturn's moon Hyperion. Composed of several narrow-angle frames and processed to match Hyperion's natural color. Taken during Cassini's flyby of this lumpy moon on 26th September 2005.
Ariel (moon).jpg
This mosaic of the four highest-resolution images of Ariel represents the most detailed Voyager 2 picture of this satellite of Uranus. The images were taken through the clear filter of Voyager's narrow-angle camera on Jan. 24, 1986, at a distance of about 130,000 kilometers (80,000 miles). Ariel is about 1,200 km (750 mi) in diameter; the resolution here is 2.4 km (1.5 mi). Much of Ariel's surface is densely pitted with craters 5 to 10 km (3 to 6 mi) across. These craters are close to the threshold of detection in this picture. Numerous valleys and fault scarps crisscross the highly pitted terrain. Voyager scientists believe the valleys have formed over down-dropped fault blocks (graben); apparently, extensive faulting has occurred as a result of expansion and stretching of Ariel's crust. The largest fault valleys, near the terminator at right, as well as a smooth region near the center of this image, have been partly filled with deposits that are younger and less heavily cratered than the pitted terrain. Narrow, somewhat sinuous scarps and valleys have been formed, in turn, in these young deposits. It is not yet clear whether these sinuous features have been formed by faulting or by the flow of fluids.
Dione in natural light.jpg
This southerly view of Dione shows enormous canyons extending from mid-latitudes on the trailing hemisphere, at right, to the moon's south polar region.

This view looks toward the Saturn-facing side of Dione (1,126 kilometers, or 700 miles across) and is centered on 22 degrees south latitude, 359 degrees west longitude. North on Dione is up; the moon's south pole is seen at bottom.

The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Feb. 8, 2008. The view was obtained at a distance of approximately 211,000 kilometers (131,000 miles) from Dione and at a Sun-Dione-spacecraft, or phase, angle of 20 degrees. Image scale is 1 kilometer (0.6 mile) per pixel.
PIA18317: Tethys the Target

Like most moons in the Solar System, Tethys is covered by impact craters. Some craters bear witness to incredibly violent events, such as the crater Odysseus (seen here at the right of the image).

While Tethys is 1,062 kilometers (660 miles) across, the crater Odysseus is 450 kilometers (280 miles) across, covering about 18 percent of the moon's surface area. A comparably sized crater on Earth would be as large as Africa!

This view looks toward the anti-Saturn hemisphere of Tethys. North on Tethys is up and rotated 42 degrees to the right. The image was taken in visible light with the Cassini spacecraft narrow-angle camera on April 11, 2015.

The view was acquired at a distance of approximately 190,000 kilometers (118,000 miles) from Tethys. Image scale is 1 kilometer (3,280 feet) per pixel.

The Cassini mission is a cooperative project of NASA, ESA (the European Space Agency) and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington. The Cassini orbiter and its two onboard cameras were designed, developed and assembled at JPL. The imaging operations center is based at the Space Science Institute in Boulder, Colorado.

For more information about the Cassini–Huygens mission visit and The Cassini imaging team homepage is at
PIA12714 Janus crop.jpg
Saturn's moon Janus shows the scars of impacts in this Cassini image of craters light and dark.

This view looks toward the Saturn-facing side of Janus (179 kilometers, 111 miles across). North on Janus is up and rotated 10 degrees to the right.

The image was taken in visible light with the Cassini spacecraft narrow-angle camera on April 7, 2010. The view was acquired at a distance of approximately 75,000 kilometers (46,000 miles) from Janus and at a Sun-Janus-spacecraft, or phase, angle of 39 degrees. Image scale is 448 meters (1,469 feet) per pixel.

The original NASA image has been modified by cropping, doubling the linear pixel density, and sharpening.
Comet 67P True color.jpg
Author/Creator: ESA/Rosetta/MPS for OSIRIS Team MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA, Licence: CC BY-SA 4.0
Rosetta’s OSIRIS team have produced a colour image of Comet 67P/Churyumov-Gerasimenko as it would be seen by the human eye. As anticipated, the comet turns out to be very grey indeed, with only slight, subtle colour variations seen across its surface.

To create an image revealing 67P’s “true” colours, the scientists superposed images taken sequentially through filters centred on red, green, and blue wavelengths.

“As it turns out, 67P/C-G looks dark grey, in reality almost as black as coal,” says the instrument’s Principal Investigator Holger Sierks from the Max Planck Institute for Solar System Research (MPS).

