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{{about|the Sun and its planetary system|other similar systems|Star system|and|Planetary system}}
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{{Use dmy dates|date=March 2016}}
{{Infobox planetary system
| title = Solar System
| image = Fanon Solar System.jpg
| image_alt = A representative image of the Solar System with sizes, but not distances, to scale
| image_size = 340px
| caption = {{longitem|The [[Sun]] and [[Planets of the solar system|planets of the Solar System]]<br />''(distances not to scale)''|style=padding:8px 0 10px 0;}}
| age = 4.568&nbsp;billion years
| location = {{longitem|{{ublist|class=nowrap |[[Local Interstellar Cloud]], [[Local Bubble]], |[[Orion–Cygnus Arm]], [[Milky Way]]}}}}
| system_mass = 1.0014 [[Solar mass]]es
| neareststar = {{longitem|{{ublist|class=nowrap |[[Proxima Centauri]]{{nbsp|2}}{{smaller|(4.25 [[Light-year|ly]])}} |[[Alpha Centauri]] {{smaller|(4.37 ly)}}}}}}
| nearestplanetary = {{nowrap|[[Proxima Centauri]] system{{nbsp|2}}{{smaller|(4.25 ly)}}}}
| semimajoraxis = {{nowrap|30.10 [[Astronomical unit|AU]]{{nbsp|2}}{{smaller|(4.503&nbsp;billion km)}}}}
| Kuiper_cliff = 50 AU
| noknown_stars = yes
| stars = 1{{nbsp|2}}{{smaller|([[Sun]])}}
| planets = {{longitem|{{smaller|{{hlist|8&nbsp;([[Mercury (planet)|Mercury]]|[[Venus]]|[[Earth]]|[[Mars]]|<br />[[Jupiter]]|[[Saturn]]|[[Uranus]]|[[Neptune]])}}}}}}
| outerplanetname = [[Neptune]]
| dwarfplanets = {{longitem|Possibly several hundred;<ref>{{cite web |url=http://www.mikebrownsplanets.com/2011/08/free-dwarf-planets.html |author=[[Michael E. Brown|Mike Brown]] |title=Free the dwarf planets! |date=23 August 2011 |work=Mike Brown's Planets}}</ref><br />five currently recognized by the [[International Astronomical Union|IAU]] {{smaller|{{hlist|([[Ceres (dwarf planet)|Ceres]]|[[Pluto]]|[[Haumea]]|[[Makemake]]|[[Eris (dwarf planet)|Eris]])}}}} }}
| satellites = {{longitem|525 {{hlist|{{smaller|(185 planetary<ref name="JPLbodies">{{cite web|title=How Many Solar System Bodies |publisher=NASA/JPL Solar System Dynamics |url=http://ssd.jpl.nasa.gov/?body_count |accessdate=20 April 2018}}</ref>}} |{{smaller|347 [[minor planet]]ary<ref name="MPMJohnston">{{cite web|date=12 April 2018|title=Asteroids with Satellites |publisher=Johnston's Archive |author=Wm. Robert Johnston |url=http://www.johnstonsarchive.net/astro/asteroidmoons.html |accessdate=20 April 2018}}</ref>)}}}}}}
| minorplanets = 778,897{{nbsp|2}}{{smaller|(as of 2018-06-21)<ref name=MPCSummary/>}}
| comets = 4,017{{nbsp|2}}{{smaller|(as of 2018-06-21)<ref name=MPCSummary>{{cite web|url=https://minorplanetcenter.net/mpc/summary|title=Latest Published Data|website=The International Astronomical Union Minor Planet Center|accessdate=21 May 2018}}</ref>}}
| roundsat = 19
| roundsatlink = List of gravitationally rounded objects of the Solar System#Satellites
| inclination = 60.19°{{nbsp|2}}{{smaller|(ecliptic)}}<!---If anyone can find a cited value for the inclination of the Solar System's invariable plane to the galactic plane, please replace this value--->
| galacticcenter = 27,000&thinsp;±&thinsp;1,000 ly
| orbitalspeed = 220 km/s
| orbitalperiod = 225–250 [[Myr]]
| spectral = [[G-type main-sequence star|G2V]]
| frostline = ≈5 AU<ref name="Mumma">{{Cite journal | last1 = Mumma | first1 = M. J. | last2 = Disanti | first2 = M. A. | last3 = Dello Russo | first3 = N. | last4 = Magee-Sauer | first4 = K. | last5 = Gibb | first5 = E. | last6 = Novak | first6 = R. | doi = 10.1016/S0273-1177(03)00578-7 | title = Remote infrared observations of parent volatiles in comets: A window on the early solar system | journal = Advances in Space Research | volume = 31 | issue = 12 | pages = 2563–2575 | year = 2003 | pmid =  | pmc = |bibcode = 2003AdSpR..31.2563M }}</ref>
| heliopause = ≈120 AU
| hillsphere = ≈1–3 ly
}}
{{Solar System navbox}}

The '''Solar System'''<ref group="lower-alpha">[[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" in their [http://www.iau.org/public/themes/naming/ naming guidelines document] {{Webarchive|url=https://web.archive.org/web/20210725053113/https://www.iau.org/public/themes/naming/ |date=25 July 2021 }}. The name is commonly rendered in lower case ("'''solar system'''"), as, for example, in the ''[[Oxford English Dictionary]]'' and [http://www.m-w.com/dictionary/solar%20system ''Merriam-Webster's 11th Collegiate Dictionary''].</ref> is the [[gravity|gravitationally]] bound system of the [[planet]]s and the [[Sun]] plus other objects that orbit it, either directly or indirectly.<ref group="lower-alpha">The [[natural satellites]] (moons) orbiting the Solar System's [[Sun's planets|planets]] are an example of the latter.</ref> Of the objects that orbit the Sun directly, the largest eight are the planets,<ref group="lower-alpha">Historically, several other bodies were once considered planets, including, from its discovery in 1930 until 2006, [[Pluto]]. See [[Former planets]].</ref> with the remainder being smaller objects, such as [[dwarf planet]]s and [[Small Solar System body|small Solar System bodies]]. Of the objects that orbit the Sun indirectly, the [[Natural satellite|moons]], two are larger than the smallest planet, [[Mercury (planet)|Mercury]].<ref group="lower-alpha">The two moons larger than Mercury are [[Ganymede (moon)|Ganymede]], which orbits [[Jupiter]], and [[Titan (moon)|Titan]], which orbits [[Saturn]]. Although bigger than Mercury, both moons have less than half the mass of Mercury.</ref>

The Solar System [[Formation and evolution of the Solar System|formed 4.6&nbsp;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 smaller inner planets, [[Mercury (planet)|Mercury]], [[Venus]], [[Earth]] and [[Mars]], are [[terrestrial planet]]s, being primarily composed of rock and metal. The four outer planets are [[giant planet]]s, being substantially more massive than the terrestrials. The two largest, Jupiter and [[Saturn]], are [[gas giant]]s, being composed mainly of [[hydrogen]] and [[helium]]; the two outermost planets, [[Uranus]] and [[Neptune]], are [[ice giant]]s, 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 planets have almost circular orbits that lie within a nearly flat disc called the [[ecliptic]].

The Solar System also contains smaller objects.{{refn |According to [[IAU definition of planet|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 [[Gravitation|gravity]] to have pulled it into a (near-)[[Sphere|spherical]] shape and that has [[Clearing the neighbourhood|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.<ref name="FinalResolution"/>
*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 [[planetesimal]]s from its neighbourhood and is also not a satellite.<ref name="FinalResolution"/> Pluto is a dwarf planet and the [[International Astronomical Union|IAU]] has recognized four other dwarf planets in the Solar System: [[Ceres (dwarf planet)|Ceres]], [[Haumea]], [[Makemake]], and [[Eris (dwarf planet)|Eris]].<ref name=name>{{cite web |date=7 November 2008 |title=Dwarf Planets and their Systems |work=Working Group for Planetary System Nomenclature (WGPSN) |url=http://planetarynames.wr.usgs.gov/append7.html#DwarfPlanets |accessdate=13 July 2008 |publisher=U.S. Geological Survey}}</ref> Other objects commonly (but not officially) treated as dwarf planets include {{mpl|2007 OR|10}}, [[90377 Sedna|Sedna]], [[90482 Orcus|Orcus]], and [[50000 Quaoar|Quaoar]].<ref>{{cite web|title=IAU Planet Definition Committee |author=Ron Ekers |publisher=International Astronomical Union |url=http://www.iau.org/public_press/news/release/iau0601/newspaper/ |accessdate=13 October 2008 |archiveurl=https://web.archive.org/web/20090603001603/http://www.iau.org/public_press/news/release/iau0601/newspaper/ |archivedate=3 June 2009 |df= }}</ref> In a reference to Pluto, other dwarf planets orbiting in the [[#Trans-Neptunian region|trans-Neptunian region]] are sometimes called "[[plutoid]]s".<ref name="IAU0804">{{cite news|date=11 June 2008 |title=Plutoid chosen as name for Solar System objects like Pluto |publisher=[[International Astronomical Union]], Paris |url=http://www.iau.org/public_press/news/release/iau0804 |accessdate=11 June 2008 |archiveurl=https://web.archive.org/web/20080613121232/http://www.iau.org/public_press/news/release/iau0804/ |archivedate=13 June 2008 |df= }}</ref>
*The remaining objects orbiting the Sun are known as [[Small Solar System body|small Solar System bodies]].<ref name="FinalResolution">{{cite news|title=The Final IAU Resolution on the definition of "planet" ready for voting |publisher=IAU |date=24 August 2006 |url=http://www.iau.org/iau0602.423.0.html |accessdate=2 March 2007 |deadurl=yes |archiveurl=https://web.archive.org/web/20090107044134/http://www.iau.org/iau0602.423.0.html |archivedate=7 January 2009 |df= }}</ref> |name=footnoteB |group=lower-alpha}} The [[asteroid belt]], which lies between the orbits of Mars and Jupiter, mostly contains objects composed, like the terrestrial planets, of rock and metal. Beyond Neptune's orbit lie the [[Kuiper belt]] and [[scattered disc]], which are populations of [[trans-Neptunian object]]s composed mostly of ices, and beyond them a newly discovered population of [[sednoid]]s. Within these populations are several dozen to possibly tens of thousands of objects large enough that they have been rounded by their own gravity.<ref name=Stern2012>{{cite web |url=http://pluto.jhuapl.edu/overview/piPerspective.php?page=piPerspective_08_24_2012 |title=The PI's Perspective |date=24 August 2012 |quote=Today we know of more than a dozen dwarf planets in the solar system |deadurl=yes |archive-url=https://web.archive.org/web/20141113225430/http://pluto.jhuapl.edu/overview/piPerspective.php?page=piPerspective_08_24_2012 |archive-date=13 November 2014}}</ref> Such objects are categorized as [[dwarf planet]]s. Identified dwarf planets include the asteroid [[Ceres (dwarf planet)|Ceres]] and the trans-Neptunian objects [[Pluto]] and [[Eris (dwarf planet)|Eris]].<ref group=lower-alpha name=footnoteB /> In addition to these two regions, various other small-body populations, including [[comet]]s, [[Centaur (minor planet)|centaurs]] and [[interplanetary dust cloud]]s, freely travel between regions. Six of the planets, at least four of the dwarf planets, and many of the smaller bodies are orbited by [[natural satellite]]s,<ref group=lower-alpha>See [[List of natural satellites of the Solar System]] for the full list of natural satellites of the eight planets and first five dwarf planets</ref> usually termed "moons" after the [[Moon]]. Each of the outer planets is encircled by [[planetary ring]]s of dust and other small objects.

The [[solar wind]], a stream of charged particles flowing outwards from the Sun, creates a bubble-like region in the [[interstellar medium]] known as the [[heliosphere]]. The [[Heliopause (astronomy)|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 comet]]s, may also exist at a distance roughly a thousand times further than the heliosphere. The Solar System is located in the [[Orion Arm]], 26,000 light-years from the center of the [[Milky Way]].

