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85-545: The Solar System is the gravitationally bound system of the Sun and the objects that orbit it. It formed about 4.6 billion years ago when a dense region of a molecular cloud collapsed, forming the Sun and a protoplanetary disc . The Sun is a typical star that maintains a balanced equilibrium by the fusion of hydrogen into helium at its core , releasing this energy from its outer photosphere . Astronomers classify it as

170-460: A G-type main-sequence star . The largest objects that orbit the Sun are the eight planets . In order from the Sun, they are four terrestrial planets ( Mercury , Venus , Earth and Mars ); two gas giants ( Jupiter and Saturn ); and two ice giants ( Uranus and Neptune ). All terrestrial planets have solid surfaces. Inversely, all giant planets do not have a definite surface, as they are mainly composed of gases and liquids. Over 99.86% of

255-521: A planetary nebula , returning some of the material that formed the Sun—but now enriched with heavier elements like carbon—to the interstellar medium . Astronomers sometimes divide the Solar System structure into separate regions. The inner Solar System includes Mercury, Venus, Earth, Mars, and the bodies in the asteroid belt . The outer Solar System includes Jupiter, Saturn, Uranus, Neptune, and

340-408: A pre-main sequence or main-sequence star. Within its deep interior, the protostar has lower temperature than an ordinary star. At its center, hydrogen-1 is not yet fusing with itself. Theory predicts, however, that the hydrogen isotope deuterium (hydrogen-2) fuses with hydrogen-1, creating helium-3 . The heat from this fusion reaction tends to inflate the protostar, and thereby helps determine

425-591: 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. The Sun is the Solar System's star and by far its most massive component. Its large mass (332,900 Earth masses ), which comprises 99.86% of all the mass in the Solar System, produces temperatures and densities in its core high enough to sustain nuclear fusion of hydrogen into helium. This releases an enormous amount of energy , mostly radiated into space as electromagnetic radiation peaking in visible light . Because

510-406: A diameter of about 250 km (160 mi) and is one of the few minor planets possessing a ring 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

595-488: A few hundred kelvins such as water, methane, ammonia, hydrogen sulfide , and carbon dioxide .) Icy substances comprise the majority of the satellites of the giant planets and small objects that lie beyond Neptune's orbit. The centaurs are icy, comet-like bodies whose semi-major axes are longer than Jupiter's and shorter than Neptune's (between 5.5 and 30 AU). These are former Kuiper belt and scattered disc objects (SDOs) that were gravitationally perturbed closer to

680-414: A few meters to hundreds of kilometers in size. Many asteroids are divided into asteroid groups and families based on their orbital characteristics. Some asteroids have natural satellites that orbit them , that is, asteroids that orbit larger asteroids. The asteroid belt occupies a torus-shaped region between 2.3 and 3.3 AU from the Sun, which lies between the orbits of Mars and Jupiter. It

765-657: A graph of radius vs. mass for various models. The most likely radii for a given neutron star mass are bracketed by models AP4 (smallest radius) and MS2 (largest radius). BE is the ratio of gravitational binding energy mass equivalent to observed neutron star gravitational mass of M with radius R , B E = 0.60 β 1 − β 2 {\displaystyle BE={\frac {0.60\,\beta }{1-{\frac {\beta }{2}}}}} β = G M R c 2 . {\displaystyle \beta ={\frac {GM}{Rc^{2}}}.} Given current values and

850-465: A high-mass star due to strong radiation pressure or to a black hole in the case of a neutron star . The gravitational binding energy of a sphere with radius R {\displaystyle R} is found by imagining that it is pulled apart by successively moving spherical shells to infinity, the outermost first, and finding the total energy needed for that. Assuming a constant density ρ {\displaystyle \rho } ,

