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{{Hatnote|This article is about the Sun and its planetary system. For other systems, see [[planetary system]] and [[star system]].}}
== Louis Vuitton Bags 2. Terry Bradshaw ==
{{pp-semi-protected|small=yes}}
{{Infobox planetary system
| title            = Solar System
| image            = [[Image:Planets2013.jpg|300px]]
| caption          = The Sun and [[planet]]s of the Solar System. Sizes are to scale, distances and illumination are not.
| age              = 4.568 billion years
| location          = [[Local Interstellar Cloud]], [[Local Bubble]], [[Orion–Cygnus Arm]], [[Milky Way]]
| system_mass      = 1.0014 [[solar mass]]es
| neareststar      = [[Proxima Centauri]] (4.22 ly), [[Alpha Centauri]] system (4.37 ly)
| nearestplanetary  = Alpha Centauri system (4.37 ly)
| semimajoraxis    = 30.10 [[Astronomical unit|AU]] (4.503 billion km)
| Kuiper_cliff      = 50 [[Astronomical unit|AU]]
| stars            = 1 <br>[[Sun]]
| noknown_stars    = yes
| planets          = 8 <br>[[Mercury (planet)|Mercury]], [[Venus]], [[Earth]], [[Mars]], [[Jupiter]], [[Saturn]], [[Uranus]], [[Neptune]]
| outerplanetname  = [[Neptune]]
| noknown_planets  = yes
| dwarfplanets      = 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=August 23, 2011 | work="Mike Brown's Planets (self-published)"}}</ref><br>5 ([[Ceres (dwarf planet)|Ceres]], [[Pluto]], [[Haumea (dwarf planet)|Haumea]], [[Makemake (dwarf planet)|Makemake]], [[Eris (dwarf planet)|Eris]]) are currently recognized by the IAU
| satellites        = 422 (173 of planets<ref name=planetarymoons>{{cite web|url=http://www.dtm.ciw.edu/users/sheppard/satellites/ |title=The Giant Planet Satellite and Moon Page|author=Sheppard, Scott S.|publisher=Departament of Terrestrial Magnetism at Carniege Institution for science|accessdate=2013-07-23}}</ref> and 249 of minor planets<ref name=MPMJohnston>{{cite web
| date=2013-12-06
| title=Asteroids with Satellites
| publisher=Johnston's Archive
| author=Wm. Robert Johnston
| url=http://www.johnstonsarchive.net/astro/asteroidmoons.html
| accessdate=2013-12-12}}</ref>)
| minorplanets      = 628,057 (as of 2013-12-12)<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=2013-12-12}}</ref>
| comets            = 3,244 (as of 2013-12-12)<ref name=JPLbodies/>
| roundsat          = 19
| roundsatlink      = List of gravitationally rounded objects of the Solar System#Satellite planemos
| inclination      = 60.19° (ecliptic) <!-- If anyone can find a cited value for the inclination of the Solar System's invariable plane to the galactic plane, then please replace this value -->
| galacticcenter    = 27,000±1,000 ly
| orbitalspeed      = 220 km/s
| orbitalperiod    = 225–250 Myr
| spectral          = [[G-type main-sequence star|G2V]]
| frostline        = ≈5 [[Astronomical unit|AU]]<ref name="Mumma">{{cite doi | 10.1016/S0273-1177(03)00578-7}}</ref>
| heliopause        = ≈120 [[Astronomical unit|AU]]
| hillsphere        = ≈1–2 ly
}}


The '''Solar System'''<ref group=lower-alpha>[[Capitalization]] of the name varies. The [[International Astronomical Union|IAU]], the authoritative body regarding astronomical nomenclature, specifies [http://www.iau.org/public_press/themes/naming/ capitalizing the names of all individual astronomical objects] ('''Solar System'''). However, 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 [[Sun]] and the objects that orbit the Sun. These are a [[planetary system]] of eight [[planet]]s<ref group=lower-alpha>Historically, several other bodies were once considered planets, including [[Pluto]] from its discovery in 1930 until 2006. For further information, see [[Planet#Former planets|Former planets]].</ref> and various secondary bodies, [[dwarf planet]]s and [[Small Solar System body|small Solar System objects]] that orbit the Sun directly,{{#tag:ref|According to [[IAU definition of planet|current definitions]], objects in orbit around the Sun are classified dynamically and physically into three categories: ''planets'', ''dwarf planets'', and ''small Solar System bodies''. A [[planet]] is any body in orbit around the Sun that has enough mass to form itself into a [[sphere|spherical]] shape and has [[Clearing the neighbourhood|cleared its immediate neighbourhood]] of all smaller objects. By this definition, the Solar System has eight known planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune. Pluto does not fit this definition, because it has not cleared its orbit of surrounding Kuiper belt objects.<ref name="FinalResolution" /> A [[dwarf planet]] is a celestial body orbiting the Sun that is massive enough to be rounded by its own gravity but has not cleared its neighbouring region of [[planetesimal]]s and is not a satellite.<ref name="FinalResolution" /> The [[International Astronomical Union|IAU]] has recognized five dwarf planets: Ceres, Pluto, Haumea, Makemake, and Eris.<ref name=name>{{cite web|date=2008-11-07 <!--11:42:58-->|title=Dwarf Planets and their Systems|work= Working Group for Planetary System Nomenclature (WGPSN) |url=http://planetarynames.wr.usgs.gov/append7.html#DwarfPlanets| accessdate=2008-07-13 | publisher= U.S. Geological Survey }}</ref> Other objects commonly accepted 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=2008-10-13}}</ref> Dwarf planets that orbit in the trans-Neptunian region are called "[[plutoid]]s", though that term is not in widespread use.<ref name="IAU0804">{{cite news
What's wrong, Goober? Did my words of truth strike a raw nerve along with you? Please direct me to the spot where I "cussed out a mystery stranger". I did no such thing. I merely told an unknown stranger to practice what they were preaching to everyone else on this thread. And when you were very aware that this is a "Public News Website" then you would know that things i said to you is the truth. Your comment discovered as you obviously thinking you were a Channel 5 or Topix moderator. You have NO RIGHT WHATSOEVER to say what you did to everyone on this thread. Only a real loser would have made the comment you probably did to everyone. Now do us all a big favor and STFU!!! Now that's [http://www.naturalseeding.co.nz/application/banner.html Louis Vuitton Bags] good advice for ya!!!<br><br>But, you might like to place more thought in to the location of one's home. Perform a little research to the distinct locations in Singapore and find the many great place for you personally. All things considered, there is actually no speed in determining. You may want to explore a few of the popular expatriate enclaves including Holland Village and Dempsey, that are usually the greatest destinations for expats thinking of buying. <br><br>India says that the close links between the organizations, as well as the 2,500 offices and 11 seminaries that JamaatudDawa maintains in Pakistan, "are of immediate concern with regard to their efforts to mobilize and orchestrate terrorist activities."On December 10, 2008 [http://www.mbctimberframe.ie/config/header.php Oakley Sunglasses Ireland] Saeed denied a hyperlink between LeT and JuD within an interview with Pakistan Geo television proclaiming that "no LashkareTaiba man is in JamaatudDawa and I haven't been a chief of LashkareTaiba."<br><br>From prostitute to leader, coal mine worker to major league ballplayer an array of professions [http://www.sunrisehealthregion.sk.ca/images/exports/text.asp Adidas Jeremy Scott Wings] are covered. It reads like a documentary (so it is). Terkel has included probably the most interesting aspects of each case study's working life, and ultimately you see why each continues to pursue their career for the reason that chosen field or at least what satisfaction they get from showing up everyday. <br><br>2. Terry Bradshaw (Quarterback) He'll be remembered as the guy who performed when he was needed to. A tough competitor, Bradshaw had a powerful arm and called their own plays throughout his football career. His physical skills and onthefield leadership played a major role in Pittsburgh Steelers history. He shined if this came to the playoffs or the Super Bowl. During his career, he passed in excess of 300 yards in a [http://www.aldes.ie/flo/menu.asp Hollister Hoodies Ireland] game only 7 times, but 3 of these performances came in the postseason, and 2 of those in Super Bowl. In 4 career Super Bowl appearances, he passed for 932 yards and 9 touchdowns, both Super Bowl records during the time of his retirement.1. Joe Greene (Defensive Tackle) The number one player on our list got the nickname Joe Greene for any reason. He was a raw and nasty player on the field, and is one of the best defenders of all time. Greene is recognized as by many to be one of the greatest defensive linemen ever, called the cornerstone of the legendary "Steel Curtain" defense. He lead one of the toughest and meanest defensive squads to ever set their feet around the turf. Feel free to comment on my articles with any constructive criticism or anything you would like to share.<ul>
|date=June 11, 2008, Paris
 
