Editing Planet (section)

===Secondary characteristics===
{{Main|Natural satellite|ring system}}
[[File:Voyager 2 - Saturn Rings - 3085 7800 2.png|thumb|upright|The [[rings of Saturn]]]]

Several planets or dwarf planets in the Solar System (such as Neptune and Pluto) have orbital periods that are in [[Orbital resonance|resonance]] with each other or with smaller bodies. This is common in satellite systems (e.g. the resonance between Io, [[Europa (moon)|Europa]], and Ganymede around Jupiter, or between Enceladus and Dione around Saturn). All except Mercury and Venus have [[natural satellite]]s, often called "moons". Earth has one, Mars has two, and the giant planets have numerous moons in complex planetary-type systems. Except for Ceres and Sedna, all the consensus dwarf planets are known to have at least one moon as well. Many moons of the giant planets have features similar to those on the terrestrial planets and dwarf planets, and some have been studied as possible abodes of life (especially Europa and Enceladus).<ref name="Grasset2000">{{cite journal | last1=Grasset |first1=O. | last2=Sotin | first2=C. | last3=Deschamps | first3=F. |title = On the internal structure and dynamic of Titan |date = 2000 |journal = Planetary and Space Science |volume = 48 | issue= 7–8 | pages = 617–636 |doi=10.1016/S0032-0633(00)00039-8 | bibcode=2000P&SS...48..617G}}</ref><ref name="Fortes2000">{{cite journal | journal = Icarus |volume= 146 |issue = 2 |pages = 444–452 |date= 2000 |doi = 10.1006/icar.2000.6400 |title = Exobiological implications of a possible ammonia-water ocean inside Titan | last=Fortes | first=A. D. |bibcode=2000Icar..146..444F}}</ref><ref>{{cite news |first=Nicola |last=Jones |date=11 December 2001 |work=New Scientist Print Edition |url=https://www.newscientist.com/article.ns?id=dn1647 |title=Bacterial explanation for Europa's rosy glow |access-date=23 August 2008 |archive-date=10 April 2008 |archive-url=https://web.archive.org/web/20080410053352/http://www.newscientist.com/article.ns?id=dn1647 }}</ref><ref name="Taubner et al. 2018">{{Cite journal| doi = 10.1038/s41467-018-02876-y| issn = 2041-1723| volume = 9| issue = 1| page = 748| last1 = Taubner| first1 = Ruth-Sophie| last2 = Pappenreiter| first2 = Patricia| last3 = Zwicker| first3 = Jennifer| last4 = Smrzka| first4 = Daniel| last5 = Pruckner| first5 = Christian| last6 = Kolar| first6 = Philipp| last7 = Bernacchi| first7 = Sébastien| last8 = Seifert| first8 = Arne H.| last9 = Krajete| first9 = Alexander| last10 = Bach| first10 = Wolfgang| last11 = Peckmann| first11 = Jörn| last12 = Paulik| first12 = Christian| last13 = Firneis| first13 = Maria G.| last14 = Schleper| first14 = Christa| last15 = Rittmann| first15 = Simon K.-M. R.| title = Biological methane production under putative Enceladus-like conditions| journal = Nature Communications| date = 27 February 2018| pmid = 29487311| pmc = 5829080| bibcode = 2018NatCo...9..748T}}</ref><ref name="Affholder et al. 2021">{{cite journal |author=Affholder, Antonin |display-authors=et al. |title=Bayesian analysis of Enceladus's plume data to assess methanogenesis |url=https://www.nature.com/articles/s41550-021-01372-6 |date=7 June 2021 |journal=[[Nature Astronomy]] |volume=5 |issue=8 |pages=805–814 |doi=10.1038/s41550-021-01372-6 |bibcode=2021NatAs...5..805A |s2cid=236220377 |access-date=7 July 2021 |archive-date=7 July 2021 |archive-url=https://web.archive.org/web/20210707121118/https://www.nature.com/articles/s41550-021-01372-6 |url-status=live }}</ref>

