Editing Solar System (section)

== Miscellaneous populations ==
=== 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>

=== Meteoroids, meteors and dust ===
{{Main|Meteoroid|Interplanetary dust cloud|Cosmic dust}}
[[File:Meteor shower in the Chilean Desert (annotated and cropped).jpg|thumb|The planets, zodiacal light and meteor shower (top left of image)]]
Solid objects smaller than one meter are usually called meteoroids and micrometeoroids (grain-sized), with the exact division between the two categories being debated over the years.<ref>{{Cite journal |last1=Rubin |first1=Alan E. |last2=Grossman |first2=Jeffrey N. |date=February 2010 |title=Meteorite and meteoroid: new comprehensive definitions |url=https://onlinelibrary.wiley.com/doi/10.1111/j.1945-5100.2009.01009.x |url-status=live |journal=Meteoritics and Planetary Science |language=en |volume=45 |issue=1 |page=114 |bibcode=2010M&PS...45..114R |doi=10.1111/j.1945-5100.2009.01009.x |s2cid=129972426 |archive-url=https://web.archive.org/web/20220325111938/https://onlinelibrary.wiley.com/doi/10.1111/j.1945-5100.2009.01009.x |archive-date=25 March 2022 |access-date=10 April 2022}}</ref> By 2017, the IAU designated any solid object having a diameter between ~30&nbsp;[[Micrometre|micrometers]] and 1&nbsp;meter as meteoroids, and depreciated the micrometeoroid categorization, instead terms smaller particles simply as 'dust particles'.<ref>{{cite web |last1= |date=30 April 2017 |title=Definition of terms in meteor astronomy |url=https://www.iau.org/static/science/scientific_bodies/commissions/f1/meteordefinitions_approved.pdf |access-date=25 July 2020 |website=International Astronomical Union |publisher=IAU Commission F1 |page=2 |archive-date=22 December 2021 |archive-url=https://web.archive.org/web/20211222205136/https://www.iau.org/static/science/scientific_bodies/commissions/f1/meteordefinitions_approved.pdf |url-status=live }}</ref>

Some meteoroids formed via disintegration of comets and asteroids, while a few formed via impact debris ejected from planetary bodies. Most meteoroids are made of silicates and heavier metals like [[nickel]] and [[iron]].<ref>{{cite web |title=Meteoroid |url=http://education.nationalgeographic.co.uk/encyclopedia/meteoroid/ |archive-url=https://web.archive.org/web/20151007141358/https://education.nationalgeographic.co.uk/encyclopedia/meteoroid/ |archive-date=7 October 2015 |access-date=24 August 2015 |work=National Geographic|date=28 May 2010 }}</ref> When passing through the Solar System, comets produce a trail of meteoroids; it is hypothesized that this is caused either by vaporization of the comet's material or by simple breakup of dormant comets. When crossing an atmosphere, these meteoroids will produce bright streaks in the sky due to [[atmospheric entry]], called [[meteor]]s. If a stream of meteoroids enter the atmosphere on parallel trajectories, the meteors will seemingly 'radiate' from a point in the sky, hence the phenomenon's name: [[meteor shower]].<ref>{{cite book | chapter=The Evolution of Meteoroid Streams | first=Iwan P. | last=Williams | title=Meteors in the Earth's Atmosphere: Meteoroids and Cosmic Dust and Their Interactions with the Earth's Upper Atmosphere | pages=13–32 | year=2002 | isbn=9780521804318 | publisher=Cambridge University Press | editor1-first=Edmond | editor1-last=Murad | editor2-first=Iwan P. | editor2-last=Williams | chapter-url=https://books.google.com/books?id=eqd4e34uE-MC&pg=PA13 }}</ref>

The inner Solar System is home to the [[interplanetary dust cloud|zodiacal dust cloud]], which is visible as the hazy [[zodiacal light]] in dark, unpolluted skies. It may be generated by collisions within the asteroid belt brought on by gravitational interactions with the planets; a more recent proposed origin is materials from planet Mars.<ref>{{Cite journal |last1=Jorgensen |first1=J. L. |last2=Benn |first2=M. |last3=Connerney |first3=J. E. P. |last4=Denver |first4=T. |last5=Jorgensen |first5=P. S. |last6=Andersen |first6=A. C. |last7=Bolton |first7=S. J. |date=March 2021 |title=Distribution of Interplanetary Dust Detected by the Juno Spacecraft and Its Contribution to the Zodiacal Light |journal=Journal of Geophysical Research: Planets |language=en |volume=126 |issue=3 |bibcode=2021JGRE..12606509J |doi=10.1029/2020JE006509 |issn=2169-9097 |s2cid=228840132 |doi-access=free}}</ref> The outer Solar System hosts a cosmic dust cloud. It extends from about {{val|10|u=AU}} to about {{val|40|u=AU}}, and was probably created by collisions within the Kuiper belt.<ref>{{Cite web |date=2003 |title=ESA scientist discovers a way to shortlist stars that might have planets |url=http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=29471 |url-status=live |archive-url=https://web.archive.org/web/20130502033116/http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=29471 |archive-date=2 May 2013 |access-date=3 February 2007 |website=ESA Science and Technology}}</ref><ref>{{Cite journal |last1=Landgraf |first1=M. |last2=Liou |first2=J.-C. |last3=Zook |first3=H. A. |last4=Grün |first4=E. |date=May 2002 |title=Origins of Solar System Dust beyond Jupiter |url=http://astron.berkeley.edu/~kalas/disksite/library/ladgraf02.pdf |url-status=live |journal=[[The Astronomical Journal]] |volume=123 |issue=5 |pages=2857–2861 |arxiv=astro-ph/0201291 |bibcode=2002AJ....123.2857L |doi=10.1086/339704 |s2cid=38710056 |archive-url=http://arquivo.pt/wayback/20160515115002/http://astron.berkeley.edu/~kalas/disksite/library/ladgraf02.pdf |archive-date=15 May 2016 |access-date=9 February 2007}}</ref>