|title=Plutoid chosen as name for Solar System objects like Pluto
  <li>[http://0937xx.com/home.php?mod=space&uid=50052&do=blog&quickforward=1&id=645567 http://0937xx.com/home.php?mod=space&uid=50052&do=blog&quickforward=1&id=645567]</li>
|publisher=[[International Astronomical Union]]
 
|url=http://www.iau.org/public_press/news/release/iau0804
  <li>[http://ldsbee.com/index.php?page=item&id=2358294 http://ldsbee.com/index.php?page=item&id=2358294]</li>
|accessdate=2008-06-11}}</ref> The remainder of the objects in orbit around the Sun are [[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=2006-08-24 |url=http://www.iau.org/iau0602.423.0.html |accessdate=2007-03-02}}</ref>|name=footnoteB|group=lower-alpha}} as well as [[natural satellite|satellites]] (moons) that orbit many planets and smaller objects. The Solar System [[Formation and evolution of the Solar System|formed 4.6 billion years ago]] from the gravitational collapse of a giant [[molecular cloud]]. The vast majority of the system's [[mass]] is in the Sun, with most of the remaining mass contained in [[Jupiter]]. The four smaller inner planets, [[Mercury (planet)|Mercury]], [[Venus]], [[Earth]] and [[Mars]], also called the [[terrestrial planets]], are primarily composed of rock and metal. The four outer planets, called the [[gas giant]]s, are substantially more massive than the terrestrials. The two largest, [[Jupiter]] and [[Saturn]], are composed mainly of hydrogen and helium; the two outermost planets, [[Uranus]] and [[Neptune]], are composed largely of substances with relatively high melting points (compared with hydrogen and helium), called [[Volatiles|ices]], such as water, ammonia and [[methane]], and are often referred to separately as "ice giants". All planets have almost circular orbits that lie within a nearly flat disc called the [[plane of the ecliptic|ecliptic plane]].
 
 
  <li>[http://www.9combo.com/forum.php?mod=viewthread&tid=149389&fromuid=4524 http://www.9combo.com/forum.php?mod=viewthread&tid=149389&fromuid=4524]</li>
The Solar System also contains regions populated by [[Small Solar System body|smaller objects]].<ref group=lower-alpha name=footnoteB /> The [[asteroid belt]], which lies between 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]], linked populations of [[trans-Neptunian object]]s composed mostly of ices. Within these populations are several dozen to more than ten thousand objects that may be large enough to have been rounded by their own gravity.<ref name=Stern2012>"Today we know of more than a dozen dwarf planets in the solar system".[http://pluto.jhuapl.edu/overview/piPerspective.php?page=piPerspective_08_24_2012 The PI's Perspective]</ref> Such objects are referred to 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]] freely travel between regions. Six of the planets, at least three 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]] for the full list of natural satellites of the eight planets and first five dwarf planets.</ref> usually termed "moons" after Earth's [[Moon]]. Each of the outer planets is encircled by [[planetary ring]]s of dust and other small objects.
 
 
  <li>[http://www.3igm.com/forum.php?mod=viewthread&tid=167977 http://www.3igm.com/forum.php?mod=viewthread&tid=167977]</li>
The [[solar wind]], a flow of [[plasma (physics)|plasma]] from the Sun, creates a [[stellar wind bubble|bubble]] in the [[interstellar medium]] known as the [[heliosphere]], which extends out to the edge of the [[scattered disc]]. The [[Oort cloud]], which is believed to be the source for [[long-period comet]]s, may also exist at a distance roughly a thousand times further than the heliosphere. The [[Heliopause (astronomy)|heliopause]] is the point at which pressure from the solar wind is equal to the opposing pressure of [[interstellar wind]]. The Solar System is located within one of the outer arms of the [[Milky Way]], which contains about 200 billion stars.
 
 
  <li>[http://enseignement-lsf.com/spip.php?article64#forum17880592 http://enseignement-lsf.com/spip.php?article64#forum17880592]</li>
==Discovery and exploration==
 
[[File:Heliocentric.jpg|thumb|right|[[Andreas Cellarius]]'s illustration of the Copernican system, from the Harmonia Macrocosmica (1660)]]
</ul>
{{Main|Discovery and exploration of the Solar System}}
For many thousands of years, humanity, with a few notable exceptions, did not recognize the existence of the Solar System. People 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,<ref>{{cite journal|title= The astronomical system of Copernicus|author=WC Rufus|journal=[[Popular Astronomy (US magazine)|Popular Astronomy]]|volume=31|page=510|year= 1923|bibcode=1923PA.....31..510R}}</ref> [[Nicolaus Copernicus]] was the first to develop a mathematically predictive [[heliocentric]] system.<ref>{{cite book |title=Copernicus, Darwin, & Freud: revolutions in the history and philosophy of science |first=Friedel |last=Weinert |publisher=[[Wiley-Blackwell]] |year=2009 |page=21 |isbn=978-1-4051-8183-9}}</ref> His 17th-century successors, [[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 governed Earth. Additionally, the invention of the telescope led to the discovery of further planets and moons. In more recent times, improvements in the telescope and the use of [[unmanned spacecraft]] have enabled the investigation of geological phenomena, such as [[mountains]] and [[Impact crater|craters]], and seasonal meteorological phenomena, such as [[clouds]], [[dust storms]], and [[ice caps]] on the other planets.
 
