Editing Solar System (section)

=== Orbits ===

[[File:Solar system orrery inner planets.gif|thumb|Animations of the Solar System's [[inner planet]]s orbiting. Each frame represents 2 days of motion.]]
[[File:Solar system orrery outer planets.gif|thumb|Animations of the Solar System's [[outer planet]]s orbiting. This animation is 100 times faster than the inner planet animation.]]

The planets and other large objects in orbit around the Sun lie near the plane of Earth's orbit, known as the [[ecliptic]]. Smaller icy objects such as comets frequently orbit at significantly greater angles to this plane.<ref name="Levison2003">{{Cite journal |last1=Levison |first1=H.F. |author-link=Harold F. Levison |last2=Morbidelli |first2=A. |date=27 November 2003 |title=The formation of the Kuiper belt by the outward transport of bodies during Neptune's migration |journal=[[Nature (journal)|Nature]] |volume=426 |issue=6965 |pages=419–421 |bibcode=2003Natur.426..419L |doi=10.1038/nature02120 |pmid=14647375 |s2cid=4395099}}</ref><ref>{{Cite journal |last1=Levison |first1=Harold F. |last2=Duncan |first2=Martin J. |date=1997 |title=From the Kuiper Belt to Jupiter-Family Comets: The Spatial Distribution of Ecliptic Comets |journal=[[Icarus (journal)|Icarus]] |volume=127 |issue=1 |pages=13–32 |bibcode=1997Icar..127...13L |doi=10.1006/icar.1996.5637}}</ref> Most of the planets in the Solar System have secondary systems of their own, being orbited by natural satellites called moons. All of the largest natural satellites are in [[synchronous rotation]], with one face permanently turned toward their parent. The four giant planets have planetary rings, thin discs of tiny particles that orbit them in unison.<ref name="bennett_4.5">{{Cite book |last1=Bennett |first1=Jeffrey O. |title=The Cosmic Perspective |last2=Donahue |first2=Megan |last3=Schneider |first3=Nicholas |last4=Voit |first4=Mark |date=2020 |publisher=Pearson |isbn=978-0-134-87436-4 |edition=9th |location=Hoboken, NJ |chapter=4.5 Orbits, Tides, and the Acceleration of Gravity |oclc=1061866912 |author-link2=Megan Donahue}}</ref>

As a result of the [[Formation and evolution of the Solar System|formation of the Solar System]], planets and most other objects orbit the Sun in the same direction that the Sun is rotating. That is, counter-clockwise, as viewed from above Earth's north pole.<ref>{{Cite magazine |last=Grossman |first=Lisa |date=13 August 2009 |title=Planet found orbiting its star backwards for first time |url=https://www.newscientist.com/article/dn17603-planet-found-orbiting-its-star-backwards-for-first-time.html |url-status=live |magazine=New Scientist |archive-url=https://web.archive.org/web/20121017083955/http://www.newscientist.com/article/dn17603-planet-found-orbiting-its-star-backwards-for-first-time.html |archive-date=17 October 2012 |access-date=10 October 2009}}</ref> There are exceptions, such as [[Halley's Comet]].<ref>{{Cite web |last=Nakano |first=Syuichi |date=2001 |title=OAA computing section circular |url=http://www.oaa.gr.jp/~oaacs/nk/nk866.htm |url-status=live |archive-url=https://web.archive.org/web/20190921103057/http://www.oaa.gr.jp/~oaacs/nk/nk866.htm |archive-date=21 September 2019 |access-date=15 May 2007 |publisher=Oriental Astronomical Association}}</ref> Most of the larger moons orbit their planets in [[Retrograde and prograde motion|prograde]] direction, matching the direction of planetary rotation; Neptune's moon [[Triton (moon)|Triton]] is the largest to orbit in the opposite, retrograde manner.<ref>{{Cite journal |last1=Agnor |first1=Craig B. |last2=Hamilton |first2=Douglas P. |date=May 2006 |title=Neptune's capture of its moon Triton in a binary–planet gravitational encounter |url=https://www.nature.com/articles/nature04792 |url-status=live |journal=[[Nature (journal)|Nature]] |language=en |volume=441 |issue=7090 |pages=192–194 |bibcode=2006Natur.441..192A |doi=10.1038/nature04792 |issn=1476-4687 |pmid=16688170 |s2cid=4420518 |archive-url=https://web.archive.org/web/20220415081402/https://www.nature.com/articles/nature04792 |archive-date=15 April 2022 |access-date=28 March 2022}}</ref> Most larger objects rotate around their own axes in the prograde direction relative to their orbit, though the rotation of Venus is retrograde.<ref>{{Cite book |last=Gallant |first=Roy A. |url=https://www.worldcat.org/oclc/6533014 |title=National Geographic Picture Atlas of Our Universe |date=1980 |publisher=National Geographic Society |isbn=0-87044-356-9 |editor-last=Sedeen |editor-first=Margaret |location=Washington, D.C. |pages=82 |oclc=6533014 |access-date=28 March 2022 |archive-url=https://web.archive.org/web/20220420161217/https://www.worldcat.org/title/national-geographic-picture-atlas-of-our-universe/oclc/6533014 |archive-date=20 April 2022 |url-status=live}}</ref>