== Discovery and exploration ==
{{ref improve section|date=July 2018}}
{{main|Discovery and exploration of the Solar System}}
[[File:Heliocentric.jpg|thumb|upright|[[Andreas Cellarius]]'s illustration of the Copernican system, from the ''Harmonia Macrocosmica'' (1660)|alt=]]
For most of history, humanity did not recognize or understand the concept of the Solar System. Most people up to the [[Late Middle Ages]]–[[Renaissance]] 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 [[Ancient Greece|Greek]] philosopher [[Aristarchus of Samos]] had speculated on a heliocentric reordering of the cosmos, [[Nicolaus Copernicus]] was the first to develop a mathematically predictive [[heliocentric]] system.<ref>{{cite magazine|title= The astronomical system of Copernicus|author=WC Rufus|magazine=[[Popular Astronomy (US magazine)|Popular Astronomy]]|volume=31|page=510|date= 1923|bibcode=1923PA.....31..510R}}</ref><ref>{{cite book |title=Copernicus, Darwin, & Freud: revolutions in the history and philosophy of science |first=Friedel |last=Weinert |publisher=[[Wiley-Blackwell]] |date=2009 |page=21 |isbn=978-1-4051-8183-9}}</ref> 

In the 17th century, [[Galileo Galilei]], [[Johannes Kepler]], and [[Isaac Newton]] developed an understanding of [[physics]] that led to the gradual acceptance of the idea that Earth moves around the Sun and that the planets are governed by the same physical laws that govern Earth. The invention of the telescope led to the discovery of further planets and moons. Improvements in the telescope and the use of [[unmanned spacecraft]] have enabled the investigation of geological phenomena, such as [[mountains]], [[Impact crater|craters]], seasonal meteorological phenomena, such as [[clouds]], [[dust storms]] and [[ice caps]] on the other planets.
{{clear}}

== Structure and composition ==
{{wide image|Solar-System.pdf|900px|'''Comprehensive overview of the Solar System.''' The Sun, planets, dwarf planets and moons are at scale for their relative sizes, not for distances. A separate distance scale is at the bottom. Moons are listed near their planets by proximity of their orbits; only the largest moons are shown.}}
The principal component of the Solar System is the Sun, a [[G-type main-sequence star|G2 main-sequence star]] that contains 99.86% of the system's known mass and dominates it gravitationally.<ref>{{cite journal |author=M Woolfson |title=The origin and evolution of the solar system |doi= 10.1046/j.1468-4004.2000.00012.x |date=2000 |journal=[[Astronomy & Geophysics]] |volume=41 |issue=1 |pages=1.12|bibcode = 2000A&G....41a..12W }}</ref> The Sun's four largest orbiting bodies, the [[giant planet]]s, 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 planet]]s, the [[dwarf planet]]s, [[List of moons|moons]], [[asteroid]]s, and [[comet]]s) together comprise less than 0.002% of the Solar System's total mass.{{refn |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),<ref>{{cite arXiv |title=Origin and dynamical evolution of comets and their reservoirs |author=Alessandro Morbidelli |date=2005 |eprint=astro-ph/0512256 |class=astro-ph}}</ref> the Kuiper belt (estimated at roughly 0.1 Earth mass)<ref name="Delsanti-Beyond_The_Planets"/> and the asteroid belt (estimated to be 0.0005 Earth mass)<ref name="Krasinsky2002"/> 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.|name=footnoteD|group=lower-alpha}}

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.<ref name = "Levison2003">{{cite journal
| last = Levison | first = H. F. | authorlink = Harold F. Levison |author2=Morbidelli, A.
 | title = The formation of the Kuiper belt by the outward transport of bodies during Neptune's migration
| journal = [[Nature (journal)|Nature]]
| volume = 426 | pages = 419–421
| publisher = | date = 27 November 2003 | language =
| url = http://www.nature.com/nature/journal/v426/n6965/abs/nature02120.html
| doi = 10.1038/nature02120 | pmid = 14647375
| accessdate = 26 May 2012
| issue = 6965|bibcode = 2003Natur.426..419L }}</ref><ref>{{cite journal|title=From the Kuiper Belt to Jupiter-Family Comets: The Spatial Distribution of Ecliptic Comets|author1=Harold F. Levison |author2=Martin J Duncan |journal=[[Icarus (journal)|Icarus]]|date=1997|pages=13–32|doi=10.1006/icar.1996.5637 |issue=1|volume=127|bibcode=1997Icar..127...13L}}</ref> All the 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).<ref>{{cite web| last = Grossman | first = Lisa | title = Planet found orbiting its star backwards for first time | publisher = New Scientist | date = 13 August 2009 | url = https://www.newscientist.com/article/dn17603-planet-found-orbiting-its-star-backwards-for-first-time.html | accessdate = 10 October 2009}}</ref> There are [[retrograde motion|exceptions]], such as [[Halley's Comet]].

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.<ref>{{cite web |title=An Overview of the Solar System |author=nineplanets.org |url=http://www.nineplanets.org/overview.html |accessdate=15 February 2007}}</ref> 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.<ref>{{cite web|title=New Horizons Set to Launch on 9-Year Voyage to Pluto and the Kuiper Belt |author=Amir Alexander |work=The Planetary Society |date=2006 |url=http://www.planetary.org/news/2006/0116_New_Horizons_Set_to_Launch_on_9_Year.html |accessdate=8 November 2006 |deadurl=yes |archiveurl=https://web.archive.org/web/20060222080327/http://www.planetary.org/news/2006/0116_New_Horizons_Set_to_Launch_on_9_Year.html |archivedate=22 February 2006 |df= }}</ref>

Most of the planets in the Solar System have secondary systems of their own, being orbited by planetary objects called [[natural satellite]]s, or moons (two of which, [[Titan (moon)|Titan]] and [[Ganymede (moon)|Ganymede]], are larger than the planet [[Mercury (planet)|Mercury]]), and, in the case of the four giant planets, by [[planetary ring]]s, 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.

{{multiple image
| align     = right
| direction = horizontal
| width1    = 140
| width2    = 137
| image1    = Ecliptic plane 3d view.gif
| image2    = Solarsystem3DJupiter.gif
| footer    = All planets of the Solar System lie very close to the [[ecliptic]]. The closer they are to the Sun, the faster they travel ''([[inner planets]] on the left, all planets except Neptune on the right)''.
}}

[[Kepler's laws of planetary motion]] describe the orbits of objects about the Sun. Following Kepler's laws, each object travels along an [[ellipse]] with the Sun at one [[focus (geometry)|focus]]. Objects closer to the Sun (with smaller [[semi-major axis|semi-major axes]]) travel more quickly because they are more affected by the Sun's gravity. 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]]''. The orbits of the planets are nearly circular, but many comets, asteroids, and Kuiper belt objects follow highly elliptical orbits. The positions of the bodies in the Solar System can be predicted using [[numerical model of the Solar System|numerical models]].

Although the Sun dominates the system by mass, it accounts for only about 2% of the [[angular momentum]].<ref name="Marochnik1995">{{cite conference | isbn=0-937707-93-7 |author1=Marochnik, L. |author2=Mukhin, L. |lastauthoramp=yes | title = Is Solar System Evolution Cometary Dominated? | booktitle = Progress in the Search for Extraterrestrial Life | date = 1995| series = Astronomical Society of the Pacific Conference Series | volume = 74 | editor = Shostak, G. S. | pages = 83 | bibcode = 1995ASPC...74...83M}}</ref><ref>{{Cite journal | last1 = Bi | first1 = S. L. | last2 = Li | first2 = T. D. | last3 = Li | first3 = L. H. | last4 = Yang | first4 = W. M. | title = Solar Models with Revised Abundance | doi = 10.1088/2041-8205/731/2/L42 | journal = The Astrophysical Journal | volume = 731 | issue = 2 | pages = L42 | year = 2011 | pmid =  | pmc = |arxiv = 1104.1032 |bibcode = 2011ApJ...731L..42B }}</ref> 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.<ref name="Marochnik1995" />

The Sun, which comprises nearly all the matter in the Solar System, is composed of roughly 98% hydrogen and helium.<ref>
{{cite web
|title=The Sun's Vital Statistics
|url=http://solar-center.stanford.edu/vitalstats.html
|publisher=Stanford Solar Center
|accessdate=29 July 2008
}}, citing {{cite book
|last=Eddy |first=J.
|title=A New Sun: The Solar Results From Skylab
|url=https://history.nasa.gov/SP-402/contents.htm
|publisher=[[NASA]]
|date=1979
|page=37
|id=NASA SP-402
}}</ref> [[Jupiter]] and [[Saturn]], which comprise nearly all the remaining matter, are also primarily composed of hydrogen and helium.<ref>{{cite web
|url = http://nssdc.gsfc.nasa.gov/planetary/factsheet/saturnfact.html
|title = Saturn Fact Sheet
|publisher = NASA
|last = Williams
|first = Dr. David R.
|accessdate = 31 July 2007
|date = 7 September 2006}}</ref><ref>{{cite web|url = http://nssdc.gsfc.nasa.gov/planetary/factsheet/jupiterfact.html|title = Jupiter Fact Sheet|publisher = NASA|last = Williams|first = Dr. David R.|accessdate = 8 August 2007|date = 16 November 2004}}</ref> 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.<ref>{{cite book|title= Encyclopedia of the solar system|author1=Paul Robert Weissman |author2=Torrence V. Johnson |date=2007|page=615|isbn=0-12-088589-1|publisher=Academic Press}}</ref> The boundary in the Solar System beyond which those volatile substances could condense is known as the [[Frost line (astrophysics)|frost line]], and it lies at roughly 5 AU from the Sun.<ref name="Mumma" />

The objects of the inner Solar System are composed mostly of rock,<ref name="Podolak Weizman et al. 1995">{{cite journal| doi = 10.1016/0032-0633(95)00061-5| last1 = Podolak| first1 = M.| last2 = Weizman| first2 = A.| last3 = Marley| first3 = M.| date=December 1995 | title = Comparative models of Uranus and Neptune| journal = Planetary and Space Science| volume = 43| issue = 12| pages = 1517–1522| pmid = | pmc = | bibcode = 1995P&SS...43.1517P| ref = {{sfnRef|Podolak Weizman et al.|1995}}}}</ref> 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]].<ref name="Podolak Podolak et al. 2000">{{cite journal| doi = 10.1016/S0032-0633(99)00088-4| last1 = Podolak| first1 = M.| last2 = Podolak| first2 = J. I.| last3 = Marley| first3 = M. S.| date=February 2000 | title = Further investigations of random models of Uranus and Neptune| journal = Planetary and Space Science| volume = 48| issue = 2–3| pages = 143–151| pmid = | pmc = | bibcode = 2000P&SS...48..143P| ref = {{sfnRef|Podolak Podolak et al.|2000}}}}</ref> 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.<ref name="Podolak Podolak et al. 2000" /> Ices, like [[water]], [[methane]], [[ammonia]], [[hydrogen sulfide]], and [[carbon dioxide]],<ref name="Podolak Weizman et al. 1995" /> have melting points up to a few hundred kelvins.<ref name="Podolak Podolak et al. 2000" /> 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.<ref name="Podolak Podolak et al. 2000" /> Icy substances comprise the majority of the satellites of the giant planets, as well as most of Uranus and Neptune (the so-called "[[ice giant]]s") and the numerous small objects that lie beyond Neptune's orbit.<ref name="Podolak Weizman et al. 1995" /><ref name=zeilik>{{cite book | page=240 | author=Michael Zellik| title=Astronomy: The Evolving Universe | edition=9th | date=2002 | publisher=[[Cambridge University Press]] | isbn=0-521-80090-0 | oclc=223304585}}</ref> Together, gases and ices are referred to as ''[[volatiles]]''.<ref name=Placxo>{{cite book|last=Placxo|first=Kevin W.|author2=Gross, Michael |title=Astrobiology: a brief introduction|date=2006|publisher=[[JHU Press]]|page=66|isbn=978-0-8018-8367-5|url=https://books.google.com/?id=2JuGDL144BEC&pg=PA66&dq=inventory+volatiles+hydrogen&q=inventory%20volatiles%20hydrogen}}</ref>

=== Distances and scales ===
The distance<!--at this precision, doesn't matter which distance is measured--> from Earth to the Sun is {{convert|1|AU|km mi|lk=on|abbr=~}}. For comparison, the radius of the Sun is {{cvt|0.0047|AU|km|sigfig=1}}. Thus, the Sun occupies 0.00001% (10<sup>−5</sup> %) of the volume of a sphere with a radius the size of Earth's orbit, whereas Earth's volume is roughly one millionth (10<sup>−6</sup>) that of the Sun. Jupiter, the largest planet, is {{convert|5.2|AU|km}} from the Sun and has a radius of {{convert|71000|km|AU|abbr=on|sigfig=2}}, whereas the most distant planet, Neptune, is {{convert|30|AU|km|abbr=on|sigfig=2}} from the Sun.

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 (for example, the [[Titius–Bode law]]),<ref>{{cite web|title=Dawn: A Journey to the Beginning of the Solar System |work=Space Physics Center: UCLA |url=http://www-ssc.igpp.ucla.edu/dawn/background.html |date=2005 |accessdate=3 November 2007 |deadurl=yes |archiveurl=https://archive.is/20120524184638/http://www-ssc.igpp.ucla.edu/dawn/background.html |archivedate=24 May 2012 |df= }}</ref> but no such theory has been accepted. The images at the beginning of this section show the orbits of the various constituents of the Solar System on different scales.

Some [[Solar System model]]s attempt to convey the relative scales involved in the Solar System on human terms. Some are small in scale (and may be mechanical—called [[Orrery|orreries]])—whereas others extend across cities or regional areas.<ref>{{cite web | url=http://www.noao.edu/education/peppercorn/pcmain.html | title= The Thousand-Yard Model &#124;subtitle Earth as a Peppercorn | author= Guy Ottewell | date=1989 | work= NOAO Educational Outreach Office | accessdate=10 May 2012 }}</ref> The largest such scale model, the [[Sweden Solar System]], uses the 110-metre (361&nbsp;ft) [[Ericsson Globe]] in [[Stockholm]] as its substitute Sun, and, following the scale, Jupiter is a 7.5-metre (25-foot) sphere at [[Arlanda International Airport]], 40&nbsp;km (25&nbsp;mi) away, whereas the farthest current object, [[90377 Sedna|Sedna]], is a 10&nbsp;cm (4&nbsp;in) sphere in [[Luleå]], 912&nbsp;km (567&nbsp;mi) away.<ref>{{cite web|title=Tours of Model Solar Systems|url=http://internal.psychology.illinois.edu/~wbrewer/solarmodel.html|archive-url=https://web.archive.org/web/20110412124455/http://internal.psychology.illinois.edu/~wbrewer/solarmodel.html|dead-url=yes|archive-date=12 April 2011|publisher=University of Illinois|accessdate=10 May 2012}}</ref><ref name=Sedna>{{cite web|url=http://www.kuriren.nu/arkiv/2005/11/17/Lokalt/1510647/Lule%C3%A5-%C3%A4r-Sedna.aspx |title=Luleå är Sedna. I alla fall om vår sol motsvaras av Globen i Stockholm. |publisher=Norrbotten Kuriren (in Swedish) |accessdate=10 May 2010 |deadurl=yes |archiveurl=https://web.archive.org/web/20100715074955/http://www.kuriren.nu/arkiv/2005/11/17/Lokalt/1510647/Lule%C3%A5-%C3%A4r-Sedna.aspx |archivedate=15 July 2010 |df= }}</ref>