The four giant planets are orbited by [[planetary ring]]s of varying size and complexity. The rings are composed primarily of dust or particulate matter, but can host tiny '[[Rings of Saturn#Propeller moonlets|moonlets]]' whose gravity shapes and maintains their structure. Although the origins of planetary rings are not precisely known, they are believed to be the result of natural satellites that fell below their parent planets' [[Roche limit]]s and were torn apart by [[tidal force]]s.<ref>{{cite journal | last1=Molnar | first1=L. A. | last2=Dunn | first2=D. E. |title=On the Formation of Planetary Rings |journal=Bulletin of the American Astronomical Society |date=1996 |volume=28 |pages=77–115 |bibcode=1996DPS....28.1815M }}</ref><ref>{{cite book | first=Encrenaz |last=Thérèse |author-link=Thérèse Encrenaz|date=2004 |title=The Solar System |edition=3rd |pages=388–390 |publisher=Springer |isbn=978-3-540-00241-3}}</ref> The dwarf planets Haumea<ref name="Ortiz2017">{{cite journal
| display-authors = etal
| last1 = Ortiz
| first1 = J. L.
| last2 = Santos-Sanz
| first2 = P.
| last3 = Sicardy
| first3 = B.
| last4 = Benedetti-Rossi
| first4 = G.
| last5 = Bérard
| first5 = D.
| last6 = Morales
| first6 = N.
| title = The size, shape, density and ring of the dwarf planet Haumea from a stellar occultation
| url = http://www.astrosurf.com/sogorb/occultations/nature24051.pdf
| journal = Nature
| volume = 550
| issue = 7675
| year = 2017
| pages = 219–223
| doi = 10.1038/nature24051
| pmid = 29022593
| bibcode = 2017Natur.550..219O
| arxiv = 2006.03113
| hdl = 10045/70230
| s2cid = 205260767
| hdl-access = free
| access-date = 6 October 2022
| archive-date = 7 November 2020
| archive-url = https://web.archive.org/web/20201107052958/http://www.astrosurf.com/sogorb/occultations/nature24051.pdf
| url-status = live
}}</ref> and Quaoar also have rings.<ref name="Morgado2023">{{Cite Q|Q116754015|display-authors=1}}</ref>

No secondary characteristics have been observed around exoplanets. The [[sub-brown dwarf]] [[Cha 110913−773444]], which has been described as a [[rogue planet]], is believed to be orbited by a tiny [[protoplanetary disc]],<ref name="Luhman">{{cite journal | journal=Astrophysical Journal |last1=Luhman |first1=K. L. | last2=Adame | first2=Lucía | last3=D'Alessio | first3=Paola | last4=Calvet | first4=Nuria|author4-link=Nuria Calvet |title= Discovery of a Planetary-Mass Brown Dwarf with a Circumstellar Disk |volume=635 | issue=1 |page=L93 |doi=10.1086/498868 |date= 2005 |bibcode=2005ApJ...635L..93L|arxiv = astro-ph/0511807 |s2cid=11685964}}
* {{cite press release |author=Whitney Clavin |date=29 November 2005 |title=A Planet With Planets? Spitzer Finds Cosmic Oddball |website=NASA |url=http://www.nasa.gov/vision/universe/starsgalaxies/spitzerf-20051129.html |access-date=10 September 2007 |archive-date=11 October 2012 |archive-url=https://web.archive.org/web/20121011011111/http://www.nasa.gov/vision/universe/starsgalaxies/spitzerf-20051129.html |url-status=dead }}</ref> and the sub-brown dwarf [[OTS 44]] was shown to be surrounded by a substantial protoplanetary disk of at least 10 Earth masses.<ref name=joergens2013_AA558>{{cite journal|last1=Joergens|first1=V.|display-authors=4|last2=Bonnefoy|first2=M.|last3=Liu|first3=Y.|last4=Bayo|first4=A.|last5=Wolf|first5=S.|last6=Chauvin|first6=G.|last7=Rojo|first7=P.|title=OTS 44: Disk and accretion at the planetary border|journal=Astronomy & Astrophysics|volume=558|number=7|date=2013|doi=10.1051/0004-6361/201322432|bibcode=2013A&A...558L...7J|arxiv = 1310.1936|page=L7|s2cid=118456052}}</ref>