To a good first approximation, [[Kepler's laws of planetary motion]] describe the orbits of objects around the Sun.<ref name=":0">{{Cite book |last1=Frautschi |first1=Steven C. |title=The Mechanical Universe: Mechanics and Heat |title-link=The Mechanical Universe |last2=Olenick |first2=Richard P. |last3=Apostol |first3=Tom M. |last4=Goodstein |first4=David L. |date=2007 |publisher=Cambridge University Press |isbn=978-0-521-71590-4 |edition=Advanced |location=Cambridge [Cambridgeshire] |oclc=227002144 |author-link=Steven Frautschi |author-link3=Tom M. Apostol |author-link4=David L. Goodstein}}</ref>{{Rp|pages=433–437}} These laws stipulate that each object travels along an [[ellipse]] with the Sun at one [[focus (geometry)|focus]], which causes the body's distance from the Sun to vary over the course of its year. A body's closest approach to the Sun is called its ''[[perihelion]]'', whereas its most distant point from the Sun is called its ''[[aphelion]]''.<ref name=":8">{{Cite book |last1=Feynman |first1=Richard P. |title=The Feynman Lectures on Physics, Volume 1 |title-link=The Feynman Lectures on Physics |last2=Leighton |first2=Robert B. |last3=Sands |first3=Matthew L. |date=1989 |publisher=Addison-Wesley Pub. Co |isbn=0-201-02010-6 |location=Reading, Mass. |oclc=531535 |author-link=Richard Feynman |author-link2=Robert B. Leighton |author-link3=Matthew Sands |orig-date=1965}}</ref>{{Rp|location=9-6}} With the exception of Mercury, the orbits of the planets are nearly circular, but many comets, asteroids, and Kuiper belt objects follow highly elliptical orbits. Kepler's laws only account for the influence of the Sun's gravity upon an orbiting body, not the gravitational pulls of different bodies upon each other. On a human time scale, these perturbations can be accounted for using [[numerical model of the Solar System|numerical models]],<ref name=":8" />{{Rp|location=9-6}} but the planetary system can change chaotically over billions of years.<ref>{{Cite journal |last1=Lecar |first1=Myron |last2=Franklin |first2=Fred A. |last3=Holman |first3=Matthew J. |last4=Murray |first4=Norman J. |date=2001 |title=Chaos in the Solar System |journal=Annual Review of Astronomy and Astrophysics |volume=39 |issue=1 |pages=581–631 |arxiv=astro-ph/0111600 |bibcode=2001ARA&A..39..581L |doi=10.1146/annurev.astro.39.1.581 |s2cid=55949289}}</ref>

The [[angular momentum]] of the Solar System is a measure of the total amount of orbital and [[rotational momentum]] possessed by all its moving components.<ref>{{Cite book |last=Piccirillo |first=Lucio |url=https://books.google.com/books?id=W0jpDwAAQBAJ&pg=PA210 |title=Introduction to the Maths and Physics of the Solar System |date=2020 |publisher=CRC Press |isbn=978-0429682803 |page=210 |access-date=10 May 2022 |archive-url=https://web.archive.org/web/20220730084321/https://www.google.com/books/edition/Introduction_to_the_Maths_and_Physics_of/W0jpDwAAQBAJ?gbpv=1&pg=PA210 |archive-date=30 July 2022 |url-status=live}}</ref> Although the Sun dominates the system by mass, it accounts for only about 2% of the angular momentum.<ref name="Marochnik1995">{{Cite conference |last1=Marochnik |first1=L. |last2=Mukhin |first2=L. |date=1995 |title=Is Solar System Evolution Cometary Dominated? |series=Astronomical Society of the Pacific Conference Series |volume=74 |page=83 |bibcode=1995ASPC...74...83M |isbn=0-937707-93-7 |book-title=Progress in the Search for Extraterrestrial Life |editor=Shostak, G.S.}}</ref><ref>{{Cite journal |last1=Bi |first1=S. L. |last2=Li |first2=T. D. |last3=Li |first3=L. H. |last4=Yang |first4=W. M. |year=2011 |title=Solar Models with Revised Abundance |journal=[[The Astrophysical Journal]] |volume=731 |issue=2 |pages=L42 |arxiv=1104.1032 |bibcode=2011ApJ...731L..42B |doi=10.1088/2041-8205/731/2/L42 |s2cid=118681206}}</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" />