935-461: A protostar is not detectable at optical wavelengths, and cannot be placed in the Hertzsprung–Russell diagram , unlike the more evolved pre-main-sequence stars. The actual radiation emanating from a protostar is predicted to be in the infrared and millimeter regimes. Point-like sources of such long-wavelength radiation are commonly seen in regions that are obscured by molecular clouds . It

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1020-1173: A shell is the negative of the gravitational potential energy: d U = − G m s h e l l m i n t e r i o r r {\displaystyle dU=-G{\frac {m_{\mathrm {shell} }m_{\mathrm {interior} }}{r}}} Integrating over all shells yields: U = − G ∫ 0 R ( 4 π r 2 ρ ) ( 4 3 π r 3 ρ ) r d r = − G 16 3 π 2 ρ 2 ∫ 0 R r 4 d r = − G 16 15 π 2 ρ 2 R 5 {\displaystyle U=-G\int _{0}^{R}{\frac {\left(4\pi r^{2}\rho \right)\left({\tfrac {4}{3}}\pi r^{3}\rho \right)}{r}}dr=-G{\frac {16}{3}}\pi ^{2}\rho ^{2}\int _{0}^{R}{r^{4}}dr=-G{\frac {16}{15}}{\pi }^{2}{\rho }^{2}R^{5}} Since ρ {\displaystyle \rho }

1105-529: 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 (4,220 °F) at its coolest) than it is on the main sequence. The expanding Sun is expected to vaporize Mercury as well as Venus, and render Earth and Mars uninhabitable (possibly destroying Earth as well). Eventually,

1190-412: A 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

1275-407: Is a great ring of debris similar to the asteroid belt, but consisting mainly of objects composed primarily of ice. It extends between 30 and 50 AU from the Sun. It is composed mainly of small Solar System bodies, although the largest few are probably large enough to be dwarf planets. There are estimated to be over 100,000 Kuiper belt objects with a diameter greater than 50 km (30 mi), but

1360-427: Is a small chance that another star will pass through the Solar System in the next few billion years. Although this could destabilize the system and eventually lead millions of years later to expulsion of planets, collisions of planets, or planets hitting the Sun, it would most likely leave the Solar System much as it is today. The Sun's main-sequence phase, from beginning to end, will last about 10 billion years for

1445-426: Is a very young star that is still gathering mass from its parent molecular cloud . It is the earliest phase in the process of stellar evolution . For a low-mass star (i.e. that of the Sun or lower), it lasts about 500,000 years. The phase begins when a molecular cloud fragment first collapses under the force of self-gravity and an opaque, pressure-supported core forms inside the collapsing fragment. It ends when

1530-419: Is only a Newtonian approximation and in relativistic conditions other factors must be taken into account as well. Planets and stars have radial density gradients from their lower density surfaces to their much denser compressed cores. Degenerate matter objects (white dwarfs; neutron star pulsars) have radial density gradients plus relativistic corrections. Neutron star relativistic equations of state include

1615-900: Is simply equal to the mass of the whole divided by its volume for objects with uniform density, therefore ρ = M 4 3 π R 3 {\displaystyle \rho ={\frac {M}{{\frac {4}{3}}\pi R^{3}}}} And finally, plugging this into our result leads to U = − G 16 15 π 2 R 5 ( M 4 3 π R 3 ) 2 = − 3 G M 2 5 R {\displaystyle U=-G{\frac {16}{15}}\pi ^{2}R^{5}\left({\frac {M}{{\frac {4}{3}}\pi R^{3}}}\right)^{2}=-{\frac {3GM^{2}}{5R}}} U = − 3 G M 2 5 R {\displaystyle U=-{\frac {3GM^{2}}{5R}}} Two bodies, placed at

1700-465: Is strong consensus among astronomers that five members of the Kuiper belt are dwarf planets . Many dwarf planet candidates are being considered, pending further data for verification. The scattered disc, which overlaps the Kuiper belt but extends out to near 500 AU, is thought to be the source of short-period comets. Scattered-disc objects are believed to have been perturbed into erratic orbits by