==Structure and composition==
[[File:Oort cloud Sedna orbit.svg|thumb|upright=1.8|left|The [[orbit]]s of the bodies in the Solar System to scale (clockwise from top left)]]
 
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 |year=2000 |journal=[[Astronomy & Geophysics]] |volume=41 |issue=1 |pages=1.12}}</ref> The Sun's four largest orbiting bodies, the [[gas giant]]s, account for 99% of the remaining mass, with Jupiter and Saturn together comprising more than 90%.{{#tag:ref|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|year=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.|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 | coauthors = 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 = 2003-11-27 | language =
| url = http://www.nature.com/nature/journal/v426/n6965/abs/nature02120.html
| doi = 10.1038/nature02120 | pmid = 14647375
| accessdate = 2012-05-26
| issue = 6965}}</ref><ref>{{cite journal|title=From the Kuiper Belt to Jupiter-Family Comets: The Spatial Distribution of Ecliptic Comets|author=Harold F. Levison, Martin J Duncan|journal=[[Icarus (journal)|Icarus]]|year=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 a long way above Earth's north pole).<ref>{{cite web| last = Grossman | first = Lisa | title = Planet found orbiting its star backwards for first time | publisher = NewScientist | date = 13 August 2009 | url = http://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 rocky asteroids, and four gas giants surrounded by the Kuiper belt of 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 gas giants.<ref>{{cite web |title=An Overview of the Solar System |author=nineplanets.org |url=http://www.nineplanets.org/overview.html |accessdate=2007-02-15}}</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 |year=2006 |url=http://www.planetary.org/news/2006/0116_New_Horizons_Set_to_Launch_on_9_Year.html |accessdate=2006-11-08}}</ref>
 
Most of the planets in the Solar System possess secondary systems of their own, being orbited by planetary objects called [[natural satellite]]s, or moons (two of which are larger than the planet [[Mercury (planet)|Mercury]]), and, in the case of the four [[gas giant]]s, 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.
 
[[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]].
 
{{multiple image
| align    = right
| direction = horizontal
| width    = 197
| image1    = Ecliptic plane 3d view.gif
| alt1      =
| image2    = Solarsystem3DJupiter.gif
| alt2      =
| footer  = Solar System showing the plane of Earth's orbit around the Sun in 3D. Mercury, Venus, Earth, and Mars are shown in both panels; the right panel also shows Jupiter making one full revolution with Saturn and Uranus making less than one full revolution.
}}
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 | author = Marochnik, L. and Mukhin, L. | title = Is Solar System Evolution Cometary Dominated? | booktitle = Progress in the Search for Extraterrestrial Life | year = 1995| series = Astronomical Society of the Pacific Conference Series | volume = 74 | editor = Shostak, G. S. | pages = 83 | url = http://adsabs.harvard.edu/abs/1995ASPC...74...83M}}</ref> due to the differential rotation within the gaseous Sun.<ref>{{cite doi | 10.1088/2041-8205/731/2/L42}}</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=2008-07-29
}}, citing {{cite book
|last=Eddy |first=J.
|title=A New Sun: The Solar Results From Skylab
|url=http://history.nasa.gov/SP-402/contents.htm
|publisher=[[NASA]]
|year=1979
|page=37
|id=NASA SP-402
}}</ref> [[Jupiter]] and [[Saturn]], which comprise nearly all the remaining matter, possess atmospheres composed of roughly 99% of these elements.<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 = 2007-07-31
|date = September 7, 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 = 2007-08-08|date = November 16, 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|author=Paul Robert Weissman, Torrence V. Johnson|year=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 doi|10.1016/0032-0633(95)00061-5}}</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 doi | 10.1016/S0032-0633(99)00088-4 }}</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 [[molecular 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 "[[Gas giant|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 | year=2002 | publisher=[[Cambridge University Press]] | isbn=0-521-80090-0 | oclc=223304585 46685453}}</ref> Together, gases and ices are referred to as ''[[volatiles]]''.<ref name=Placxo>{{cite book|last=Placxo|first=Kevin W.|coauthors=Gross, Michael|title=Astrobiology: a brief introduction|year=2006|publisher=[[JHU Press]]|page=66|isbn=978-0-8018-8367-5|url=http://books.google.com/?id=2JuGDL144BEC&pg=PA66&dq=inventory+volatiles+hydrogen&q=inventory%20volatiles%20hydrogen}}</ref>
 
===Distances and scales===
[[File:Size planets comparison.jpg|upright=1.4|thumb|right|Planets of the Solar System to scale. Jupiter and Saturn (top row), Uranus and Neptune (top middle), Earth and Venus (bottom middle), Mars and Mercury.]]
 
The distance<!--at this precision, doesn't matter which distance is measured--> from Earth to the Sun is {{convert|1|AU|km|lk=on}}. For comparison, the radius of the Sun is {{convert|.0047|AU|km|abbr=on|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 million (10<sup>6</sup>) times smaller than 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|year=2005|accessdate=2007-11-03}}</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 on Earth attempt to convey the relative scales involved in the Solar System on human terms. Some are 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 The Earth as a Peppercorn | author= Guy Ottewell | year=1989 | work= NOAO Educational Outreach Office | accessdate=2012-05-10 }}</ref> The largest such scale model, the [[Sweden Solar System]], uses the 110-metre (361-ft) [[Ericsson Globe]] in [[Stockholm]] as its substitute Sun, and, following the scale, Jupiter is a 7.5-metre (25-foot) sphere at [[Arlanda International Airport]], 40&nbsp;km (25&nbsp;mi) away, whereas the farthest current object, Sedna, is a 10-cm (4-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|publisher=University of Illinois|accessdate=2012-05-10}}</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=2010-05-10}}</ref>
 