If the Sun–Neptune distance is [[Solar System model|scaled]] to 100 metres, then the Sun would be about 3&nbsp;cm in diameter (roughly two-thirds the diameter of a golf ball), the giant planets would be all smaller than about 3&nbsp;mm, and Earth's diameter along with that of the other terrestrial planets would be smaller than a flea (0.3&nbsp;mm) at this scale.<ref>See, for example, {{cite web | date=9 July 2004 | url=http://www.nasa.gov/audience/foreducators/5-8/features/F_Solar_System_Scale.html | title=Solar System Scale | work=NASA Educator Features | author=Office of Space Science | accessdate=2 April 2013 | archive-date=27 August 2016 | archive-url=https://web.archive.org/web/20160827184323/http://www.nasa.gov/audience/foreducators/5-8/features/F_Solar_System_Scale.html | dead-url=yes }}</ref>

{{wide image|Solarsystemobjectsinscale.jpg|5000px|{{center|The Solar System. Distances are to scale, objects are not.}}}}

{{Clear}}
{{Distance from Sun using EasyTimeline}}

== Formation and evolution ==
{{main|Formation and evolution of the Solar System}}
The Solar System formed 4.568&nbsp;billion years ago from the gravitational collapse of a region within a large [[molecular cloud]].{{refn |group=lower-alpha |The date is based on the oldest [[inclusion (mineral)|inclusions]] found to date in [[meteorite]]s, {{val|4568.2|+0.2|-0.4}} million years, and is thought to be the date of the formation of the first solid material in the collapsing nebula.<ref>{{cite journal |last1=Bouvier |first1=A. |last2=Wadhwa |first2=M. |year=2010 |title=The age of the Solar System redefined by the oldest Pb–Pb age of a meteoritic inclusion |url= |journal=Nature Geoscience |volume=3 |issue=9| pages=637–641 |doi=10.1038/NGEO941 |bibcode=2010NatGe...3..637B}}</ref>}} This initial cloud was likely several light-years across and probably birthed several stars.<ref name="Arizona">{{cite web |title=Lecture 13: The Nebular Theory of the origin of the Solar System |url=http://atropos.as.arizona.edu/aiz/teaching/nats102/mario/solar_system.html |work=University of Arizona |accessdate=27 December 2006}}</ref> 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 [[solar nebula|pre-solar nebula]],<ref>{{Cite conference|title=The chemical composition of the pre-solar nebula |author=Irvine, W. M.|booktitle=Cometary exploration; Proceedings of the International Conference |volume=1|pages=3|date=1983 |bibcode=1983coex....1....3I}}</ref> 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.<ref name="Arizona" /> As the contracting nebula rotated faster, it began to flatten into a [[protoplanetary disc]] with a diameter of roughly 200&nbsp;[[Astronomical unit|AU]]<ref name="Arizona" /> and a hot, dense [[protostar]] at the centre.<ref>{{Cite journal |last=Greaves |first=Jane S. |date=7 January 2005 |title=Disks Around Stars and the Growth of Planetary Systems |journal=[[Science (journal)|Science]] |volume=307 | issue=5706 |pages=68–71 |doi=10.1126/science.1101979 |pmid=15637266 |bibcode=2005Sci...307...68G}}</ref><ref>{{cite web |date=5 April 2000 |url=http://www.nap.edu/openbook.php?record_id=1732&page=21|title=Present Understanding of the Origin of Planetary Systems |publisher=National Academy of Sciences |accessdate=19 January 2007}}</ref> The planets formed by [[accretion (astrophysics)|accretion]] from this disc,<ref>{{cite journal | doi= 10.1086/429160 | title= Chondrule-forming Shock Fronts in the Solar Nebula: A Possible Unified Scenario for Planet and Chondrite Formation | date= 2005 | author= Boss, A. P. | journal=[[The Astrophysical Journal]] | volume= 621 | issue= 2 | pages= L137 | last2= Durisen | first2= R. H. | bibcode=2005ApJ...621L.137B|arxiv = astro-ph/0501592 }}</ref> 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, leaving the planets, dwarf planets, and leftover [[small Solar System body|minor bodies]].
[[File:Solarnebula.jpg|thumb|upright=1.25|left|Artist's concept of the early Solar System|link=Special:FilePath/Solarnebula.jpg]]
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]]. 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.

Within 50 million years, the pressure and density of [[hydrogen]] in the centre of the protostar became great enough for it to begin [[nuclear fusion|thermonuclear fusion]].<ref name=Yi2001>{{cite journal |author1=Sukyoung Yi |author2=Pierre Demarque |author3=Yong-Cheol Kim |author4=Young-Wook Lee |author5=Chang H. Ree |author6=Thibault Lejeune |author7=Sydney Barnes | title=Toward Better Age Estimates for Stellar Populations: The ''Y''<sup>2</sup> Isochrones for Solar Mixture | journal=[[Astrophysical Journal Supplement]] | arxiv=astro-ph/0104292 | date=2001 | volume=136 |issue=2 | pages=417–437 | doi=10.1086/321795 | bibcode=2001ApJS..136..417Y}}</ref> The temperature, reaction rate, pressure, and density increased until [[hydrostatic equilibrium]] was achieved: the thermal pressure equalled the force of gravity. At this point, the Sun became a [[main sequence|main-sequence]] star.<ref>{{cite journal |author1=A. Chrysostomou |author2=P. W. Lucas | title=The Formation of Stars | journal=[[Contemporary Physics]] | date=2005 | volume=46 | issue=1 | pages=29–40 | bibcode=2005ConPh..46...29C | doi=10.1080/0010751042000275277}}</ref> The main-sequence phase, from beginning to end, will last about 10&nbsp;billion years for the Sun compared to around two billion years for all other phases of the Sun's pre-[[stellar remnant|remnant]] life combined.<ref name=mnras386_1>{{cite journal |author1=Schröder, K.-P. |author2=Connon Smith, Robert | title=Distant future of the Sun and Earth revisited | journal=Monthly Notices of the Royal Astronomical Society |date=May 2008 | volume=386 | issue=1 | pages=155–163 | bibcode=2008MNRAS.386..155S | doi=10.1111/j.1365-2966.2008.13022.x |arxiv = 0801.4031 }}</ref> Solar wind from the Sun created the [[heliosphere]] and swept away the remaining gas and dust from the protoplanetary disc into interstellar space, ending the planetary formation process. The Sun is growing brighter; early in its main-sequence life its brightness was 70% that of what it is today.<ref>{{cite journal|title=Towards a Solution to the Early Faint Sun Paradox: A Lower Cosmic Ray Flux from a Stronger Solar Wind|author=Nir J. Shaviv|journal=[[Journal of Geophysical Research]]|doi=10.1029/2003JA009997|arxiv=astroph/0306477|date=2003|volume=108|issue=A12|page=1437|bibcode=2003JGRA..108.1437S}}</ref>

The Solar System will remain roughly as we know it today until the hydrogen in the core of the Sun has been entirely converted to helium, which will occur roughly 5&nbsp;billion years from now. This will mark the end of the Sun's main-sequence life. At this 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 much 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 vastly increased surface area, the surface of the Sun will be considerably cooler (2,600 K at its coolest) than it is on the main sequence.<ref name=mnras386_1 /> 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 move away into space, leaving a [[white dwarf]], an extraordinarily dense object, half the original mass of the Sun but only the size of Earth.<ref>{{cite web |author=Pogge, Richard W. |date=1997 |url=http://www.astronomy.ohio-state.edu/~pogge/Lectures/vistas97.html |title=The Once & Future Sun |work=New Vistas in Astronomy |accessdate=7 December 2005 |archiveurl= https://web.archive.org/web/20050527094435/http://www-astronomy.mps.ohio-state.edu/Vistas/ |archivedate=27 May 2005 |deadurl=yes}}</ref> 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 [[metallicity|heavier elements]] like carbon—to the interstellar medium.

== Sun ==
{{main|Sun}}
[[File:Planets and sun size comparison.jpg|thumb|upright=1.25|Size comparison of the [[Sun]] and the [[planet]]s]]

The Sun is the Solar System's [[star]] and by far its most massive component. Its large mass (332,900 Earth masses),<ref>{{cite web|title=Sun: Facts & Figures|publisher=NASA|url=http://solarsystem.nasa.gov/planets/profile.cfm?Object=Sun&Display=Facts&System=Metric |accessdate=14 May 2009 |archiveurl = https://web.archive.org/web/20080102034758/http://solarsystem.nasa.gov/planets/profile.cfm?Object=Sun&Display=Facts&System=Metric |archivedate = 2 January 2008}}</ref> which comprises 99.86% of all the mass in the Solar System,<ref name=Woolfson00>
{{Cite journal
 |last=Woolfson |first=M.
 |date=2000
 |title=The origin and evolution of the solar system
 |journal=[[Astronomy & Geophysics]]
 |volume=41 |issue=1 |page=12
 |bibcode=2000A&G....41a..12W
 |doi=10.1046/j.1468-4004.2000.00012.x
 |ref=harv
}}</ref> produces temperatures and densities in its [[solar core|core]] high enough to sustain [[nuclear fusion]] of [[hydrogen]] into [[helium]], making it a [[main sequence|main-sequence]] star.<ref>{{cite book|last=Zirker|first=Jack B.|title=Journey from the Center of the Sun|date=2002|publisher=[[Princeton University Press]]|isbn=978-0-691-05781-1|pages=120–127}}</ref> This releases an enormous amount of [[energy]], mostly [[radiant energy|radiated]] into [[outer space|space]] as [[electromagnetic radiation]] peaking in [[visible light]].<ref>{{cite web|title=Why is visible light visible, but not other parts of the spectrum?|publisher=The Straight Dome|date=2003|url=http://www.straightdope.com/columns/read/2085/why-is-visible-light-visible-but-not-other-parts-of-the-spectrum|accessdate=14 May 2009}}</ref>

The Sun is a [[G-type main-sequence star|G2-type main-sequence star]]. Hotter main-sequence stars are more luminous. The Sun's temperature is intermediate between that of the [[O-type main-sequence star|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 dwarf]]s, make up 85% of the stars in the Milky Way.<ref name=sun>{{cite news |first=Ker |last=Than |title=Astronomers Had it Wrong: Most Stars are Single |publisher=SPACE.com |date=30 January 2006 |url=http://www.space.com/scienceastronomy/060130_mm_single_stars.html |accessdate=1 August 2007}}</ref><ref>{{Cite conference|date=2001|pages=119 |author1=Smart, R. L. |author2=Carollo, D. |author3=Lattanzi, M. G. |author4=McLean, B. |author5=Spagna, A. |booktitle=Ultracool Dwarfs: New Spectral Types L and T |editor1=Hugh R. A. Jones |editor2=Iain A. Steele |publisher=[[Springer (publisher)|Springer]] |title=The Second Guide Star Catalogue and Cool Stars|bibcode=2001udns.conf..119S}}</ref>

The Sun is a [[Population I stars|population I star]]; it has a higher abundance of elements heavier than hydrogen and helium ("[[metallicity|metals]]" in astronomical parlance) than the older population II stars.<ref>{{cite journal |author1=T. S. van Albada |author2=Norman Baker |title=On the Two Oosterhoff Groups of Globular Clusters |journal=[[The Astrophysical Journal]] |volume=185 |date=1973 |pages=477–498 |doi=10.1086/152434 |bibcode=1973ApJ...185..477V}}</ref> 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".<ref>{{cite journal |title=An Estimate of the Age Distribution of Terrestrial Planets in the Universe: Quantifying Metallicity as a Selection Effect |author=Charles H. Lineweaver |journal=[[Icarus (journal)|Icarus]] |date=9 March 2001 |arxiv=astro-ph/0012399 |doi=10.1006/icar.2001.6607 |volume=151 |issue=2 |pages=307–313 |bibcode=2001Icar..151..307L}}</ref>

== Interplanetary medium ==
{{main|Interplanetary medium|Solar wind}}
[[File:Heliospheric-current-sheet.gif|thumb|upright=1.25|left|The [[heliospheric current sheet]]]]
The vast majority of the Solar System consists of a near-[[vacuum]] known as the [[interplanetary medium]]. Along with [[Sunlight|light]], the Sun radiates a continuous stream of charged particles (a [[plasma (physics)|plasma]]) known as the [[solar wind]]. This stream of particles spreads outwards at roughly 1.5&nbsp;million kilometres per hour,<ref>{{cite web |title=Solar Physics: The Solar Wind |work=Marshall Space Flight Center |date=16 July 2006<!--11:42:58--> |url=http://solarscience.msfc.nasa.gov/SolarWind.shtml |accessdate=3 October 2006}}</ref> creating a tenuous atmosphere that permeates the interplanetary medium out to at least 100&nbsp;AU ''(see {{section link||Heliosphere}})''.<ref name="Voyager" /> Activity on the Sun's surface, such as [[solar flare]]s and [[coronal mass ejection]]s, disturb the heliosphere, creating [[space weather]] and causing [[geomagnetic storm]]s.<ref name="SunFlip">{{cite web|url=https://science.nasa.gov/headlines/y2001/ast15feb_1.htm |title=The Sun Does a Flip |accessdate=4 February 2007 |last=Phillips |first=Tony |date=15 February 2001 |work=NASA–Science News |deadurl=yes |archiveurl=https://web.archive.org/web/20090512121817/https://science.nasa.gov/headlines/y2001/ast15feb_1.htm |archivedate=12 May 2009 |df= }}</ref> 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.<ref>{{cite web|url=https://science.nasa.gov/headlines/y2003/22apr_currentsheet.htm |title=A Star with two North Poles |date=22 April 2003 |work=NASA–Science News |deadurl=yes |archiveurl=https://web.archive.org/web/20090718014855/https://science.nasa.gov/headlines/y2003/22apr_currentsheet.htm |archivedate=18 July 2009 |df= }}</ref><ref>{{cite journal|last1=Riley |bibcode=2002JGRA.107g.SSH8R |first1=Pete |title=Modeling the heliospheric current sheet: Solar cycle variations |doi=10.1029/2001JA000299 |date=2002 |volume=107 |journal=[[Journal of Geophysical Research]] |url=http://ulysses.jpl.nasa.gov/science/monthly_highlights/2002-July-2001JA000299.pdf |deadurl=yes |archiveurl=https://web.archive.org/web/20090814052347/http://ulysses.jpl.nasa.gov/science/monthly_highlights/2002-July-2001JA000299.pdf |archivedate=14 August 2009 |df= }}</ref>

[[Earth's magnetic field]] stops [[Earth's atmosphere|its atmosphere]] from being stripped away by the solar wind.<ref>{{cite web | url=https://science.nasa.gov/science-news/science-at-nasa/1998/ast08dec98_1/ | title=Solar Wind blows some of Earth's atmosphere into space | date=8 December 1998 | work=Science@NASA Headline News | access-date=3 August 2018 | archive-date=8 April 2022 | archive-url=https://web.archive.org/web/20220408025859/https://science.nasa.gov/science-news/science-at-nasa/1998/ast08dec98_1/ | dead-url=yes }}</ref> 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.<ref>{{cite journal |last=Lundin |first=Richard |date=9 March 2001 |title=Erosion by the Solar Wind |journal=[[Science (journal)|Science]] |volume=291 |issue=5510 |page=1909 |doi=10.1126/science.1059763 |pmid=11245195}}</ref> [[Coronal mass ejection]]s 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 [[Aurora (astronomy)|aurorae]] seen near the [[Earth's magnetic field#Magnetic poles|magnetic poles]].

