View source for Rings of Saturn

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[[File:PIA17172 Saturn eclipse mosaic bright crop.jpg|thumb|upright=1.35|The full set of rings, imaged on [[The Day the Earth Smiled|July 19, 2013]] as Saturn eclipses the Sun from the vantage of the [[Cassini–Huygens|''Cassini'' orbiter]], {{convert|1.2|e6km|abbr=off|frac=4}} distant. Earth appears as [[Pale Blue Dot|a dot]] at 4 o'clock, between the [[#G Ring|G]] and [[#E Ring|E]] rings{{snd}}with its brightness artificially exaggerated in this photograph.]]

[[Saturn]] has the most extensive and complex [[ring system]] of any planet in the [[Solar System]]. The rings consist of particles in orbit around the planet and are made almost entirely of water ice, with a trace component of [[Rock (geology)|rocky material]]. Particles range from micrometers to meters in size.<ref name="Questions">{{cite web |last=Porco |first=Carolyn |author-link=Carolyn Porco |date=2022-07-05 |title=Common Questions |url=https://ciclops.org/sci/common_questions.php.html#ring |url-status=live |archive-url=https://web.archive.org/web/20230801063632/https://ciclops.org/sci/common_questions.php.html#ring |archive-date=2023-08-01 |access-date=2022-09-22 |work=CICLOPS Cassini Imaging Central Laboratory for Operations}}</ref> There is no consensus as to what mechanism facilitated their formation: while investigations using theoretical models suggested they formed early in the Solar System's existence,<ref name="Tiscareno">{{cite book |first=M. S. |last=Tiscareno | editor-last=Kalas | editor-first=P. | editor2-last=French | editor2-first=L. | contribution=Planetary Rings | arxiv=1112.3305v2 | title=Planets, Stars and Stellar Systems | pages=61–63 | year=2012 | publisher=Springer  |doi=10.1007/978-94-007-5606-9_7 |isbn=978-94-007-5605-2 |s2cid=118494597}}</ref> newer data from ''[[Cassini–Huygens|Cassini]]'' suggests a more recent date of formation.<ref name="IessMilitzer2019">{{cite journal|last1= Iess|first1= L.|last2= Militzer|first2= B.|last3= Kaspi|first3= Y.|last4= Nicholson|first4= P.|last5= Durante|first5= D.|last6= Racioppa|first6= P.|last7= Anabtawi|first7= A.|last8= Galanti|first8= E.|last9= Hubbard|first9= W.|last10= Mariani|first10=M. J.|last11= Tortora|first11= P.|last12= Wahl|first12= S.|last13= Zannoni|first13= M.|title= Measurement and implications of Saturn's gravity field and ring mass|journal= Science|volume= 364|issue= 6445|year= 2019|article-number= eaat2965|doi= 10.1126/science.aat2965|pmid= 30655447|hdl= 10150/633328|hdl-access= free|bibcode= 2019Sci...364.2965I|s2cid= 58631177}}</ref> In September 2023, astronomers reported studies suggesting that the rings of Saturn may have resulted from the collision of two moons "a few hundred million years ago".<ref name="TAJ-20230927" /><ref name="NYT-210230928" />

Though light reflected from the rings increases Saturn's [[apparent brightness]], they are not themselves visible from Earth with the [[naked eye]]. In 1610, the year after his first observations with a [[telescope]], [[Galileo Galilei]] became the first person to observe Saturn's rings, though he could not see them well enough to discern their true nature. In 1655, [[Christiaan Huygens]] was the first person to describe them as a disk surrounding Saturn.<ref name="history_of_the_rings" /> The concept that Saturn's rings are made up of a series of tiny ringlets can be traced to [[Pierre-Simon Laplace]],<ref name="history_of_the_rings" /> although true gaps are few{{snd}}it is more correct to think of the rings as an [[Annulus (mathematics)|annular disk]] with [[concentric]] local [[maxima and minima]] in density and brightness.<ref name="Tiscareno" /> 

The rings have numerous gaps where particle density drops sharply: two opened by known moons embedded within them, and many others at locations of known destabilizing [[orbital resonance]]s with the [[moons of Saturn]]. Other gaps remain unexplained. Stabilizing resonances, on the other hand, are responsible for the longevity of several rings, such as the [[#Colombo Gap and Titan Ringlet|Titan Ringlet]] and the [[#G Ring|G Ring]]. Well beyond the main rings is the [[#Phoebe ring|Phoebe ring]], which is presumed to originate from [[Phoebe (moon)|Phoebe]] and thus share its [[Retrograde and prograde motion|retrograde]] orbital motion. It is aligned with the plane of Saturn's orbit. Saturn has an axial tilt of 27 degrees, so this ring is tilted at an angle of 27 degrees to the more visible rings orbiting above Saturn's equator.

== History ==
=== Early observations ===
[[File:Anillos de Satruno - Galileo Galilei.png|thumb|Detail of Galileo's drawing of [[Saturn]] in a letter to [[Belisario Vinta]] (1610)]]
[[Galileo Galilei]] was the first to observe the rings of Saturn in 1610 using his telescope, but was unable to identify them as such. He wrote to the [[Cosimo II de' Medici, Grand Duke of Tuscany|Duke of Tuscany]] that "The planet Saturn is not alone, but is composed of three, which almost touch one another and never move nor change with respect to one another. They are arranged in a line parallel to the [[zodiac]], and the middle one (Saturn itself) is about three times the size of the lateral ones."<ref name="Whitehouse2009">{{cite book|last= Whitehouse|first= David| title= Renaissance Genius: Galileo Galilei and His Legacy to Modern Science|url= https://archive.org/details/renaissancegeniu0000whit|url-access= registration|year= 2009|publisher= Sterling Publishing Company, Inc.|isbn=978-1-4027-6977-1|page=[https://archive.org/details/renaissancegeniu0000whit/page/100 100]|oclc= 434563173}}</ref> He also described the rings as Saturn's "ears". In 1612 the Earth passed through the plane of the rings and they became invisible. Mystified, Galileo remarked "I do not know what to say in a case so surprising, so unlooked for and so novel."<ref name="history_of_the_rings" /> He mused, "Has Saturn swallowed his children?" — referring to the myth of the [[Titan (mythology)|Titan]] [[Cronus|Saturn]] devouring his offspring to forestall the prophecy of them overthrowing him.<ref name="Whitehouse2009" /><ref name= "Deiss2016">{{cite journal|last1= Deiss|first1=B. M.|last2= Nebel|first2= V.|title=On a Pretended Observation of Saturn by Galileo|journal=Journal for the History of Astronomy |volume= 29|issue= 3|year= 2016|pages= 215–220|doi= 10.1177/002182869802900301|s2cid=118636820}}</ref> He was further confused when the rings again became visible in 1613.<ref name="history_of_the_rings">{{cite web |last1=Baalke |first1=Ron |date=1999-04-29 |title=Historical Background of Saturn's Rings |url=http://www2.jpl.nasa.gov/saturn/back.html |archive-url=https://web.archive.org/web/20090321071339/http://www2.jpl.nasa.gov/saturn/back.html |archive-date=2009-03-21 |access-date=2007-05-23 |work=Saturn Ring Plane Crossings of 1995–1996 |publisher=Jet Propulsion Laboratory |language=en}}</ref>

Early [[astronomer]]s used [[anagram]]s as a form of [[commitment scheme]] to lay claim to new discoveries before their results were ready for publication. Galileo used the anagram "''{{shy|smaismrmil|mepoeta|leumibu|nenugt|tauiras}}''" for ''Altissimum planetam tergeminum observavi'' ("I have observed the most distant planet to have a triple form") for discovering the rings of Saturn.<ref>[[Johannes Kepler]] published Galileo's logogriph in the preface to his ''Dioptrice'' (1611):
*  {{cite book |last1=Kepler |first1=Johannes |title=Dioptrice |date=1611 |publisher=David Frank |location=Augsburg, (Germany) |page=15 of the preface |url=https://archive.org/details/DioptriceByJohannesKeplerAkaIoannisKepleri/page/n25/mode/2up |language=la}}
*  English translation:  {{cite book |last1=Carlos |first1=Edward Stafford |title=The Sidereal Messenger of Galileo Galilei and a Part of the Preface to Kepler's Dioptrics ... |date=1888 |publisher=Rivingtons |location=London, England |pages=79–111 |url=https://archive.org/details/siderealmessenge80gali/page/86/mode/2up}}  See pp. 87–88.
Galileo's solution to his logogriph about Saturn was conveyed in a letter of 13 November 1610 to Giuliano de Medici, ambassador from the Grand Duke of Tuscany to Emperor Rudolph of the Holy Roman Empire. 
*  {{cite book |last1=Galilei |first1=Galileo |title=Le Opere di Galileo Galilei |date=1900 |publisher=G. Barbera |location=Florence, Italy |volume=10 |page=474 |url=https://archive.org/details/leoperedigalile00lamigoog/page/474/mode/2up |language=it, la}}</ref><ref>See also:
*  {{cite journal |last1=Partridge |first1=E. A. |last2=Whitaker |first2=H. C. |title=Galileo's work on Saturn's rings — a historical correction |journal=Popular Astronomy |date=1896 |volume=3 |pages=408–414 |bibcode=1896PA......3..408P |url=https://articles.adsabs.harvard.edu//full/1896PA......3..408P/0000408.000.html}}
*  {{cite journal |last1=van Helden |first1=Albert |title=Saturn and his anses |journal=Journal for the History of Astronomy |date=1974 |volume=5 |issue=2 |pages=105–121 |doi=10.1177/002182867400500204 |bibcode=1974JHA.....5..105V |s2cid=220913252 |url=https://articles.adsabs.harvard.edu//full/1974JHA.....5..105V/0000105.000.html}}</ref><ref name="prs.2007a">{{cite book |display-authors=1 |last1=Miner |first1=Ellis D. |last2=Wessen |first2=Randii R. |last3=Cuzzi |first3=Jeffrey N. |chapter=The scientific significance of planetary ring systems |title=Planetary Ring Systems |chapter-url=https://archive.org/details/planetaryringsys0000mine |chapter-url-access=registration |series=Springer Praxis Books in Space Exploration |publisher=Praxis |date=2007 |pages=[https://archive.org/details/planetaryringsys0000mine/page/1 1–16] |doi=10.1007/978-0-387-73981-6_1 |isbn=978-0-387-34177-4 |url=https://archive.org/details/planetaryringsys0000mine/page/1 }}</ref>

In 1657 [[Christopher Wren]] became Professor of Astronomy at Gresham College, London. He had been making observations of the planet Saturn from around 1652 with the aim of explaining its appearance. His hypothesis was written up in ''De corpore saturni,'' in which he came close to suggesting the planet had a ring. However, Wren was unsure whether the ring was independent of the planet, or physically attached to it. Before Wren's hypothesis was published [[Christiaan Huygens]] presented his hypothesis of the rings of Saturn. Immediately Wren recognised this as a better hypothesis than his own and ''De corpore saturni'' was never published. [[Robert Hooke]] was another early observer of the rings of Saturn, and noted the casting of shadows on the rings.<ref name="ff.saturn">{{Cite journal |last=Alexander |first=A. F. O'D. |date=1962 |title=The Planet Saturn |journal=Quarterly Journal of the Royal Meteorological Society |publisher=Faber and Faber Limited |volume=88 |issue=377 |pages=108–109 |bibcode=1962QJRMS..88..366D |doi=10.1002/qj.49708837730 |isbn=978-0-486-23927-9 |place=London}}</ref>

=== Huygens' ring hypothesis and later developments ===
[[File:Huygens Systema Saturnium.jpg|thumb|Huygens' ring hypothesis in ''Systema Saturnium'' (1659)]]
[[Christiaan Huygens]] began grinding lenses with his father [[Constantijn Huygens]] in 1655 and was able to observe Saturn with greater detail using a 43× power refracting telescope that he designed himself. He was the first to suggest that [[Saturn]] was surrounded by a ring detached from the planet, and famously published the letter string "''{{not a typo|{{shy|aaaaaaa|ccccc|deeeeeg|hiiiiiii|llllmm|nnnnnnnnn|oooopp|qrrs|tttttuuuuu}}}}''".<ref>{{cite book |last1=Borello |first1=Petro |title=De Vero Telescopii Inventore ... |trans-title=On the true inventor of the telescope ... |date=1655 |publisher=Adriaan Vlacq |location=The Hague, Netherlands |pages=62–63 |url=https://bibdig.museogalileo.it/Teca/Viewer?an=300919 |language=la}}  Huygens' logogriph appears in the reproduction of a letter by him (''De Saturni Luna'' (On Saturn's moon)), at the bottom of p. 63 of the ''Liber Secundus de Conspiciliis'' ... [Book Two, On [early] Telescopes ... ], in which the pages are numbered separately from those in the first book.</ref> Three years later, he revealed it to mean ''Annulo cingitur, tenui, plano, nusquam coherente, ad eclipticam inclinato'' ("[Saturn] is surrounded by a thin, flat, ring, nowhere touching [the body of the planet], inclined to the ecliptic").<ref>{{cite book |last1=Huygens |first1=Christiaan |title=Systema Saturnium |date=1659 |publisher=Adriaan Vlacq |location=The Hague, Netherlands |page=47 |url=https://library.si.edu/digital-library/book/cristianihugeni00huyga-0 |language=la}}</ref><ref name="history_of_the_rings" /><ref name="Campbell1937">{{Cite book |last=Campbell |first=John W. Jr. |author-link=John W. Campbell |url=http://jolomo.net/solarsystem/1937.04.html |title=Beyond the Life Line |date=April 1937 |series=[[Astounding Stories]] |pages=81–85 |chapter=Notes |chapter-url=http://jolomo.net/solarsystem/notes.html}}</ref> He published his ring hypothesis in ''Systema Saturnium'' (1659) which also included his discovery of Saturn's moon, [[Titan (moon)|Titan]], as well as the first clear outline of the dimensions of the [[Solar System]].<ref>{{Cite journal|url=http://adsabs.harvard.edu/full/2004ESASP1278...11V|title=2004ESASP1278...11V Page 11|journal=Titan - from Discovery to Encounter|bibcode=2004ESASP1278...11V|last1=Van Helden|first1=Albert|year=2004|volume=1278|page=11}}</ref>

In 1675, [[Giovanni Domenico Cassini]] determined that Saturn's ring was composed of multiple smaller rings with gaps between them;<ref>{{cite journal |last1=Cassini |title=Observations nouvelles touchant le globe & l'anneau de Saturne |journal=Mémoires de l'Académie Royale des Sciences |date=1677 |volume=10 |pages=404–405 |url=https://babel.hathitrust.org/cgi/pt?id=mdp.39015075984354&view=1up&seq=466&skin=2021 |trans-title=New observations concerning the globe and the ring of Saturn |language=fr}}</ref> the largest of these gaps was later named the [[#Cassini Division|Cassini Division]]. This division is a {{convert|4800|km|mi|adj=mid|-wide}} region between the [[#A Ring structures|A ring]] and [[#B Ring|B Ring]].<ref name="Cassini Division">{{cite web |title=Saturn's Cassini Division |url=http://starchild.gsfc.nasa.gov/docs/StarChild/solar_system_level2/cassini_division.html |publisher=StarChild |access-date=2007-07-06 }}</ref>

In 1787, [[Pierre-Simon Laplace]] proved that a uniform solid ring would be unstable and suggested that the rings were composed of a large number of solid ringlets.<ref>{{cite journal |last1=La Place |title=Mémoire sur la théorie de l'anneau de Saturne |journal=Mémoires de l'Académie Royale des Sciences de Paris |date=1787 |pages=249–267 |url=https://www.biodiversitylibrary.org/item/89047#page/355/mode/1up |trans-title=Memoir on the theory of the ring of Saturn |language=fr}}</ref><ref name="history_of_the_rings" /><ref name = "Maxwell1859" />

In 1859, [[James Clerk Maxwell]] demonstrated that a nonuniform solid ring, solid ringlets or a continuous fluid ring would also not be stable, indicating that the ring must be composed of numerous small particles, all independently orbiting Saturn.<ref>{{cite book |last1=Maxwell |first1=J. Clerk |title=On the stability of the motion of Saturn's rings |date=1859 |publisher=Macmillan and Co. |location=Cambridge England |bibcode=1859osms.book.....M |url=https://books.google.com/books?id=XPhaAAAAcAAJ}}  This work had been submitted, in 1856, as an entry for the Adams prize from the University of Cambridge.</ref><ref name = "Maxwell1859">{{cite web |url=http://www-history.mcs.st-andrews.ac.uk/~history/Extras/Maxwell_Saturn.html |title=James Clerk Maxwell on the nature of Saturn's rings |date=March 2006 |publisher=JOC/EFR |access-date=2007-07-08 }}</ref> Later, [[Sofia Kovalevskaya]] also found that Saturn's rings cannot be liquid ring-shaped bodies.<ref>{{cite journal |last1=Kowalewsky |first1=Sophie |title=Zusätze und Bemerkungen zu Laplace's Untersuchungen über die Gestalt der Saturnsringe |journal=Astronomische Nachrichten |date=1885 |volume=111 |pages=37–46 |bibcode=1885AN....111...37K |url=https://babel.hathitrust.org/cgi/pt?id=pst.000055392198&view=1up&seq=27&skin=2021 |trans-title=Addenda to and comments on Laplace's investigations of the form of Saturn's rings |language=de}}  This work, with two others, had been submitted in 1874 to the University of Göttingen as her doctoral dissertation.</ref><ref>{{cite web |url=http://www.encyclopedia.com/topic/Sonya_Kovalevsky.aspx#1-1G2:2830902377-full |title=Kovalevsky, Sonya (or Kovalevskaya, Sofya Vasilyevna). Entry from Complete Dictionary of Scientific Biography |date=2013 }}</ref> Spectroscopic studies of the rings which were carried out independently in 1895 by [[James Keeler]] of the [[Allegheny Observatory]] and by [[Aristarkh Belopolsky]] of the [[Pulkovo Observatory]] showed that Maxwell's analysis was correct.<ref>{{cite journal |last=Keeler |first=J. E. |date=1895 |title=A spectroscopic proof of the meteoric constitution of Saturn's rings |journal=[[Astrophysical Journal]] |volume=1 |pages=416–427 |doi=10.1086/140074 |bibcode=1895ApJ.....1..416K |s2cid=4032782 |url=https://babel.hathitrust.org/cgi/pt?id=mdp.39015073165006&view=1up&seq=391&skin=2021 |url-access=subscription }}</ref><ref>{{cite journal |last1=Бѣлополъский |first1=Ар. |title=Изслѣдованіе смѣщенія линій въ спектҏѣ Сатурна и его кольца |journal=Иӡвѣстія Императорской Академіи Наукъ (Bulletin of the Imperial Academy of Science) |date=1895 |series=5th series |volume=3 |issue=4 |pages=379–403 |url=https://www.biodiversitylibrary.org/item/97471#page/495/mode/1up |trans-title=An investigation of the shift of lines in the spectrum of Saturn and of its ring |language=ru}}</ref>