If the Sun–Neptune distance is [[Solar System model|scaled]] to the length of a football pitch of about 100 metres, then the Sun is about 3&nbsp;cm in diameter (roughly two-thirds the diameter of a golf ball) at one goal line with the gas giants all smaller than about 3&nbsp;mm and Neptune found at the opposite goal line. Earth's diameter along with the other terrestrial planets would be smaller than a flea (0.3&nbsp;mm) at this scale.<ref>See, e.g., {{cite web | 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}}</ref>
 
{{-}}
{{Distance from Sun using EasyTimeline}}
 
==Formation and evolution==
{{Main|Formation and evolution of the Solar System}}
[[File:Solarnebula.jpg|thumb|Artist's concept of the early Solar System]]
The Solar System formed 4.568 billion years ago from the gravitational collapse of a region within a large [[molecular cloud]].<ref>The date is based on the oldest [[inclusion (mineral)|inclusion]]s found to date in [[meteorite]]s, and is thought to be the date of the formation of the first solid material in the collapsing nebula.<br>A. Bouvier and M. Wadhwa. "The age of the solar system redefined by the oldest Pb-Pb age of a meteoritic inclusion." ''Nature Geoscience,'' in press, 2010. {{doi|10.1038/NGEO941}}</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=2006-12-27}}</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|year=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=2005-01-07 |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=2000-04-05 |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=2007-01-19}}</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 | year= 2005 | author= Boss, A. P. | journal=[[The Astrophysical Journal]] | volume= 621 | issue= 2 | pages= L137 | last2= Durisen | first2= R. H. | bibcode=2005ApJ...621L.137B}}</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]].
 
Due to their higher boiling points, only metals and silicates could exist in the warm inner Solar System close to the Sun, and these would 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 | author= Sukyoung Yi; Pierre Demarque; Yong-Cheol Kim; Young-Wook Lee; Chang H. Ree; Thibault Lejeune; Sydney Barnes | title=Toward Better Age Estimates for Stellar Populations: The <math>Y^{2}</math> Isochrones for Solar Mixture | journal=[[Astrophysical Journal Supplement]] | arxiv=astro-ph/0104292 | year=2001 | volume=136 | pages=417 | 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 equaled the force of gravity. At this point the Sun became a [[main sequence|main-sequence]] star.<ref>{{cite journal | author=A. Chrysostomou, P. W. Lucas | title=The Formation of Stars | journal=[[Contemporary Physics]] | year=2005 | volume=46 | issue=1 | page=29 | bibcode=2005ConPh..46...29C | doi=10.1080/0010751042000275277}}</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 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 5.4 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 collapse, 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>{{cite journal|author=K. P. Schroder, Robert Cannon Smith|title=Distant future of the Sun and Earth revisited|journal=[[Monthly Notices of the Royal Astronomical Society]] |volume=386|issue=1 |pages=155–163 |year=2008 |doi=10.1111/j.1365-2966.2008.13022.x |bibcode=2008MNRAS.386..155S}}</ref> The expanding Sun is expected to vaporize Mercury and Venus and render Earth uninhabitable as the [[habitable zone]] moves out to the orbit of Mars. 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 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.|year=1997|url=http://www.astronomy.ohio-state.edu/~pogge/Lectures/vistas97.html|title=The Once & Future Sun|format=lecture notes|work=[http://www-astronomy.mps.ohio-state.edu/Vistas/ New Vistas in Astronomy]|accessdate=2005-12-07|archiveurl = http://web.archive.org/web/20050527094435/http://www-astronomy.mps.ohio-state.edu/Vistas/ |archivedate = May 27, 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=1.4|The Sun compared to the planets]]
 
The Sun is the Solar System's [[star]], and by far its chief 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=2009-05-14 |archiveurl = http://web.archive.org/web/20080102034758/http://solarsystem.nasa.gov/planets/profile.cfm?Object=Sun&Display=Facts&System=Metric |archivedate = 2008-01-02}}</ref> produces temperatures and densities in its [[Sun#Core|core]] high enough to sustain [[nuclear fusion]],<ref>{{cite book|last=Zirker|first=Jack B.|title=Journey from the Center of the Sun|year=2002|publisher=[[Princeton University Press]]|isbn=978-0-691-05781-1|pages=120–127}}</ref> which releases enormous amounts of [[energy]], mostly [[radiant energy|radiated]] into [[outer space|space]] as [[electromagnetic radiation]], peaking in the 400–700&nbsp;nm band of [[visible light]].<ref>{{cite web|title=Why is visible light visible, but not other parts of the spectrum?|publisher=The Straight Dome|year=2003|url=http://www.straightdope.com/columns/read/2085/why-is-visible-light-visible-but-not-other-parts-of-the-spectrum|accessdate=2009-05-14}}</ref>
 
The Sun is a type G2 [[main sequence|main-sequence]] star. Compared to the majority of stars in the [[Milky Way]], the Sun is rather large and bright.<ref name=sun>{{cite news |first=Ker |last=Than |title=Astronomers Had it Wrong: Most Stars are Single |publisher=SPACE.com |date=January 30, 2006 |url=http://www.space.com/scienceastronomy/060130_mm_single_stars.html |accessdate=2007-08-01}}</ref> Stars are classified by the [[Hertzsprung–Russell diagram]], a graph that plots the brightness of stars with their surface [[temperature]]s. Generally, hotter stars are brighter. Stars following this pattern are said to be on the [[main sequence]], and the Sun lies right in the middle of it. Stars brighter and hotter than the Sun are rare, whereas substantially dimmer and cooler stars, known as [[red dwarf]]s, are common, making up 85% of the stars in the galaxy.<ref name=sun/><ref>{{Cite conference|year=2001|pages=119 |author=Smart, R. L.; Carollo, D.; Lattanzi, M. G.; McLean, B.; Spagna, A.|booktitle=Ultracool Dwarfs: New Spectral Types L and T |editor=Hugh R. A. Jones and Iain A. Steele |publisher=[[Springer (publisher)|Springer]] |title=The Second Guide Star Catalogue and Cool Stars|bibcode=2001udns.conf..119S}}</ref>
 
Evidence suggests that the Sun's position on the main sequence puts it in the "prime of life" for a star, not yet having exhausted its store of hydrogen for nuclear fusion. The Sun is growing brighter; early in its history 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|year=2003|volume=108|issue=A12|page=1437|bibcode=2003JGRA..108.1437S}}</ref>
 
The Sun is a [[Population I stars|population I star]]; it was born in the later stages of the [[Timeline of the Big Bang|universe's evolution]] and thus contains more elements heavier than hydrogen and helium ("[[metallicity|metals]]" in astronomical parlance) than the older population II stars.<ref>{{cite journal |author=T. S. van Albada, Norman Baker |title=On the Two Oosterhoff Groups of Globular Clusters |journal=[[Astrophysical Journal]] |volume=185 |year=1973 |pages=477–498 |doi=10.1086/152434 |bibcode=1973ApJ...185..477V}}</ref> Elements heavier than hydrogen and helium were formed in the [[solar core|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=2001-03-09 |arxiv=astro-ph/0012399 |doi=10.1006/icar.2001.6607 |volume=151 |issue=2 |pages=307–313 |bibcode=2001Icar..151..307L}}</ref>
 