The heliosphere and planetary magnetic fields (for those planets that have them) partially shield the Solar System from high-energy interstellar particles called [[cosmic ray]]s. 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.<ref name="Langner_et_al_2005">{{cite journal |last=Langner |first=U. W. |author2=M. S. Potgieter |date=2005 |title=Effects of the position of the solar wind termination shock and the heliopause on the heliospheric modulation of cosmic rays |journal=[[Advances in Space Research]] |volume=35 |issue=12 |pages=2084–2090 |doi=10.1016/j.asr.2004.12.005 |bibcode=2005AdSpR..35.2084L}}</ref>

The interplanetary medium is home to at least two disc-like regions of [[cosmic dust]]. The first, the [[interplanetary dust cloud|zodiacal dust cloud]], lies in the inner Solar System and causes the [[zodiacal light]]. It was likely formed by collisions within the asteroid belt brought on by gravitational interactions with the planets.<ref>{{cite web|date=1998 |title=Long-term Evolution of the Zodiacal Cloud |url=http://astrobiology.arc.nasa.gov/workshops/1997/zodiac/backman/IIIc.html |accessdate=3 February 2007 |deadurl=yes |archiveurl=https://web.archive.org/web/20060929030040/http://astrobiology.arc.nasa.gov/workshops/1997/zodiac/backman/IIIc.html |archivedate=29 September 2006 |df= }}</ref> The second dust cloud extends from about 10&nbsp;AU to about 40&nbsp;AU, and was probably created by similar collisions within the [[Kuiper belt]].<ref>{{cite web |date=2003 |title=ESA scientist discovers a way to shortlist stars that might have planets |work=ESA Science and Technology |url=http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=29471 |accessdate=3 February 2007}}</ref><ref>{{cite journal |last=Landgraf |first=M. |author2=Liou, J.-C. |author3=Zook, H. A. |author4=Grün, E. |date=May 2002 |title=Origins of Solar System Dust beyond Jupiter |journal=[[The Astronomical Journal]] |volume=123 |issue=5 |pages=2857–2861 |doi=10.1086/339704 |url=http://astron.berkeley.edu/~kalas/disksite/library/ladgraf02.pdf |accessdate=9 February 2007 |bibcode=2002AJ....123.2857L |arxiv=astro-ph/0201291 |archive-date=15 May 2016 |archive-url=http://arquivo.pt/wayback/20160515115002/http://astron.berkeley.edu/~kalas/disksite/library/ladgraf02.pdf |dead-url=yes }}</ref>

== Inner Solar System ==
The '''inner Solar System''' is the region comprising the [[#Terrestrial planets|terrestrial planets]] and the [[#Asteroid belt|asteroid belt]].<ref name=inner>{{cite web|title=Inner Solar System |publisher=NASA Science (Planets) |url=http://nasascience.nasa.gov/planetary-science/exploring-the-inner-solar-system |accessdate=9 May 2009 |deadurl=yes |archiveurl=https://web.archive.org/web/20090511182050/http://nasascience.nasa.gov/planetary-science/exploring-the-inner-solar-system |archivedate=11 May 2009 |df= }}</ref> Composed mainly of [[silicate]]s and metals, 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 (astrophysics)|frost line]], which is a little less than 5 [[Astronomical unit|AU]] (about 700 million km) from the Sun.<ref>{{cite web |url=http://www.astronoo.com/en/articles/frost-line.html |title=Frost line or snow line or ice line in the solar system |website=Astronoo |access-date=28 November 2017}}</ref>

=== {{anchor|Terrestrial planets}} Inner planets ===
{{main|Terrestrial planet}}
[[File:Telluric planets size comparison.jpg|thumb|upright=1.25|The inner planets. From left to right: [[Earth]], [[Mars]], [[Venus]], and [[Mercury (planet)|Mercury]] (sizes to scale).]]
The four terrestrial or '''inner planets''' have dense, [[rock (geology)|rocky]] compositions, few or no [[natural satellite|moons]], and no [[planetary ring|ring systems]]. They are composed largely of [[Refractory (planetary science)|refractory]] minerals, such as the [[silicate]]s, which form their [[crust (geology)|crusts]] and [[mantle (geology)|mantles]], and metals, such as [[iron]] and [[nickel]], which form their [[planetary core|cores]]. Three of the four inner planets (Venus, Earth and Mars) have [[atmosphere]]s substantial enough to generate [[weather]]; all have [[impact crater]]s and [[tectonics|tectonic]] surface features, such as [[rift valley]]s and [[volcano]]es. 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).

==== Mercury ====
{{main|Mercury (planet)}}
:Mercury (0.4&nbsp;[[Astronomical unit|AU]] from the Sun) is the closest planet to the Sun and the smallest planet in the Solar System (0.055 Earth masses). Mercury has no natural satellites; besides impact craters, its only known geological features are lobed ridges or [[rupes]] that were probably produced by a period of contraction early in its history.<ref>Schenk P., Melosh H. J. (1994), ''Lobate Thrust Scarps and the Thickness of Mercury's Lithosphere'', Abstracts of the 25th Lunar and Planetary Science Conference, 1994LPI....25.1203S</ref> Mercury's very tenuous atmosphere consists of atoms blasted off its surface by the solar wind.<ref>{{cite web |date=2006 |author=Bill Arnett |title=Mercury |work=The Nine Planets |url=http://www.nineplanets.org/mercury.html |accessdate=14 September 2006}}</ref> 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.<ref>{{cite journal | last1 = Benz | first1 = W. | last2 = Slattery | first2 = W. L. | last3 = Cameron | first3 = A. G. W. | year = 1988 | title = Collisional stripping of Mercury's mantle | url = | journal = Icarus | volume = 74 | issue = 3| pages = 516–528 | doi=10.1016/0019-1035(88)90118-2|bibcode = 1988Icar...74..516B }}</ref><ref>{{cite journal | last1 = Cameron | first1 = A. G. W. | year = 1985 | title = The partial volatilization of Mercury | url = | journal = Icarus | volume = 64 | issue = 2| pages = 285–294 | doi=10.1016/0019-1035(85)90091-0|bibcode = 1985Icar...64..285C }}</ref>

==== Venus ====
{{main|Venus}}
:Venus (0.7 AU from the Sun) is close in size to Earth (0.815 Earth masses) 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 [[Celsius|°C]] (752&nbsp;°F), most likely due to the amount of [[greenhouse gas]]es in the atmosphere.<ref>{{cite journal |author=Mark Alan Bullock |title=The Stability of Climate on Venus |publisher=Southwest Research Institute |date=1997 |url=http://www.boulder.swri.edu/~bullock/Homedocs/PhDThesis.pdf |format=PDF |accessdate=26 December 2006 |deadurl=yes |archiveurl=https://web.archive.org/web/20070614202751/http://www.boulder.swri.edu/~bullock/Homedocs/PhDThesis.pdf |archivedate=14 June 2007 |df=dmy-all }}</ref> No definitive evidence of current geological activity has been detected on Venus, but it has no magnetic field that would prevent depletion of its substantial atmosphere, which suggests that its atmosphere is being replenished by volcanic eruptions.<ref>{{cite web |date=1999 |author=Paul Rincon |title=Climate Change as a Regulator of Tectonics on Venus |work=Johnson Space Center Houston, TX, Institute of Meteoritics, University of New Mexico, Albuquerque, NM |url=http://www.boulder.swri.edu/~bullock/Homedocs/Science2_1999.pdf |format=PDF |accessdate=19 November 2006 |deadurl=yes |archiveurl=https://web.archive.org/web/20070614202807/http://www.boulder.swri.edu/~bullock/Homedocs/Science2_1999.pdf |archivedate=14 June 2007 |df=dmy-all }}</ref>

==== Earth ====
{{main|Earth}}
:Earth (1 AU 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.<ref name=life>{{cite web |title=What are the characteristics of the Solar System that lead to the origins of life? |publisher=NASA Science (Big Questions) |url=https://science.nasa.gov/planetary-science/big-questions/what-are-the-characteristics-of-the-solar-system-that-lead-to-the-origins-of-life-1/ |accessdate=30 August 2011 |archive-date=15 September 2011 |archive-url=https://web.archive.org/web/20110915154635/http://science.nasa.gov/planetary-science/big-questions/what-are-the-characteristics-of-the-solar-system-that-lead-to-the-origins-of-life-1/ |dead-url=yes }}</ref> 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]].<ref>{{cite web |title=Earth's Atmosphere: Composition and Structure |author=Anne E. Egger, M.A./M.S. |work=VisionLearning.com |url=http://www.visionlearning.com/library/module_viewer.php?c3=&mid=107&l=|accessdate=26 December 2006}}</ref> It has one natural satellite, the [[Moon]], the only large satellite of a terrestrial planet in the Solar System.

==== Mars ====
{{main|Mars}}
:Mars (1.5&nbsp;AU from the Sun) is smaller than Earth and Venus (0.107 Earth masses). It has an atmosphere of mostly [[carbon dioxide]] with a surface pressure of 6.1 millibars (roughly 0.6% of that of Earth).<ref>{{cite book|title= Encyclopaedia of the Solar System|editor=Lucy-Ann McFadden|display-editors=etal|chapter=Mars Atmosphere: History and Surface Interactions|author1=David C. Gatling |author2=Conway Leovy |pages=301–314|date=2007}}</ref> Its surface, peppered with vast 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.<ref>{{cite web |date=2004 |title=Modern Martian Marvels: Volcanoes? |author=David Noever |work=NASA Astrobiology Magazine |url=http://www.astrobio.net/news/modules.php?op=modload&name=News&file=article&sid=1360&mode=thread&order=0&thold=0 |accessdate=23 July 2006}}</ref> Its red colour comes from [[iron(III) oxide|iron oxide]] (rust) in its soil.<ref>{{cite web|title=Mars: A Kid's Eye View|publisher=NASA|url=http://solarsystem.nasa.gov/planets/profile.cfm?Object=Mars&Display=Kids|accessdate=14 May 2009|archive-date=20 October 2014|archive-url=https://web.archive.org/web/20141020111930/http://solarsystem.nasa.gov/planets/profile.cfm?Object=Mars&Display=Kids|dead-url=yes}}</ref> Mars has two tiny natural satellites ([[Deimos (moon)|Deimos]] and [[Phobos (moon)|Phobos]]) thought to be either captured [[asteroid]]s,<ref>{{cite web |date=2004 |title=A Survey for Outer Satellites of Mars: Limits to Completeness |author1=Scott S. Sheppard |author2=David Jewitt |author3=Jan Kleyna |last-author-amp=yes |work=[[Astronomical Journal]] |url=http://www2.ess.ucla.edu/~jewitt/papers/2004/SJK2004.pdf|accessdate=26 December 2006}}</ref> or ejected debris from a massive impact early in Mars's history.<ref>{{cite journal|author=Pascal Rosenblatt, Sébastien Charnoz, Kevin M. Dunseath, Mariko Terao-Dunseath, Antony Trinh, Ryuki Hyodo, Hidenori Genda, Stéven Toupin|title=Accretion of Phobos and Deimos in an extended debris disc stirred by transient moons|journal=Nature Geoscience|year=2016|doi=10.1038/ngeo2742|bibcode=2016NatGe...9..581R}}</ref>

=== Asteroid belt ===
{{main|Asteroid belt}}
[[File:InnerSolarSystem-en.png|thumb|The donut-shaped [[asteroid belt]] is located between the orbits of [[Mars]] and [[Jupiter]].
{| style="width:100%;"
|-
| valign=top |
{{legend2|#FFFF00|border=1px solid #B3B300|[[Sun]]}}<br />
{{legend2|#6ad768|border=1px solid #36C133|[[Jupiter trojan]]s}}<br />
{{legend2|#007DD6|border=1px solid #00508A|[[Planet|Planetary orbit]]}}
| valign=top |
{{legend2|#e9e9e9|border=1px solid #999999|[[Asteroid belt]]}}<br />
{{legend2|#d39300|border=1px solid #855D00|[[Hilda family|Hilda asteroids]]}}<br />
{{legend2|#c90000|border=1px solid #940000|[[Near-Earth object|NEOs]] {{small|(selection)}}}}
|}
]]

[[Asteroid]]s except for the largest, Ceres, are classified as [[Small Solar System body|small Solar System bodies]]<ref group=lower-alpha name=footnoteB /> and are composed mainly of [[refractory (astronomy)|refractory]] rocky and metallic [[mineral]]s, with some ice.<ref>{{cite web|title=IAU Planet Definition Committee |publisher=International Astronomical Union |date=2006 |url=http://www.iau.org/public_press/news/release/iau0601/newspaper/ |accessdate=1 March 2009 |deadurl=yes |archiveurl=https://web.archive.org/web/20090603001603/http://www.iau.org/public_press/news/release/iau0601/newspaper/ |archivedate=3 June 2009 |df= }}</ref><ref>{{cite web|title=Are Kuiper Belt Objects asteroids? Are large Kuiper Belt Objects planets? |publisher=[[Cornell University]] |url=http://curious.astro.cornell.edu/question.php?number=601 |accessdate=1 March 2009 |deadurl=yes |archiveurl=https://web.archive.org/web/20090103110110/http://curious.astro.cornell.edu/question.php?number=601 |archivedate=3 January 2009 }}</ref> They range from a few metres to hundreds of kilometres in size. Asteroids smaller than one meter are usually called [[meteoroid]]s and [[micrometeoroids]] (grain-sized), depending on different, somewhat arbitrary definitions.