Four robotic spacecraft have observed Saturn's rings from the vicinity of the planet. ''[[Pioneer 11]]''{{'}}s closest approach to Saturn occurred in September 1979 at a distance of {{cvt|20900|km}}.<ref name="NasaPioneer11">{{cite web | last=Dunford | first=Bill | title=Pioneer 11 – In Depth | work=NASA web site | url=https://solarsystem.nasa.gov/missions/pioneer11/indepth | access-date=2015-12-03 | archive-url=https://web.archive.org/web/20151208051756/https://solarsystem.nasa.gov/missions/pioneer11/indepth | archive-date=2015-12-08 }}</ref> ''Pioneer 11'' was responsible for the discovery of the F ring.<ref name="NasaPioneer11"/> ''[[Voyager 1]]''{{'}}s closest approach occurred in November 1980 at a distance of {{cvt|64200|km}}.<ref name="JplVoyager">{{cite web | last=Angrum | first=Andrea | title=Voyager – The Interstellar Mission | work= JPL/NASA web site | url=http://voyager.jpl.nasa.gov/news/factsheet.html | access-date=2015-12-03 }}</ref> A failed photopolarimeter prevented ''Voyager 1'' from observing Saturn's rings at the planned resolution; nevertheless, images from the spacecraft provided unprecedented detail of the ring system and revealed the existence of the G ring.<ref name="NasaVoyager1">{{cite web | last=Dunford | first=Bill | title=Voyager 1 – In Depth | work= NASA web site | url=https://solarsystem.nasa.gov/missions/voyager1/indepth | archive-url=https://web.archive.org/web/20151003054711/http://solarsystem.nasa.gov/missions/voyager1/indepth | archive-date=2015-10-03 | access-date=2015-12-03 }}</ref> ''[[Voyager 2]]''{{'}}s closest approach occurred in August 1981 at a distance of {{cvt|41000|km}}.<ref name="JplVoyager"/> ''Voyager 2''{{'}}s working photopolarimeter allowed it to observe the ring system at higher resolution than ''Voyager 1'', and to thereby discover many previously unseen ringlets.<ref name="NasaVoyager2">{{cite web | last=Dunford | first=Bill | title=Voyager 2 – In Depth | work= NASA web site | url=https://solarsystem.nasa.gov/missions/voyager2/indepth | access-date=2015-12-03 }}</ref> [[Cassini–Huygens|''Cassini'']] spacecraft entered into orbit around Saturn in July 2004.<ref name="NasaCassiniDates">{{cite web | last=Dunford | first=Bill | title=Cassini – Key Dates | work=NASA web site | url=https://solarsystem.nasa.gov/missions/cassini/dates | access-date=2015-12-03 | archive-date=2017-04-13 | archive-url=https://web.archive.org/web/20170413070348/https://solarsystem.nasa.gov/missions/cassini/dates }}</ref> ''Cassini''{{'s}} images of the rings are the most detailed to-date, and are responsible for the discovery of yet more ringlets.<ref name="JplCassiniRings">{{cite web | last=Piazza | first=Enrico | title=Cassini Solstice Mission: About Saturn & Its Moons | work= JPL/NASA web site | url=http://saturn.jpl.nasa.gov/science/index.cfm?SciencePageID=55 | access-date=2015-12-03 }}</ref>

The rings are named alphabetically in the order they were discovered:<ref name=NASAsaturn>{{cite web |url=http://solarsystem.nasa.gov/planets/profile.cfm?Object=Saturn&Display=Rings |title=Solar System Exploration: Planets: Saturn: Rings |work=Solar System Exploration |archive-url=https://web.archive.org/web/20100527141504/http://solarsystem.nasa.gov/planets/profile.cfm?Object=Saturn&Display=Rings |archive-date=2010-05-27 }}</ref> A and B in 1675 by [[Giovanni Domenico Cassini]], C in 1850 by [[William Cranch Bond]] and his son [[George Phillips Bond]], D in 1933 by [[Nikolai Barabashov]] and {{ill|Boris Semeykin|uk|Сємейкін Борис Євгенович}}, E in 1967 by [[Walter A. Feibelman]], F in 1979 by ''[[Pioneer 11]]'', and G in 1980 by ''[[Voyager 1]]''. The main rings are, working outward from the planet, C, B and A, with the Cassini Division, the largest gap, separating Rings B and A. Several fainter rings were discovered more recently. The D Ring is exceedingly faint and closest to the planet. The narrow F Ring is just outside the A Ring. Beyond that are two far fainter rings named G and E. The rings show a tremendous amount of structure on all scales, some related to perturbations by Saturn's moons, but much unexplained.<ref name=NASAsaturn/>

In September 2023, astronomers reported studies suggesting that the rings of Saturn may have resulted from the collision of two moons "a few hundred million years ago".<ref name="NYT-210230928">{{cite news |last=Andrew |first=Robin George |title=Saturn's Rings May Have Formed in a Surprisingly Recent Crash of 2 Moons - Researchers completed a complex simulation that supports the idea that the giant planet's jewelry emerged hundreds of millions of years ago, not billions. |url=https://www.nytimes.com/2023/09/28/science/saturn-rings-moons-formation.html |date=28 September 2023 |work=[[The New York Times]] |url-status=live |archive-url=https://archive.today/20230929044637/https://www.nytimes.com/2023/09/28/science/saturn-rings-moons-formation.html |archive-date=29 September 2023 |access-date=29 September 2023 }}</ref><ref name="TAJ-20230927">{{Cite journal |last=Teodoro |first=L. F. A. |display-authors=et al |date=2023 |title=A Recent Impact Origin of Saturn's Rings and Mid-sized Moons |journal=The Astrophysical Journal |volume=955 |issue=2 |page=137 |arxiv=2309.15156 |bibcode=2023ApJ...955..137T |doi=10.3847/1538-4357/acf4ed |issn=0004-637X |doi-access=free}}</ref>

== Saturn's axial inclination ==
Saturn's axial tilt is 26.7°, meaning that widely varying views of the rings, of which the visible ones occupy its equatorial plane, are obtained from Earth at different times.<ref name="fact">{{cite web |url=http://nssdc.gsfc.nasa.gov/planetary/factsheet/saturnfact.html |title=Saturn Fact Sheet |publisher=NASA |last=Williams |first=David R. |access-date=12 October 2017 |date=23 December 2016 |archive-url=https://web.archive.org/web/20170717071200/https://nssdc.gsfc.nasa.gov/planetary/factsheet/saturnfact.html |archive-date=17 July 2017 }}</ref> Earth makes passes through the ring plane every 13 to 15 years, about every half Saturn year, and there are about equal chances of either a single or three crossings occurring in each such occasion. The most recent ring plane crossings were on 22 May 1995, 10 August 1995, 11 February 1996, 4 September 2009 and 23 March 2025; upcoming events will occur on 15 October 2038, 1 April 2039 and 9 July 2039. Favorable ring plane crossing viewing opportunities (with Saturn not close to the Sun) only come during triple crossings.<ref name = "RPX1995">{{cite web |url= https://pds.nasa.gov/ds-view/pds/viewMissionProfile.jsp?MISSION_NAME=SATURN%20RING%20PLANE%20CROSSING%201995|title= Saturn Ring Plane Crossing 1995|date= 1997|website= pds.nasa.gov|publisher= NASA|access-date= 2020-02-11|archive-url= https://web.archive.org/web/20200211075638/https://pds.nasa.gov/ds-view/pds/viewMissionProfile.jsp?MISSION_NAME=SATURN%20RING%20PLANE%20CROSSING%201995|archive-date= 2020-02-11}}</ref><ref name = "HST1995">{{cite web |url= https://hubblesite.org/contents/news-releases/1995/news-1995-25.html|title= Hubble Views Saturn Ring-Plane Crossing|date= 5 June 1995|website= hubblesite.org|publisher= NASA|access-date= 2020-02-11|archive-url= https://web.archive.org/web/20200211080600/https://hubblesite.org/contents/news-releases/1995/news-1995-25.html|archive-date= 2020-02-11}}</ref><ref name = "Lakdawalla2009">{{cite web |url= https://www.planetary.org/blogs/emily-lakdawalla/2009/2084.html|title= Happy Saturn ring plane crossing day!|last= Lakdawalla|first= E.|author-link= Emily Lakdawalla|date= 2009-09-04|website= www.planetary.org/blogs|publisher= [[The Planetary Society]]|access-date= 2020-02-11}}</ref>

Saturn's [[equinox#Equinoxes on other planets|equinox]]es, when the Sun passes through the ring plane, are not evenly spaced. The sun passes south to north through the ring plane when Saturn's heliocentric longitude is 173.6 degrees (e.g. 11 August 2009), about the time Saturn crosses from Leo to Virgo. 15.7 years later Saturn's longitude reaches 353.6 degrees and the sun passes to the south side of the ring plane. On each orbit the Sun is north of the ring plane for 15.7 Earth years, then south of the plane for 13.7 years.{{efn |At 0.0565, Saturn's [[orbital eccentricity]] is the largest of the Solar System's [[giant planet]]s, and over three times Earth's. Its [[aphelion]] is reached close to its northern hemisphere [[summer solstice]].<ref name="Proctor1865">{{Cite book |last=Proctor |first=R. A. |author-link=Richard A. Proctor |url=https://archive.org/details/saturnanditssys00unkngoog |title=Saturn and Its System |publisher=Longman, Green, Longman, Roberts, & Green |year=1865 |location=London |page=166 |oclc=613706938}}</ref>| group = n }} Dates for north-to-south crossings include 19 November 1995 and 6 May 2025, with south-to-north crossings on 11 August 2009 and 23 January 2039.<ref name="Lakdawalla2016">{{cite web |url= http://www.planetary.org/blogs/emily-lakdawalla/2016/06031044-oppositions-conjunctions-rpx.html |title= Oppositions, conjunctions, seasons, and ring plane crossings of the giant planets |last= Lakdawalla |first= E. |author-link= Emily Lakdawalla |date=7 July 2016 |website= planetary.org/blogs |publisher= [[The Planetary Society]] |access-date=17 February 2020}}</ref> During the period around an equinox the illumination of most of the rings is greatly reduced, making possible unique observations highlighting features that depart from the ring plane.<ref name = "PIA11667">{{cite web |url= https://photojournal.jpl.nasa.gov/catalog/PIA11667|title= PIA11667: The Rite of Spring|date= 21 September 2009|website= photojournal.jpl.nasa.gov|publisher= NASA/JPL|access-date= 2020-02-17}}</ref>

== Physical characteristics ==
[[File:Unraveling Saturn's Rings.jpg|thumb|upright=1|Simulated image using color to present [[radio occultation|radio-occultation]]-derived particle size data. The [[attenuation]] of 0.94-, 3.6-, and 13-cm signals sent by ''Cassini'' through the rings to Earth shows abundance of particles of sizes similar to or larger than those wavelengths. Purple (B, inner A Ring) means few particles are <&nbsp;5 cm (all signals similarly attenuated). Green and blue (C, outer A Ring) mean particles <&nbsp;5 cm and <&nbsp;1 cm, respectively, are common. White areas (B Ring) are too dense to transmit adequate signal. Other evidence shows rings A to C have a broad range of particle sizes, up to m across.]]

The dense main rings extend from {{convert|7,000|km|mi|abbr=on}} to {{convert|80,000|km|mi|abbr=on}} away from Saturn's equator, whose radius is {{convert|60,300|km|mi|abbr=on}} (see [[#Major subdivisions|Major subdivisions]]). With an estimated local thickness of as little as 10 meters (32' 10")<ref>{{cite web |url=https://www.sciencedaily.com/releases/2005/11/051110220809.htm |title=Researchers Find Gravitational Wakes In Saturn's Rings |author=Cornell University News Service |date=2005-11-10 |website=ScienceDaily |access-date=2008-12-24 }}</ref> and as much as 1&nbsp;km (1093 yards),<ref>{{cite web|url=http://solarsystem.nasa.gov/planets/profile.cfm?Object=Saturn&Display=Rings|title=Saturn: Rings|publisher=NASA|archive-url=https://web.archive.org/web/20100527141504/http://solarsystem.nasa.gov/planets/profile.cfm?Object=Saturn&Display=Rings|archive-date=2010-05-27}}</ref> they are composed of 99.9% pure water [[ice]] with a smattering of impurities that may include [[tholin]]s or [[silicate]]s.<ref name="ic.193">{{cite journal |title=A close look at Saturn's rings with Cassini VIMS |display-authors=1 |last=Nicholson |first=P.D. |author2=16 co-authors |journal=[[Icarus (journal)|Icarus]] |date=2008 |volume=193 |issue=1 |pages=182–212 |doi=10.1016/j.icarus.2007.08.036 |bibcode=2008Icar..193..182N }}</ref> The main rings are primarily composed of particles smaller than 10 m.<ref name="Zebker85">{{cite journal |title=Saturn's rings – Particle size distributions for thin layer model |display-authors=1 |last1=Zebker |first1=H.A. |last2=Marouf |first2=E.A. |last3=Tyler |first3=G.L. |journal=[[Icarus (journal)|Icarus]] |date=1985 |volume=64 |issue=3 |pages=531–548 |doi=10.1016/0019-1035(85)90074-0 |bibcode=1985Icar...64..531Z }}</ref>

''Cassini'' directly measured the mass of the ring system via their gravitational effect during its final set of orbits that passed between the rings and the cloud tops, yielding a value of 1.54 (± 0.49) × 10<sup>19</sup> kg, or 0.41 ± 0.13 [[Mimas]] masses.<ref name="IessMilitzer2019" /> This is around two-thirds the mass of the Earth's entire [[Antarctic ice sheet]], spread across a surface area 80 times larger than that of Earth.<ref>{{cite web |url=http://www.the-cryosphere.net/7/375/2013/tc-7-375-2013.pdf |title=Bedmap2: improved ice bed, surface and thickness datasets for Antarctica |author1=P. Fretwell |author2=H. D. Pritchard |date=31 July 2012 |website=The Cryosphere |access-date=13 May 2023 |pages=15–16|display-authors=etal}}</ref><ref name="Koren2019">{{Cite web|url=https://www.theatlantic.com/science/archive/2019/01/saturn-rings-cassini/580696/|title=The Massive Mystery of Saturn's Rings|last= Koren|first= M.|date= 2019-01-17|website=The Atlantic|language=en-US|access-date=2019-01-21}}</ref> The estimate is close to the value of 0.40 Mimas masses derived from ''Cassini'' observations of density waves in the A, B and C rings.<ref name="IessMilitzer2019" /> It is a small fraction of the total mass of Saturn (about 0.25&nbsp;[[parts per billion|ppb]]). Earlier ''Voyager'' observations of density waves in the A and B rings and an optical depth profile had yielded a mass of about 0.75 Mimas masses,<ref name="Esposito1983">{{cite journal|last1= Esposito|first1=L. W.|last2= O'Callaghan|first2= M.|last3= West|first3=R. A.|title= The structure of Saturn's rings: Implications from the Voyager stellar occultation|journal= Icarus|volume= 56|issue= 3|year= 1983|pages= 439–452|doi= 10.1016/0019-1035(83)90165-3|bibcode=1983Icar...56..439E}}</ref> with later observations and computer modeling suggesting that was an underestimate.<ref>{{cite journal |display-authors=1 |last1=Stewart |first1=Glen R. |last2=Robbins |first2=S. J. |last3=Colwell |first3=J. E. |title=Evidence for a Primordial Origin of Saturn's Rings |journal=Bulletin of the American Astronomical Society |date=October 2007 |volume=39 |series=American Astronomical Society, DPS meeting #39 |page=420 |bibcode=2007DPS....39.0706S }}</ref>