==Interplanetary medium==
[[File:Heliospheric-current-sheet.gif|left|thumb|The [[heliospheric current sheet]]]]
{{Main|Interplanetary medium|Heliosphere}}
 
The vast majority of the volume 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 million kilometres (932 thousand miles) per hour,<ref>{{cite web |title=Solar Physics: The Solar Wind |work=Marshall Space Flight Center |date=2006-07-16<!--11:42:58--> |url=http://solarscience.msfc.nasa.gov/SolarWind.shtml |accessdate=2006-10-03}}</ref> creating a tenuous atmosphere (the heliosphere) that permeates the interplanetary medium out to at least 100&nbsp;AU (see [[#Heliopause|heliopause]]).<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=http://science.nasa.gov/headlines/y2001/ast15feb_1.htm |title=The Sun Does a Flip |accessdate=2007-02-04 |last=Phillips |first=Tony |date=2001-02-15 |work=Science@NASA}}</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>[http://science.nasa.gov/headlines/y2003/22apr_currentsheet.htm A Star with two North Poles], April 22, 2003, Science @ NASA</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 |year=2002 |volume=107 |journal=[[Journal of Geophysical Research]] |url=http://ulysses.jpl.nasa.gov/science/monthly_highlights/2002-July-2001JA000299.pdf}}</ref>
 
[[Earth's magnetic field]] stops [[Earth's atmosphere|its atmosphere]] from being stripped away by the solar wind. Venus and Mars do not have magnetic fields, and as a result, the solar wind causes their atmospheres to gradually bleed away into space.{{dubious|date=January 2014|reason=Venus has a very thick atmosphere}}<ref>{{cite journal |last=Lundin |first=Richard |date=2001-03-09 |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. |coauthors=M. S. Potgieter |year=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 interactions with the planets.<ref>{{cite web |year=1998 |title=Long-term Evolution of the Zodiacal Cloud |url=http://astrobiology.arc.nasa.gov/workshops/1997/zodiac/backman/IIIc.html |accessdate=2007-02-03}}</ref> The second dust cloud extends from about 10 AU to about 40 AU, and was probably created by similar collisions within the [[Kuiper belt]].<ref>{{cite web |year=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=2007-02-03}}</ref><ref>{{cite journal |last=Landgraf |first=M. |coauthors=Liou, J.-C.; Zook, H. A.; 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=2007-02-09 |bibcode=2002AJ....123.2857L}}</ref>
 
==Inner Solar System==
The inner Solar System is the traditional name for the region comprising the terrestrial planets and asteroids.<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=2009-05-09}}</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 shorter than the distance between the orbits of Jupiter and Saturn.
 
===Inner planets=== <!--This heading linked from [[Extrasolar planet]]-->
{{Main|Terrestrial planet}}
[[File:Telluric planets size comparison.jpg|thumb|upright=1.4|The inner planets. From left to right: [[Earth]], [[Mars]], [[Venus]], and [[Mercury (planet)|Mercury]] (sizes to scale, interplanetary distances not)]]
 
The four inner or terrestrial 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====
: [[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, and its only known geological features besides impact craters are lobed ridges or [[rupes]], 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 almost negligible atmosphere consists of atoms blasted off its surface by the solar wind.<ref>{{cite web |year=2006 |author=Bill Arnett |title=Mercury |work=The Nine Planets |url=http://www.nineplanets.org/mercury.html |accessdate=2006-09-14}}</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>Benz, W., Slattery, W. L., Cameron, A. G. W. (1988), ''Collisional stripping of Mercury's mantle'', Icarus, v. 74, p. 516–528.</ref><ref>Cameron, A. G. W. (1985), ''The partial volatilization of Mercury'', Icarus, v. 64, p. 285–294.</ref>
 
====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°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 |year=1997 |url=http://www.boulder.swri.edu/~bullock/Homedocs/PhDThesis.pdf |format=PDF |accessdate=2006-12-26 }}</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 frequently replenished by volcanic eruptions.<ref>{{cite web |year=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=2006-11-19}}</ref>
 
====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=http://science.nasa.gov/planetary-science/big-questions/what-are-the-characteristics-of-the-solar-system-that-lead-to-the-origins-of-life-1/ |accessdate=2011-08-30}}</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=2006-12-26}}</ref> It has one natural satellite, the [[Moon]], the only large satellite of a terrestrial planet in the Solar System.
 
====Mars====
: [[Mars]] (1.5&nbsp;AU from the Sun) is smaller than Earth and Venus (0.107 Earth masses). It possesses 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 et al.|chapter=Mars Atmosphere: History and Surface Interactions|author=David C. Gatling, Conway Leovy|pages=301–314|year=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 |year=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=2006-07-23}}</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=2009-05-14}}</ref> Mars has two tiny natural satellites ([[Deimos (moon)|Deimos]] and [[Phobos (moon)|Phobos]]) thought to be captured [[asteroid]]s.<ref>{{cite web |year=2004 |title=A Survey for Outer Satellites of Mars: Limits to Completeness |author=Scott S. Sheppard, David Jewitt, and Jan Kleyna |work=[[Astronomical Journal]] |url=http://www2.ess.ucla.edu/~jewitt/papers/2004/SJK2004.pdf|accessdate=2006-12-26}}</ref>
 
===Asteroid belt===
{{Main|Asteroid belt}}
[[File:InnerSolarSystem-en.png|thumb|Image of the [[asteroid belt]] (white), the [[Jupiter trojan]]s (green), the [[Hilda family|Hildas]] (orange), and [[near-Earth object|near-Earth asteroids]].]]
 