1785-472: Is the gravitational constant , M is the mass of the sphere, and R is its radius. Assuming that the Earth is a sphere of uniform density (which it is not, but is close enough to get an order-of-magnitude estimate) with M = 5.97 × 10  kg and r = 6.37 × 10  m , then U = 2.24 × 10  J . This is roughly equal to one week of the Sun 's total energy output. It is 37.5 MJ/kg , 60% of

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1870-464: Is thought to be remnants from the Solar System's formation that failed to coalesce because of the gravitational interference of Jupiter. The asteroid belt contains tens of thousands, possibly millions, of objects over one kilometer in diameter. Despite this, the total mass of the asteroid belt is unlikely to be more than a thousandth of that of Earth. The asteroid belt is very sparsely populated; spacecraft routinely pass through without incident. Below are

1955-475: Is to the Sun, a hypothesis has arisen 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. The orbits of Solar System planets are nearly circular. Compared to many other systems, they have smaller orbital eccentricity . Although there are attempts to explain it partly with

2040-510: Is unknown. The zone of habitability of the Solar System is conventionally located in the inner Solar System, where planetary surface or atmospheric temperatures admit the possibility of liquid water . Habitability might be possible in subsurface oceans of various outer Solar System moons. Compared to many extrasolar systems, the Solar System stands out in lacking planets interior to the orbit of Mercury. The known Solar System lacks super-Earths , planets between one and ten times as massive as

2125-548: The ADM mass of the system, as it is manifest in its gravitational interaction with other distant systems, and the sum of the energies of all the atoms and other elementary particles of the system if disassembled. For a spherical body of uniform density , the gravitational binding energy U is given in newtonian gravity by the formula U = − 3 G M 2 5 R {\displaystyle U=-{\frac {3GM^{2}}{5R}}} where G

2210-491: The Milky Way galaxy. The Solar System formed at least 4.568 billion years ago from the gravitational collapse of a region within a large molecular cloud . This initial cloud was likely several light-years across and probably birthed several stars. 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

2295-650: The Platonic solids , but ongoing discoveries have invalidated these hypotheses. Some Solar System models attempt to convey the relative scales involved in the Solar System in human terms. Some are small in scale (and may be mechanical—called orreries )—whereas others extend across cities or regional areas. The largest such scale model, the Sweden Solar System , uses the 110-meter (361-foot) Avicii Arena in Stockholm as its substitute Sun, and, following

2380-452: The asteroid belt (between Mars's and Jupiter's orbit) and the Kuiper belt (just outside Neptune's orbit). Six planets, seven dwarf planets, and other bodies have orbiting natural satellites , which are commonly called 'moons'. The Solar System is constantly flooded by the Sun's charged particles , the solar wind , forming the heliosphere . Around 75–90 astronomical units from the Sun,

2465-495: The frost line , and it lies at roughly five times the Earth's distance from the Sun. The planets and other large objects in orbit around the Sun lie near the plane of Earth's orbit, known as the ecliptic . Smaller icy objects such as comets frequently orbit at significantly greater angles to this plane. Most of the planets in the Solar System have secondary systems of their own, being orbited by natural satellites called moons. All of

2550-417: The fusor stars in the Milky Way . The Sun is a population I star , having formed in the spiral arms of the Milky Way galaxy. It has a higher abundance of elements heavier than hydrogen and helium (" metals " in astronomical parlance) than the older population II stars in the galactic bulge and halo . Elements heavier than hydrogen and helium were formed in the cores of ancient and exploding stars, so

2635-535: The grand tack hypothesis suggests that a final inward migration of Jupiter dispersed much of the asteroid belt, leading to the Late Heavy Bombardment of the inner planets. The Solar System remains in a relatively stable, slowly evolving state by following isolated, gravitationally bound orbits around the Sun. Although the Solar System has been fairly stable for billions of years, it is technically chaotic , and may eventually be disrupted . There

