Editing Solar System (section)

=== Comets ===
{{Main|Comet}}

[[File:Comet_Hale-Bopp_1995O1.jpg|thumb|[[Comet Hale–Bopp]] seen in 1997]]
Comets are [[small Solar System bodies]], typically only a few kilometers 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.<ref>{{Cite web |date=19 December 2019 |title=In Depth: Comets |url=https://solarsystem.nasa.gov/asteroids-comets-and-meteors/comets/in-depth |url-status=live |archive-url=https://web.archive.org/web/20220331200633/https://solarsystem.nasa.gov/asteroids-comets-and-meteors/comets/in-depth |archive-date=31 March 2022 |access-date=31 March 2022 |website=NASA Science: Solar System Exploration}}</ref>

Short-period comets have orbits lasting less than two hundred years. Long-period comets have orbits lasting thousands of years. Short-period comets are thought to originate in the Kuiper belt, whereas long-period comets, such as [[Comet Hale–Bopp|Hale–Bopp]], are thought to originate in the Oort cloud. Many comet groups, such as the [[Kreutz sungrazer]]s, formed from the breakup of a single parent.<ref>{{Cite journal |last=Sekanina |first=Zdeněk |date=2001 |title=Kreutz sungrazers: the ultimate case of cometary fragmentation and disintegration? |journal=Publications of the Astronomical Institute of the Academy of Sciences of the Czech Republic |volume=89 |pages=78–93 |bibcode=2001PAICz..89...78S}}</ref> Some comets with [[hyperbolic trajectory|hyperbolic]] orbits may originate outside the Solar System, but determining their precise orbits is difficult.<ref name="hyperbolic">{{Cite journal |last=Królikowska |first=M. |date=2001 |title=A study of the original orbits of ''hyperbolic'' comets |journal=[[Astronomy & Astrophysics]] |volume=376 |issue=1 |pages=316–324 |bibcode=2001A&A...376..316K |doi=10.1051/0004-6361:20010945 |doi-access=free}}</ref> Old comets whose volatiles have mostly been driven out by solar warming are often categorized as asteroids.<ref>{{Cite journal |last=Whipple |first=Fred L. |date=1992 |title=The activities of comets related to their aging and origin |journal=[[Celestial Mechanics and Dynamical Astronomy]] |volume=54 |issue=1–3 |pages=1–11 |bibcode=1992CeMDA..54....1W |doi=10.1007/BF00049540 |s2cid=189827311}}</ref>