The asteroid belt occupies the orbit between Mars and Jupiter, between 2.3 and 3.3&nbsp;AU 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.<ref>{{cite journal
 |author1      = Petit, J.-M.
 |author2      = Morbidelli, A.
 |author3      = Chambers, J.
 |title        = The Primordial Excitation and Clearing of the Asteroid Belt
 |journal      = [[Icarus (journal)|Icarus]]
 |date         = 2001
 |volume       = 153
 |issue        = 2
 |pages        = 338–347
 |url          = http://www.gps.caltech.edu/classes/ge133/reading/asteroids.pdf
 |format       = PDF
 |accessdate   = 22 March 2007
 |doi          = 10.1006/icar.2001.6702
 |bibcode      = 2001Icar..153..338P
 |archive-date = 21 February 2007
 |archive-url  = https://web.archive.org/web/20070221085835/http://www.gps.caltech.edu/classes/ge133/reading/asteroids.pdf
 |dead-url     = yes
}}</ref> The asteroid belt contains tens of thousands, possibly millions, of objects over one kilometre in diameter.<ref>{{cite web |date=2002 |title=New study reveals twice as many asteroids as previously believed |work=ESA |url=http://www.esa.int/esaCP/ESAASPF18ZC_index_0.html|accessdate=23 June 2006}}</ref> Despite this, the total mass of the asteroid belt is unlikely to be more than a thousandth of that of Earth.<ref name=Krasinsky2002>{{cite journal |authorlink=Georgij A. Krasinsky |first=G. A. |last=Krasinsky |author2=[[Elena V. Pitjeva|Pitjeva, E. V.]] |author3=Vasilyev, M. V. |author4=Yagudina, E. I. |bibcode=2002Icar..158...98K |title=Hidden Mass in the Asteroid Belt |journal=[[Icarus (journal)|Icarus]] |volume=158 |issue=1 |pages=98–105 |date=July 2002 |doi=10.1006/icar.2002.6837}}</ref> The asteroid belt is very sparsely populated; [[Space probe|spacecraft]] routinely pass through without incident.

==== Ceres ====
{{main|Ceres (dwarf planet)}}
[[File:PIA22083-Ceres-DwarfPlanet-GravityMapping-20171026.gif|thumb|left|Ceres - map of gravity fields: red is high; blue, low.]]
:Ceres (2.77&nbsp;AU) is the largest asteroid, a [[protoplanet]], and a dwarf planet.<ref group=lower-alpha name=footnoteB /> It has a diameter of slightly under 1,000&nbsp;km, 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, and was reclassified to asteroid in the 1850s as further observations revealed additional asteroids.<ref>{{cite web |title=History and Discovery of Asteroids |format=DOC |work=NASA |url=http://dawn.jpl.nasa.gov/DawnClassrooms/1_hist_dawn/history_discovery/Development/a_modeling_scale.doc |accessdate=29 August 2006}}</ref> It was classified as a dwarf planet in 2006 when the [[IAU definition of planet|definition of a planet]] was created.

==== Asteroid groups ====

: Asteroids in the asteroid belt are divided into [[asteroid group]]s and [[Asteroid family|families]] based on their orbital characteristics. [[Asteroid moon]]s are asteroids that orbit larger asteroids. They are not as clearly distinguished as planetary moons, sometimes being almost as large as their partners. The asteroid belt also contains [[main-belt comet]]s, which may have been the source of Earth's water.<ref>{{cite web |date=2006 |author=Phil Berardelli |title=Main-Belt Comets May Have Been Source of Earths Water |work=SpaceDaily |url=http://www.spacedaily.com/reports/Main_Belt_Comets_May_Have_Been_Source_Of_Earths_Water.html |accessdate=23 June 2006 |archive-date=16 August 2011 |archive-url=https://web.archive.org/web/20110816083413/http://www.spacedaily.com/reports/Main_Belt_Comets_May_Have_Been_Source_Of_Earths_Water.html |dead-url=yes }}</ref>

: [[Jupiter trojan]]s are located in either of Jupiter's [[L5 point|L<sub>4</sub> or L<sub>5</sub> 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 family|Hilda asteroids]] are in a 2:3 [[Orbital resonance|resonance]] with Jupiter; that is, they go around the Sun three times for every two Jupiter orbits.<ref name=Barucci>{{cite book|last=Barucci|first=M. A.|author2=Kruikshank, D.P. |author3=Mottola S. |author4= Lazzarin M. |date=2002 |chapter=Physical Properties of Trojan and Centaur Asteroids|title=Asteroids III|publisher=University of Arizona Press|pages=273–87|location=Tucson, Arizona}}</ref>

: The inner Solar System also contains [[near-Earth object|near-Earth asteroids]], many of which cross the orbits of the inner planets.<ref name = "MorbidelliAstIII">{{cite journal|url = http://www.boulder.swri.edu/~bottke/Reprints/Morbidelli-etal_2002_AstIII_NEOs.pdf|title = Origin and Evolution of Near-Earth Objects|journal = Asteroids III|editor = W. F. Bottke Jr. |editor2=A. Cellino |editor3=P. Paolicchi |editor4=R. P. Binzel|pages = 409–422|date=January 2002|publisher = University of Arizona Press|format=PDF|bibcode = 2002aste.book..409M|first1= A.|last1= Morbidelli |last2 = Bottke|first2 = W. F.|last3 = Froeschlé|first3 = Ch.|last4 = Michel|first4 = P.}}</ref> Some of them are [[potentially hazardous object]]s.

==Outer Solar System==
The outer region of the Solar System is home to the [[giant planet]]s and their large moons. The [[Centaur (minor planet)|centaurs]] and many [[short-period comet]]s 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.

===Outer planets===
{{main|Outer planets|Giant planet}}[[File:Size planets comparison.jpg|upright=1.25|thumb|The outer planets (in the background) [[Jupiter]], [[Saturn]], [[Uranus]] and [[Neptune]], compared to the inner planets [[Earth]], [[Venus]], [[Mars]] and [[Mercury (planet)|Mercury]] (in the foreground).]]

The four outer planets, or giant planets (sometimes called Jovian planets), collectively make up 99% of the mass known to orbit the Sun.<ref group=lower-alpha name=footnoteD /> Jupiter and Saturn are together more than 400 times the mass of Earth and consist overwhelmingly of hydrogen and helium; Uranus and Neptune are far less massive (<20 Earth masses each) and are composed primarily of ices. For these reasons, some astronomers suggest they belong in their own category, "ice giants".<ref>{{cite web|title=Formation of Giant Planets |author1=Jack J. Lissauer |author2=David J. Stevenson |work=NASA Ames Research Center; California Institute of Technology |date=2006 |url=http://www.gps.caltech.edu/uploads/File/People/djs/lissauer&stevenson(PPV).pdf |format=PDF |accessdate=16 January 2006 |deadurl=yes |archiveurl=https://web.archive.org/web/20090326060004/http://www.gps.caltech.edu/uploads/File/People/djs/lissauer%26stevenson%28PPV%29.pdf |archivedate=26 March 2009 |df= }}</ref> All four giant planets have [[Planetary ring|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.

====Jupiter====
{{main|Jupiter}}
:Jupiter (5.2&nbsp;AU), at 318 Earth masses, 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]]. Jupiter has [[Moons of Jupiter|79 known satellites]]. The four largest, [[Ganymede (moon)|Ganymede]], [[Callisto (moon)|Callisto]], [[Io (moon)|Io]], and [[Europa (moon)|Europa]], show similarities to the terrestrial planets, such as volcanism and internal heating.<ref>{{cite web|title=Geology of the Icy Galilean Satellites: A Framework for Compositional Studies |author=Pappalardo, R T |work=Brown University |date=1999 |url=http://www.agu.org/cgi-bin/SFgate/SFgate?&listenv=table&multiple=1&range=1&directget=1&application=fm99&database=%2Fdata%2Fepubs%2Fwais%2Findexes%2Ffm99%2Ffm99&maxhits=200&=%22P11C-10%22 |accessdate=16 January 2006 |deadurl=yes |archiveurl=https://web.archive.org/web/20070930165551/http://www.agu.org/cgi-bin/SFgate/SFgate?&listenv=table&multiple=1&range=1&directget=1&application=fm99&database=%2Fdata%2Fepubs%2Fwais%2Findexes%2Ffm99%2Ffm99&maxhits=200&=%22P11C-10%22 |archivedate=30 September 2007 |df= }}</ref> Ganymede, the largest satellite in the Solar System, is larger than Mercury.

====Saturn====
{{main|Saturn}}
:Saturn (9.5&nbsp;AU), distinguished by its extensive [[Rings of Saturn|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 Earth masses. Saturn is the only planet of the Solar System that is less dense than water.<ref name=preserve>{{cite web|url=http://www.preservearticles.com/201101233659/saturn-the-most-beautiful-planet-of-our-solar-system.html |title=Saturn – The Most Beautiful Planet of our solar system |work=Preserve Articles |date=23 January 2011 |accessdate=24 July 2011 |archiveurl=https://www.webcitation.org/62D9uTOJ0?url=http://www.preservearticles.com/201101233659/saturn-the-most-beautiful-planet-of-our-solar-system.html |archivedate=5 October 2011 |deadurl=no |df= }}</ref> The rings of Saturn are made up of small ice and rock particles. Saturn has [[Moons of Saturn|62 confirmed satellites]] composed largely of ice. Two of these, [[Titan (moon)|Titan]] and [[Enceladus]], show signs of geological activity.<ref>{{cite journal|last1=Kargel|first1=J. S.|title=Cryovolcanism on the icy satellites|journal=Earth, Moon, and Planets|volume=67|pages=101–113|date=1994|doi=10.1007/BF00613296|bibcode=1995EM&P...67..101K}}</ref> Titan, the second-largest moon in the Solar System, is larger than Mercury and the only satellite in the Solar System with a substantial atmosphere.

====Uranus====
{{main|Uranus}}
:Uranus (19.2&nbsp;AU), at 14 Earth masses, is the lightest 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]]. It has a much colder core than the other giant planets and radiates very little heat into space.<ref>{{cite journal |title=10 Mysteries of the Solar System|journal=[[Astronomy Now]] |volume=19 |page=65 |date=2005 |bibcode=2005AsNow..19h..65H |author1=Hawksett |first1=David |last2=Longstaff |first2=Alan |last3=Cooper |first3=Keith |last4=Clark |first4=Stuart }}</ref> Uranus has [[Moons of Uranus|27 known satellites]], the largest ones being [[Titania (moon)|Titania]], [[Oberon (moon)|Oberon]], [[Umbriel (moon)|Umbriel]], [[Ariel (moon)|Ariel]], and [[Miranda (moon)|Miranda]].

====Neptune====
{{main|Neptune}}
:Neptune (30.1 AU), though slightly smaller than Uranus, is more massive (equivalent to 17 Earths) and hence more [[Density|dense]]. It radiates more internal heat, but not as much as Jupiter or Saturn.<ref>{{Cite journal|title=Post Voyager comparisons of the interiors of Uranus and Neptune |author1=Podolak, M. |author2=Reynolds, R. T. |author3=Young, R. | date=1990|pages=1737–1740|issue=10|volume=17|doi=10.1029/GL017i010p01737 |bibcode=1990GeoRL..17.1737P|journal=Geophysical Research Letters}}</ref> Neptune has [[Moons of Neptune|14 known satellites]]. The largest, [[Triton (moon)|Triton]], is geologically active, with [[geyser]]s of [[liquid nitrogen]].<ref>{{cite web|title=The Plausibility of Boiling Geysers on Triton |author=Duxbury, N. S., Brown, R. H. |work=Beacon eSpace |date=1995 |url=http://trs-new.jpl.nasa.gov/dspace/handle/2014/28034?mode=full |accessdate=16 January 2006 |deadurl=yes |archiveurl=https://web.archive.org/web/20090426005806/http://trs-new.jpl.nasa.gov/dspace/handle/2014/28034?mode=full |archivedate=26 April 2009 |df= }}</ref> Triton is the only large satellite with a [[retrograde orbit]]. Neptune is accompanied in its orbit by several [[minor planet]]s, termed [[Neptune trojan]]s, that are in 1:1 [[Orbital resonance|resonance]] with it.