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2720-426: The heliosphere , which spans much of the Solar System. Along with light , the Sun radiates a continuous stream of charged particles (a plasma ) called the solar wind . This stream spreads outwards at speeds from 900,000 kilometres per hour (560,000 mph) to 2,880,000 kilometres per hour (1,790,000 mph), filling the vacuum between the bodies of the Solar System. The result is a thin , dusty atmosphere, called

2805-552: The interplanetary medium , which extends to at least 100 AU . Activity on the Sun's surface, such as solar flares and coronal mass ejections , disturbs the heliosphere, creating space weather and causing geomagnetic storms . 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

2890-416: The magnetic poles . The largest stable 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. The inner Solar System is the region comprising the terrestrial planets and the asteroids . Composed mainly of silicates and metals, the objects of the inner Solar System are relatively close to

2975-559: The pre-solar nebula collapsed, conservation of angular momentum caused it to rotate faster. The center, where most of the mass collected, became increasingly hotter than the surroundings. As the contracting nebula spun faster, it began to flatten into a protoplanetary disc with a diameter of roughly 200 AU and a hot, dense protostar at the center. The planets formed by accretion from this disc, in which dust and gas gravitationally attracted each other, coalescing to form ever larger bodies. Hundreds of protoplanets may have existed in

3060-456: The Earth, although the hypothetical Planet Nine , if it does exist, could be a super-Earth orbiting in the edge of the Solar System. Uncommonly, it has only small terrestrial 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). As many of these super-Earths are closer to their respective stars than Mercury

3145-469: 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. The Kuiper belt

3230-544: The Solar System is home to the giant planets and their large moons. The centaurs and many short-period comets 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 planets of the inner Solar System because their lower temperatures allow these compounds to remain solid, without significant sublimation . The four outer planets, called giant planets or Jovian planets, collectively make up 99% of

3315-527: The Solar System's mass is in the Sun and nearly 90% of the remaining mass is in Jupiter and Saturn. There is a strong consensus among astronomers that the Solar System has at least nine dwarf planets : Ceres , Orcus , Pluto , Haumea , Quaoar , Makemake , Gonggong , Eris , and Sedna . There are a vast number of small Solar System bodies , such as asteroids , comets , centaurs , meteoroids , and interplanetary dust clouds . Some of these bodies are in

3400-399: The Solar System, created by heat and light pressure from the early 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. The boundary in the Solar System beyond which those volatile substances could coalesce is known as

3485-404: The Sun by the outer planets, and are expected to become comets or be ejected out of the Solar System. While most centaurs are inactive and asteroid-like, some exhibit cometary activity, such as the first centaur discovered, 2060 Chiron , which has been classified as a comet (95P) because it develops a coma just as comets do when they approach the Sun. The largest known centaur, 10199 Chariklo , has

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3570-454: The Sun compared to around two billion years for all other subsequent phases of the Sun's pre- remnant life combined. 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

3655-434: The Sun dominates the system by mass, it accounts for only about 2% of the angular momentum. 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. The radius of the Sun is 0.0047 AU (700,000 km; 400,000 mi). Thus, the Sun occupies 0.00001% (1 part in 10) of

3740-495: The Sun fuses hydrogen at its core, 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 but shorter lived. 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

3825-400: The Sun is growing brighter; early in its main-sequence life its brightness was 70% that of what it is today. 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. Solar wind from the Sun created the heliosphere and swept away

3910-470: 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. Members of the classical Kuiper belt are sometimes called "cubewanos", after the first of their kind to be discovered, originally designated 1992 QB 1 , (and has since been named Albion); they are still in near primordial, low-eccentricity orbits. Currently, there

3995-413: 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. Besides solar energy, the primary characteristic of the Solar System enabling

4080-490: The Sun, the larger the distance between its orbit and the orbit of the next nearest 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 and Johannes Kepler's model based on