[[File:PIA23170-Saturn-Rings-IR-Map-20190613.jpg|thumb|upright=1|Saturn and its A, B and C rings in visible and (inset) infrared light. In the false-color IR view, greater water ice content and larger grain size lead to blue-green color, while greater non-ice content and smaller grain size yield a reddish hue.]]
Although the largest gaps in the rings, such as the Cassini Division and [[#Encke Gap|Encke Gap]], can be seen from Earth, the [[Voyager program|Voyager]] spacecraft discovered that the rings have an intricate structure of thousands of thin gaps and ringlets. This structure is thought to arise, in several different ways, from the gravitational pull of Saturn's many moons. Some gaps are cleared out by the passage of tiny moonlets such as [[Pan (moon)|Pan]],<ref name="Burns2001">{{cite encyclopedia |display-authors=1 |last1=Burns |first1=J.A. |last2=Hamilton |first2=D.P. |last3=Showalter |first3=M.R. |title=Dusty Rings and Circumplanetary Dust: Observations and Simple Physics |encyclopedia=Interplanetary Dust|date=2001 |publisher=Springer |place=Berlin |editor=Grun, E. |editor2=Gustafson, B. A. S. |editor3=Dermott, S. T. |editor4=Fechtig H. |pages=641–725 |bibcode=2001indu.book..641B |isbn=978-3-540-42067-5 |url=http://www.astro.umd.edu/~hamilton/research/preprints/BurHamSho01.pdf }}</ref> many more of which may yet be discovered, and some ringlets seem to be maintained by the gravitational effects of small [[shepherd satellite]]s (similar to [[Prometheus (moon)|Prometheus]] and [[Pandora (moon)|Pandora]]'s maintenance of the F ring). Other gaps arise from resonances between the orbital period of particles in the gap and that of a more massive moon further out; [[Mimas]] maintains the Cassini Division in this manner.<ref name="ic.34">{{cite journal|title=The formation of the Cassini division in Saturn's rings|display-authors=1|last1=Goldreich |first1=Peter |last2=Tremaine |first2=Scott |journal=[[Icarus (journal)|Icarus]] |date=1978| volume=34 |issue=2 |pages=240–253 |doi=10.1016/0019-1035(78)90165-3 |bibcode=1978Icar...34..240G }}</ref> Still more structure in the rings consists of spiral waves raised by the inner moons' periodic gravitational perturbations at less disruptive resonances.{{citation needed|date=July 2008}}
Data from the ''Cassini'' space probe indicate that the rings of Saturn possess their own atmosphere, independent of that of the planet itself. The atmosphere is composed of molecular [[oxygen]] gas (O<sub>2</sub>) produced when ultraviolet light from the Sun interacts with water ice in the rings. Chemical reactions between water molecule fragments and further [[ultraviolet]] stimulation create and eject, among other things, O<sub>2</sub>. According to models of this atmosphere, H<sub>2</sub> is also present. The O<sub>2</sub> and H<sub>2</sub> atmospheres are so sparse that if the entire atmosphere were somehow condensed onto the rings, it would be about one atom thick.<ref>{{cite news |url=https://news.bbc.co.uk/2/hi/science/nature/4640641.stm |title=Saturn rings have own atmosphere |date=2005-07-01 |last=Rincon |first=Paul |publisher=[[British Broadcasting Corporation]] |access-date=2007-07-06 }}</ref> The rings also have a similarly sparse OH (hydroxide) atmosphere. Like the O<sub>2</sub>, this atmosphere is produced by the disintegration of water molecules, though in this case the disintegration is done by energetic [[ion]]s that bombard water molecules ejected by Saturn's moon [[Enceladus]]. This atmosphere, despite being extremely sparse, was detected from Earth by the Hubble Space Telescope.<ref name="aas.644">{{cite journal |title=The Enceladus and OH Tori at Saturn |date=2006 |bibcode=2006ApJ...644L.137J |display-authors=1 |last=Johnson |first=R. E. |author2=Smith, H. T. |author3=Tucker, O. J. |author4=Liu, M. |author5=Burger, M. H. |author6=Sittler, E. C. |author7=Tokar, R. L. |volume=644 |pages=L137 |journal=The Astrophysical Journal |doi=10.1086/505750 |issue=2 |s2cid=37698445 |url=http://pdfs.semanticscholar.org/240c/f27408a746dfc8b0084a2203fc10cd2b9f9c.pdf |archive-url=https://web.archive.org/web/20200412142258/http://pdfs.semanticscholar.org/240c/f27408a746dfc8b0084a2203fc10cd2b9f9c.pdf |archive-date=2020-04-12 }}</ref>
Saturn shows complex patterns in its brightness.<ref>{{cite web |url=https://www.researchgate.net/publication/242343176|title=Wideband photoelectric magnitude measurements of Saturn in 2000 |last=Schmude |first=Richard W Junior |date=2001 |publisher=Georgia Journal of Science |access-date=2007-10-14 }}</ref> Most of the variability is due to the changing aspect of the rings,<ref name="brightness">{{cite journal |title= Wideband photometric magnitude measurements of Saturn made during the 2005–06 Apparition |last= Schmude|first= Richard Jr. |date= 2006-09-22|journal= Georgia Journal of Science |id = {{ProQuest|230557408}}}}</ref><ref>{{cite web |url=http://findarticles.com/p/articles/mi_qa4015/is_200301/ai_n9338203 |title=Saturn in 2002–03 |last=Schmude |first=Richard W Jr |date=2003 |publisher=Georgia Journal of Science |access-date=2007-10-14 }}</ref> and this goes through two cycles every orbit. However, superimposed on this is variability due to the [[orbital eccentricity|eccentricity]] of the planet's orbit that causes the planet to display brighter oppositions in the northern hemisphere than it does in the southern.<ref>{{cite journal |last= Henshaw|first= C.|url= https://www.britastro.org/journal_old/113-1.htm#articles |title= Variability in Saturn |journal= Journal of the British Astronomical Association|publisher=[[British Astronomical Association]] |date= February 2003 |volume= 113| issue= 1|page= 40|bibcode= 2003JBAA..113...40H|access-date=2017-12-20}}</ref>

[[File:Top view of the rings of Saturn by Cassini - October 10, 2013.jpg|thumb|upright=1.35|''Cassini'' space probe view of the unilluminated side of Saturn's rings (October 10, 2013).]]
In 1980, ''Voyager 1'' made a fly-by of Saturn that showed the F ring to be composed of three narrow rings that appeared to be braided in a complex structure; it is now known that the outer two rings consist of knobs, kinks and lumps that give the illusion of braiding, with the less bright third ring lying inside them.{{citation needed|date=July 2008}}

New images of the rings taken around the 11 August 2009 equinox of Saturn by NASA's ''Cassini'' spacecraft have shown that the rings extend significantly out of the nominal ring plane in a few places. This displacement reaches as much as {{convert|4|km|abbr=on}} at the border of the [[#Keeler Gap|Keeler Gap]], due to the out-of-plane orbit of [[Daphnis (moon)|Daphnis]], the moon that creates the gap.<ref>{{cite web |title=Surprising, Huge Peaks Discovered in Saturn's Rings |url=http://www.space.com/scienceastronomy/090921-new-saturn-ring-images.html |date=2009-09-21 |work=SPACE.com Staff |publisher=space.com |access-date=2009-09-26 }}</ref>

== Formation and evolution of main rings ==
Estimates of the age of Saturn's rings vary widely, depending on the approach used. They have been considered to possibly be very old, dating to the formation of Saturn itself. However, data from ''Cassini'' suggest they are much younger, having most likely formed within the last 100 million years, and may thus be between 10 million and 100 million years old.<ref name="IessMilitzer2019" /><ref name="Gohd-surprisingly">{{Cite news|url= http://www.astronomy.com/news/2019/01/saturns-rings-are-surprisingly-young|title=Saturn's rings are surprisingly young|first= Chelsea|last= Gohd|date= 17 January 2019|website= Astronomy.com|access-date= 2019-01-21}}</ref> This recent origin scenario is based on a new, low mass estimate modeling of the rings' dynamical evolution, and measurements of the flux of interplanetary dust, which feed into an estimate of the rate of ring darkening over time.<ref name="IessMilitzer2019" /> Since the rings are continually losing material, they would have been more massive in the past than at present.<ref name="IessMilitzer2019" /> The mass estimate alone is not very diagnostic, since high mass rings that formed early in the Solar System's history would have evolved by now to a mass close to that measured.<ref name="IessMilitzer2019" /> Based on current depletion rates, they may disappear in 300 million years.<ref name="RingAgePressRelease">{{cite web | title=NASA Research Reveals Saturn is Losing Its Rings at "Worst-Case-Scenario" Rate | date=10 December 2018 | url=https://www.nasa.gov/press-release/goddard/2018/ring-rain | access-date=2020-06-29 }}</ref><ref name="ODonoghue2019">{{cite journal |last1=O'Donoghjue |first1=James |last2=Moore |first2=Luke |display-authors=1 |date=April 2019 |title=Observations of the chemical and thermal response of 'ring rain' on Saturn's ionosphere |url=https://www.sciencedirect.com/science/article/abs/pii/S0019103518302999 |journal=Icarus |volume=322 |pages=251–206 |doi=10.1016/j.icarus.2018.10.027 |bibcode=2019Icar..322..251O |access-date=2020-06-29|hdl=2381/43180 |s2cid=126351855 |hdl-access=free }}</ref>

There are two main hypotheses regarding the origin of Saturn's inner rings. A hypothesis originally proposed by [[Édouard Roche]] in the 19th century is that the rings were once a moon of Saturn (named Veritas, after a [[Veritas|Roman goddess]] who hid in a well). According to the hypothesis, the moon's orbit decayed until it was close enough to be ripped apart by [[tidal force]]s (see [[Roche limit]]).<ref name="Roche_limit">{{cite web |url=http://www2.jpl.nasa.gov/saturn/back.html |title=Historical Background of Saturn's Rings |work=1849 Roche Proposes Tidal Break-up |first=Ron |last=Baalke |publisher=Jet Propulsion Laboratory |access-date=2008-09-13 |archive-url=https://web.archive.org/web/20090321071339/http://www2.jpl.nasa.gov/saturn/back.html |archive-date=2009-03-21 }}</ref> Numerical simulations carried out in 2022 support this hypothesis; the authors of that study proposed the name "[[Chrysalis (hypothetical moon)|Chrysalis]]" for the destroyed moon.<ref>{{cite journal |last1=Wisdom |first1=Jack |last2=Dbouk |first2=Rola |last3=Militzer |first3=Burkhard |last4=Hubbard |first4=William |last5=Nimmo |first5=Francis |last6=Downey |first6=Brynna |last7=French |first7=Richard |date=September 15, 2022 |title=Loss of a satellite could explain Saturn's obliquity and young rings |url=https://www.science.org/doi/10.1126/science.abn1234 |journal=[[Science (journal)|Science]] |volume=377 |issue=6612 |pages=1285–1289 |doi=10.1126/science.abn1234 |pmid=36107998 |bibcode=2022Sci...377.1285W |s2cid=252310492 |access-date=September 16, 2022|hdl=1721.1/148216 |hdl-access=free |url-access=subscription }}</ref> A variation on this hypothesis is that this moon disintegrated after being struck by a large [[comet]] or [[asteroid]].<ref>{{cite web|url= https://science.nasa.gov/headlines/y2002/12feb_rings.htm|title=The Real Lord of the Rings|date= 2002-02-12|work= nasa.gov|archive-url= https://web.archive.org/web/20100323172559/http://science.nasa.gov/headlines/y2002/12feb_rings.htm|archive-date= 2010-03-23}}</ref> The second hypothesis is that the rings were never part of a moon, but are instead left over from the original [[nebula]]r material from which Saturn formed.{{citation needed|date=July 2008}}
[[File:Saturn Ring Material.jpg|thumb|upright=1.1|A 2007 [[artist's impression]] of the aggregates of icy particles that form the 'solid' portions of Saturn's rings. These elongated clumps are continually forming and dispersing. The largest particles are a few meters across.]]
{{multiple image |header=Saturn's rings and [[Moons of Saturn|moons]] |caption_align=center |width=200 |direction=vertical
|image1=PIA18283-SaturnRings-TethysHyperionPrometheus-20140714.jpg
|caption1=Tethys, [[Hyperion (moon)|Hyperion]] and [[Prometheus (moon)|Prometheus]]
|image2=PIA18353-SaturnRingsMoons-JanusTethys-20151027.jpg
|caption2=Tethys and [[Janus (moon)|Janus]]
}}
A more traditional version of the disrupted-moon hypothesis is that the rings are composed of debris from a moon 400 to 600&nbsp;km (200 to 400 miles) in diameter, slightly larger than [[Mimas]]. The last time there were collisions large enough to be likely to disrupt a moon that large was during the [[Late Heavy Bombardment]] some four billion years ago.<ref name="Kerr2008a">{{cite journal |last=Kerr |first=Richard A |date=2008 |title=Saturn's Rings Look Ancient Again |journal=[[Science (journal)|Science]] |volume=319 |issue=5859 |page=21 |doi=10.1126/science.319.5859.21a |pmid=18174403|s2cid=30937575 }}</ref>

A more recent variant of this type of hypothesis by [[Robin Canup|R. M. Canup]] is that the rings could represent part of the remains of the icy mantle of a much larger, Titan-sized, differentiated moon that was stripped of its outer layer as it spiraled into the planet during the formative period when Saturn was still surrounded by a gaseous nebula.<ref name="NatGeo_2010">{{cite magazine | last= Choi | first=C. Q. | url=http://news.nationalgeographic.com/news/2010/12/101213-saturn-rings-moon-ice-jupiter-science-space/| archive-url=https://web.archive.org/web/20101215155552/http://news.nationalgeographic.com/news/2010/12/101213-saturn-rings-moon-ice-jupiter-science-space/| archive-date=December 15, 2010|magazine=National Geographic|title=Saturn's Rings Made by Giant "Lost" Moon, Study Hints |date=2010-12-13 | access-date=2012-11-05 }}</ref><ref name="Canup_2010">
{{cite journal |last=Canup |first=R. M. |author-link=Robin M. Canup |title=Origin of Saturn's rings and inner moons by mass removal from a lost Titan-sized satellite |journal=[[Nature (journal)|Nature]] |volume=468 |issue=7326 |pages=943–6|date=2010-12-12 |doi=10.1038/nature09661 |pmid=21151108 |bibcode=2010Natur.468..943C |s2cid=4326819 }}</ref> This would explain the scarcity of rocky material within the rings. The rings would initially have been much more massive (≈1,000 times) and broader than at present; material in the outer portions of the rings would have coalesced into the innermost moons of Saturn (those closest to Saturn), out to [[Tethys (moon)|Tethys]], also explaining the lack of rocky material in the composition of most of these moons.<ref name="Canup_2010" /> Subsequent collisional or cryovolcanic evolution of Enceladus, which is another of these moons, might then have caused selective loss of ice from this moon, raising its density to its current value of 1.61 g/cm<sup>3</sup>, compared to values of 1.15 for Mimas and 0.97 for Tethys.<ref name="Canup_2010" />

The idea of massive early rings was subsequently extended to explain the formation of Saturn's moons out to Rhea.<ref name="Charnoz_2011">{{cite journal |display-authors=1 |last1=Charnoz |first1=S.  |last2=Crida |first2=A. |last3=Castillo-Rogez |first3=J. C. |last4=Lainey |first4=V. |last5=Dones |first5=L. |last6=Karatekin |first6=Ö. |last7=Tobie |first7=G. |last8=Mathis |first8=S. |last9=Le Poncin-Lafitte |first9=C. |last10=Salmon |first10=J. |title=Accretion of Saturn's mid-sized moons during the viscous spreading of young massive rings: Solving the paradox of silicate-poor rings versus silicate-rich moons |journal=[[Icarus (journal)|Icarus]] |volume=216 |issue=2 |pages=535–550 |date=December 2011 |doi=10.1016/j.icarus.2011.09.017 |bibcode=2011Icar..216..535C |arxiv=1109.3360 |s2cid=119222398 }}</ref> If the initial massive rings contained chunks of rocky material (>100&nbsp;km; 60 miles across) as well as ice, these silicate bodies would have accreted more ice and been expelled from the rings, due to gravitational interactions with the rings and tidal interaction with Saturn, into progressively wider orbits. Within the [[Roche limit]], bodies of rocky material are dense enough to accrete additional material, whereas less-dense bodies of ice are not. Once outside the rings, the newly formed moons could have continued to evolve through random mergers. This process may explain the variation in silicate content of Saturn's moons out to Rhea, as well as the trend towards less silicate content closer to Saturn. Rhea would then be the oldest of the moons formed from the primordial rings, with moons closer to Saturn being progressively younger.<ref name="Charnoz_2011" />

The brightness and purity of the water ice in Saturn's rings have also been cited as evidence that the rings are much younger than Saturn,<ref name="Gohd-surprisingly"/> as the infall of meteoric dust would have led to a darkening of the rings. However, new research indicates that the B Ring may be massive enough to have diluted infalling material and thus avoided substantial darkening over the age of the Solar System. Ring material may be recycled as clumps from within the rings and are then disrupted by impacts. This would explain the apparent youth of some of the material within the rings.<ref name="NASAOldTimers">{{cite news | title=Saturn's Rings May Be Old Timers | work=NASA/JPL and University of Colorado | date=2007-12-12 | url= https://www.nasa.gov/mission_pages/cassini/media/cassini20071212.html | access-date=2008-01-24 | url-status=live | archive-url=https://web.archive.org/web/20071220202616/http://saturn1.jpl.nasa.gov/news/press-release-details.cfm?newsID=798 | archive-date=2007-12-20 }}</ref> Evidence suggesting a recent origin of the C ring has been gathered by researchers analyzing data from the [[Cassini-Huygens#Instruments|Cassini Titan Radar Mapper]], which focused on analyzing the proportion of rocky silicates within this ring. If much of this material was contributed by a recently disrupted [[Centaur (small Solar System body)|centaur]] or moon, the age of this ring could be on the order of 100 million years or less. On the other hand, if the material came primarily from micrometeoroid influx, the age would be closer to a billion years.<ref name="Zhang2017">{{cite journal|last1= Zhang|first1= Z.|last2= Hayes|first2= A.G.|last3= Janssen|first3= M.A.|last4= Nicholson|first4= P.D.|last5= Cuzzi|first5= J.N.|last6=de Pater|first6= I.|last7= Dunn|first7= D.E.|last8= Estrada|first8= P.R.|last9= Hedman|first9= M.M.|title= Cassini microwave observations provide clues to the origin of Saturn's C ring|journal= Icarus|volume= 281|year= 2017|pages=297–321|doi= 10.1016/j.icarus.2016.07.020|bibcode= 2017Icar..281..297Z}}</ref>

The ''Cassini'' UVIS team, led by [[Larry Esposito]], used stellar [[occultation]] to discover 13 objects, ranging from 27 meters (89') to 10&nbsp;km (6 miles) across, within the [[F ring]]. They are translucent, suggesting they are temporary aggregates of ice boulders a few meters across. Esposito believes this to be the basic structure of the Saturnian rings, particles clumping together, then being blasted apart.<ref name="ic.217">{{cite journal |display-authors=1 |last1=Esposito |first1=L.W. |last2=Albers |first2=N. |last3=Meinke |first3=B.K. |last4=Screcevic |first4=M. |last5=Madhusudhanan |first5=P. |last6=Colwell |first6=J.E. |last7=Jerousek |first7=R.G. |title=A predator–prey model for moon-triggered clumping in Saturn's rings |journal=Icarus |date=January 2012  |volume=217 |issue=1 |pages=103–114 |doi=10.1016/j.icarus.2011.09.029 |bibcode=2012Icar..217..103E}}</ref>