As explained in earlier blog posts for the NAVCAM images, the intensity of the images has been enhanced to span the full range from black to white, in order to make surface details visible. But the colours have not been enhanced: the comet really is very grey.

A more detailed first analysis nevertheless reveals that the comet reflects red light slightly more efficiently than other wavelengths. This is a well-known phenomenon observed at many other small bodies in the Solar System and is due to the small size of the surface grains. That does not, however, mean that the comet would look red to the human eye. Natural sunlight peaks in the green part of the spectrum and the response of the human eye is similarly matched. Thus, overall, the comet would look rather grey to the human eye, as seen here.
Neptune - Voyager 2 (29347980845) flatten crop.jpg
Uploader's notes: The original NASA/Cowart PNG image has been modified by flattening (combining layers), cropping and converting to JPEG format.

Original caption released with image:
Voyager 2 Narrow Angle Camera image of Neptune taken on August 20, 1989 as the spacecraft approached the planet for a flyby on August 25. The Great Dark Spot, flanked by cirrus clouds, is at center. A smaller dark storm, Dark Spot Jr., is rotating into view at bottom left. Additionally, a patch of white cirrus clouds to its north, named "Scooter" for its rapid motion relative to other features, is visible.

This image was constructed using orange, green and synthetic violet (50/50 blend of green filter and UV filter images) taken between 626 and 643 UT.

Image Credit: NASA / JPL / Voyager-ISS / Justin Cowart
Yellow Arrow Down.png
A yellow arrow pointing down
PIA17202 - Approaching Enceladus.jpg
Original caption: NASA's Cassini spacecraft captured this view as it neared icy Enceladus for its closest-ever dive past the moon's active south polar region. The view shows heavily cratered northern latitudes at top, transitioning to fractured, wrinkled terrain in the middle and southern latitudes. The wavy boundary of the moon's active south polar region -- Cassini's destination for this flyby -- is visible at bottom, where it disappears into wintry darkness.

This view looks towards the Saturn-facing side of Enceladus. North on Enceladus is up and rotated 23 degrees to the right. The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Oct. 28, 2015.

The view was acquired at a distance of approximately 60,000 miles (96,000 kilometers) from Enceladus and at a Sun-Enceladus-spacecraft, or phase, angle of 45 degrees. Image scale is 1,896 feet (578 meters) per pixel.
Uranus as seen by NASA's Voyager 2 (remastered).png
This picture is color and brightness-corrected based on File:Uranus true colour.jpg. Fringes from the original color image is omitted.
Original caption: This is an image of the planet Uranus taken by the spacecraft Voyager 2 in 1986. The Voyager project is managed for NASA by the Jet Propulsion Laboratory.
Phobos colour 2008.jpg
Color image of Phobos, imaged by the Mars Reconnaissance Orbiter on 23 March 2008.

The High Resolution Imaging Science Experiment (HiRISE) camera on NASA's Mars Reconnaissance Orbiter took two images of the larger of Mars' two moons, Phobos, within 10 minutes of each other on 23 March 2008. This is the first, taken from a distance of about 6,800 kilometers (about 4,200 miles). It is presented in color by combining data from the camera's blue-green, red, and near-infrared channels.

The illuminated part of Phobos seen in the images is about 21 kilometers (13 miles) across. The most prominent feature in the images is the large crater Stickney in the lower right. With a diameter of 9 kilometers (5.6 miles), it is the largest feature on Phobos.

The color data accentuate details not apparent in black-and-white images. For example, materials near the rim of Stickney appear bluer than the rest of Phobos. Based on analogy with materials on our own moon, this could mean this surface is fresher, and therefore younger, than other parts of Phobos.

A series of troughs and crater chains is obvious on other parts of the moon. Although many appear radial to Stickney in this image, recent studies from the European Space Agency's Mars Express orbiter indicate that they are not related to Stickney. Instead, they may have formed when material ejected from impacts on Mars later collided with Phobos. The lineated textures on the walls of Stickney and other large craters are landslides formed from materials falling into the crater interiors in the weak Phobos gravity (less than one one-thousandth of the gravity on Earth).

In the full-resolution version of this image, a pixel encompasses 6.8 meters (22 feet), providing a resolution (smallest visible feature) of about 20 meters (about 65 feet). The image is in the HiRISE catalog as PSP_007769_9010.

NASA's Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Mars Reconnaissance Orbiter for NASA's Science Mission Directorate, Washington. Lockheed Martin Space Systems, Denver, is the prime contractor for the project and built the spacecraft. The High Resolution Imaging Science Experiment is operated by the University of Arizona, Tucson, and the instrument was built by Ball Aerospace & Technologies Corp., Boulder, Colo.