4165-498: The Sun; the radius of this entire region is less than the distance between the orbits of Jupiter and Saturn. This region is within the frost line , which is a little less than 5 AU from the Sun. 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 silicates —which form their crusts and mantles —and metals such as iron and nickel which form their cores . Three of

4250-490: The absolute value of the potential energy per kilogram at the surface. The actual depth-dependence of density, inferred from seismic travel times (see Adams–Williamson equation ), is given in the Preliminary Reference Earth Model (PREM). Using this, the real gravitational binding energy of Earth can be calculated numerically as U = 2.49 × 10  J . According to the virial theorem ,

4335-399: The bodies in the Kuiper belt . 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 . The principal component of the Solar System is the Sun, a G-type main-sequence star that contains 99.86% of the system's known mass and dominates it gravitationally. The Sun's four largest orbiting bodies,

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4420-431: 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. The ejected outer layers may form

4505-432: The dense core accrues mass from its larger, surrounding cloud, self-gravity begins to overwhelm pressure, and collapse begins. Theoretical modeling of an idealized spherical cloud initially supported only by gas pressure indicates that the collapse process spreads from the inside toward the outside. Spectroscopic observations of dense cores that do not yet contain stars indicate that contraction indeed occurs. So far, however,

4590-409: The descriptions of the three largest bodies in the asteroid belt. They are all considered to be relatively intact protoplanets , a precursor stage before becoming a fully-formed planet (see List of exceptional asteroids ): Hilda asteroids are in a 3:2 resonance with Jupiter; that is, they go around the Sun three times for every two Jovian orbits. They lie in three linked clusters between Jupiter and

4675-496: The distance R from each other and reciprocally not moving, exert a gravitational force on a third body slightly smaller when R is small. This can be seen as a negative mass component of the system, equal, for uniformly spherical solutions, to: M b i n d i n g = − 3 G M 2 5 R c 2 {\displaystyle M_{\mathrm {binding} }=-{\frac {3GM^{2}}{5Rc^{2}}}} For example,

4760-439: The early Solar System, but they either merged or were destroyed or ejected, leaving the planets, dwarf planets, and leftover minor bodies . 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 (within the frost line ). They would eventually form the rocky planets of Mercury, Venus, Earth, and Mars. Because these refractory materials only comprised

4845-555: The fact that Earth is a gravitationally-bound sphere of its current size costs 2.494 21 × 10   kg of mass (roughly one fourth the mass of Phobos – see above for the same value in Joules ), and if its atoms were sparse over an arbitrarily large volume the Earth would weigh its current mass plus 2.494 21 × 10  kg kilograms (and its gravitational pull over a third body would be accordingly stronger). It can be easily demonstrated that this negative component can never exceed

4930-452: 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 higher metallicity is thought to have been crucial to the Sun's development of a planetary system because the planets formed from the accretion of "metals". The region of space dominated by the Solar magnetosphere is

5015-404: 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. Asteroids except for the largest, Ceres, are classified as small Solar System bodies and are composed mainly of carbonaceous , refractory rocky and metallic minerals, with some ice. They range from

5100-437: 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. The Sun is composed of roughly 98% hydrogen and helium, as are Jupiter and Saturn. A composition gradient exists in

5185-402: The gravitational binding energy of a star is about two times its internal thermal energy in order for hydrostatic equilibrium to be maintained. As the gas in a star becomes more relativistic , the gravitational binding energy required for hydrostatic equilibrium approaches zero and the star becomes unstable (highly sensitive to perturbations), which may lead to a supernova in the case of

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5270-567: The gravitational influence of Neptune's early outward migration . Most scattered disc objects have perihelia within the Kuiper belt but aphelia far beyond it (some more than 150 AU from the Sun). SDOs' orbits can be inclined up to 46.8° from the ecliptic plane. 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". Some astronomers classify centaurs as inward-scattered Kuiper belt objects along with