Research based on rates of infall into Saturn favors a younger ring system age of hundreds of millions of years. Ring material is continually spiraling down into Saturn; the faster this infall, the shorter the lifetime of the ring system. One mechanism involves gravity pulling electrically charged water ice grains down from the rings along planetary magnetic field lines, a process termed 'ring rain'. This flow rate was inferred to be 432–2870&nbsp;kg/s using ground-based [[Keck telescope]] observations; as a consequence of this process alone, the rings will be gone in ~{{val|292|818|124}} million years.<ref name="ODONO">{{cite journal |last1=O'Donoghue |first1=James |last2=Moore |first2=Luke |last3=Connerney |first3=Jack |last4=Melin |first4=Henrik |last5=Stallard |first5=Tom |last6=Miller |first6=Steve |last7=Baines |first7=Kevin H. |title=Observations of the chemical and thermal response of 'ring rain' on Saturn's ionosphere |journal=Icarus |volume=322 |pages=251–260 |date=November 2018 |doi=10.1016/j.icarus.2018.10.027 |hdl=2381/43180 |url=https://leicester.figshare.com/articles/Observations_of_the_chemical_and_thermal_response_of_ring_rain_on_Saturn_s_ionosphere/10205006/files/18395402.pdf |bibcode=2019Icar..322..251O |s2cid=126351855 |hdl-access=free }}</ref> While traversing the gap between the rings and planet in September 2017, the [[Cassini-Huygens|''Cassini'' spacecraft]] detected an equatorial flow of charge-neutral material from the rings to the planet of 4,800–44,000&nbsp;kg/s.<ref name="jhwaite">{{cite journal |last1=Waite |first1=J. H. |last2=Perryman |first2=R. S. |last3=Perry |first3=M. E. |last4=Miller |first4=K. E. |last5=Bell |first5=J. |last6=Cravens |first6=T. E. |last7=Glein |first7=C. R. |last8=Grimes |first8=J. |last9=Hedman |first9=M. |last10=Cuzzi |first10=J. |last11=Brockwell |first11=T. |last12=Teolis |first12=B. |last13=Moore |first13=L. |last14=Mitchell |first14=D. G. |last15=Persoon |first15=A. |last16=Kurth |first16=W. S. |last17=Wahlund |first17=J.-E. |last18=Morooka |first18=M. |last19=Hadid |first19=L. Z. |last20=Chocron |first20=S. |last21=Walker |first21=J. |last22=Nagy |first22=A. |last23=Yelle |first23=R. |last24=Ledvina |first24=S. |last25=Johnson |first25=R. |last26=Tseng |first26=W. |last27=Tucker |first27=O. J. |last28=Ip |first28=W.-H. |title=Chemical interactions between Saturn's atmosphere and its rings |journal=Science |date=5 October 2018 |volume=362 |issue=6410 |article-number=eaat2382 |doi=10.1126/science.aat2382 |pmid=30287634 |bibcode=2018Sci...362.2382W |doi-access=free |hdl=2027.42/149200 |hdl-access=free }}</ref> Assuming this influx rate is stable, adding it to the continuous 'ring rain' process implies the rings may be gone in under 100 million years.<ref name="ODONO"/><ref>{{Cite web|url=http://www.sci-techuniverse.com/2018/12/saturn-is-officially-losing-its-rings.html|title=Saturn is Officially Losing its Rings and Shockingly at Much Faster Rate than Expected|website=Sci-Tech Universe|access-date=2018-12-28}}</ref>

== Subdivisions and structures within the rings ==
The densest parts of the Saturnian ring system are the A and B Rings, which are separated by the Cassini Division (discovered in 1675 by [[Giovanni Domenico Cassini]]). Along with the C Ring, which was discovered in 1850 and is similar in character to the Cassini Division, these regions constitute the ''main rings''. The main rings are denser and contain larger particles than the tenuous ''dusty rings''. The latter include the D Ring, extending inward to Saturn's cloud tops, the G and E Rings and others beyond the main ring system. These diffuse rings are characterised as "dusty" because of the small size of their particles (often about a [[μm]]); their chemical composition is, like the main rings, almost entirely water ice. The narrow F Ring, just off the outer edge of the A Ring, is more difficult to categorize; parts of it are very dense, but it also contains a great deal of dust-size particles.
{{Clear}}
{{wide image|Saturn's rings dark side mosaic.jpg|2200px|Natural-color mosaic of ''Cassini'' narrow-angle camera images of the unilluminated side of Saturn's D, C, B, A and F rings (left to right) taken on May 9, 2007 (distances are to the planet's center).}}
{{wide image|Saturn's rings in visible light and radio.jpg|1800px|Oblique (4 degree angle) ''Cassini'' images of Saturn's C, B, and A rings (left to right; the F ring is faintly visible in the full size upper image if viewed at sufficient brightness). Upper image: natural color mosaic of ''Cassini'' narrow-angle camera photos of the illuminated side of the rings taken on December 12, 2004. Lower image: simulated view constructed from a [[radio occultation]] observation conducted on May 3, 2005. Color in the lower image is used to represent information about ring particle sizes (see the caption of the article's second image for an explanation).}}

=== Physical parameters of the rings ===

==== Major subdivisions ====
{| class="wikitable"
|-
! Name{{Efn|Names as designated by the [[International Astronomical Union]], unless otherwise noted. Broader separations between named rings are termed divisions, while narrower separations within named rings are called gaps.|name=one}}!! Distance from Saturn's<br/>center (km){{Efn|Data mostly from the [https://planetarynames.wr.usgs.gov/Page/Rings#saturn Gazetteer of Planetary Nomenclature], a [http://nssdc.gsfc.nasa.gov/planetary/factsheet/satringfact.html NASA factsheet] and several papers.<ref name="Ringlets">{{cite journal |last1=Porco |first1=C. |author-link=Carolyn Porco |last2=Nicholson |first2=P. D. |last3=Borderies |first3=N. |last4=Danielson |first4=G. E. |last5=Goldreich |first5=P. |last6=Holberg |first6=J. B. |last7=Lane |first7=A. L. |display-authors=1 |date=October 1984 |title=The Eccentric Saturnian Ringlets at 1.29R<sub>S</sub> and 1.45R<sub>S</sub> |journal=Icarus |volume=60 |issue=1 |pages=1–16 |bibcode=1984Icar...60....1P |doi=10.1016/0019-1035(84)90134-9}}</ref><ref name="OuterCRing">{{cite journal |last1=Porco |first1=C. C. |author-link=Carolyn Porco |last2=Nicholson |first2=P. D. |display-authors=1 |date=November 1987 |title=Eccentric features in Saturn's outer C ring |journal=Icarus |volume=72 |issue=2 |pages=437–467 |bibcode=1987Icar...72..437P |doi=10.1016/0019-1035(87)90185-0}}</ref><ref name="InnerCassini">{{cite journal |last1=Flynn |first1=B. C. |last2=Cuzzi |first2=J. N. |display-authors=1 |date=November 1989 |title=Regular Structure in the Inner Cassini Division of Saturn's Rings |url=https://zenodo.org/record/1253900 |journal=Icarus |volume=82 |issue=1 |pages=180–199 |bibcode=1989Icar...82..180F |doi=10.1016/0019-1035(89)90030-4}}</ref>|name=two}}!! Width (km){{Efn|name=two}}!! Thickness (m) !!Notes
|-
| [[#D Ring|D Ring]] || align=center|66,900 –76,517 || align="center" |7,500 ||  align="center" |<30 || Suspected by Pierre Geurin (1967), confirmed by Pioneer 11 (1979)<ref>Jürgen Blunck, Solar System Moons: Discovery and Mythology, Springer Science & Business Media - 2009, pages 62-63</ref>
|-
| [[#C Ring|C Ring]] || align=center|74,658 – 92,000 || align="center" |17,500 || align=center|5 || Discovered by [[William Cranch Bond|William]] and [[George Phillips Bond|George Bond]] in 1850<ref name="Harland" />
|-
| [[#B Ring|B Ring]] || align=center|92,000 –117,580 || align="center" |25,500 || align=center|5-15 || Discovered, along with the A ring, by [[Galileo Galilei]] in 1610. Ring structure revealed by [[Christiaan Huygens|Huygens]] in 1655<ref name="history_of_the_rings" />
|-
| [[#Cassini Division|Cassini Division]] || align=center|117,580 –122,170 || align="center" |4,700 || align="center" |&nbsp;||  Discovered by [[Giovanni Cassini]] in 1676<ref>Jürgen Blunck, Solar System Moons: Discovery and Mythology, Springer Science & Business Media - 2009, pages 62-63</ref>
|-
| [[#A Ring|A Ring]] || align=center|122,170 –136,775 || align="center" |14,600 || align=center|10-30 || Discovered, along with the B ring, by [[Galileo Galilei]] in 1610. Ring structure revealed by [[Christiaan Huygens|Huygens]] in 1655<ref name="history_of_the_rings" />
|-
| [[#Roche Division|Roche Division]] || align=center|136,775 – 139,380 || align="center" |2,600 || align="center" |&nbsp;|| Bordered by F Ring (Pioneer 11 discovery - 1979), named after the spacecraft then after [[Édouard Roche]] (2007)<ref>Jürgen Blunck, Solar System Moons: Discovery and Mythology, Springer Science & Business Media - 2009, pages 62-63</ref>
|-
| [[#F Ring|F Ring]] || align=center|140,180{{Efn|distance is to centre of gaps, rings and ringlets that are narrower than 1,000&nbsp;km (600 miles)|name=three}}|| align="center" |30 – 500 ||  align="center" |&nbsp; ||  Discovered by Pioneer 11 (1979)<ref name="Gehrels1980" /><ref>Jürgen Blunck, Solar System Moons: Discovery and Mythology, Springer Science & Business Media - 2009, pages 62-63</ref>
|-
| [[#Janus/Epimetheus Ring|Janus/Epimetheus Ring]]{{Efn|unofficial name|name=four}}|| align="center" |149,000 – 154,000 || align="center" |5,000 ||  align="center" |&nbsp; ||  [[Janus (moon)|Janus]] and [[Epimetheus (moon)|Epimetheus]]
|-
| [[#G Ring|G Ring]] || align=center|166,000 –175,000 || align="center" |9,000 ||  align="center" |&nbsp; || First imaged by Voyager 1 (1980)<ref name="NasaVoyager1"/>
|-
| [[#Methone Ring Arc|Methone Ring Arc]]{{Efn|name=four}}|| align="center" |194,230 || align=center|? ||  align="center" |&nbsp; || [[Methone (moon)|Methone]]
|-
| [[#Anthe Ring Arc|Anthe Ring Arc]]{{Efn|name=four}}|| align="center" |197,665 || align=center|? ||  align="center" |&nbsp; || [[Anthe (moon)|Anthe]]
|-
| [[#Pallene Ring|Pallene Ring]]{{Efn|name=four}}|| align="center" |211,000 – 213,500 || align="center" |2,500 ||  align="center" |&nbsp; || [[Pallene (moon)|Pallene]]
|-
| [[#E Ring|E Ring]] || align=center|180,000 – 480,000 || align="center" |300,000 ||  align="center" |>2000&nbsp;km || Observed in 1907 by [[Georges Fournier]]; confirmed by Walter Feibelman in 1980<ref name="history_of_the_rings" /><ref name="Feibelman1980">{{Cite journal |last1=Feibelman |first1=A. W. |last2=Klinglesmith |first2=D. A. |date=1980-07-11 |title=Saturn's E Ring Revisited |url=https://www.science.org/doi/10.1126/science.209.4453.277 |journal=Science |language=en |volume=209 |issue=4453 |pages=277–279 |doi=10.1126/science.209.4453.277 |pmid=17807117 |bibcode=1980Sci...209..277F |issn=0036-8075|url-access=subscription }}</ref>
|-
| [[#Phoebe ring|Phoebe Ring]] || align=center|~4,000,000 – >13,000,000 || 9,900,000 –12,800,000<ref name="HamiltonSkrutskie2015" />|| 2,330,000&nbsp;km || Composed of material ejected by impacts on the moon [[Phoebe (moon)|Phoebe]]; discovered in 2009 by Anne Verbiscer, Michael Skrutskie, and Douglas Hamilton<ref name="HamiltonSkrutskie2015" /><ref name="Verbiscer" /><ref name="NASA2017" />
|}

==== C Ring structures ====
{| class="wikitable"
|-
! Name{{Efn|name=one}}!! Distance from Saturn's<br/>center (km){{Efn|name=two}}{{Efn|name=three}}!! Width (km){{Efn|name=two}}!! Named after
|-
| [[#Colombo Gap and Titan Ringlet|Colombo Gap]] || align=center|77,870 || align="center" |150 || [[Giuseppe Colombo|Giuseppe "Bepi" Colombo]]
|-
| [[#Colombo Gap and Titan Ringlet|Titan Ringlet]] || align=center|77,870 || align="center" |25 || [[Titan (moon)|Titan]], moon of Saturn
|-
| [[#Maxwell Gap and Ringlet|Maxwell Gap]] || align=center|87,491 || align="center" |270 || [[James Clerk Maxwell]]
|-
| [[#Maxwell Gap and Ringlet|Maxwell Ringlet]]|| align="center" |87,491 || align="center" |64 || James Clerk Maxwell
|-
| Bond Gap || align="center" |88,700 || align="center" |30 || [[William Cranch Bond]] and [[George Phillips Bond]]
|-
| 1.470R<sub>S</sub> Ringlet || align="center" |88,716 || align="center" |16 || its radius
|-
| 1.495R<sub>S</sub> Ringlet || align="center" |90,171 || align="center" |62 || its radius
|-
| Dawes Gap || align="center" |90,210 || align="center" |20 || [[William Rutter Dawes]]
|}

==== Cassini Division structures ====
* Source:<ref name="NewGapNames">{{cite web | last=Lakdawalla | first=E. | title=New names for gaps in the Cassini Division within Saturn's rings | work= Planetary Society blog | publisher=[[Planetary Society]] | date=2009-02-09 | url= http://www.planetary.org/blogs/emily-lakdawalla/2009/1835.html | access-date=2017-12-20 }}</ref>
{| class="wikitable"
|-
! Name{{Efn|name=one}}!! Distance from Saturn's<br/>center (km){{Efn|name=two}}{{Efn|name=three}}!! Width (km){{Efn|name=two}}!! Named after
|-
| [[#Huygens Gap|Huygens Gap]] || align=center|117,680 || align="center" |285–400 || [[Christiaan Huygens]]
|-
| [[#Huygens Gap|Huygens Ringlet]]|| align="center" |117,848 || align="center" |~17 || Christiaan Huygens
|-
| Herschel Gap || align="center" |118,234 || align="center" |102 || [[William Herschel]]
|-
| Russell Gap || align="center" |118,614 || align="center" |33 || [[Henry Norris Russell]]
|-
| Jeffreys Gap || align="center" |118,950 || align="center" |38 || [[Harold Jeffreys]]
|-
| Kuiper Gap || align="center" |119,405 || align="center" |3 || [[Gerard Kuiper]]
|-
| Laplace Gap || align="center" |119,967 || align="center" |238 || [[Pierre-Simon Laplace]]
|-
| Bessel Gap || align="center" |120,241 || align="center" |10 || [[Friedrich Bessel]]
|-
| Barnard Gap || align="center" |120,312 || align="center" |13 || [[Edward Emerson Barnard]]
|}

==== A Ring structures ====
{| class="wikitable"
|-
! Name{{Efn|name=one}}!! Distance from Saturn's<br/>center (km){{Efn|name=two}}{{Efn|name=three}}!! Width (km){{Efn|name=two}}!! Named after
|-
| [[#Encke Gap|Encke Gap]] || align=center|133,589 || align="center" |325 || [[Johann Encke]]
|-
| [[#Keeler Gap|Keeler Gap]] || align=center|136,505 || align="center" |35 || [[James Keeler]]
|}
{{Clear}}

== D Ring ==
[[File:PIA18313 Saturn's D ring and inner C ring.jpg|thumb|A ''Cassini'' image of the faint D Ring, with the inner C Ring below]]
The D Ring is the innermost ring, and is very faint. In 1980, ''[[Voyager 1]]'' detected within this ring three ringlets designated D73, D72 and D68, with D68 being the discrete ringlet nearest to Saturn. Some 25 years later, ''Cassini'' images showed that D72 had become significantly broader and more diffuse, and had moved planetward by 200&nbsp;km (100 miles).<ref name="Hedman" />

Present in the D Ring is a finescale structure with waves 30&nbsp;km (20 miles) apart. First seen in the gap between the C Ring and D73,<ref name="Hedman">{{cite journal |display-authors=1 |last1=Hedman |first1=Matthew M. |last2=Burns |first2=Joseph A |last3=Showalter |first3=Mark R. |title=Saturn's dynamic D ring |journal=Icarus |date=2007 |volume=188 |issue=1 |pages=89–107 |doi=10.1016/j.icarus.2006.11.017 |url=http://ciclops.org/media/sp/2007/2678_7440_0.pdf |bibcode=2007Icar..188...89H }}</ref> the structure was found during Saturn's 2009 equinox to extend a radial distance of 19,000&nbsp;km (12,000 miles) from the D Ring to the inner edge of the B Ring.<ref name="forensic">{{cite web |display-authors=1 |last1=Mason |first1=J. |last2=Cook |first2=J.-R. C. |title=Forensic sleuthing ties ring ripples to impacts |work=CICLOPS press release |publisher=Cassini Imaging Central Laboratory for Operations |date=2011-03-31 | url=https://ciclops.org/view/6762/FORENSIC-SLEUTHING-TIES-RING-RIPPLES-TO-IMPACTS.html |access-date=2022-09-22 }}</ref><ref name="extensive">{{cite web |title=Extensive spiral corrugations |work=PIA 11664 caption |publisher=NASA / Jet Propulsion Laboratory / Space Science Institute |date=2011-03-31 |url=https://ciclops.org/view/5722/Extensive_Spiral_Corrugations.html |access-date=2022-09-22 }}</ref> The waves are interpreted as a spiral pattern of vertical corrugations of 2 to 20 m amplitude;<ref name="tilting">{{cite web |title=Tilting Saturn's rings | work=PIA 12820 caption | publisher=NASA / Jet Propulsion Laboratory / Space Science Institute | date=2011-03-31 | url=http://www.ciclops.org/view/6748/Tilting_Saturns_Rings | access-date=2011-04-04 }}</ref> the fact that the period of the waves is decreasing over time (from 60&nbsp;km; 40 miles in 1995 to 30&nbsp;km; 20 miles by 2006) allows a deduction that the pattern may have originated in late 1983 with the impact of a cloud of debris (with a mass of ≈10<sup>12</sup> kg) from a disrupted comet that tilted the rings out of the equatorial plane.<ref name="Hedman" /><ref name="forensic" /><ref name="Hedman2">{{cite journal |display-authors=1 |last1=Hedman |first1=M. M. |last2=Burns |first2=J. A. |last3=Evans |first3=M. W. |last4=Tiscareno |first4=M. S. |last5=Porco |first5=C. C. |title=Saturn's curiously corrugated C Ring |journal=[[Science (journal)|Science]] |volume=332 |issue=6030 |pages=708–11 |date=2011-03-31 |doi=10.1126/science.1202238 |bibcode=2011Sci...332..708H |pmid=21454753|citeseerx=10.1.1.651.5611 |s2cid=11449779 }}</ref> A similar spiral pattern in [[Rings of Jupiter#Main ring|Jupiter's main ring]] has been attributed to a perturbation caused by impact of material from [[Comet Shoemaker-Levy 9]] in 1994.<ref name="forensic" /><ref name="Jupiter's Ring">{{cite web |title=Subtle Ripples in Jupiter's Ring |work=PIA 13893 caption |publisher=NASA / Jet Propulsion Laboratory-Caltech / SETI |date=2011-03-31 |url=http://www.ciclops.org/view/6760/Subtle_Ripples_in_Jupiters_Ring |access-date=2011-04-04 }}</ref><ref name="Showalter">{{cite journal |display-authors=1 |last1=Showalter |first1=M. R. |last2=Hedman |first2=M. M. |last3=Burns |first3=J. A. |title=The impact of comet Shoemaker-Levy 9 sends ripples through the rings of Jupiter |journal=[[Science (journal)|Science]] |volume=332 |issue=6030 |pages=711–3 |date=2011-03-31 |doi=10.1126/science.1202241 |bibcode=2011Sci...332..711S |pmid=21454755|s2cid=27371440 |url=https://pdfs.semanticscholar.org/60ad/a53885fb7ec3566f9c3c26bbf5f9df9a47fd.pdf |archive-url=https://web.archive.org/web/20200212230930/https://pdfs.semanticscholar.org/60ad/a53885fb7ec3566f9c3c26bbf5f9df9a47fd.pdf |archive-date=2020-02-12 }}</ref>

== C Ring ==
{{Redirect|C Ring||C ring (disambiguation){{!}}Cring}}
[[File:PIA06540 Outer C Ring.jpg|thumb|View of the outer C Ring; the Maxwell Gap with the Maxwell Ringlet on its right side are above and right of center. The Bond Gap is above a broad light band towards the upper right; the Dawes Gap is within a dark band just below the upper right corner.]]