, Licence: CC-BY-SA-3.0

Carl Sagan Planet Walk, Ithaca, NY. The Sun.

PIA00040 Umbrielx2.47.jpg
Original Caption Released with Image: The southern hemisphere of Umbriel displays heavy cratering in this Voyager 2 image, taken Jan. 24, 1986, from a distance of 557,000 kilometers (346,000 miles). This frame, taken through the clear-filter of Voyager's narrow-angle camera, is the most detailed image of Umbriel, with a resolution of about 10 km (6 mi). Umbriel is the darkest of Uranus' larger moons and the one that appears to have experienced the lowest level of geological activity. It has a diameter of about 1,200 km (750 mi) and reflects only 16 percent of the light striking its surface; in the latter respect, Umbriel is similar to lunar highland areas. Umbriel is heavily cratered but lacks the numerous bright ray craters seen on the other large Uranian satellites; this results in a relatively uniform surface albedo (reflectivity). The prominent crater on the terminator (upper right) is about 110 km (70 mi) across and has a bright central peak. The strangest feature in this image (at top) is a curious bright ring, the most reflective area seen on Umbriel. The ring is about 140 km (90 miles) in diameter and lies near the satellite's equator. The nature of the ring is not known, although it might be a frost deposit, perhaps associated with an impact crater. Spots against the black background are due to 'noise' in the data. The Voyager project is managed for NASA by the Jet Propulsion Laboratory.

The original NASA image has been modified by cropping, increasing the linear pixel density by a factor of 2.47, and converting from .TIF to .JPG format.
Phoebe cassini.jpg
Phoebe, as imaged by the Cassini probe.
UltimaThule CA06 color 20190516.png
This composite image of the primordial contact binary Kuiper Belt Object 2014 MU69 (nicknamed Ultima Thule) – featured on the cover of the May 17 issue of the journal Science – was compiled from data obtained by NASA's New Horizons spacecraft as it flew by the object on Jan. 1, 2019. The image combines enhanced color data (close to what the human eye would see) with detailed high-resolution panchromatic pictures.
En-Solar System-article.ogg

Speaker: Thrownfootfalls

Authors of the article, Licence: CC BY-SA 3.0

This is a spoken word version of the Wikipedia article: Solar System

TW Hydrae protoplanetary disc horizontal.jpg
Author/Creator: S. Andrews (Harvard-Smithsonian CfA), ALMA (ESO/NAOJ/NRAO), Licence: CC BY 4.0
ALMA image of the planet-forming disc around the young, Sun-like star TW Hydrae. The inset image (upper right) zooms in on the gap nearest to the star, which is at the same distance as the Earth is from the Sun, suggesting an infant version of our home planet could be emerging from the dust and gas. The additional concentric light and dark features represent other planet-forming regions farther out in the disc.
Solar System true color.jpg
Author/Creator: CactiStaccingCrane, Licence: CC BY-SA 4.0
Finally... the true color of the Solar System! Dwarf planets are sorted by radius ascending from top down, with four main classifications from right to left: Asteroid belt (Ceres, above the Jovian moons), Kuiper belt (Orcus, Quaoar, Makemake, Haumea, Pluto), scattered disk (Gonggong, Eris), and detached objects (Sedna)
Planet and moon credits: User:MotloAstro (Sun); NASA (Mercury, Venus, Earth, Jupiter [with ESA], Saturn, Uranus, Neptune, Io, Europa, Ganymede, Callisto, Mimas, Enceladus, Tethys, Dione, Rhea, Titan, Iapetus, Miranda, Ariel, Umbriel, Titania, Oberon, Triton); ESA (Mars); User:Grevera (Moon)
Dwarf planets + moons credit: NASA and ESA
Mercury in true color.jpg
This is a cropped bottom right image from the original four image mosaic PIA11364: Mercury's "True" Color is in the Eye of the Beholder.