[[Asteroid]]s are [[Small Solar System body|small Solar System bodies]]<ref group=lower-alpha name=footnoteB /> composed mainly of [[refractory (astronomy)|refractory]] rocky and metallic [[mineral]]s, with some ice.<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=2009-03-01}}</ref>
 
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
| author=Petit, J.-M.; Morbidelli, A.; Chambers, J.
| title=The Primordial Excitation and Clearing of the Asteroid Belt
| journal=[[Icarus (journal)|Icarus]]
| year=2001
| volume=153
| issue=2
| pages=338–347
| url=http://www.gps.caltech.edu/classes/ge133/reading/asteroids.pdf
| format=PDF
| accessdate=2007-03-22 | doi = 10.1006/icar.2001.6702
| bibcode=2001Icar..153..338P
}}</ref>
 
Asteroids range in size from hundreds of kilometres across to microscopic. All asteroids except the largest, Ceres, are classified as small Solar System bodies.<ref>{{cite web|title=IAU Planet Definition Committee|publisher=International Astronomical Union|year=2006|url=http://www.iau.org/public_press/news/release/iau0601/newspaper/|accessdate=2009-03-01}}</ref>
 
The asteroid belt contains tens of thousands, possibly millions, of objects over one kilometre in diameter.<ref>{{cite web |year=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=2006-06-23}}</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 |coauthors=[[Elena V. Pitjeva|Pitjeva, E. V.]]; Vasilyev, M. V.; 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. Asteroids with diameters between 10 and 10<sup>−4</sup>&nbsp;m are called [[meteoroid]]s.<ref>{{cite journal |date=September 1995 |title=On the Definition of the Term Meteoroid |journal=[[Quarterly Journal of the Royal Astronomical Society]] |volume=36 |issue=3 |pages=281–284 |bibcode=1995QJRAS..36..281B}}</ref>
 
====Ceres====
[[Ceres (dwarf planet)|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 1000&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=2006-08-29}}</ref> It was classified as a dwarf planet in 2006.
 
====Asteroid groups====
Asteroids in the asteroid belt are divided into [[asteroid group]]s and [[:Category:Asteroid groups and families|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 |year=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=2006-06-23}}</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.|coauthors=Kruikshank, D.P.; Mottola S.; Lazzarin M.|year=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 is also dusted with [[Near-Earth asteroid|rogue 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., A. Cellino, P. Paolicchi, and R. P. Binzel|pages = 409–422|date=January 2002|publisher = University of Arizona Press|format=PDF|bibcode = 2002aste.conf..409M}}</ref>
 
==Outer Solar System==
The outer region of the Solar System is home to the gas giants and their large moons. Many short-period comets, including the [[Centaur (planetoid)|centaurs]], 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 the rocky denizens of the inner Solar System because the colder temperatures allow these compounds to remain solid.
 
===Outer planets===
{{Main|Outer planets|Gas giant}}
[[File:Gas giants in the solar system.jpg|thumb|From top to bottom: [[Neptune]], [[Uranus]], [[Saturn]], and [[Jupiter]] (Montage with approximate colour and size)]]
 
The four outer planets, or gas giants (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 each many tens of times the mass of Earth and consist overwhelmingly of hydrogen and helium; Uranus and Neptune are far less massive (<20 Earth masses) and possess more ices in their makeup. For these reasons, some astronomers suggest they belong in their own category, "ice giants".<ref>{{cite web |title=Formation of Giant Planets |author=Jack J. Lissauer, David J. Stevenson |work=NASA Ames Research Center; California Institute of Technology |year=2006 |url=http://www.gps.caltech.edu/uploads/File/People/djs/lissauer&stevenson(PPV).pdf|format=PDF |accessdate=2006-01-16}}</ref> All four gas giants 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====
: [[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|67 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 |year=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=2006-01-16}}</ref> Ganymede, the largest satellite in the Solar System, is larger than Mercury.
 
====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, making it the least dense planet in the Solar System.<ref name=universetoday>{{cite web|title=Density of Saturn|url=http://archive.is/LCrCb|work=Fraser Cain|publisher=universetoday.com|accessdate=2013-08-09}}</ref> The rings of Saturn are made up of small ice and rock particles.
: Saturn has [[Moons of Saturn|62 confirmed satellites]]; two of which, [[Titan (moon)|Titan]] and [[Enceladus (moon)|Enceladus]], show signs of geological activity, though they are largely [[Cryovolcano|made of ice]].<ref>{{cite journal|last1=Kargel|first1=J. S.|title=Cryovolcanism on the icy satellites|journal=Earth, Moon, and Planets|volume=67|pages=101–113|year=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====
: [[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 gas giants and radiates very little heat into space.<ref>{{cite journal |title=10 Mysteries of the Solar System|journal=[[Astronomy Now]] |volume=19 |pages=65 |year=2005 |bibcode=2005AsNow..19h..65H }}</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====
: [[Neptune]] (30 AU), though slightly smaller than Uranus, is more massive (equivalent to 17 Earths) and therefore 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 |author=Podolak, M.; Reynolds, R. T.; Young, R. | year=1990|pages=1737|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 |year=1995 |url=http://trs-new.jpl.nasa.gov/dspace/handle/2014/28034?mode=full |accessdate=2006-01-16 }}</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 |author=John Stansberry, Will Grundy, Mike Brown, Dale Cruikshank, John Spencer, David Trilling, Jean-Luc Margot|booktitle=The Solar System Beyond Neptune |arxiv=astro-ph/0702538|pages=161 |year=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 |year=1995 |author=Patrick Vanouplines |title=Chiron biography |work=Vrije Universitiet Brussel |url=http://www.vub.ac.be/STER/www.astro/chibio.htm |accessdate=2006-06-23}}</ref>
 
==Comets==
{{Main|Comet}}
[[File:Comet c1995o1.jpg|upright|thumb|[[Comet Hale–Bopp]]]]
 
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 believed to originate in the Kuiper belt, whereas long-period comets, such as [[Comet Hale–Bopp|Hale–Bopp]], are believed to originate in the [[Oort cloud]]. Many comet groups, such as the [[Kreutz Sungrazers]], formed from the breakup of a single parent.<ref>{{cite journal |author=Sekanina, Zdeněk |year=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. |year=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 |year=1992 |doi=10.1007/BF00049540 |bibcode=1992CeMDA..54....1W}}</ref>
 
==Trans-Neptunian region==
The area beyond Neptune, or the "[[trans-Neptunian object|trans-Neptunian region]]", is still [[Timeline of Solar System exploration|largely unexplored]]. It appears to consist overwhelmingly 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 known as the "outer Solar System", though others use that term to mean the region beyond the asteroid belt.
 
===Kuiper belt===
{{Main|Kuiper belt}}
[[File:Outersolarsystem objectpositions labels comp.png|left|thumb|200px|Plot of all Kuiper belt objects known in 2007, set against the four outer planets]]
 
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 et al. |chapter=Kuiper Belt Objects: Physical Studies|author=Stephen C. Tegler|pages=605–620|year=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 |year=2006 |author=Audrey Delsanti and David Jewitt |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=2007-01-03|archiveurl = http://web.archive.org/web/20070129151907/http://www.ifa.hawaii.edu/faculty/jewitt/papers/2006/DJ06.pdf |archivedate = January 29, 2007|deadurl=yes}}</ref> Many Kuiper belt objects have multiple satellites,<ref>{{cite doi | 10.1086/501524 }}</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| author=Chiang ''et al.'' | 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 | year=2003 | doi=10.1086/375207 | accessdate=2009-08-15 | 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 | first10=R. M.}}</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 |year=2005 |author=M. W. Buie, R. L. Millis, L. H. Wasserman, J. L. Elliot, S. D. Kern, K. B. Clancy, E. I. Chiang, A. B. Jordan, K. J. Meech, R. M. Wagner, 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 |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, {{mpl|(15760) 1992 QB|1}}, 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=2006-12-26 |date=2006-08-24}}</ref>
 
====Pluto and Charon====
{{TNO imagemap}}
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.
 