The C Ring is a wide but faint ring located inward of the [[#B Ring|B Ring]]. It was discovered in 1850 by [[William Cranch Bond|William]] and [[George Phillips Bond|George Bond]], though [[William R. Dawes]] and [[Johann Galle]] also saw it independently. [[William Lassell]] termed it the "Crepe Ring" because it seemed to be composed of darker material than the brighter A and B Rings.<ref name="Harland">Harland, David M., ''Mission to Saturn: Cassini and the Huygens Probe'', Chichester: Praxis Publishing, 2002.</ref>

Its vertical thickness is estimated at 5 meters (16'), its mass at around 1.1{{E-sp|18}} kg, and its [[optical depth]] varies from 0.05 to 0.12.{{citation needed|date=July 2008}} That is, between 5 and 12 percent of light shining perpendicularly through the ring is blocked, so that when seen from above, the ring is close to transparent. The 30-km wavelength spiral corrugations first seen in the D Ring were observed during Saturn's equinox of 2009 to extend throughout the C Ring (see above).

=== Colombo Gap and Titan Ringlet ===
The Colombo Gap lies in the inner C Ring. Within the gap lies the bright but narrow Colombo Ringlet, centered at 77,883&nbsp;km (48,394 miles) from Saturn's center, which is slightly [[ellipse|elliptical]] rather than circular. This ringlet is also called the Titan Ringlet as it is governed by an orbital resonance with the moon [[Titan (moon)|Titan]].<ref name="Porco1984" /> At this location within the rings, the length of a ring particle's [[apsidal precession]] is equal to the length of Titan's orbital motion, so that the outer end of this eccentric ringlet always points towards Titan.<ref name="Porco1984">{{cite journal |display-authors=1 |last1=Porco |first1=C. |author-link=Carolyn Porco |last2=Nicholson |first2=P. D. |author-link2=Phil Nicholson |last3=Borderies |first3=N. |last4=Danielson |first4=G. E. |last5=Goldreich |first5=P. |author-link5=Peter Goldreich |last6=Holdberg |first6=J. B. |last7=Lane |first7=A. L. |title=The eccentric Saturnian ringlets at 1.29R<sub>s</sub> and 1.45R<sub>s</sub> |journal=[[Icarus (journal)|Icarus]] |volume=60 | issue=1 |pages=1–16 |date= October 1984|doi=10.1016/0019-1035(84)90134-9 |bibcode=1984Icar...60....1P}}</ref>

=== Maxwell Gap and Ringlet ===
The Maxwell Gap lies within the outer part of the C Ring. It also contains a dense non-circular ringlet, the Maxwell Ringlet. In many respects this ringlet is similar to the [[Rings of Uranus#ε ring|ε ring of Uranus]]. There are wave-like structures in the middle of both rings. While the wave in the ε ring is thought to be caused by Uranian moon [[Cordelia (moon)|Cordelia]], no moon has been discovered in the Maxwell gap as of July 2008.<ref name="Porco2005">{{cite journal |title=Cassini Imaging Science: Initial Results on Saturn'sRings and Small Satellites |journal=Science |date=2005 |volume=307 |pages=1226–1236 |doi=10.1126/science.1108056 |url=http://ciclops.org/sci/docs/RingsSatsPaper.pdf |pmid=15731439 |issue=5713 |bibcode=2005Sci...307.1226P |display-authors=1 |last1=Porco |first1=C.C. |last2=Baker |first2=E.|last3=Barbara|first3=J. |last4=Beurle |first4=K |last5=Brahic |first5=A |last6=Burns |first6=JA |last7=Charnoz |first7=S |last8=Cooper |first8=N |last9=Dawson |first9=DD |s2cid=1058405 }}</ref>

== B Ring ==
The B Ring is the largest, brightest, and most massive of the rings. Its thickness is estimated as 5 to 15 m and its optical depth varies from 0.4 to greater than 5,<ref name="Hedman2016" /> meaning that >99% of the light passing through some parts of the B Ring is blocked. The B Ring contains a great deal of variation in its density and brightness, nearly all of it unexplained. These are concentric, appearing as narrow ringlets, though the B Ring does not contain any gaps.{{citation needed|date=July 2008}} In places, the outer edge of the B Ring contains vertical structures deviating up to 2.5&nbsp;km (1½ miles) from the main ring plane, a significant deviation from the vertical thickness of the main A, B and C rings, which is generally only about 10 meters (about 30 feet). Vertical structures can be created by unseen embedded moonlets.<ref name=peaks>{{cite web |title=The Tallest Peaks |url=https://solarsystem.nasa.gov/resources/141/the-tallest-peaks/ |website=NASA Solar System Exploration |date=November 2010 |access-date=21 February 2023}} {{PD-notice}}</ref>

A 2016 study of spiral density waves using stellar occultations indicated that the B Ring's surface density is in the range of 40 to 140 g/cm<sup>2</sup>, lower than previously believed, and that the ring's optical depth has little correlation with its mass density (a finding previously reported for the A and C rings).<ref name="Hedman2016">{{cite journal|last1= Hedman|first1= M.M.|last2= Nicholson|first2= P.D.|title=The B-ring's surface mass density from hidden density waves: Less than meets the eye?|journal= Icarus|volume= 279|pages= 109–124|date= 2016-01-22|doi= 10.1016/j.icarus.2016.01.007|arxiv = 1601.07955 |bibcode = 2016Icar..279..109H |s2cid= 119199474}}</ref><ref name="NASA-20160202">{{cite web |last=Dyches |first=Preston |title=Saturn's Rings: Less than Meets the Eye? |url=http://www.jpl.nasa.gov/news/news.php?feature=4886 |work=[[NASA]] |date=2 February 2016 |access-date=3 February 2016 }}</ref> The total mass of the B Ring was estimated to be somewhere in the range of 7 to {{val|24|e=18}} kg. This compares to a mass for [[Mimas]] of {{val|37.5|e=18}} kg.<ref name="Hedman2016" />

{{multiple image
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| image1 = PIA21628 - B Ring fine structure in color.jpg
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| caption1 = High resolution (about 3 km per pixel) color view of the inner-central B Ring (98,600 to 105,500 km; 61,300 to 65,600 miles from Saturn's center). The structures shown (from 40 km; 25 miles wide ringlets at center to 300–500 km; 200 to 300 miles wide bands at right) remain sharply defined at scales below the resolution of the image.
| image2 = PIA11668 B ring peaks 2x crop.jpg
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| caption2 = The B Ring's outer edge, viewed near equinox, where shadows are cast by vertical structures up to 2.5 km (1½ miles) high, probably created by unseen embedded moonlets. The Cassini Division is at top.<ref name=peaks/>{{efn |The image was taken in visible light with the Cassini spacecraft narrow-angle camera on July 26, 2009. The view was acquired at a distance of approximately 336,000 kilometers (209,000 miles) from Saturn and at a sun-Saturn-spacecraft, or phase, angle of 132 degrees. Image scale is 2 kilometers (1 mile) per pixel.<ref name=peaks/>}}
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{{clear}}

=== Spokes ===
[[File:Saturn ring spokes PIA11144 secs15.5to23 20080926.ogv|thumb|Dark spokes mark the B ring's sunlit side in low [[Phase angle (astronomy)|phase angle]] Cassini images. This is a low-bitrate video. [[:File:Saturn ring spokes PIA11144 300px secs15.5to23 20080926.ogv|Lo-res version of this video]]]]
Until 1980, the structure of the rings of Saturn was explained as being caused exclusively by the action of [[gravitation]]al forces. Then images from the Voyager spacecraft showed radial features in the [[#B Ring|B Ring]], known as ''spokes'',<ref>{{Cite journal | last1 = Smith | first1 = B. A. | last2 = Soderblom | first2 = L. | last3 = Batson | first3 = R. | last4 = Bridges | first4 = P. | last5 = Inge | first5 = J. | last6 = Masursky | first6 = H. | last7 = Shoemaker | first7 = E. | last8 = Beebe | first8 = R. | last9 = Boyce | first9 = J. | last10 = Briggs | first10 = G. | last11 = Bunker | first11 = A. | last12 = Collins | first12 = S. A. | last13 = Hansen | first13 = C. J. | last14 = Johnson | first14 = T. V. | last15 = Mitchell | first15 = J. L. | last16 = Terrile | first16 = R. J. | last17 = Cook Af | first17 = A. F. | last18 = Cuzzi | first18 = J. | last19 = Pollack | first19 = J. B. | last20 = Danielson | first20 = G. E. | last21 = Ingersoll | first21 = A. P. | last22 = Davies | first22 = M. E. | last23 = Hunt | first23 = G. E. | last24 = Morrison | first24 = D. | last25 = Owen | first25 = T. | last26 = Sagan | first26 = C. | last27 = Veverka | last28 = Strom | first28 = R. | first29 = V. E. | last29 = Suomi | first27 = J. | doi = 10.1126/science.215.4532.504 | title = A New Look at the Saturn System: The Voyager 2 Images | journal = Science | volume = 215 | issue = 4532 | pages = 504–537 | year = 1982 | pmid =  17771273|bibcode = 1982Sci...215..504S | s2cid = 23835071 }}</ref><ref name="Spokes 2">{{cite web | archive-url = https://web.archive.org/web/20101213160840/http://www.planetary.org/explore/topics/saturn/rings.html |url=http://www.planetary.org/explore/topics/saturn/rings.html |title=The Alphabet Soup of Saturn's Rings |publisher=The Planetary Society |date=2007 |archive-date= 2010-12-13|access-date=2007-07-24}}</ref> which could not be explained in this manner, as their persistence and rotation around the rings was not consistent with gravitational [[orbital mechanics]].<ref name = "Hamilton2004"/> The spokes appear dark in [[backscatter]]ed light, and bright in [[Forward scatter|forward-scattered]] light; the transition occurs at a [[Phase angle (astronomy)|phase angle]] near 60[[Degree (angle)|°]]. The leading hypothesis regarding the spokes' composition is that they consist of [[microscopic]] dust particles suspended away from the main ring by [[electrostatic]] repulsion, as they rotate almost [[synchronization|synchronously]] with the [[magnetosphere]] of Saturn. The precise mechanism generating the spokes is still unknown. It has been suggested that the electrical disturbances might be caused by either [[lightning]] bolts in Saturn's [[atmosphere]] or [[micrometeoroid]] impacts on the rings.<ref name = "Hamilton2004">{{cite web |url=http://www.solarviews.com/eng/saturnrings.htm |title=Saturn's Magnificent Rings |first=Calvin |last=Hamilton |date=2004 |access-date=2007-07-25 }}</ref> Alternatively, it is proposed that the spokes are very similar to a phenomenon known as [[lunar horizon glow]] or dust levitation, and caused by intense electric fields across the terminator of ring particles, not electrical disturbances.<ref name = "Hirata et al. 2022">{{cite journal |title=Dust release from cold ring particles as a mechanism of spoke formation in Saturn's rings |first=N.|last=Hirata |journal=Icarus |date=2022 |volume=378 |article-number=114920 |doi=10.1016/j.icarus.2022.114920 |arxiv=2205.07008 |bibcode=2022Icar..37814920H }}</ref>

The spokes were not observed again until some twenty-five years later, this time by the ''Cassini'' space probe. The spokes were not visible when ''Cassini'' arrived at Saturn in early 2004. Some scientists speculated that the spokes would not be visible again until 2007, based on models attempting to describe their formation. Nevertheless, the ''Cassini'' imaging team kept looking for spokes in images of the rings, and they were next seen in images taken on 5 September 2005.<ref name="Spokes">{{cite web |url=http://www.space.com/scienceastronomy/050915_cassini_spokes.html |title=Cassini Probe Spies Spokes in Saturn's Rings |date=2005-09-15 |publisher=Imaginova Corp. |first=Tarig |last=Malik |access-date=2007-07-06}}</ref>

The spokes appear to be a [[season]]al phenomenon, disappearing in the Saturnian midwinter and midsummer and reappearing as Saturn comes closer to [[equinox]]. Suggestions that the spokes may be a seasonal effect, varying with Saturn's 29.7-year orbit, were supported by their gradual reappearance in the later years of the Cassini mission.<ref name="Mitchell2006">{{cite journal |display-authors=1 |last1=Mitchell |first1=C.J. |last2=Horanyi |first2=M. |last3=Havnes |first3=O. |last4=Porco |first4=C.C. |title=Saturn's Spokes: Lost and Found |journal=Science |volume=311 |date=2006 |doi=10.1126/science.1123783 |url=http://ciclops.org/media/sp/2007/2683_7445_0.pdf |pmid=16543455 |issue=5767 |bibcode=2006Sci...311.1587M |pages=1587–9 |citeseerx=10.1.1.368.1168 |s2cid=36767835 }}</ref>

=== Moonlet ===
In 2009, during equinox, a moonlet embedded in the B ring was discovered from the shadow it cast. It is estimated to be {{Convert|400|m|abbr=on}} in diameter.<ref>{{cite web|url=http://saturn.jpl.nasa.gov/photos/imagedetails/index.cfm?imageId=3617|title=Cassini Solstice Mission: A Small Find Near Equinox|work=Cassini Solstice Mission|access-date=2009-11-16|archive-url=https://web.archive.org/web/20091010124459/http://saturn.jpl.nasa.gov/photos/imagedetails/index.cfm?imageId=3617|archive-date=2009-10-10}}</ref> The moonlet was given the provisional designation [[S/2009 S 1]].

== Cassini Division ==
[[File:Cassini Division.jpg|thumb|The Cassini Division imaged from the ''Cassini'' spacecraft. The Huygens Gap lies at its right border; the Laplace Gap is towards the center. A number of other, narrower gaps are also present. The moon in the background is [[Mimas]].]]
The Cassini Division is a region {{convert|4800|km|mi|abbr=on|}} in width between Saturn's [[#A Ring structures|A Ring]] and [[#B Ring|B Ring]]. It was discovered in 1675 by [[Giovanni Cassini]] at the [[Paris Observatory]] using a [[refracting telescope]] that had a 2.5-inch [[objective lens]] with a 20-foot-long [[focal length]] and a 90x [[magnification]].<ref>{{cite book|last=Webb|first=Thomas William|title=Celestial Objects for Common Telescopes|url=https://archive.org/details/celestialobject02webbgoog|year=1859|publisher=Longman, Green, Longman, and Roberts|page=[https://archive.org/details/celestialobject02webbgoog/page/n154 130]}}</ref><ref>Archie Frederick Collins, The greatest eye in the world: astronomical telescopes and their stories, page 8</ref> From Earth it appears as a thin black gap in the rings. However, ''Voyager'' discovered that the gap is itself populated by ring material bearing much similarity to the [[#C Ring|C Ring]].<ref name=Porco2005/> The division may appear bright in views of the unlit side of the rings, since the relatively low density of material allows more light to be transmitted through the thickness of the rings.

The inner edge of the Cassini Division is governed by a strong orbital resonance. Ring particles at this location orbit twice for every orbit of the moon [[Mimas]].<ref>{{cite web|url=http://www.astronomy.ohio-state.edu/~pogge/Ast161/Unit6/rings.html|title=Lecture 41: Planetary Rings|work=ohio-state.edu}}</ref> The resonance causes Mimas' pulls on these ring particles to accumulate, destabilizing their orbits and leading to a sharp cutoff in ring density. Many of the other gaps between ringlets within the Cassini Division, however, are unexplained.<ref>{{Cite web|last1=O'Connor|first1=J. J.|last2=Robertson|first2=E. F.|date=2003|title=Giovanni Cassini - Biography|url=https://mathshistory.st-andrews.ac.uk/Biographies/Cassini/|website=Maths History|publisher=School of Mathematics and Statistics University of St. Andrews, Scotland}}</ref>

=== Huygens Gap ===
Discovered in 1981 through images sent back by Voyager 2,<ref>[https://www.oxfordreference.com/display/10.1093/oi/authority.20110803095952305;jsessionid=204660F2C7866CF5C082FB40FFC0EA83 Overview, Huygens Gap, Oxford Reference, oxfordreference.com]</ref> the Huygens Gap is located at the inner edge of the Cassini Division. It contains the dense, eccentric Huygens Ringlet in the middle. This ringlet exhibits irregular [[azimuthal]] variations of geometrical width and optical depth, which may be caused by the nearby 2:1 resonance with [[Mimas]] and the influence of the eccentric outer edge of the B-ring. There is an additional narrow ringlet just outside the Huygens Ringlet.<ref name=Porco2005/>

== A Ring ==
{{Redirect|A Ring|the letter|Å}}
[[File:PIA06534 Encke Division.jpg|thumb|The central ringlet of the A Ring's Encke Gap coincides with [[Pan (moon)|Pan]]'s orbit, implying its particles oscillate in [[horseshoe orbit]]s.]]
The A Ring is the outermost of the large, bright rings. Its inner boundary is the [[#Cassini Division|Cassini Division]] and its sharp outer boundary is close to the orbit of the small moon [[Atlas (moon)|Atlas]]. The A Ring is interrupted at a location 22% of the ring width from its outer edge by the [[#Encke Gap|Encke Gap]]. A narrower gap 2% of the ring width from the outer edge is called the [[#Keeler Gap|Keeler Gap]].