===Centaurs===
{{main|Centaur (minor planet)}}
The centaurs are icy comet-like bodies whose orbits have semi-major axes greater than Jupiter's (5.5&nbsp;AU) and less than Neptune's (30&nbsp;AU). The largest known centaur, [[10199 Chariklo]], has a diameter of about 250&nbsp;km.<ref name=spitzer>{{Cite conference|title=Physical Properties of Kuiper Belt and Centaur Objects: Constraints from Spitzer Space Telescope |author1=John Stansberry |author2=Will Grundy |author3=Mike Brown |author4=Dale Cruikshank |author5=John Spencer |author6=David Trilling |author7=Jean-Luc Margot |booktitle=The Solar System Beyond Neptune |arxiv=astro-ph/0702538|pages=161 |date=2007|bibcode=2008ssbn.book..161S}}</ref> The first centaur discovered, [[2060 Chiron]], has also been classified as comet (95P) because it develops a coma just as comets do when they approach the Sun.<ref>{{cite web|date=1995 |author=Patrick Vanouplines |title=Chiron biography |work=Vrije Universitiet Brussel |url=http://www.vub.ac.be/STER/www.astro/chibio.htm |accessdate=23 June 2006 |deadurl=yes |archiveurl=https://web.archive.org/web/20090502122306/http://www.vub.ac.be/STER/www.astro/chibio.htm |archivedate=2 May 2009 |df= }}</ref>

==Comets==
[[File:Comet-Hale-Bopp-29-03-1997 hires adj.jpg|upright|thumb|[[Hale–Bopp]] seen in 1997]]
{{main|Comet}}

Comets are small Solar System bodies,<ref group=lower-alpha name=footnoteB /> 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 [[sublimation (chemistry)|sublimate]] and [[ion]]ise, creating a [[coma (cometary)|coma]]: a long tail of gas and dust often visible to the naked eye.

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 [[Comet Hale–Bopp|Hale–Bopp]], are thought to originate in the [[#Oort cloud|Oort cloud]]. Many comet groups, such as the [[Kreutz Sungrazers]], formed from the breakup of a single parent.<ref>{{cite journal |author=Sekanina, Zdeněk |date=2001 |title=Kreutz sungrazers: the ultimate case of cometary fragmentation and disintegration? |volume=89 |journal=Publications of the Astronomical Institute of the Academy of Sciences of the Czech Republic |pages=78–93 |bibcode=2001PAICz..89...78S}}</ref> Some comets with [[hyperbolic trajectory|hyperbolic]] orbits may originate outside the Solar System, but determining their precise orbits is difficult.<ref name="hyperbolic">{{cite journal |last=Królikowska |first=M. |date=2001 |title=A study of the original orbits of ''hyperbolic'' comets |journal=[[Astronomy & Astrophysics]] |volume=376 |issue=1 |pages=316–324 |doi=10.1051/0004-6361:20010945 |bibcode=2001A&A...376..316K}}</ref> Old comets that have had most of their volatiles driven out by solar warming are often categorised as asteroids.<ref>{{cite journal |last1=Whipple |first1=Fred L. |title=The activities of comets related to their aging and origin |journal=[[Celestial Mechanics and Dynamical Astronomy]] |volume=54 |pages=1–11 |date=1992 |doi=10.1007/BF00049540 |bibcode=1992CeMDA..54....1W}}</ref>

== Trans-Neptunian region ==
Beyond the orbit of Neptune lies the area of the "[[trans-Neptunian object|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 [[Orbital inclination|tilted toward the plane]] of the Solar System and reaches much further out than the Kuiper belt. The entire region is still [[Timeline of Solar System exploration|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.<ref>{{cite web |url=http://www.americanscientist.org/issues/feature/2015/1/journey-to-the-solar-systems-third-zone/1 |title=Journey to the Solar System's Third Zone |author=[[Alan Stern]] |work=American Scientist |date=February 2015}}</ref>

=== Kuiper belt ===
{{main|Kuiper belt}}

[[File:Kuiper belt plot objects of outer solar system.png|thumb|Known objects in the [[Kuiper belt]]
{| style="width: 100%;"
|-
| valign=top |
{{legend2|#FFFF00|border=1px solid #B3B300|[[Sun]]}}<br />
{{legend2|#aaaaaa|border=1px solid #777777|[[Jupiter trojan]]s}}<br />
{{legend2|#FF4D4D|border=1px solid #FF0000|[[Giant planet]]s}}
| valign=top |
{{legend2|#66CCFF|border=1px solid #00AAFF|[[Kuiper belt]]}}<br />
{{legend2|#FFB657|border=1px solid #FF950A|[[Scattered disc]]}}<br />
{{legend2|#A300A3|border=1px solid #550055|[[Neptune trojan]]s}}
|}
]]

[[File:EightTNOs.png|thumb|Size comparison of some large [[trans-Neptunian object|TNOs]] with Earth: {{dp|Pluto}} and [[Moons of Pluto|its moons]], {{dp|Eris}}, {{dp|Makemake}}, {{dp|Haumea}}, [[90377 Sedna|Sedna]], {{mpl|2007 OR|10}}, [[50000 Quaoar|Quaoar]], and [[90482 Orcus|Orcus]].]]

The Kuiper belt is a great ring of debris similar to the asteroid belt, but consisting mainly of objects composed primarily of ice.<ref name=physical>{{cite book|title=Encyclopedia of the Solar System|editor=Lucy-Ann McFadden |display-editors=etal |chapter=Kuiper Belt Objects: Physical Studies|author=Stephen C. Tegler|pages=605–620|date=2007}}</ref> It extends between 30 and 50&nbsp;AU from the Sun. Though it is estimated to contain anything from dozens to thousands of dwarf planets, it is composed mainly of small Solar System bodies. Many of the larger Kuiper belt objects, such as [[50000 Quaoar|Quaoar]], [[20000 Varuna|Varuna]], and [[90482 Orcus|Orcus]], may prove to be dwarf planets with further data. There are estimated to be over 100,000 Kuiper belt objects with a diameter greater than 50&nbsp;km, but the total mass of the Kuiper belt is thought to be only a tenth or even a hundredth the mass of Earth.<ref name="Delsanti-Beyond_The_Planets">{{cite web |date=2006 |author1=Audrey Delsanti |author2=David Jewitt |lastauthoramp=yes |title=The Solar System Beyond The Planets |work=Institute for Astronomy, University of Hawaii |url=http://www.ifa.hawaii.edu/faculty/jewitt/papers/2006/DJ06.pdf |format=PDF |accessdate=3 January 2007|archiveurl = https://web.archive.org/web/20070129151907/http://www.ifa.hawaii.edu/faculty/jewitt/papers/2006/DJ06.pdf |archivedate = 29 January 2007|deadurl=yes}}</ref> Many Kuiper belt objects have multiple satellites,<ref>{{cite journal| doi = 10.1086/501524| last1 = Brown| first1 = M. E.| authorlink = Michael E. Brown| last2 = Van Dam| first2 = M. A.| last3 = Bouchez| first3 = A. H.| last4 = Le Mignant| first4 = D.| last5 = Campbell| first5 = R. D.| last6 = Chin| first6 = J. C. Y.| last7 = Conrad| first7 = A.| last8 = Hartman| first8 = S. K.| last9 = Johansson| first9 = E. M.| last10 = Lafon| first10 = R. E.| last11 = Rabinowitz| first11 = D. L. Rabinowitz| last12 = Stomski| first12 = P. J., Jr.| last13 = Summers| first13 = D. M.| last14 = Trujillo| first14 = C. A.| last15 = Wizinowich| first15 = P. L.| year = 2006| title = Satellites of the Largest Kuiper Belt Objects| journal = The Astrophysical Journal| volume = 639| issue = 1| pages = L43–L46| pmid = | pmc = | arxiv = astro-ph/0510029| bibcode = 2006ApJ...639L..43B| url = http://web.gps.caltech.edu/~mbrown/papers/ps/gab.pdf| format = PDF| accessdate = 19 October 2011| ref = {{sfnRef|Brown Van Dam et al.|2006}}
}}</ref> and most have orbits that take them outside the plane of the ecliptic.<ref name=trojan>{{cite journal | url=http://www.boulder.swri.edu/~buie/biblio/pub047.pdf |format=PDF | last=Chiang |first=E. I. | title=Resonance Occupation in the Kuiper Belt: Case Examples of the 5:2 and Trojan Resonances | journal=[[The Astronomical Journal]] | volume=126 | issue=1 | pages=430–443 | date=2003 | doi=10.1086/375207 | accessdate=15 August 2009 | last2=Jordan | first2=A. B. | last3=Millis | first3=R. L. | last4=Buie | first4=M. W. | last5=Wasserman | first5=L. H. | last6=Elliot | first6=J. L. | last7=Kern | first7=S. D. | last8=Trilling | first8=D. E. | last9=Meech | first9=K. J. |displayauthors=9| bibcode=2003AJ....126..430C |last10=Wagner | first10=R. M.|arxiv = astro-ph/0301458 }}</ref>

The Kuiper belt can be roughly divided into the "[[Classical Kuiper belt object|classical]]" belt and the [[Resonant trans-Neptunian object|resonances]].<ref name=physical/> Resonances are orbits linked to that of Neptune (e.g. twice for every three Neptune orbits, or once for every two). The first resonance begins within the orbit of Neptune itself. The classical belt consists of objects having no resonance with Neptune, and extends from roughly 39.4&nbsp;AU to 47.7&nbsp;AU.<ref>{{cite journal |date=2005 |author1=M. W. Buie |author2=R. L. Millis |author3=L. H. Wasserman |author4=J. L. Elliot |author5=S. D. Kern |author6=K. B. Clancy |author7=E. I. Chiang |author8=A. B. Jordan |author9=K. J. Meech |author10=R. M. Wagner |author11=D. E. Trilling |title=Procedures, Resources and Selected Results of the Deep Ecliptic Survey |journal=[[Earth, Moon, and Planets]] |volume=92 |issue=1 |pages=113–124 |arxiv=astro-ph/0309251 |bibcode=2003EM&P...92..113B |doi=10.1023/B:MOON.0000031930.13823.be}}</ref> Members of the classical Kuiper belt are classified as [[Classical Kuiper belt object|cubewanos]], after the first of their kind to be discovered, [[15760 Albion]] (which previously had the provisional designation 1992 QB<sub>1</sub>), and are still in near primordial, low-eccentricity orbits.<ref>{{cite web |url=http://sait.oat.ts.astro.it/MSAIS/3/PDF/20.pdf |format=PDF |title=Beyond Neptune, the new frontier of the Solar System |author=E. Dotto1, M. A. Barucci2, and M. Fulchignoni |accessdate=26 December 2006 |date=24 August 2006 |archive-date=25 August 2014 |archive-url=https://web.archive.org/web/20140825122005/http://sait.oat.ts.astro.it/MSAIS/3/PDF/20.pdf |dead-url=yes }}</ref>

==== Pluto and Charon ====
{{main|Pluto|Charon (moon)}}
: The dwarf planet Pluto (39&nbsp;AU average) 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&nbsp;AU from the Sun at perihelion (within the orbit of Neptune) to 49.5&nbsp;AU at aphelion. Pluto has a 3:2 [[orbital resonance|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 [[plutino]]s.<ref name="Fajans_et_al_2001">{{Cite journal |last=Fajans |first=J. |author2=L. Frièdland |date=October 2001 |title=Autoresonant (nonstationary) excitation of pendulums, Plutinos, plasmas, and other nonlinear oscillators |journal=[[American Journal of Physics]] |volume=69 |issue=10 |pages=1096–1102 |doi=10.1119/1.1389278 |url=http://ist-socrates.berkeley.edu/~fajans/pub/pdffiles/AutoPendAJP.pdf |accessdate=26 December 2006 |bibcode=2001AmJPh..69.1096F |deadurl=yes |archiveurl=https://web.archive.org/web/20110607210435/http://ist-socrates.berkeley.edu/~fajans/pub/pdffiles/AutoPendAJP.pdf |archivedate=7 June 2011 |df=dmy-all }}</ref>

:Charon, the largest of [[Moons of Pluto|Pluto's moons]], is sometimes described as part of a [[binary system (astronomy)|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 (moon)|Styx]], [[Nix (moon)|Nix]], [[Kerberos (moon)|Kerberos]], and [[Hydra (moon)|Hydra]], orbit within the system.

==== Makemake and Haumea ====
{{main|Makemake|Haumea}}

:Makemake (45.79&nbsp;AU average), although smaller than Pluto, is the largest known object in the [[Classical Kuiper belt object|''classical'' Kuiper belt]] (that is, a Kuiper belt object not in a confirmed [[Resonant trans-Neptunian object|resonance]] with Neptune). Makemake is the brightest object in the Kuiper belt after Pluto. It was named and designated a dwarf planet in 2008.<ref name=name/> Its orbit is far more inclined than Pluto's, at 29°.<ref name=Buie136472>{{cite web
|author=Marc W. Buie
|date=5 April 2008
|title=Orbit Fit and Astrometric record for 136472
|publisher=SwRI (Space Science Department)
|url=http://www.boulder.swri.edu/~buie/kbo/astrom/136472.html
|accessdate=15 July 2012
|authorlink=Marc W. Buie}}</ref>

:Haumea (43.13&nbsp;AU average) is in an orbit similar to Makemake except that it is in a 7:12 orbital resonance with Neptune.<ref name="brownlargest">{{cite web
| title = The largest Kuiper belt objects
| author = Michael E. Brown
| work = Caltech
| url = http://www.gps.caltech.edu/~mbrown/papers/ps/kbochap.pdf
| format = PDF
| accessdate = 15 July 2012}}</ref> It is about the same size as Makemake and has two natural satellites. A rapid, 3.9-hour rotation gives it a flattened and elongated shape. It was named and designated a dwarf planet in 2008.<ref name="iaunews">{{cite web
| title = News Release&nbsp;– IAU0807: IAU names fifth dwarf planet Haumea
| work = International Astronomical Union
| date = 17 September 2008
| url = http://www.iau.org/news/pressreleases/detail/iau0807/
| accessdate = 15 July 2012
| archive-date = 30 July 2015
| archive-url = https://web.archive.org/web/20150730184735/http://www.iau.org/news/pressreleases/detail/iau0807/
| dead-url = yes
}}</ref>

=== Scattered disc ===
{{main|Scattered disc}}
The scattered disc, which overlaps the Kuiper belt but extends much further outwards, 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 [[Formation and evolution of the Solar System#Planetary migration|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&nbsp;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".<ref>{{cite web |date=2005 |author=David Jewitt |title=The 1000 km Scale KBOs |work=University of Hawaii |url=http://www2.ess.ucla.edu/~jewitt/kb/big_kbo.html |accessdate=16 July 2006}}</ref> Some astronomers also classify centaurs as inward-scattered Kuiper belt objects along with the outward-scattered residents of the scattered disc.<ref>{{cite web |url=http://www.minorplanetcenter.org/iau/lists/Centaurs.html |title=List of Centaurs and Scattered-Disk Objects |work=IAU: Minor Planet Center |accessdate=2 April 2007}}</ref>

==== Eris ====
{{main|Eris (dwarf planet)}}
:Eris (68&nbsp;AU average) is the largest known scattered disc object, and caused a debate about what constitutes a planet, because it is 25% more massive than Pluto<ref name="Brown Schaller 2007">{{cite journal| doi = 10.1126/science.1139415| last1 = Brown| first1 = Michael E.| authorlink = Michael E. Brown| last2 = Schaller| first2 = Emily L.| date = 15 June 2007| title = The Mass of Dwarf Planet Eris| journal = Science| volume = 316| issue = 5831| page = 1585| pmid = 17569855| pmc = | bibcode = 2007Sci...316.1585B| ref = harv}}</ref> and about the same diameter. It is the most massive of the known dwarf planets. It has one known moon, [[Dysnomia (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.