[[Charon (moon)|Charon]], Pluto's largest moon, is sometimes described as part of a [[binary system (astronomy)|binary system]] with Pluto, as the two bodies orbit a [[Earth-Moon barycenter|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]], are known to orbit within the system.
 
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. |coauthors=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=2006-12-26}}</ref>
 
====Makemake and Haumea====
[[Makemake (dwarf planet)|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, it is 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=2008-04-05
|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=2012-07-15
|authorlink=Marc W. Buie}}</ref>
 
[[Haumea (dwarf planet)|Haumea]] (43.13&nbsp;AU average) is in an orbit similar to Makemake except that it is caught 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 = 2012-07-15}}</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 = 2008-09-17
| url = http://www.iau.org/public_press/news/release/iau0807/
| accessdate = 2012-07-15}}</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 believed 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 have aphelia farther 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 |year=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=2006-07-16}}</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=2007-04-02}}</ref>
 
====Eris====
[[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 doi | 10.1126/science.1139415 }}</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:Local Interstellar Clouds with motion arrows.jpg|thumb|Beyond the heliosphere is the interstellar medium, consisting of various clouds of gases. (see [[Local Interstellar Cloud]])]]
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 outer limit of the solar wind's influence is roughly four times Pluto's distance from the Sun; this ''[[Heliopause (astronomy)|heliopause]]'' is considered the beginning of the [[interstellar medium]].<ref name="Voyager" /> The Sun's [[Hill sphere]], the effective range of its gravitational dominance, is believed to extend up to a thousand times farther.<ref name=Littmann>{{cite book|last=Littmann|first=Mark|title=Planets Beyond: Discovering the Outer Solar System|year=2004|pages=162–163|publisher=Courier Dover Publications|isbn=978-0-486-43602-9}}</ref>
 
===Heliopause===
[[File:IBEX all sky map.jpg|thumb|left|[[Energetic neutral atoms]] map of heliosheath and heliopause by [[IBEX]]. Credit: NASA/Goddard Space Flight Center Scientific Visualization Studio.]]
<!-- [[File:NewHeliopause 558121.jpg|thumb|300px|NASA image of the heliosheath and heliopause]] -->
 
The heliosphere is divided into two separate regions. The solar wind travels at roughly 400&nbsp;km/s until it collides with the [[interstellar wind]]; the flow of plasma in the [[interstellar medium]]. The collision occurs at the [[termination shock]], which is roughly 80–100 AU from the Sun upwind of the interstellar medium and roughly 200 AU from the Sun downwind.<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 believed to look and behave very much like a comet's tail, extending outward for a further 40 AU on the upwind side but tailing many times that distance downwind; evidence from the Cassini and [[Interstellar Boundary Explorer]] spacecraft has suggested that it is forced into a bubble shape by the constraining action of the interstellar magnetic field.<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|year=2009|accessdate=2009-12-20}}</ref> The outer boundary of the heliosphere, the [[Heliopause (astronomy)|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=2007-04-02}}</ref> Both ''[[Voyager 1]]'' and ''[[Voyager 2]]'' are reported to have passed the termination shock and entered the heliosheath, at 94 and 84 AU from the Sun, respectively.<ref>{{cite journal | doi=10.1126/science.1117684 |date=September 2005 | author=Stone, E. C.; Cummings, A. C.; McDonald, F. B.; Heikkila, B. C.; Lal, N.; 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 | author=Stone, E. C.; Cummings, A. C.; McDonald, F. B.; Heikkila, B. C.; Lal, N.; Webber, W. R. | title=An asymmetric solar wind termination shock | volume=454 | issue=7200 | pages=71–4 | pmid=18596802 | journal=[[Nature (journal)|Nature]] }}</ref> ''Voyager 1'' is also reported to have reached the heliopause.<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}}</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<ref name="fahr">{{cite journal |year=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 }} See Figures 1 and 2.</ref> as well as solar magnetic fields prevailing to the south, e.g. it is bluntly shaped with the northern hemisphere extending 9 AU farther than the southern hemisphere. 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 web | date=June 24, 2002 |author=P. C. Frisch (University of Chicago) |title=The Sun's Heliosphere & Heliopause | work=[[Astronomy Picture of the Day]] | url=http://antwrp.gsfc.nasa.gov/apod/ap020624.html |accessdate=2006-06-23}}</ref>
 
Due to a lack of data, the 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 back to Earth.<ref>{{cite web | year=2007 | title=Voyager: Interstellar Mission | work=NASA Jet Propulsion Laboratory | url=http://voyager.jpl.nasa.gov/mission/interstellar.html |accessdate=2008-05-08}}</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. et al. | booktitle= Physics of the Inner Heliosheath: Voyager Observations, Theory, and Future Prospects |series=[[AIP Conference Proceedings]] |volume=858 |pages=341–347 |year=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=http://space.newscientist.com/article/mg19325850.900-interstellar-space-and-step-on-it.html |date=2007-01-05 |accessdate=2007-02-05 | author=Anderson, Mark}}</ref>
 
===Detached objects===
{{main|Detached object}}
[[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 as 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 |year=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=2006-06-23}}</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 |year=2004 |url=http://www.gps.caltech.edu/~mbrown/sedna/ |work=CalTech |accessdate=2007-05-02}}</ref> Sedna is very likely a dwarf planet, though its shape has yet to be determined.
 
===Oort cloud===
{{Main|Oort cloud}}
[[File:Kuiper oort.jpg|thumb|250px|An artist's rendering of the Oort cloud, the Hills cloud, and the Kuiper belt (inset)]]
 
The Oort cloud is a hypothetical spherical cloud of up to a trillion icy objects that is believed 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 believed 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 |year=2001 |author=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=http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=11214311&dopt=Citation |accessdate=2006-11-19}}</ref><ref>{{cite web |year=2006 |author=Bill Arnett |title=The Kuiper Belt and the Oort Cloud |work=nineplanets.org |url=http://www.nineplanets.org/kboc.html |accessdate=2006-06-23}}</ref>
 
===Boundaries===
{{See also|Vulcanoid asteroid|Planets beyond Neptune|Nemesis (hypothetical star)|Tyche (hypothetical planet)}}
 
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 |author=T. Encrenaz, JP. Bibring, M. Blanc, MA. Barucci, F. Roques, PH. Zarka |publisher=Springer |year=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 |year=2004 |pages=312–315 |volume=148 |journal=[[Icarus (journal)|Icarus]] |author=Durda D. D.; Stern S. A.; Colwell W. B.; Parker J. W.; Levison H. F.; 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.
 