5355-488: The infalling gas is depleted, leaving a pre-main-sequence star , which contracts to later become a main-sequence star at the onset of hydrogen fusion producing helium. The modern picture of protostars, summarized above, was first suggested by Chushiro Hayashi in 1966. In the first models, the size of protostars was greatly overestimated. Subsequent numerical calculations clarified the issue, and showed that protostars are only modestly larger than main-sequence stars of

5440-448: The influence of the Sun's gravity upon an orbiting body, not the gravitational pulls of different bodies upon each other. On a human time scale, these perturbations can be accounted for using numerical models , but the planetary system can change chaotically over billions of years. The angular momentum of the Solar System is a measure of the total amount of orbital and rotational momentum possessed by all its moving components. Although

5525-413: The larger moons orbit their planets in prograde direction, matching the direction of planetary rotation; Neptune's moon Triton is the largest to orbit in the opposite, retrograde manner. Most larger objects rotate around their own axes in the prograde direction relative to their orbit, though the rotation of Venus is retrograde. To a good first approximation, Kepler's laws of planetary motion describe

5610-488: The largest natural satellites are in synchronous rotation , with one face permanently turned toward their parent. The four giant planets have planetary rings, thin discs of tiny particles that orbit them in unison. 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. That is, counter-clockwise, as viewed from above Earth's north pole. There are exceptions, such as Halley's Comet . Most of

5695-437: The main asteroid belt. Trojans are bodies located within another body's gravitationally stable Lagrange points : L 4 , 60° ahead in its orbit, or L 5 , 60° behind in its orbit. Every planet except Mercury and Saturn is known to possess at least 1 trojan. The Jupiter trojan population is roughly equal to that of the asteroid belt. After Jupiter, Neptune possesses the most confirmed trojans, at 28. The outer region of

5780-468: The mass orbiting the Sun. All four giant planets have multiple moons and a ring system, although only Saturn's rings are easily observed from Earth. Jupiter and Saturn are composed mainly of gases with extremely low melting points, such as hydrogen, helium, and neon , hence their designation as gas giants . Uranus and Neptune are ice giants , meaning they are largely composed of 'ice' in the astronomical sense (chemical compounds with melting points of up to

5865-483: The masses of a shell and the sphere inside it are: m s h e l l = 4 π r 2 ρ d r {\displaystyle m_{\mathrm {shell} }=4\pi r^{2}\rho \,dr} and m i n t e r i o r = 4 3 π r 3 ρ {\displaystyle m_{\mathrm {interior} }={\frac {4}{3}}\pi r^{3}\rho } The required energy for

5950-547: The orbits of objects around the Sun. These laws stipulate that each object travels along an ellipse with the Sun at one focus , which causes the body's distance from the Sun to vary 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 . With the exception of Mercury, the orbits of the planets are nearly circular, but many comets, asteroids, and Kuiper belt objects follow highly elliptical orbits. Kepler's laws only account for

6035-413: The outward-scattered residents of the scattered disc. Gravitationally bound The gravitational binding energy can be conceptually different within the theories of newtonian gravity and Albert Einstein 's theory of gravity called General Relativity . In newtonian gravity, the binding energy can be considered to be the linear sum of the interactions between all pairs of microscopic components of

6120-632: The positive component of a system. A negative binding energy greater than the mass of the system itself would indeed require that the radius of the system be smaller than: R ≤ 3 G M 5 c 2 {\displaystyle R\leq {\frac {3GM}{5c^{2}}}} which is smaller than 3 10 {\textstyle {\frac {3}{10}}} its Schwarzschild radius : R ≤ 3 10 r s {\displaystyle R\leq {\frac {3}{10}}r_{\mathrm {s} }} and therefore never visible to an external observer. However this