The thickness of the A Ring is estimated to be 10 to 30 m, its surface density from 35 to 40 g/cm<sup>2</sup> and its total mass as 4 to {{val|5|e=18}} kg<ref name="Hedman2016" /> (just under the mass of [[Hyperion (moon)|Hyperion]]). Its optical depth varies from 0.4 to 0.9.<ref name="Hedman2016" />

Similarly to the B Ring, the A Ring's outer edge is maintained by orbital resonances, albeit in this case a more complicated set. It is primarily acted on by the 7:6 resonance with [[Janus (moon)|Janus]] and [[Epimetheus (moon)|Epimetheus]], with other contributions from the 5:3 resonance with [[Mimas]] and various resonances with [[Prometheus (moon)|Prometheus]] and [[Pandora (moon)|Pandora]].<ref>{{cite journal |last1=El Moutamid |first1=Maryame |first2=Philip D. |last2=Nicholson |first3=Richard G. |last3=French |first4=Matthew S. |author5-link=Carl D. Murray |last4=Tiscareno |first5=Carl D. |last5=Murray |first6=Michael W. |last6=Evans |first7=Colleen McGhee |last7=French |first8=Matthew M. |last8=Hedman |first9=Joseph A. |last9=Burns |date=1 October 2015 |title=How Janus' Orbital Swap Affects the Edge of Saturn's A Ring? |journal=Icarus |volume=279 |pages=125–140 |arxiv=1510.00434 |bibcode=2016Icar..279..125E |doi=10.1016/j.icarus.2015.10.025 |s2cid=51785280}}</ref><ref name="Spahn2019">{{cite arXiv |last1=Spahn |first1=Frank |last2=Hoffmann |first2=Holger |last3=Seiß |first3=Martin |last4=Seiler |first4=Michael |last5=Grätz |first5=Fabio M. |title=The radial density profile of Saturn's A ring |date=19 June 2019 |class=astro-ph.EP |language=en|eprint=1906.08036 }}</ref> Other orbital resonances also excite many [[Density wave theory|spiral density waves]] in the A Ring (and, to a lesser extent, other rings as well), which account for most of its structure. These waves are described by the same physics that describes the [[spiral galaxy|spiral arms of galaxies]]. Spiral bending waves, also present in the A Ring and also described by the same theory, are [[Transverse wave|vertical corrugations]] in the ring rather than [[Longitudinal wave|compression waves.]]<ref>{{Cite web|url=https://solarsystem.nasa.gov/resources/14291/two-kinds-of-wave|title=Two Kinds of Wave|website=NASA Solar System Exploration|date=29 October 2008 |access-date=2019-05-30}}</ref>

In April 2014, NASA scientists reported observing the possible formative stage of a new moon near the outer edge of the A Ring.<ref name="NASA-20140414a">{{cite web |display-authors=1 |last1=Platt |first1=Jane |last2=Brown |first2=Dwayne |title=NASA Cassini Images May Reveal Birth of a Saturn Moon |url=http://www.jpl.nasa.gov/news/news.php?release=2014-112 |date=14 April 2014 |publisher=[[NASA]] }}</ref><ref name="Murray2014">{{Cite journal | doi = 10.1016/j.icarus.2014.03.024| title = The discovery and dynamical evolution of an object at the outer edge of Saturn's a ring| journal = Icarus| date = 2014-03-28| last1 = Murray | first1 = C. D. | last2 = Cooper | first2 = N. J. | last3 = Williams | first3 = G. A. | last4 = Attree | first4 = N. O. | last5 = Boyer | first5 = J. S. | bibcode=2014Icar..236..165M | volume=236 | pages=165–168| url = http://qmro.qmul.ac.uk/xmlui/handle/123456789/7568}}</ref>

=== Encke Gap ===
<!-- This section is linked from [[Saturn]] -->
[[File:PIA06099 Enke Gap.jpg|thumb|[[Pan (moon)|Pan]]'s motion through the [[#A Ring structures|A ring]]'s [[#Encke Gap|Encke Gap]] induces edge waves and (non-self-propagating) [[spiral]]ing wakes<ref>[http://photojournal.jpl.nasa.gov/catalog/PIA09883 NASA.gov]</ref> ahead of and inward of it. The other more tightly wound bands are [[Density wave theory|spiral density waves]].]]
The Encke Gap is a 325-km (200 mile) wide gap within the [[#A Ring structures|A ring]], centered at a distance of 133,590&nbsp;km (83,000 miles) from Saturn's center.<ref name="factsheet1">{{cite web |url=http://nssdc.gsfc.nasa.gov/planetary/factsheet/satringfact.html |title=Saturnian Rings Fact Sheet |publisher=NASA |last=Williams |first=David R |access-date=2008-07-22 }}</ref> It is caused by the presence of the small moon [[Pan (moon)|Pan]],<ref name=Esposito2002/> which orbits within it. Images from the ''Cassini'' probe have shown that there are at least three thin, knotted ringlets within the gap.<ref name="Porco2005" /> [[Density wave theory|Spiral density waves]] visible on both sides of it are induced by resonances with nearby [[Moons of Saturn|moons]] exterior to the rings, while Pan induces an additional set of spiralling wakes.<ref name="Porco2005" />

[[Johann Encke]] himself did not observe this gap; it was named in honour of his ring observations. The gap itself was discovered by [[James Edward Keeler]] in 1888.<ref name="Harland" /> The second major gap in the [[#A Ring structures|A ring]], discovered by ''Voyager'', was named the Keeler Gap in his honor.<ref>{{Cite journal | last1 = Osterbrock | first1 = D. E. | last2 = Cruikshank | first2 = D. P. | doi = 10.1016/0019-1035(83)90139-2 | title = J.E. Keeler's discovery of a gap in the outer part of the a ring | journal = Icarus | volume = 53 | issue = 2 | page = 165 | year = 1983 | bibcode = 1983Icar...53..165O}}</ref>

The Encke Gap is a ''gap'' because it is entirely within the A Ring. There was some ambiguity between the terms ''gap'' and ''division'' until the IAU clarified the definitions in 2008; before that, the separation was sometimes called the "Encke Division".<ref name="Enke">{{cite web | last=Blue | first=J. | title=Encke Division Changed to Encke Gap | work=USGS Astrogeology Science Center | publisher=[[USGS]] | date=2008-02-06 | url=https://astrogeology.usgs.gov/HotTopics/index.php?/archives/320-Encke-Division-Changed-to-Encke-Gap.html | access-date=2010-09-02 }}</ref>

=== Keeler Gap ===
[[File:Daphnis edge wave shadows.jpg|thumb|View of Daphnis orbiting in the Keeler Gap, creating waves that cast shadows across the rings]]
The Keeler Gap is a 42-km (26 mile) wide gap in the [[#A Ring structures|A ring]], approximately 250&nbsp;km (150 miles) from the ring's outer edge. The small moon [[Daphnis (moon)|Daphnis]], discovered 1 May 2005, orbits within it, keeping it clear.<ref name=Porco2007>{{cite journal |display-authors=1 |last1=Porco |first1=C.C. |last2=Thomas |first2=P.C. |last3=Weiss |first3=J.W. |last4=Richardson |first4=D.C. |title=Saturn's Small Inner Satellites: Clues to Their Origins |date=2007 |volume=318 |pages=1602–1607 |doi=10.1126/science.1143977 |journal=Science |url=http://ciclops.org/media/sp/2007/4691_10256_0.pdf |pmid=18063794 |issue=5856 |bibcode=2007Sci...318.1602P |s2cid=2253135 }}</ref> The moon's passage induces waves in the edges of the gap (this is also influenced by its slight orbital eccentricity).<ref name=Porco2005/> Because the orbit of Daphnis is slightly inclined to the ring plane, the waves have a component that is perpendicular to the ring plane, reaching a distance of 1500&nbsp;m "above" the plane.<ref>{{cite web | last=Mason | first=Joe | title=Saturn's Approach To Equinox Reveals Never-before-seen Vertical Structures In Planet's Rings | work=CICLOPS web site | date=11 June 2009 | url=http://ciclops.org/view.php?id=5680 | access-date=2009-06-13 | archive-date=2009-06-15 | archive-url=https://web.archive.org/web/20090615101154/http://ciclops.org/view.php?id=5680 }}</ref><ref name="EdgeWaves">{{cite journal |display-authors=1 |last1=Weiss |first1=J. W. |last2=Porco |first2=C. C. |last3=Tiscareno |first3=M. S. |title=Ring Edge Waves and the Masses of Nearby Satellites |journal=The Astronomical Journal |volume=138 |issue=1 |pages=272–286 |date=11 June 2009 |doi=10.1088/0004-6256/138/1/272 |bibcode=2009AJ....138..272W |citeseerx=10.1.1.653.4033 |s2cid=49572420 }}</ref>

The Keeler gap was discovered by ''Voyager'', and named in honor of the astronomer [[James Edward Keeler]]. Keeler had in turn discovered and named the [[#Encke Gap|Encke Gap]] in honor of [[Johann Encke]].<ref name="Harland" />

=== Propeller moonlets ===
[[File:First moonlets PIA07792.jpg|thumb|upright=1|Location of the first four moonlets detected in the A ring.]]
In 2006, four tiny "[[moonlet]]s" were found in ''Cassini'' images of the A Ring.<ref name="Tiscareno2006">{{cite journal | title=''100-m-diameter moonlets in Saturn's A ring from observations of 'propeller' structures'' | journal=Nature | date=2006 | volume=440 | pages=648–650 | doi=10.1038/nature04581 | pmid=16572165 | issue=7084 |bibcode=2006Natur.440..648T | display-authors=1 | first1=Matthew S. |last1=Tiscareno | last2=Burns | first2=Joseph A. | last3=Hedman | first3=Matthew M. | last4=Porco | first4=Carolyn C. | last5=Weiss | first5=John W. | last6=Dones | first6=Luke | last7=Richardson | first7=Derek C. | last8=Murray | first8=Carl D. | s2cid=9688977 }}</ref> The moonlets themselves are only about a hundred meters in diameter, too small to be seen directly; what ''Cassini'' sees are the "propeller"-shaped disturbances the moonlets create, which are several km (miles) across. It is estimated that the A Ring contains thousands of such objects. In 2007, the discovery of eight more moonlets revealed that they are largely confined to a 3,000&nbsp;km (2000 mile) belt, about 130,000&nbsp;km (80,000 miles) from Saturn's center,<ref name="Sremcevic2007">{{cite journal | title=''A belt of moonlets in Saturn's A ring'' | journal=Nature | date=2007 | volume=449 | pages=1019–1021 | doi=10.1038/nature06224 | pmid=17960236 | issue=7165|bibcode=2007Natur.449.1019S | display-authors=1 | first1=Miodrag |last1=Sremčević | last2=Schmidt | first2=Jürgen | last3=Salo | first3=Heikki | last4=Seiß | first4=Martin | last5=Spahn | first5=Frank | last6=Albers | first6=Nicole | s2cid=4330204 }}</ref> and by 2008 over 150 propeller moonlets had been detected.<ref name="Tiscareno2008">{{cite journal | title=''The population of propellers in Saturn's A Ring'' | journal=[[Astronomical Journal]] | date=2008 | volume=135 | issue=3 | pages=1083–1091 | doi=10.1088/0004-6256/135/3/1083 | bibcode=2008AJ....135.1083T | display-authors=1 | first1=Matthew S. |last1=Tiscareno | last2=Burns | first2=Joseph A. | last3=Hedman | first3=Matthew M. | last4=c. Porco | first4=Carolyn|arxiv=0710.4547 | s2cid=28620198 }}</ref> One that has been tracked for several years has been nicknamed ''[[Bleriot (moonlet)|Bleriot]]''.<ref name="Bleriot_Recaptured">{{cite web | last=Porco | first=C. | author-link=Carolyn Porco | title=Bleriot Recaptured | work= CICLOPS web site | publisher=NASA/JPL-Caltech/Space Science Institute | date=2013-02-25 | url=https://ciclops.org/view/7459/Bleriot-Recaptured.html | access-date=2022-09-22 }}</ref>

== Roche Division ==
[[File:Roche division, rings of Saturn.jpg|thumb|The Roche Division (passing through image center) between the A Ring and the F Ring. [[Atlas (moon)|Atlas]], the Encke Gap, and the Keeler Gap are visible.]]
The separation between the [[#A Ring structures|A ring]] and the [[#F Ring|F Ring]] has been named the Roche Division in honor of the French physicist [[Édouard Roche]].<ref>{{cite web|url=https://planetarynames.wr.usgs.gov/append8.html|title=Planetary Names: Ring and Ring Gap Nomenclature|work=usgs.gov}}</ref> The Roche Division should not be confused with the [[Roche limit]] which is the distance at which a large object is so close to a planet (such as Saturn) that the planet's [[tidal force]]s will pull it apart.<ref name="wolf">{{cite web |url=http://scienceworld.wolfram.com/physics/RocheLimit.html |title=Eric Weisstein's World of Physics – Roche Limit |publisher=scienceworld.wolfram.com |date=2007 |first=Eric W. |last=Weisstein |access-date=2007-09-05 }}</ref> Lying at the outer edge of the main ring system, the Roche Division is in fact close to Saturn's Roche limit, which is why the rings have been unable to [[Accretion (astrophysics)|accrete]] into a moon.<ref name="two">{{cite web |url=http://www2.jpl.nasa.gov/saturn/faq.html#roche |archive-url=https://web.archive.org/web/19991105133931/http://www.jpl.nasa.gov/saturn/faq.html#roche |archive-date=1999-11-05 |title=What is the Roche limit? |publisher=NASA–JPL |author=NASA |access-date=2007-09-05 }}</ref>

Like the [[#Cassini Division|Cassini Division]], the Roche Division is not empty but contains a sheet of material.{{citation needed|date=July 2008}} The character of this material is similar to the tenuous and dusty D, E, and G Rings.{{citation needed|date=July 2008}} Two locations in the Roche Division have a higher concentration of dust than the rest of the region. These were discovered by the ''Cassini'' probe imaging team and were given [[Astronomical naming conventions#Natural satellites of planets|temporary designations]]: R/2004 S 1, which lies along the orbit of the moon [[Atlas (moon)|Atlas]]; and R/2004 S 2, centered at 138,900&nbsp;km (86,300 miles) from Saturn's center, inward of the orbit of [[Prometheus (moon)|Prometheus]].<ref>{{Cite web|url=http://www.cbat.eps.harvard.edu/iauc/08400/08401.html|title=IAUC 8401: S/2004 S 3, S/2004 S 4,, R/2004 S 1; 2004eg, 2004eh,, 2004ei|website=www.cbat.eps.harvard.edu}}</ref><ref>{{Cite web|url=http://www.cbat.eps.harvard.edu/iauc/08400/08432.html|title=IAUC 8432: Sats, RINGS OF SATURN; 2004fc|website=www.cbat.eps.harvard.edu}}</ref>

== F Ring ==<!-- This section is linked from [[Pandora (moon)]] -->
[[File:PIA07712 - F ring animation.ogv|thumb|The small moons Pandora (left) and Prometheus (right) orbit on either side of the F ring. Prometheus acts as a ring shepherd and is followed by dark channels that it has [http://ciclops.org/view.php?id=3806 carved] into the inner strands of the ring.]]
The F Ring is the outermost discrete ring of Saturn and perhaps the most active ring in the Solar System, with features changing on a timescale of hours.<ref name=Murray /> It is located 3,000&nbsp;km (2000 miles) beyond the outer edge of the [[#A Ring structures|A ring]].<ref name="KarttunenKröger2007">{{Cite book |last1=Karttunen |first1=H. |url=https://books.google.com/books?id=DjeVdb0sLEAC |title=Fundamental astronomy |last2=Kröger |first2=P. |last3=Oja |first3=H. |last4=Donner |first4=K. J. |last5=Poutanen |first5=M. |date=2007 |publisher=Springer |isbn=978-3-540-34144-4 |edition=5th |location=Berlin New York |oclc=804078150 |display-authors=1}}</ref> The ring was discovered in 1979 by the [[Pioneer 11]] imaging team.<ref name="Gehrels1980">{{Cite journal | last1 = Gehrels | first1 = T. | last2 = Baker | first2 = L. R. | last3 = Beshore | first3 = E. | last4 = Blenman | first4 = C. | last5 = Burke | first5 = J. J. | last6 = Castillo | first6 = N. D. | last7 = Dacosta | first7 = B. | last8 = Degewij | first8 = J. | last9 = Doose | first9 = L. R. | last10 = Fountain | first10 = J. W. | last11 = Gotobed | first11 = J. | last12 = Kenknight | first12 = C. E. | last13 = Kingston | first13 = R. | last14 = McLaughlin | first14 = G. | last15 = McMillan | first15 = R. | last16 = Murphy | first16 = R. | last17 = Smith | first17 = P. H. | last18 = Stoll | first18 = C. P. | last19 = Strickland | first19 = R. N. | last20 = Tomasko | first20 = M. G. | last21 = Wijesinghe | first21 = M. P. | last22 = Coffeen | first22 = D. L. | last23 = Esposito | first23 = L. | doi = 10.1126/science.207.4429.434 | title = Imaging Photopolarimeter on Pioneer Saturn | journal = Science | volume = 207 | issue = 4429 | pages = 434–439 | year = 1980 | pmid =  17833555| bibcode = 1980Sci...207..434G| s2cid = 25033550 }}</ref> It is very thin, just a few hundred km in radial extent. While the traditional view has been that it is held together by two [[shepherd satellite|shepherd moons]], [[Prometheus (moon)|Prometheus]] and [[Pandora (moon)|Pandora]], which orbit inside and outside it,<ref name=Esposito2002>{{cite journal |last=Esposito |first=L. W. |author-link=Larry W. Esposito |title=Planetary rings |journal=Reports on Progress in Physics |date=2002 |volume=65 |issue=12 |pages=1741–1783 |doi=10.1088/0034-4885/65/12/201 |bibcode=2002RPPh...65.1741E |s2cid=250909885 }}</ref> recent studies indicate that only Prometheus contributes to the confinement.<ref name = "LakdawallaE2014">{{cite web | last = Lakdawalla | first = E. | author-link = Emily Lakdawalla
 | title = On the masses and motions of mini-moons: Pandora's not a "shepherd," but Prometheus still is
 | publisher = [[Planetary Society]] | date = 2014-07-05
 | url = http://www.planetary.org/blogs/emily-lakdawalla/2014/07010001-ringmoons-shepherds.html
 | access-date = 2015-04-17 }}</ref><ref name="Cuzzi2014">{{cite journal|last1=Cuzzi|first1=J. N.|last2=Whizin|first2=A. D.|last3=Hogan|first3=R. C.|last4=Dobrovolskis|first4=A. R.|last5=Dones|first5=L. |last6=Showalter|first6=M. R.|last7=Colwell|first7=J. E.|last8=Scargle|first8=J. D.|title=Saturn's F Ring core: Calm in the midst of chaos|journal=Icarus|volume=232|date=April 2014|pages=157–175|issn=0019-1035|doi=10.1016/j.icarus.2013.12.027|bibcode=2014Icar..232..157C}}</ref> Numerical simulations suggest the ring was formed when Prometheus and Pandora collided with each other and were partially disrupted.<ref name="Hyodo2015">{{cite journal|last1=Hyodo|first1=R.|last2=Ohtsuki|first2=K.|title=Saturn's F ring and shepherd satellites a natural outcome of satellite system formation|journal=Nature Geoscience|date=2015-08-17|doi=10.1038/ngeo2508|volume=8|issue=9|pages=686–689|bibcode = 2015NatGe...8..686H }}</ref>