In November 2012 NASA announced that as [[Voyager 1]] approached the transition zone to the outer limit of the Solar System, its instruments detected a sharp intensification of the magnetic field. No change in the direction of the magnetic field had occurred, which NASA scientists then interpreted to indicate that Voyager 1 had not yet left the Solar System.<ref>{{cite web |url=http://www.nasa.gov/mission_pages/voyager/voyager20121203.html |title=NASA Voyager 1 Encounters New Region in Deep Space |last1=Greicius |first1=Tony |last2= |first2= |date=3 December 2012 |work= |publisher=NASA |accessdate=26 January 2013}}</ref>
 
==Galactic context==
{{imageframe|width=300|caption=Position of the Solar System within the Milky Way|content=
{{Superimpose
  | base = Milky Way Arms ssc2008-10.svg
  | base_width = 300px
  | 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 = 142
  | y = 55
}} }}
 
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 200 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
|year=2000
|accessdate = 2007-05-10
}}</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 |author=R. Drimmel, D. N. Spergel |year=2001 |pages=181–202 |volume=556 |doi=10.1086/321556 |journal=[[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.
|coauthors=et al.
|title=A Geometric Determination of the Distance to the Galactic Center
|journal=[[Astrophysical Journal]]
|volume=597 |issue=2 |pages=L121–L124
|year=2003
|doi=10.1086/380188
|bibcode=2003ApJ...597L.121E
}}</ref> and its speed within the galaxy is about 220 [[metre per second|kilometres per second]] (140&nbsp;mi/s), so that it completes one revolution every 225–250 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 |year=2002 |work=The Physics Factbook |accessdate=2007-04-02}}</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 |year=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=2007-02-12}}</ref> The plane of the ecliptic lies at an angle of about 60° to the [[galactic plane]].{{Refn|If ψ is the angle between the [[Ecliptic pole|north pole of the ecliptic]] and the north [[galactic pole]] then:
:<math>\cos\psi=\cos(\beta_g)\cos(\beta_e)\cos(\alpha_g-\alpha_e)+\sin(\beta_g)\sin(\beta_e)</math>,
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. | coauthors=Brunthaler, A. | title=The Proper Motion of Sagittarius A* | journal=[[The Astrophysical Journal]] | volume=616 | issue=2 | page=883 | doi=10.1086/424960 | month=2004 | year=2004 | bibcode=2004ApJ...616..872R}}</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°.|group=lower-alpha}}
 
The Solar System's location in the galaxy is a factor in the [[evolution]] 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. 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 |year=2001 |author=Leslie Mullen |title=Galactic Habitable Zones |work=Astrobiology Magazine |url=http://www.astrobio.net/news/modules.php?op=modload&name=News&file=article&sid=139 |accessdate=2006-06-23}}</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]] 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 hypothesised 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 |year=2005 |author=|title=Supernova Explosion May Have Caused Mammoth Extinction |work=Physorg.com |url=http://www.physorg.com/news6734.html |accessdate=2007-02-02}}</ref>
 
===Neighbourhood===
The Solar System is currently located in the [[Local Interstellar Cloud]] or Local Fluff. It is thought to be near the neighbouring [[G-Cloud]], but it is unknown 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], NASA, 05-06-2013</ref><ref>[http://www.centauri-dreams.org/?p=14203 Into the Interstellar Void], Centauri Dreams, 05-06-2013</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 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=http://science.nasa.gov/headlines/y2003/06jan_bubble.htm |accessdate=2006-07-23}}</ref>
 
There are relatively few [[List of nearest stars|stars within ten light years]] (95 trillion km, or 60 trillion mi) 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]] Alpha Centauri C (also known as [[Proxima Centauri]]) orbits the pair at a distance of 0.2 light years. The stars next closest to the Sun are the red dwarfs [[Barnard's Star]] (at 5.9 light years), [[Wolf 359]] (7.8 light years), and [[Lalande 21185]] (8.3 light years). The largest star within ten light years is [[Sirius]], a bright [[main sequence|main-sequence]] star roughly twice the Sun's mass and orbited by a [[white dwarf]] called Sirius B. It lies 8.6 light years away. The remaining systems within ten light years are the binary red-dwarf system [[Luyten 726-8]] (8.7 light years) and the solitary red dwarf [[Ross 154]] (9.7 light years).<ref>{{cite web |title=Stars within 10 light years |url=http://www.solstation.com/stars/s10ly.htm|work=SolStation |accessdate=2007-04-02}}</ref> The Solar System's closest solitary Sun-like star is [[Tau Ceti]], which lies 11.9 light years away. 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=2007-04-02}}</ref> The closest known [[extrasolar planet]] to the Sun lies around Alpha Centauri B. Its one confirmed planet, [[Alpha Centauri Bb]], is at least 1.1 times Earth's mass and orbits its star every 3.236 days.<ref>{{cite doi | 10.1038/nature11572}}</ref>
 
{{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]].'')}}
 
==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 [[Pluto]] and [[Eris (dwarf planet)|Eris]], because these have not been imaged in high quality.
{{SolarSummary}}
 
==See also==
{{Solar System navbox}}
* [[Astronomical symbols]]
* [[List of gravitationally rounded objects of the Solar System]]
* [[List of geological features of the Solar System]]
* [[Planetary mnemonic]]
* [[Solar System in fiction]]
* {{Wikipedia books link|Solar System}}
{{clear}}
 
==Notes==
{{Reflist|group=lower-alpha|30em}}
 
==References==
{{Reflist|30em}}
 
==External links==
{{Sister project links|Solar System}}
* [http://solarsystem.nasa.gov/planets/profile.cfm?Object=SolarSys&Display=Overview Solar System Profile] by [http://solarsystem.nasa.gov/index.cfm NASA's Solar System Exploration]
* [http://space.jpl.nasa.gov NASA's Solar System Simulator]
* [http://www.jpl.nasa.gov/solar_system NASA/JPL Solar System main page]
{{Solar system table}}
{{Nearest systems|1}}
{{Earth's location}}
{{Systems}}
{{featured article}}
 
[[Category:Planetary science]]
[[Category:Planetary systems]]
[[Category:Solar System| ]]
[[Category:Space science]]
 
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Latest revision as of 19:32, 30 November 2014

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