6205-425: The predicted outward spread of the collapse region has not been observed. The gas that collapses toward the center of the dense core first builds up a low-mass protostar, and then a protoplanetary disk orbiting the object. As the collapse continues, an increasing amount of gas impacts the disk rather than the star, a consequence of angular momentum conservation. Exactly how material in the disk spirals inward onto

6290-442: The presence of life is the heliosphere and planetary magnetic fields (for those planets that have them). These magnetic fields 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

6375-437: The protostar is not yet understood, despite a great deal of theoretical effort. This problem is illustrative of the larger issue of accretion disk theory, which plays a role in much of astrophysics. Regardless of the details, the outer surface of a protostar consists at least partially of shocked gas that has fallen from the inner edge of the disk. The surface is thus very different from the relatively quiescent photosphere of

6460-510: The remaining gas and dust from the protoplanetary disc into interstellar space. Following the dissipation of the protoplanetary disk , the Nice model proposes that gravitational encounters between planetisimals and the gas giants caused each to migrate into different orbits. This led to dynamical instability of the entire system, which scattered the planetisimals and ultimately placed the gas giants in their current positions. During this period,

6545-417: The same mass. This basic theoretical result has been confirmed by observations, which find that the largest pre-main-sequence stars are also of modest size. Star formation begins in relatively small molecular clouds called dense cores. Each dense core is initially in balance between self-gravity, which tends to compress the object, and both gas pressure and magnetic pressure , which tend to inflate it. As

6630-576: The scale, Jupiter is a 7.5-meter (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. At that scale, the distance to Proxima Centauri would be roughly 8 times further than the Moon is from Earth. If the Sun–Neptune distance is scaled to 100 metres (330 ft), then

6715-500: The size of the youngest observed pre-main-sequence stars. The energy generated from ordinary stars comes from the nuclear fusion occurring at their centers. Protostars also generate energy, but it comes from the radiation liberated at the shocks on its surface and on the surface of its surrounding disk. The radiation thus created must traverse the interstellar dust in the surrounding dense core. The dust absorbs all impinging photons and reradiates them at longer wavelengths. Consequently,

6800-404: The solar wind is halted, resulting in the heliopause . This is the boundary of the Solar System to interstellar space . The outermost region of the Solar System is the theorized Oort cloud , the source for long-period comets , extending to a radius of 2,000–200,000 AU . The closest star to the Solar System, Proxima Centauri , is 4.25 light-years (269,000 AU) away. Both stars belong to

6885-494: The star mass M expressed relative to the solar mass, M x = M M ⊙ , {\displaystyle M_{x}={\frac {M}{M_{\odot }}},} then the relativistic fractional binding energy of a neutron star is B E = 885.975 M x R − 738.313 M x {\displaystyle BE={\frac {885.975\,M_{x}}{R-738.313\,M_{x}}}} Protostar A protostar

6970-471: The system, while in General Relativity, this is only approximately true if the gravitational fields are all weak. When stronger fields are present within a system, the binding energy is a nonlinear property of the entire system, and it cannot be conceptually attributed among the elements of the system. In this case the binding energy can be considered to be the (negative) difference between

7055-477: 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. Within 50 million years, the pressure and density of hydrogen in the center of the protostar became great enough for it to begin thermonuclear fusion . As helium accumulates at its core,

7140-452: The total mass of the Kuiper belt is thought to be only a tenth or even a hundredth the mass of Earth. Many Kuiper belt objects have satellites, and most have orbits that are substantially inclined (~10°) to the plane of the ecliptic. The Kuiper belt can be roughly divided into the " classical " belt and the resonant trans-Neptunian objects . The latter have orbits whose periods are in a simple ratio to that of Neptune: for example, going around

7225-399: The volume of a sphere with a radius the size of Earth's orbit, whereas Earth's volume is roughly 1 millionth (10) that of the Sun. Jupiter, the largest planet, is 5.2 AU 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 from the Sun. With a few exceptions, the farther a planet or belt is from

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