More recent closeup images from the ''[[Cassini–Huygens|Cassini]]'' probe show that the F Ring consists of one core ring and a spiral strand around it.<ref name="Charnoz2005">{{cite journal |title=Cassini Discovers a Kinematic Spiral Ring Around Saturn |journal=Science |date=2005 |volume=310 |pages=1300–1304 |doi=10.1126/science.1119387 |url=http://ciclops.org/media/sp/2007/2672_7431_0.pdf |pmid=16311328 |issue=5752 |bibcode=2005Sci...310.1300C |last1=Charnoz |first1=S. |last2=Porco |first2=C.C . |last3=Deau |first3=E. |last4=Brahic |first4=A |last5=Spitale |first5=JN |last6=Bacques |first6=G |last7=Baillie |first7=K |s2cid=6502280 |display-authors=1 }}</ref> They also show that when Prometheus encounters the ring at its [[apoapsis]], its gravitational attraction creates kinks and knots in the F Ring as the moon 'steals' material from it, leaving a dark channel in the inner part of the ring. Since Prometheus orbits Saturn more rapidly than the material in the F ring, each new channel is carved about 3.2 degrees in front of the previous one.<ref name=Murray/>

In 2008, further dynamism was detected, suggesting that small unseen moons orbiting within the F Ring are continually passing through its narrow core because of perturbations from Prometheus. One of the small moons was tentatively identified as [[S/2004 S 6]].<ref name=Murray>{{cite journal |display-authors=1 |last1=Murray |first1=C. D. |last2=Beurle |first2=K. |last3=Cooper |first3=N. J. |last4=Evans |first4=M. W. |last5=Williams |first5=G. A. |last6=Charnoz |first6=S. |title=The determination of the structure of Saturn's F ring by nearby moonlets |journal=Nature |volume=453 |pages=739–744 |date=June 5, 2008 |doi=10.1038/nature06999 |pmid=18528389 |issue=7196 |bibcode=2008Natur.453..739M |s2cid=205213483 |url=https://hal-cea.archives-ouvertes.fr/cea-00930885/file/mur.pdf }}</ref>

As of 2023, the clumpy structure of the ring "is thought to be caused by the presence of thousands of small parent bodies (1.0 to 0.1 km in size) that collide and produce dense strands of micrometer- to centimeter-sized particles that re-accrete over a few months onto the parent bodies in a steady-state regime."<ref name="Morgado2023">{{Cite Q|Q116754015|display-authors=1}}</ref>
{{Clear}}
{{wide image|F Ring perturbations PIA08412.jpg|2200px|A mosaic of 107 images showing 255° (about 70%) of the F Ring as it would appear if straightened out, showing the kinked primary strand and the spiral secondary strand. The radial width (top to bottom) is 1,500&nbsp;km (1000 miles).}}

== Outer rings ==
[[File:Saturn outer rings labeled.svg|thumb|The outer rings seen back-illuminated by the [[Sun]]]]

=== Janus/Epimetheus Ring ===
A faint dust ring is present around the region occupied by the orbits of [[Janus (moon)|Janus]] and [[Epimetheus (moon)|Epimetheus]], as revealed by images taken in forward-scattered light by the [[Cassini spacecraft|''Cassini'' spacecraft]] in 2006. The ring has a radial extent of about 5,000&nbsp;km (3000 miles).<ref name="Cassini_eclipse1">NASA Planetary Photojournal [http://photojournal.jpl.nasa.gov/catalog/PIA08328 PIA08328: Moon-Made Rings]</ref> Its source is particles blasted off the moons' surfaces by meteoroid impacts, which then form a diffuse ring around their orbital paths.<ref name="Cassini_eclipse2">{{cite web| url = https://saturn.jpl.nasa.gov/news/2372/nasa-finds-saturns-moons-may-be-creating-new-rings/
 | title = NASA Finds Saturn's Moons May Be Creating New Rings| date = 2006-10-11| website = Cassini Legacy 1997–2007| publisher = [[Jet Propulsion Lab]]| access-date = 2017-12-20| archive-url= https://web.archive.org/web/20061016081210/http://saturn.jpl.nasa.gov/news/press-release-details.cfm?newsID=698|archive-date= 2006-10-16}}</ref>

=== G Ring ===
The G Ring is a very thin, faint ring about halfway between the [[#F Ring|F Ring]] and the beginning of the [[#E Ring|E Ring]], with its inner edge about 15,000&nbsp;km (10,000 miles) inside the orbit of [[Mimas]]. It contains a single distinctly brighter arc near its inner edge (similar to the arcs in the [[rings of Neptune]]) that extends about one-sixth of its circumference, centered on the half-km (500 yard) diameter moonlet [[Aegaeon (moon)|Aegaeon]], which is held in place by a 7:6 orbital resonance with Mimas.<ref name="Hedman2007">{{cite journal| title=The Source of Saturn's G Ring |first1=M. M. |display-authors=1 |last1=Hedman |first2=J. A. |last2=Burns |first3=M. S. |last3=Tiscareno |first4=C. C. |last4=Porco |first5=G. H. |last5=Jones |first6=E. |last6=Roussos |first7=N. |last7=Krupp |first8=C. |last8=Paranicas |first9=S. |last9=Kempf |journal=Science |volume=317 |pages=653–656 |date=2007 |doi=10.1126/science.1143964 |pmid=17673659 |url=http://ciclops.org/media/sp/2007/3882_9284_0.pdf |issue=5838 |bibcode=2007Sci...317..653H |s2cid=137345 }}</ref><ref>{{cite web|url=https://ciclops.org/view_popup.php%3Fid=5518.html|access-date=2022-09-22|title=S/2008 S 1. (NASA Cassini Saturn Mission Images)|work=ciclops.org}}</ref> The arc is believed to be composed of icy particles up to a few m in diameter, with the rest of the G Ring consisting of dust released from within the arc. The radial width of the arc is about 250&nbsp;km (150 miles), compared to a width of 9,000&nbsp;km (6000 miles) for the G Ring as a whole.<ref name="Hedman2007" /> The arc is thought to contain matter equivalent to a small icy moonlet about a hundred m in diameter.<ref name="Hedman2007" /> Dust released from Aegaeon and other source bodies within the arc by [[micrometeoroid]] impacts drifts outward from the arc because of interaction with [[Magnetosphere of Saturn|Saturn's]] [[magnetosphere]] (whose [[Plasma (physics)|plasma]] corotates with Saturn's [[magnetic field]], which rotates much more rapidly than the orbital motion of the G Ring). These tiny particles are steadily eroded away by further impacts and dispersed by plasma drag. Over the course of thousands of years the ring gradually loses mass,<ref>{{cite news| url=https://www.newscientist.com/article/dn12406-saturn-ring-created-by-remains-of-longdead-moon.html| title=Saturn ring created by remains of long-dead moon| date=2 August 2007| publisher=NewScientist.com news service| first=Anna| last=Davison }}</ref> which is replenished by further impacts on Aegaeon.

=== Methone Ring Arc ===
A faint ring arc, first detected in September 2006, covering a longitudinal extent of about 10 degrees is associated with the moon [[Methone (moon)|Methone]]. The material in the arc is believed to represent dust ejected from Methone by micrometeoroid impacts. The confinement of the dust within the arc is attributable to a 14:15 resonance with Mimas (similar to the mechanism of confinement of the arc within the G ring).<ref name="arcs announcement">{{cite web | last=[[Carolyn Porco|Porco C. C.]] | title=More Ring Arcs for Saturn | work=Cassini Imaging Central Laboratory for Operations web site | date=2008-09-05 | url=http://ciclops.org/view_event/90/More_Ring_Arcs_for_Saturn | access-date=2008-09-05 | display-authors=etal | archive-date=2008-10-10 | archive-url=https://web.archive.org/web/20081010150303/http://ciclops.org/view_event/90/More_Ring_Arcs_for_Saturn }}</ref><ref name="HedmanMurray2009">{{cite journal|display-authors=1|last1=Hedman |first1=M. M.|last2=Murray|first2=C. D.|last3=Cooper|first3=N. J.|last4=Tiscareno|first4=M. S. |last5=Beurle|first5=K. |last6=Evans|first6=M. W.|last7=Burns|first7=J. A.|title=Three tenuous rings/arcs for three tiny moons |journal=Icarus |volume=199 |issue=2 |date=2008-11-25 |pages=378–386 |doi=10.1016/j.icarus.2008.11.001|bibcode=2009Icar..199..378H }}</ref> Under the influence of the same resonance, Methone librates back and forth in its orbit with an amplitude of 5° of longitude.

=== Anthe Ring Arc ===
[[File:PIA11101 Anthe ring arc.jpg|thumb|The Anthe Ring Arc – the bright spot is [[Anthe (moon)|Anthe]]]]
A faint ring arc, first detected in June 2007, covering a longitudinal extent of about 20 degrees is associated with the moon [[Anthe (moon)|Anthe]]. The material in the arc is believed to represent dust knocked off Anthe by micrometeoroid impacts. The confinement of the dust within the arc is attributable to a 10:11 resonance with Mimas. Under the influence of the same resonance, Anthe drifts back and forth in its orbit over 14° of longitude.<ref name="arcs announcement" /><ref name="HedmanMurray2009" />

=== Pallene Ring ===
A faint dust ring shares [[Pallene (moon)|Pallene's]] orbit, as revealed by images taken in forward-scattered light by the ''Cassini'' spacecraft in 2006.<ref name="Cassini_eclipse1" /> The ring has a radial extent of about 2,500&nbsp;km (1500 miles). Its source is particles blasted off Pallene's surface by meteoroid impacts, which then form a diffuse ring around its orbital path.<ref name="Cassini_eclipse2" /><ref name="HedmanMurray2009" />

=== E Ring ===
<!-- This section is linked from [[Enceladus (moon)]] -->

[[File:E ring with Enceladus.jpg|thumb|alt=View of the E right with Enceladus and its south polar jets.|The backlit E ring, with [[Enceladus]] silhouetted against it. The moon's [[Tiger stripes (Enceladus)|south polar jets]] erupt brighty below it.]]
Unconfirmed until 1980,<ref name="Feibelman1980" /> the existence of the E ring was a subject of debate among astronomers at least as far back as 1908. In a narrative timeline of Saturn observations, [[Arthur Francis O'Donel Alexander]] attributes<ref name="Alexander1962">{{Cite book |last=Alexander |first=Arthur Francis O'Donel |url=https://archive.org/details/planetsaturnhist0000alex/page/314/mode/2up |title=The planet Saturn: a history of observation, theory and discovery |publisher=Faber & Faber |year=1962 |location=London |pages=189-190, 314-316 |language=en}}</ref> the first observation of what would come to be called the E Ring to [[Georges Fournier]], who on 5 September 1907 at [[Mont Revard]] observed a "luminous zone" "surrounding the outer bright ring." The next year, on 7 October 1908, E. Schaer independently observed "a new dusky ring...surrounding the bright rings of Saturn" at the Geneva Observatory. Following up on Schaer's discovery, W. Boyer, T. Lewis, and [[Arthur Eddington]] found signs of a discontinuous ring matching Schaer's description, but described their observations as "uncertain." After [[Edward Emerson Barnard|Edward Barnard]], using the what was at the time the [[Yerkes 41-inch reflector|world's best telescope]], failed to find signs of a ring. [[E. M. Antoniadi]] argued for the ring's existence in a 1909 publication, recalling a observations by William Wray on 26 December 1861 of a "very faint light...so as to give the impression that it was the dusky ring,"<ref>{{Cite journal |last=Wray |first=William |date=1863-01-01 |title=Observations on Saturn |journal=Monthly Notices of the Royal Astronomical Society |volume=23 |page=85 |doi=10.1093/mnras/23.3.85 |doi-access=free |bibcode=1863MNRAS..23...85W |issn=0035-8711 |quote=A prolongation of very faint light stretched on either side from the dark shade on the ball, overlapping the fine line of light formed by the edge of the ring, to the extent of about one-third its length, and so as to give the impression that it was the dusky ring, very much thicker than the bright rings, and seen edgewise, projected on the sky. }}</ref><ref>{{Cite journal |last=Antoniadi |first=E.-M. |date=1909 |title=Nouvelles de la Science, Variétés |url=https://ui.adsabs.harvard.edu/abs/1909BSAFR..23..504A |journal=Bulletin de la Société Astronomique de France et Revue Mensuelle d'Astronomie |language=fr |volume=23 |page=504 |bibcode=1909BSAFR..23..504A |via=}}</ref> but after Barnard's negative result most astronomers became skeptical of the E Ring's existence.<ref name="Alexander1962" />

Unlike the A, B, and C rings, the E Ring's small optical depth and large vertical extent mean it is best viewed edge-on, which is only possible once every 14–15 years,<ref name="Feibelman1967">{{Cite journal |last=Feibelman |first=W. A. |date=20 May 1967 |title=Concerning the "D" Ring of Saturn |url=https://www.nature.com/articles/214793a0 |journal=Nature |language=en |volume=214 |issue=5090 |pages=793–794 |doi=10.1038/214793a0 |bibcode=1967Natur.214..793F |issn=0028-0836|url-access=subscription }}</ref> so perhaps for this reason, it was not until the 1960s that the E Ring was again the subject of observations. Although some sources credit [[Walter Feibelman]] with the E Ring's discovery in 1966,<ref name="history_of_the_rings" /><ref name="NASAsaturn" /> his paper published the following year announcing the observations begins by acknowledging the existing controversy and the long record of observations both supporting and disputing the ring's existence, and carefully stresses his interpretation of the data as a new ring as "tentative only."<ref name="Feibelman1967" /> A reanalysis of [[Walter Feibelman|Feibelman]]'s original observations, conducted in anticipation of the coming Saturn flyby by Pioneer 11, once again called the evidence for this outer ring "shaky."<ref>{{Cite journal |last1=Smith |first1=Bradford A. |last2=Cook |first2=Allan F. |last3=Feibelman |first3=Walter A. |last4=Beebe |first4=Reta F. |date=July 1975 |title=On a suspected ring external to the visible rings of Saturn |url=https://linkinghub.elsevier.com/retrieve/pii/0019103575900123 |journal=Icarus |language=en |volume=25 |issue=3 |pages=466–469 |doi=10.1016/0019-1035(75)90012-3|bibcode=1975Icar...25..466S |hdl=2060/19740026172 |hdl-access=free }}</ref> Even polarimetric observations by Pioneer 11 failed to conclusively identify E Ring during its 1979 flyby, though "its existence was inferred from [particle, radiation, and magnetic field measurements]."<ref name="Feibelman1980" /> Only after a digital reanalysis of the 1966 observations as well as several independent observations using ground- and space-based telescopes existence was finally confirmed in a 1980 paper by [[Walter Feibelman|Feibelman]] and Klinglesmith.<ref name="Feibelman1980" />
[[File:PIA17191-SaturnMoon-Enceladus-TendrilSims-20150414.jpg|thumb|alt=Comparison of Saturn's E Ring tendrils between Cassini photos and computer simulations.|E Ring tendrils from Enceladus geysers - comparison of images (a, c) with computer simulations.]]