== Farthest regions ==
[[File:Solarmap.png|thumb|From the Sun to the nearest star: The Solar System on a [[logarithmic scale]] in [[astronomical unit]]s (AU)]]

The point at which the Solar System ends and interstellar space begins is not precisely defined because its outer boundaries are shaped by two separate 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|heliosphere]], is considered the beginning of the [[interstellar medium]].<ref name="Voyager" /> 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 theorized [[#Oort cloud|Oort cloud]].<ref name=Littmann>{{cite book|last=Littmann|first=Mark|title=Planets Beyond: Discovering the Outer Solar System|date=2004|pages=162–163|publisher=Courier Dover Publications|isbn=978-0-486-43602-9}}</ref>

=== {{anchor|Heliopause}} Heliosphere ===
{{main|Heliosphere}}
[[File:NewHeliopause 558121.jpg|thumb|left|The bubble-like [[heliosphere]] with its various transitional regions moving through the [[interstellar medium]]]]

The heliosphere is a [[stellar-wind bubble]], a region of space dominated by the Sun, which radiates at roughly 400&nbsp;km/s its [[solar wind]], a stream of charged particles, until it collides with the wind of the [[interstellar medium]].

The collision occurs at the ''termination shock'', which is roughly 80–100&nbsp;AU from the Sun upwind of the interstellar medium and roughly 200&nbsp;AU from the Sun downwind.<ref name=fahr /> Here the wind slows dramatically, condenses and becomes more turbulent,<ref name=fahr /> forming a great oval structure known as the ''heliosheath''. This structure is thought to look and behave very much like a comet's tail, extending outward for a further 40&nbsp;AU on the upwind side but tailing many times that distance downwind; evidence from ''[[Cassini (spacecraft)|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.<ref>{{cite web|title=Cassini's Big Sky: The View from the Center of Our Solar System|author=NASA/JPL|url=http://www.jpl.nasa.gov/news/features.cfm?feature=2370&msource=F20091119&tr=y&auid=5615216|date=2009|accessdate=20 December 2009}}</ref>

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.<ref name="Voyager">{{cite web |url=http://www.nasa.gov/vision/universe/solarsystem/voyager_agu.html |title=Voyager Enters Solar System's Final Frontier |work=NASA |accessdate=2 April 2007 |archive-date=16 May 2020 |archive-url=https://web.archive.org/web/20200516082547/https://www.nasa.gov/vision/universe/solarsystem/voyager_agu.html |dead-url=yes }}</ref> [[Voyager 1]] and [[Voyager 2]] are reported to have passed the termination shock and entered the heliosheath, at 94 and 84&nbsp;AU from the Sun, respectively.<ref>{{cite journal |doi=10.1126/science.1117684 |date=September 2005 |author1=Stone, E. C. |author2=Cummings, A. C. |author3=McDonald, F. B. |author4=Heikkila, B. C. |author5=Lal, N. |author6=Webber, W. R. |title=Voyager 1 explores the termination shock region and the heliosheath beyond |volume=309 |issue=5743 |pages=2017–20 |pmid=16179468 |journal=[[Science (journal)|Science]] |bibcode=2005Sci...309.2017S}}</ref><ref>{{cite journal |doi=10.1038/nature07022 |date=July 2008 |author1=Stone, E. C. |author2=Cummings, A. C. |author3=McDonald, F. B. |author4=Heikkila, B. C. |author5=Lal, N. |author6=Webber, W. R. |title=An asymmetric solar wind termination shock |volume=454 |issue=7200 |pages=71–4 |pmid=18596802 |journal=[[Nature (journal)|Nature]] |bibcode = 2008Natur.454...71S}}</ref> Voyager 1 is reported to have crossed the heliopause in August 2012.<ref name="NASA-20130912">{{cite web |last1=Cook |first1=Jia-Rui C. |last2=Agle |first2=D. C. |last3=Brown |first3=Dwayne |title=NASA Spacecraft Embarks on Historic Journey into Interstellar Space |url=http://www.nasa.gov/mission_pages/voyager/voyager20130912.html |work=[[NASA]] |date=12 September 2013 |accessdate=12 September 2013 |archive-date=11 June 2020 |archive-url=https://web.archive.org/web/20200611233345/https://www.nasa.gov/mission_pages/voyager/voyager20130912.html |dead-url=yes }}</ref>

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 field]]s prevailing to the south, e.g. it is bluntly shaped with the northern hemisphere extending 9&nbsp;AU farther than the southern hemisphere.<ref name="fahr">{{cite journal |date=2000 |title=A 5-fluid hydrodynamic approach to model the Solar System-interstellar medium interaction |journal=[[Astronomy & Astrophysics]] | volume=357 | page=268 |url=http://aa.springer.de/papers/0357001/2300268.pdf | format=PDF | bibcode=2000A&A...357..268F |author1=Fahr |first1=H. J. |last2=Kausch |first2=T. |last3=Scherer |first3=H. }} See Figures 1 and 2.</ref> 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]].<ref>{{Cite APOD | date=24 June 2002 |title=The Sun's Heliosphere & Heliopause |access-date=23 June 2006}}</ref>
[[File:Oort cloud Sedna orbit.svg|thumb|Zooming out the Solar System:
{{bulleted list |inner Solar System and Jupiter|outer Solar System and Pluto|orbit of Sedna (detached object) |inner part of the Oort Cloud}}
]]

Due to a lack of data, conditions in local interstellar space are not known for certain. It is expected that [[NASA]]'s [[Voyager program|Voyager spacecraft]], as they pass the heliopause, will transmit valuable data on radiation levels and solar wind to Earth.<ref>{{cite web | date=2007 | title=Voyager: Interstellar Mission | work=NASA Jet Propulsion Laboratory | url=http://voyager.jpl.nasa.gov/mission/interstellar.html |accessdate=8 May 2008}}</ref> How well the heliosphere shields the Solar System from cosmic rays is poorly understood. A NASA-funded team has developed a concept of a "Vision Mission" dedicated to sending a probe to the heliosphere.<ref>{{cite conference |title=Innovative Interstellar Explorer |author=R. L. McNutt, Jr. |display-authors=etal | booktitle= Physics of the Inner Heliosheath: Voyager Observations, Theory, and Future Prospects |series=[[AIP Conference Proceedings]] |volume=858 |pages=341–347 |date=2006 |bibcode=2006AIPC..858..341M |doi=10.1063/1.2359348}}</ref><ref>{{cite web |title=Interstellar space, and step on it! |work=New Scientist |url=https://www.newscientist.com/article/mg19325850.900-interstellar-space-and-step-on-it.html |date=5 January 2007 |accessdate=5 February 2007 | author=Anderson, Mark}}</ref>

=== Detached objects ===
{{main|Detached object|Sednoid}}
[[90377 Sedna]] (520 AU average) is a large, reddish object with a gigantic, highly elliptical orbit that takes it from about 76&nbsp;AU at perihelion to 940&nbsp;AU at aphelion and takes 11,400 years to complete. [[Michael E. Brown|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 {{mpl-|148209|2000 CR|105}}, which has a perihelion of 45&nbsp;AU, an aphelion of 415&nbsp;AU, and an orbital period of 3,420 years.<ref>{{cite web |date=2004 |author=David Jewitt |title=Sedna – 2003 VB<sub>12</sub> |work=University of Hawaii |url=http://www2.ess.ucla.edu/~jewitt/kb/sedna.html|accessdate=23 June 2006}}</ref> 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.<ref>{{cite web |title=Sedna |author=Mike Brown |date=2004 |url=http://www.gps.caltech.edu/~mbrown/sedna/ |work=Caltech |accessdate=2 May 2007}}</ref> 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 {{mpl|2012 VP|113}}, discovered in 2012. Its aphelion is only half that of Sedna's, at 400–500 AU.<ref name="jpldata 2012 VP113">
{{cite web
|type=2013-10-30 last obs
|title=JPL Small-Body Database Browser: (2012 VP113)
|url=http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=2012VP113
|publisher=Jet Propulsion Laboratory
|accessdate=26 March 2014
}}
</ref><ref name="Physorg">
{{cite web
| url=http://phys.org/news/2014-03-edge-solar.html
| title=A new object at the edge of our Solar System discovered
| work=Physorg.com
| date=26 March 2014
}}
</ref>

=== Oort cloud ===
{{main|Oort cloud}}
[[File:Kuiper oort-en.svg|thumb|Schematic of the hypothetical {{nowrap|[[Oort cloud]]}}, with a spherical outer cloud and a disc-shaped inner cloud]]
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&nbsp;AU (around 1&nbsp;[[light-year]] (ly)), and possibly to as far as 100,000&nbsp;AU (1.87&nbsp;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]].<ref>{{cite web |date=2001 |vauthors=Stern SA, Weissman PR |title=Rapid collisional evolution of comets during the formation of the Oort cloud. |work=Space Studies Department, Southwest Research Institute, Boulder, Colorado| url=https://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=11214311&dopt=Citation |accessdate=19 November 2006}}</ref><ref>{{cite web |date=2006 |author=Bill Arnett |title=The Kuiper Belt and the Oort Cloud |work=nineplanets.org |url=http://www.nineplanets.org/kboc.html |accessdate=23 June 2006}}</ref>

=== Boundaries ===
{{See also|Vulcanoid|Planets beyond Neptune|Planet Nine}}
Much of the Solar System is still unknown. The Sun's gravitational field is estimated to dominate the gravitational forces of [[List of nearest stars|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.<ref>{{cite book |title=The Solar System: Third edition |author1=T. Encrenaz |author2=JP. Bibring |author3=M. Blanc |author4=MA. Barucci |author5=F. Roques |author6=PH. Zarka |publisher=Springer |date=2004 |page=1}}</ref> 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. There are also ongoing studies of the region between Mercury and the Sun.<ref>{{cite journal |date=2004 |pages=312–315 |volume=148 |journal=[[Icarus (journal)|Icarus]] |author1=Durda D. D. |author2=Stern S. A. |author3=Colwell W. B. |author4=Parker J. W. |author5=Levison H. F. |author6=Hassler D. M. |title=A New Observational Search for Vulcanoids in SOHO/LASCO Coronagraph Images |doi=10.1006/icar.2000.6520 |bibcode=2000Icar..148..312D}}</ref> Objects may yet be discovered in the Solar System's uncharted regions.

Currently, the furthest known objects, such as [[Comet West]], have aphelia around 70,000 AU from the Sun, but as the Oort cloud becomes better known, this may change.