Original Caption Released with Image:

   Given the WAC’s ability to take images through 11 narrow-band color filters, it is natural to wonder what does Mercury look like in “true” color such as would be seen by the human eye. However, creating such a natural color view is not as simple as it may seem. Shown here are four images of Mercury. The image in the top left is the previously released grayscale monochrome single WAC filter (430-nanometer) image (PIA11245); the remaining three images are three-color composites, produced by placing the same three WAC filter images with peak sensitivities at 480, 560, and 630 nanometers in the blue, green, and red channels, respectively. The differences between the color representations result from how the brightness and contrast of each individual WAC filter image was adjusted before it was combined into a color picture. In the top right view, all of the three filter images were stretched using the same brightness and contrast settings. In the bottom left picture, the brightness and contrast of each of the three filter images were determined independent of the others. In the bottom right, the brightness and contrast settings used in the upper right version were slightly adjusted to make each of the three filter images span a similar range of brightness and contrast values.
   So which color representation is “correct” for Mercury? The answer to that would indeed depend on the eye of the beholder. Every individual sees color differently; the human eye has a range of sensitivities that vary from person to person, resulting in different perceptions of “true” color. In addition, the three MDIS filter bands are narrow, and light at wavelengths between their peaks is not detected, unlike the human eye. In general, in light visible to the human eye, Mercury’s surface shows only very subtle color variations, as seen in the three images here. However, when images from all 11 WAC filters are statistically compared and contrasted, these subtle color variations can be greatly enhanced, resulting in extremely colorful representations of Mercury’s surface, such as seen in a high-resolution image of Thākur crater (PIA11365).
   Date Acquired: October 6, 2008
   Image Mission Elapsed Time (MET): 131775256, 131775260, 131775264, 131775268
   Instrument: Wide Angle Camera (WAC) of the Mercury Dual Imaging System (MDIS)
   Resolution: 5 kilometers/pixel (3 miles/pixel)
   Scale: Mercury’s diameter is 4880 kilometers (3030 miles)
Spacecraft Altitude: 27,000 kilometers (17,000 miles)
Potw1749a Pallas crop.png
Author/Creator: Credit: ESO/Vernazza et al., Licence: CC BY 4.0
VLT's SPHERE spies rocky worlds

From the description at File:Potw1749a.tif:

These images were taken by ESO's SPHERE (Spectro-Polarimetric High-Contrast Exoplanet Research) instrument, installed on the Very Large Telescope at the Paranal Observatory, Chile. These strikingly-detailed views reveal four of the millions of rocky bodies in the main asteroid belt, a ring of asteroids between Mars and Jupiter that separates the rocky inner planets of the Solar System from the gaseous and icy outer planets.

Clockwise from top left, the asteroids shown here are 29 Amphitrite, 324 Bamberga, 2 Pallas, and 89 Julia. Named after the Greek goddess Pallas Athena, 2 Pallas is about 510 kilometres wide. This makes it the third largest asteroid in the main belt and one of the biggest asteroids in the entire Solar System. It contains about 7% of the mass of the entire asteroid belt — so hefty that it was once classified as a planet. A third of the size of 2 Pallas, 89 Julia is thought to be named after St Julia of Corsica. Its stony composition led to its classification as an S-type asteroid. Another S-type asteroid is 29 Amphitrite, which was only discovered in 1854. 324 Bamberga, one of the largest C-type asteroid in the asteroid belt, was discovered even later: Johann Palisa found it in 1892. Today, it is understood that C-type asteroids may actually be bodies from the outer Solar System following the migration of the giant planets. As such, they may contain ice in their interior.

Although the asteroid belt is often portrayed in science fiction as a place of violent collisions, packed full of large rocks too dangerous for even the most skilled of space pilots to navigate, it is actually very sparse. In total, the asteroid belt contains just 4% of the mass of the Moon, with about half of this mass contained in the four largest residents: Ceres, 4 Vesta, 2 Pallas, and 10 Hygiea.
NGC7293 (2004).jpg
The Helix Nebula: a Gaseous Envelope Expelled By a Dying Star
About the Object
  • Object Name: Helix Nebula, NGC 7293 or "The Eye of God"
  • Object Description: Planetary Nebula
  • Position (J2000): R.A. 22h 29m 48.20s
Dec. -20° 49' 26.0"
  • Constellation: Aquarius
  • Distance: About 690 light-years (213 parsecs)
  • Dimensions: The image is roughly 28.7 arcminutes (5.6 light-years or 1.7 parsecs) across.
About the Data
  • Instruments: ACS/WFC on Hubble Space Telescope (HST) and Mosaic II Camera on CTIO 4m telescope
  • Exposure Time: 4.5 hours (HST) and 10 minutes (CTIO)
  • Filters: F502N ([O III]) and F658N (Ha) (for the HST); c6009 (H alpha)and kc6014 ([O III]) for the CTIO
Image properties
  • Centered on white dwarfed and cropped
  • Downsampled to 3200x3200
  • Saved as jpg, quality 8/10, 5 scans
  • Stitching errors manually fixed