The E Ring is the second outermost ring and is extremely wide; it consists of many tiny (micron and sub-micron) particles of water ice with silicates, carbon dioxide and ammonia.<ref>{{cite journal | last1=Hillier | first1=JK | last2=Green | first2=SF | title=The composition of Saturn's E Ring | journal=[[Monthly Notices of the Royal Astronomical Society]] | volume=377 | issue=4 | pages=1588–1596 | date=June 2007 | bibcode=2007MNRAS.377.1588H | doi=10.1111/j.1365-2966.2007.11710.x | last3=McBride | first3=N. | last4=Schwanethal | first4=J. P. | last5=Postberg | first5=F. | last6=Srama | first6=R. | last7=Kempf | first7=S. | last8=Moragas-Klostermeyer | first8=G. | last9=McDonnell | first9=J. A. M. | last10=Grun | first10=E. | display-authors=1 | doi-access=free }}</ref> The E Ring is distributed between the orbits of [[Mimas]] and [[Titan (moon)|Titan]].<ref name="Hedman_2012">{{cite journal | display-authors=1 | last1=Hedman | first1=M. M.| last2=Burns | first2=J. A. | last3=Hamilton | first3=D. P. | last4=Showalter | first4=M. R. | date=2012 | title=The three-dimensional structure of Saturn's E Ring | journal=Icarus | volume=217 | issue= 1| pages=322–338 | doi=10.1016/j.icarus.2011.11.006 | arxiv=1111.2568|bibcode=2012Icar..217..322H | s2cid=1432112 }}</ref> Unlike the other rings, it is composed of microscopic particles rather than macroscopic ice chunks. In 2005, the source of the E Ring's material was determined to be [[cryovolcanic]] plumes<ref name="Spahn">{{cite journal | title=Cassini Dust Measurements at Enceladus and Implications for the Origin of the E Ring | journal=Science | volume=311 | issue=5766 | pages=1416–8 | date=2006-03-10 | doi=10.1126/science.1121375 | pmid=16527969 |bibcode=2006Sci...311.1416S | display-authors=1 | last1=Spahn | first1=F. | last2=Schmidt | first2=J | last3=Albers | first3=N | last4=Hörning | first4=M | last5=Makuch | first5=M | last6=Seiss | first6=M | last7=Kempf | first7=S | last8=Srama | first8=R | last9=Dikarev | first9=V | last10=Helfert | first10=Stefan | last11=Moragas-Klostermeyer | first11=Georg | last12=Krivov | first12=Alexander V. | last13=Sremčević | first13=Miodrag | last14=Tuzzolino | first14=Anthony J. | last15=Economou | first15=Thanasis | last16=Grün | first16=Eberhard | citeseerx=10.1.1.466.6748 | s2cid=33554377 }}</ref><ref name="Porco Helfenstein et al. 2006">{{cite journal| doi = 10.1126/science.1123013| last1 = Porco| first1 = C. C.| author-link1 = Carolyn Porco| last2 = Helfenstein| first2 = P.| last3 = Thomas| first3 = P. C.| last4 = Ingersoll| first4 = A. P.| last5 = Wisdom| first5 = J.| last6 = West| first6 = R.| last7 = Neukum| first7 = G.| last8 = Denk| first8 = T.| last9 = Wagner| first9 = R.| date = 10 March 2006| title = Cassini Observes the Active South Pole of Enceladus| journal = Science| volume = 311| issue = 5766| pages = 1393–1401| pmid = 16527964| bibcode = 2006Sci...311.1393P| s2cid = 6976648| ref = {{sfnRef|Porco Helfenstein et al. 2006}}| url = https://authors.library.caltech.edu/36593/7/PorcoCC.SOM.pdf}}</ref> emanating from the [[Tiger stripes (Enceladus)|"tiger stripes"]] of the [[Enceladus#South polar region|south polar region]] of the moon [[Enceladus]].<ref name="E ring">{{cite news |url=http://www.nasa.gov/jpl/cassini/icy-tendrils-reaching-into-saturn-ring-traced-to-their-source/ |title=Icy Tendrils Reaching into Saturn Ring Traced to Their Source |work=NASA News |date=14 April 2015 |access-date=2015-04-15 |archive-date=2015-04-16 |archive-url=https://web.archive.org/web/20150416034254/http://www.nasa.gov/jpl/cassini/icy-tendrils-reaching-into-saturn-ring-traced-to-their-source/ }}</ref><ref>{{cite journal |last1=Kempf |first1=Sascha |last2=Beckmann |first2=Uwe |last3=Schmidt |first3=Jürgen |title=How the Enceladus dust plume feeds Saturn’s E ring |journal=Icarus |date=April 2010 |volume=206 |issue=2 |pages=446–457 |doi=10.1016/j.icarus.2009.09.016}}</ref> Unlike the main rings, the E Ring is more than 2,000&nbsp;km (1000 miles) thick and increases with its distance from Enceladus.<ref name="Hedman_2012" /> Tendril-like structures observed within the E Ring can be related to the emissions of the most active south polar jets of Enceladus.<ref name="Mitchell2015">{{cite journal|last1=Mitchell|first1=C. J.|last2=Porco|first2=C. C.|last3=Weiss|first3=J. W.|title=Tracking the geysers of Enceladus into Saturn's E ring|journal=The Astronomical Journal|volume=149|issue=5|date=2015-04-15|page=156|issn=1538-3881|doi=10.1088/0004-6256/149/5/156|bibcode=2015AJ....149..156M|s2cid=55091776|url=http://pdfs.semanticscholar.org/f82d/44310816a81e32d6e2cfe0b17e89615a8e5b.pdf|archive-url=https://web.archive.org/web/20190308193220/http://pdfs.semanticscholar.org/f82d/44310816a81e32d6e2cfe0b17e89615a8e5b.pdf|archive-date=2019-03-08}}</ref>

Particles of the E Ring tend to accumulate on moons that orbit within it. The equator of the leading hemisphere of [[Tethys (moon)|Tethys]] is tinted slightly blue due to infalling material.<ref>{{cite journal| doi = 10.1016/j.icarus.2010.08.016| last1 = Schenk | first1 = P.| last2 = Hamilton | first2 = D. P.| last3 = Johnson | first3 = R. E.| last4 = McKinnon | first4 = W. B.| last5 = Paranicas | first5 = C.| last6 = Schmidt | first6 = J.| last7 = Showalter | first7 = M. R.| date=January 2011 | title = Plasma, plumes and rings: Saturn system dynamics as recorded in global color patterns on its midsize icy satellites| journal = Icarus| volume = 211| issue = 1| bibcode = 2011Icar..211..740S |pages=751–53}}</ref> The trojan moons [[Telesto (moon)|Telesto]], [[Calypso (moon)|Calypso]], [[Helene (moon)|Helene]] and [[Polydeuces (moon)|Polydeuces]] are particularly affected as their orbits move up and down the ring plane. This results in their surfaces being coated with bright material that smooths out features.<ref>{{cite web | last = Mason | first = Betsy | date = February 15, 2010 | title = New Close-Ups of Saturn's Moons Mimas and Calypso | work = wired.com | publisher = Condé Nast Digital | url = https://www.wired.com/wiredscience/2010/02/gallery-mimas/ | access-date = 2011-12-23}}</ref>

=== Phoebe ring ===
[[File:Infrared Ring Around Saturn.jpg|thumb|upright=1|The Phoebe ring's huge extent dwarfs the main rings. Inset: 24 μm [[Spitzer Space Telescope|Spitzer]] image of part of the ring]]

In October 2009, the discovery of a tenuous disk of material just interior to the orbit of [[Phoebe (moon)|Phoebe]] was reported. The disk was aligned edge-on to Earth at the time of discovery. This disk can be loosely described as another ring. Although very large (as seen from Earth, the apparent size of two full moons<ref name="NASA2017">{{cite web |url=https://www.nasa.gov/mission_pages/spitzer/news/spitzer-20091006.html |title=NASA Space Telescope Discovers Largest Ring Around Saturn |publisher=NASA |date=July 3, 2017 |access-date=2017-11-06 |archive-date=2017-05-30 |archive-url=https://web.archive.org/web/20170530050221/https://www.nasa.gov/mission_pages/spitzer/news/spitzer-20091006.html }}</ref>), the ring is virtually invisible. It was discovered using [[NASA]]'s [[infrared]] [[Spitzer Space Telescope]],<ref>{{Cite web|url=https://jpl.nasa.gov/|title=JPL|website=NASA Jet Propulsion Laboratory (JPL)}}</ref> and was seen over the entire range of the observations, which extended from 128 to 207 times the radius of Saturn,<ref name="Verbiscer">{{cite journal |display-authors=1 |last1=Verbiscer |first1=Anne |last2=Skrutskie |first2=Michael |last3=Hamilton |first3=Douglas |title=Saturn's largest ring |journal=[[Nature (journal)|Nature]] |doi=10.1038/nature08515 |date=2009-10-07 |pmid=19812546 |volume=461 |issue=7267 |pages=1098–100 |bibcode=2009Natur.461.1098V |s2cid=4349726 }}</ref> with calculations indicating that it may extend outward up to 300 Saturn radii and inward to the orbit of [[Iapetus (moon)|Iapetus]] at 59 Saturn radii.<ref name=sciencenews_large_ring/> The ring was subsequently studied using the [[Wide-field Infrared Survey Explorer|WISE]], ''[[Herschel Space Observatory|Herschel]]'' and ''Cassini'' spacecraft;<ref name="Tamayo2014">{{cite journal | display-authors=1 | last1=Tamayo | first1=D. | last2=Hedman | first2=M. M. | last3=Burns | first3=J. A.  | title=First observations of the Phoebe ring in optical light | journal=[[Icarus (journal)|Icarus]] | volume= 233| pages= 1–8| date=2014-01-23 | doi=10.1016/j.icarus.2014.01.021  | arxiv=1401.6166 | bibcode=2014Icar..233....1T| s2cid=40032407 }}</ref> WISE observations show that it extends from at least between 50 and 100 to 270 Saturn radii (the inner edge is lost in the planet's glare).<ref name="HamiltonSkrutskie2015">{{cite journal|last1=Hamilton|first1=Douglas P.|last2=Skrutskie|first2=Michael F.|last3=Verbiscer|first3=Anne J.|last4=Masci|first4=Frank J.|title=Small particles dominate Saturn's Phoebe ring to surprisingly large distances|journal=Nature|volume=522|issue=7555|date=2015-06-10|pages=185–187|doi=10.1038/nature14476|pmid=26062508|bibcode = 2015Natur.522..185H |s2cid=4464735}}</ref> Data obtained with WISE indicate the ring particles are small; those with radii greater than 10&nbsp;cm comprise 10% or less of the cross-sectional area.<ref name="HamiltonSkrutskie2015"/>

Phoebe orbits the planet at a distance ranging from 180 to 250 radii. The ring has a thickness of about 40 radii.<ref>{{cite web |url=http://www.nasa.gov/mission_pages/spitzer/multimedia/spitzer-20091007b.html |title=The King of Rings |publisher=NASA, Spitzer Space Telescope center |date=2009-10-07 |access-date=2009-10-07 |archive-date=2009-10-10 |archive-url=https://web.archive.org/web/20091010072014/http://www.nasa.gov/mission_pages/spitzer/multimedia/spitzer-20091007b.html }}</ref> Because the ring's particles are presumed to have originated from impacts ([[micrometeoroid]] and larger) on Phoebe, they should share its [[Retrograde motion#Retrograde orbit|retrograde orbit]],<ref name=sciencenews_large_ring>{{cite journal|last=Cowen|first=Rob|url=https://www.sciencenews.org/article/largest-known-planetary-ring-discovered|title=Largest known planetary ring discovered|journal=[[Science News]]|date=2009-10-06|access-date=2022-05-30}}</ref> which is opposite to the orbital motion of the next inner moon, [[Iapetus (moon)|Iapetus]]. This ring lies in the plane of Saturn's orbit, or roughly the [[ecliptic]], and thus is tilted 27 degrees from Saturn's [[equatorial plane]] and the other rings. Phoebe is [[inclination|inclined]] by 5° with respect to Saturn's orbit plane (often written as 175°, due to Phoebe's retrograde orbital motion), and its resulting vertical excursions above and below the ring plane agree closely with the ring's observed thickness of 40 Saturn radii.

The existence of the ring was proposed in the 1970s by [[Steven Soter]].<ref name=sciencenews_large_ring/> The discovery was made by Anne J. Verbiscer and Michael F. Skrutskie (of the [[University of Virginia]]) and Douglas P. Hamilton (of the [[University of Maryland, College Park]]).<ref name="Verbiscer" /><ref name="NatureNews">{{cite journal |last=Grayson |first=Michelle |url=http://www.nature.com/news/2009/091007/full/news.2009.979.html |title=Huge 'ghost' ring discovered around Saturn|journal=Nature News|date=2009-10-07 |doi=10.1038/news.2009.979 |url-access=subscription }}</ref> The three had studied together at [[Cornell University]] as graduate students.<ref>{{cite news |title=U-Va., U-Md. astronomers find another Saturn ring |first=Martin |last=Weil |newspaper=[[The Washington Post]] |date=Oct 25, 2009 |page=4C |url=https://www.washingtonpost.com/wp-dyn/content/article/2009/10/24/AR2009102402506.html |access-date=2012-09-02 }}</ref>

Ring material migrates inward due to [[Poynting–Robertson effect|reemission of solar radiation]],<ref name="Verbiscer" /> with a speed inversely proportional to particle size; a 3&nbsp;cm particle would migrate from the vicinity of Phoebe to that of Iapetus over the age of the Solar System.<ref name="HamiltonSkrutskie2015"/> The material would thus strike the leading hemisphere of Iapetus. Infall of this material causes a slight darkening and reddening of the leading hemisphere of Iapetus (similar to what is seen on the Uranian moons [[Oberon (moon)|Oberon]] and [[Titania (moon)|Titania]]) but does not directly create the dramatic [[Iapetus (moon)#Two-tone coloration|two-tone coloration]] of that moon.<ref name="Denk">{{cite journal | title=Iapetus: Unique Surface Properties and a Global Color Dichotomy from Cassini Imaging | journal=Science | volume= 327| issue=5964 | pages=435–9 | date=2009-12-10 | doi=10.1126/science.1177088 | pmid=20007863|bibcode=2010Sci...327..435D | display-authors=1 | last1=Denk | first1=T. | last2=Neukum | first2=G. | last3=Roatsch | first3=T. | last4=Porco | first4=C. C. | last5=Burns | first5=J. A. | last6=Galuba | first6=G. G. | last7=Schmedemann | first7=N. | last8=Helfenstein | first8=P. | last9=Thomas | first9=P. C. | last10=Wagner | first10=Roland J. | last11=West | first11=Robert A. | s2cid=165865 | url=https://pdfs.semanticscholar.org/cb9e/8affb1d9afe7cb6165c7407643d7a49c622f.pdf | archive-url=https://web.archive.org/web/20200227002405/https://pdfs.semanticscholar.org/cb9e/8affb1d9afe7cb6165c7407643d7a49c622f.pdf | archive-date=2020-02-27 }}</ref> Rather, the infalling material initiates a [[positive feedback]] [[thermal runaway|thermal self-segregation process]] of ice [[Sublimation (chemistry)|sublimation]] from warmer regions, followed by vapor condensation onto cooler regions. This leaves a dark residue of "lag" material covering most of the equatorial region of Iapetus's leading hemisphere, which contrasts with the bright ice deposits covering the polar regions and most of the trailing hemisphere.<ref name="jpl779">{{cite web | title=Cassini Is on the Trail of a Runaway Mystery | work=NASA Mission News | publisher=NASA | date=8 October 2007 | url=https://www.nasa.gov/mission_pages/cassini/media/cassini20071008.html | access-date=2017-12-20 | archive-date=2017-12-14 | archive-url=https://web.archive.org/web/20171214003719/https://www.nasa.gov/mission_pages/cassini/media/cassini20071008.html }}</ref><ref name="Mason">{{cite web |display-authors=1 |last1=Mason |first1=J. |last2=Martinez |first2=M. |last3=Balthasar |first3=H. |title=Cassini Closes In On The Centuries-old Mystery Of Saturn's Moon Iapetus |work=CICLOPS website newsroom |publisher=[[Space Science Institute]] |date=2009-12-10 |url=http://ciclops.org/view.php?id=6033 |access-date=2009-12-22 |archive-date=2012-02-03 |archive-url=https://web.archive.org/web/20120203132024/http://ciclops.org/view.php?id=6033 }}</ref><ref name="Spencer">{{cite journal |display-authors=1 |last1=Spencer |first1=J. R. |last2=Denk |first2=T. | title=Formation of Iapetus' Extreme Albedo Dichotomy by Exogenically Triggered Thermal Ice Migration | journal=Science |volume= 327|issue=5964 |pages=432–5 |date=2009-12-10 |doi=10.1126/science.1177132 |pmid=20007862 |bibcode=2010Sci...327..432S |citeseerx=10.1.1.651.4218 |s2cid=20663944 }}</ref>

== See also ==
* [[Galileo Galilei]] – the first person to observe Saturn's rings, in 1610
* [[Christiaan Huygens]] – the first to propose that there was a ring surrounding Saturn, in 1655
* [[Giovanni Cassini]] – discovered the separation between the A and B rings (the Cassini Division), in 1675
* [[Édouard Roche]] – French astronomer who described how a satellite that comes within the [[Roche limit]] of Saturn could break up and form the rings

==Notes==
{{notelist}}

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

== External links ==
{{Commons category|Rings of Saturn}}
* [https://web.archive.org/web/20050826083057/http://pds-rings.seti.org/saturn/saturn.html Planetary Rings Node: Saturn's Ring System]
* [https://web.archive.org/web/20100527141504/http://solarsystem.nasa.gov/planets/profile.cfm?Object=Saturn&Display=Rings Saturn's Rings] by [http://solarsystem.nasa.gov NASA's Solar System Exploration]
* [https://planetarynames.wr.usgs.gov/Page/Rings#saturn Rings of Saturn nomenclature] from the [http://planetarynames.wr.usgs.gov USGS planetary nomenclature page]
* [https://www.space.com/29624-giant-saturn-ring-even-bigger.html Biggest Ring Around Saturn Just Got Supersized] (retrieved 2017-12-20 from Space.com)
* [http://www.bridgingthegaps.ie/2017/04/planetary_ring_systems_with_dr_mark_showalter/ Everything a Curious Mind Should Know About Planetary Ring Systems with Dr Mark Showalter] (Waseem Akhtar podcast with [[Mark Showalter]])
* [https://www.flickr.com/photos/136797589@N04/34335296582/ High-resolution animation] by Seán Doran of the backlit rings
* [https://www.youtube.com/watch?v=ac1i4iOg5rs High-resolution animation] by Kevin M. Gill of a flyover of the outer B Ring at equinox (it starts getting less uniform after the first minute); see [https://www.flickr.com/photos/kevinmgill/albums/72157691101106214 Rings album] for more
* [https://vimeo.com/295655973 High-resolution animation] by Nick Stevens of Saturn and its rings from an equatorial and a polar orbit, and from a [https://vimeo.com/322426761 dive below the rings]; see [https://vimeo.com/starbase1/videos listing] for more

{{Saturn}}
{{Planetary rings}}
{{Moons of Saturn}}
{{Galileo Galilei}}
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[[Category:Rings of Saturn| ]]
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[[Category:Astronomical objects discovered in 1610|16101001]]
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[[Category:Planetary rings|Saturn]]