== Galactic context ==
{{imageframe
|width=220
|caption=Diagram of the [[Milky Way]] with the position of the Solar System marked by a yellow arrow
|content=
{{Superimpose
 |base         = Milky Way Arms ssc2008-10.svg
 |base_width   = 220px
 |base_alt     = Position of the Solar System within the Milky Way
 |base_caption = Position of the Solar System within the Milky Way
 |float        = Yellow Arrow Down.png
 |float_width  = 16px
 |x            = 102
 |y            = 32
}} }}

The Solar System is located in the [[Milky Way]], a [[barred spiral galaxy]] with a diameter of about 100,000 [[light-year]]s containing about 100&nbsp;billion stars.<ref name="fn9">
{{cite press
 |last=English |first=J.
 |title=Exposing the Stuff Between the Stars
 |url = http://www.ras.ucalgary.ca/CGPS/press/aas00/pr/pr_14012000/pr_14012000map1.html
 |publisher=Hubble News Desk
 |date=2000
 |accessdate = 10 May 2007
}}</ref> The Sun resides in one of the Milky Way's outer spiral arms, known as the [[Orion–Cygnus Arm]] or Local Spur.<ref>{{cite journal |title=Three Dimensional Structure of the Milky Way Disk |author1=R. Drimmel |author2=D. N. Spergel |date=2001 |pages=181–202 |volume=556 |doi=10.1086/321556 |journal=[[The Astrophysical Journal]] |arxiv=astro-ph/0101259 |bibcode=2001ApJ...556..181D}}</ref> The Sun lies between 25,000 and 28,000 light-years from the [[Galactic Centre]],<ref name="distance2">
{{cite journal
 |last=Eisenhauer |first=F.
 |display-authors=etal
 |title=A Geometric Determination of the Distance to the Galactic Center
 |journal=[[The Astrophysical Journal]]
 |volume=597 |issue=2 |pages=L121–L124
 |date=2003
 |doi=10.1086/380188
 |bibcode=2003ApJ...597L.121E
 |arxiv = astro-ph/0306220
}}</ref> and its speed within the Milky Way is about 220&nbsp;km/s, so that it completes one revolution every 225–250&nbsp;million years. This revolution is known as the Solar System's [[galactic year]].<ref>{{cite web |title=Period of the Sun's Orbit around the Galaxy (Cosmic Year) |first=Stacy |last=Leong |url=http://hypertextbook.com/facts/2002/StacyLeong.shtml |date=2002 |work=The Physics Factbook |accessdate=2 April 2007}}</ref> The [[solar apex]], the direction of the Sun's path through interstellar space, is near the constellation [[Hercules (constellation)|Hercules]] in the direction of the current location of the bright star [[Vega]].<ref>{{cite web|date=2003 |author=C. Barbieri |title=Elementi di Astronomia e Astrofisica per il Corso di Ingegneria Aerospaziale V settimana |work=IdealStars.com |url=http://dipastro.pd.astro.it/planets/barbieri/Lezioni-AstroAstrofIng04_05-Prima-Settimana.ppt |accessdate=12 February 2007 |deadurl=yes |archiveurl=https://web.archive.org/web/20050514103931/http://dipastro.pd.astro.it/planets/barbieri/Lezioni-AstroAstrofIng04_05-Prima-Settimana.ppt |archivedate=14 May 2005 |df= }}</ref> The plane of the ecliptic lies at an angle of about 60° to the [[galactic plane]].{{Refn |group=lower-alpha |1=If <math>\psi</math> is the angle between the [[Ecliptic pole|north pole of the ecliptic]] and the north [[galactic pole]] then:
<br/>{{big|1=<math>\cos\psi=\cos(\beta_g)\cos(\beta_e)\cos(\alpha_g-\alpha_e)+\sin(\beta_g)\sin(\beta_e)</math>}}<br/>
where <math>\beta_g</math> = 27° 07′ 42.01″ and <math>\alpha_g</math> = 12h 51m 26.282 are the declination and right ascension of the north galactic pole,<ref>{{cite journal |last=Reid|first=M.J. |author2=Brunthaler, A. |title=The Proper Motion of Sagittarius A* |journal=[[The Astrophysical Journal]] |volume=616 |issue=2 |page=883 |doi=10.1086/424960 |date=2004 |bibcode=2004ApJ...616..872R |arxiv=astro-ph/0408107}}</ref> whereas <math>\beta_e</math> = 66° 33′ 38.6″ and <math>\alpha_e</math> = 18h 0m 00 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°.}}

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.<ref name="astrobiology" /><ref>{{cite journal |author=O. Gerhard |title=Pattern speeds in the Milky Way |date=2011 |journal=Mem. S.A.It. Suppl. |volume=18 |page=185 |arxiv=1003.2489 |bibcode=2011MSAIS..18..185G}}</ref> Therefore, the Sun passes through arms only rarely. Because spiral arms are home to a far larger concentration of [[supernova]]e, gravitational instabilities, and radiation that could disrupt the Solar System, this has given Earth long periods of stability for life to evolve.<ref name="astrobiology">{{cite web |date=18 May 2001 |author=Leslie Mullen |title=Galactic Habitable Zones |work=Astrobiology Magazine |url=http://www.astrobio.net/news-exclusive/galactic-habitable-zones-2/ |accessdate=24 April 2015}}</ref> The Solar System also 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|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.<ref name=astrobiology /> Even at the Solar System's current location, some scientists have speculated that recent supernovae may have adversely affected life in the last 35,000 years, by flinging pieces of expelled stellar core towards the Sun, as radioactive dust grains and larger, comet-like bodies.<ref>{{cite web |date=2005 |title=Supernova Explosion May Have Caused Mammoth Extinction |work=Physorg.com |url=http://www.physorg.com/news6734.html |accessdate=2 February 2007}}</ref>

=== Neighbourhood ===
[[File:Local Interstellar Clouds with motion arrows.jpg|thumb|Beyond the heliosphere is the interstellar medium, consisting of various clouds of gases. The Solar System currently moves through the [[Local Interstellar Cloud]].]]
The Solar System is in the [[Local Interstellar Cloud]] or Local Fluff. It is thought to be near the neighbouring [[G-Cloud]] but it is not known if the Solar System is embedded in the Local Interstellar Cloud, or if it is in the region where the Local Interstellar Cloud and G-Cloud are interacting.<ref>[http://interstellar.jpl.nasa.gov/interstellar/probe/introduction/neighborhood.html Our Local Galactic Neighborhood] {{Webarchive|url=https://web.archive.org/web/20131121061128/http://interstellar.jpl.nasa.gov/interstellar/probe/introduction/neighborhood.html |date=21 November 2013 }}, NASA, 5 June 2013</ref><ref>[http://www.centauri-dreams.org/?p=14203 Into the Interstellar Void], Centauri Dreams, 5 June 2013</ref> The Local Interstellar Cloud is an area of denser cloud in an otherwise sparse region known as the [[Local Bubble]], an hourglass-shaped cavity in the [[interstellar medium]] roughly 300 light-years (ly) across. The bubble is suffused with high-temperature plasma, that suggests it is the product of several recent supernovae.<ref>{{cite web|title=Near-Earth Supernovas |work=NASA |url=https://science.nasa.gov/headlines/y2003/06jan_bubble.htm |accessdate=23 July 2006 |deadurl=yes |archiveurl=https://web.archive.org/web/20060813160705/https://science.nasa.gov/headlines/y2003/06jan_bubble.htm |archivedate=13 August 2006 |df= }}</ref>

There are relatively few [[list of nearest stars|stars within ten light-years of the Sun]]. The closest is the triple star system [[Alpha Centauri]], which is about 4.4 light-years away. Alpha Centauri A and B are a closely tied pair of Sun-like stars, whereas the small [[red dwarf]], [[Proxima Centauri]], orbits the pair 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.<ref>{{cite journal|last1=Anglada-Escudé|first1=Guillem|last2=Amado|first2=Pedro J.|last3=Barnes|first3=John|last4=Berdiñas|first4=Zaira M.|last5=Butler|first5=R. Paul|last6=Coleman|first6=Gavin A. L.|last7=de la Cueva|first7=Ignacio|last8=Dreizler|first8=Stefan|last9=Endl|first9=Michael|last10=Giesers|first10=Benjamin|last11=Jeffers|first11=Sandra V.|last12=Jenkins|first12=James S.|last13=Jones|first13=Hugh R. A.|last14=Kiraga|first14=Marcin|last15=Kürster|first15=Martin|last16=López-González|first16=Marίa J.|last17=Marvin|first17=Christopher J.|last18=Morales|first18=Nicolás|last19=Morin|first19=Julien|last20=Nelson|first20=Richard P.|last21=Ortiz|first21=José L.|last22=Ofir|first22=Aviv|last23=Paardekooper|first23=Sijme-Jan|last24=Reiners|first24=Ansgar|last25=Rodríguez|first25=Eloy|last26=Rodrίguez-López|first26=Cristina|last27=Sarmiento|first27=Luis F.|last28=Strachan|first28=John P.|last29=Tsapras|first29=Yiannis|last30=Tuomi|first30=Mikko|last31=Zechmeister|first31=Mathias|title=A terrestrial planet candidate in a temperate orbit around Proxima Centauri|journal=Nature|date=25 August 2016|volume=536|issue=7617|pages=437–440|doi=10.1038/nature19106|url=http://www.nature.com/nature/journal/v536/n7617/full/nature19106.html|language=en|issn=0028-0836|pmid=27558064|arxiv = 1609.03449 |bibcode = 2016Natur.536..437A }}</ref> The stars next closest to the Sun are the red dwarfs [[Barnard's Star]] (at 5.9&nbsp;ly), [[Wolf 359]] (7.8&nbsp;ly), and [[Lalande 21185]] (8.3&nbsp;ly).

The largest nearby star is [[Sirius]], a bright [[main sequence|main-sequence]] star roughly 8.6 light-years away and roughly twice the Sun's mass and that is orbited by a [[white dwarf]], Sirius B. The nearest [[brown dwarf]]s are the binary [[Luhman 16]] system at 6.6 light-years. Other systems within ten light-years are the binary red-dwarf system [[Luyten 726-8]] (8.7&nbsp;ly) and the solitary red dwarf [[Ross 154]] (9.7&nbsp;ly).<ref>{{cite web |title=Stars within 10 light years |url=http://www.solstation.com/stars/s10ly.htm |work=SolStation |accessdate=2 April 2007 |archive-date=16 February 2007 |archive-url=https://web.archive.org/web/20070216125505/http://www.solstation.com/stars/s10ly.htm |dead-url=yes }}</ref> 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 60% of its luminosity.<ref>{{cite web |title=Tau Ceti |url=http://www.solstation.com/stars/tau-ceti.htm |work=SolStation |accessdate=2 April 2007 |archive-date=3 January 2007 |archive-url=https://web.archive.org/web/20070103202726/http://www.solstation.com/stars/tau-ceti.htm |dead-url=yes }}</ref> The closest known [[rogue planet|free-floating planetary-mass object]] to the Sun is [[WISE 0855−0714]],<ref>[http://iopscience.iop.org/2041-8205/786/2/L18/article Discovery of a ~250 K Brown Dwarf at 2 pc from the Sun], K. L. Luhman 2014 ApJ 786 L18. {{DOI|10.1088/2041-8205/786/2/L18}}</ref> an object with a mass less than 10 Jupiter masses roughly 7 light-years away.
{{wide image|Earth's Location in the Universe (JPEG).jpg|2000px|A diagram of Earth's location in the [[observable Universe]]. (''[[:File:Earth's Location in the Universe SMALLER (JPEG).jpg|Click here for an alternate image]].'')}}

=== Comparison with extrasolar systems ===
Compared to other [[planetary system]]s the Solar System stands out in lacking planets interior to the orbit of Mercury.<ref name=Martin082015>[https://arxiv.org/abs/1508.00931 The Solar System as an Exoplanetary System], Rebecca G. Martin, Mario Livio, (Submitted on 4 August 2015)</ref><ref>[http://aasnova.org/2015/09/25/how-normal-is-our-solar-system/ How Normal is Our Solar System?], By Susanna Kohler on 25 September 2015</ref> The known Solar System also lacks [[super-Earth]]s ([[Planet Nine]] could be a super-Earth beyond the known Solar System).<ref name=Martin082015/> 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.<ref name=Martin082015/> This led to 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.<ref>[https://arxiv.org/abs/1502.06558 Consolidating and Crushing Exoplanets: Did it happen here?], Kathryn Volk, Brett Gladman, (Submitted on 23 February 2015 (v1), last revised 27 May 2015 (this version, v2))</ref><ref>[http://www.astrobio.net/news-exclusive/mercury-sole-survivor-of-close-orbiting-planets Mercury Sole Survivor of Close Orbiting Planets], By Nola Taylor Redd - 8 June 2015</ref>

The orbits of Solar System planets are nearly circular. Compared to other systems, they have smaller [[orbital eccentricity]].<ref name=Martin082015/> 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.<ref name=Martin082015/><ref>[https://arxiv.org/abs/astro-ph/0404240 Final Stages of Planet Formation], Peter Goldreich, Yoram Lithwick, Re'em Sari, (Submitted on 13 April 2004)</ref>

==Visual summary==
This section is a sampling of Solar System bodies, selected for size and quality of imagery, and sorted by volume. Some omitted objects are larger than the ones included here, notably [[Eris (dwarf planet)|Eris]], because these have not been imaged in high quality.
{{/SolarSummary}}
{| class="wikitable" style="margin:0.5em auto; width:600px;"
|-
! ''[[Voyager 1]]'' views the Solar System from over 6&nbsp;billion km from Earth.
|-
| style="font-size:88%" | [[File:PIA00453-SolarSystem-VenusEarthJupiterSaturnUranusNeptune-Voyager1-19960913.jpg|600px]]
<center>[[Venus]], [[Earth]] (''[[Pale Blue Dot]]''), [[Jupiter]], [[Saturn]], [[Uranus]], [[Neptune]] (13 September 1996).</center>
|}

==See also==
{{Wikipedia books|Solar System}}
{{Div col}}
* [[Astronomical symbols]]
* [[Ephemeris]] is a compilation of positions of naturally occurring astronomical objects as well as artificial satellites in the sky at a given time or times.
* [[HIP 11915]] (a [[solar analog]] whose planets contains a Jupiter analog)
* [[Lists of geological features of the Solar System]]
* [[List of gravitationally rounded objects of the Solar System]]
* [[List of Solar System extremes]]
* [[Outline of the Solar System]]
* [[Planetary mnemonic]]
* [[Solar System in fiction]]
{{div col end}}

==Notes==
{{Reflist|30em|group=lower-alpha}}

==References==
{{Reflist|30em}}

==External links==
{{Sister project links|Solar System|d=Q544|n=Category:Space|s=Category:Planetary astronomy}}
* {{cite EB1911|wstitle=Solar System|volume=25 |pages=157–158 |short=x}}
* [https://web.archive.org/web/20140426232154/http://logic-law.com/index.php?title=A_Cosmic_History_of_Human_Evolution#Development_of_the_Solar_System A Cosmic History of the Solar System]
* [http://www.joshworth.com/a-tediously-accurate-map-of-the-solar-system/ A Tediously Accurate Map of the Solar System (web based scroll map scaled to the Moon being 1 pixel)] {{Webarchive|url=https://web.archive.org/web/20160630160808/http://www.joshworth.com/a-tediously-accurate-map-of-the-solar-system/ |date=30 June 2016 }}
* [http://space.jpl.nasa.gov NASA's Solar System Simulator]
* [http://www.jpl.nasa.gov/solar_system NASA/JPL Solar System main page]
* [http://solarsystem.nasa.gov/planets/profile.cfm?Object=SolarSys&Display=Overview Solar System Profile] by [https://web.archive.org/web/20060425235742/http://solarsystem.nasa.gov/index.cfm NASA's Solar System Exploration]

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